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Defra Research Project Final Report for WU0101 – Opportunities for reducing water use in Agriculture(project ended 30 November 2006)

Defra Project WU0101

Opportunities for Reducing Water use in Agriculture

Dr Andrew J. Thompson1

Dr John A. King2

Dr Ken A. Smith2

Don H. Tiffin2

1. Warwick HRI, University of Warwick, Wellesbourne, Warwick, Warwickshire,CV35 9EF. [email protected] http://www2.warwick.ac.uk/fac/sci/whri/research/plantwateruse/

2. ADAS, Woodthorne, Wergs Road, Wolverhampton, WV6 8TQ. http://www.adas.co.uk/

June 2007

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Executive Summary

Aims and objectivesThe aim of this study was to identify new and existing areas of research and knowledge transfer that will create opportunities for reducing water use in English and Welsh agriculture. The objectives were as follows:

To identify geographical regions and agricultural sectors where research and knowledge transfer activities have the potential to lead to significant reductions in water use

To review current and emerging technologies aimed at saving water in agriculture To review existing initiatives and case studies related to saving water in agriculture To identify and prioritise research areas and to seek consensus from an expert group

Summary of findingsThe aim of reducing water inputs in agriculture is two-fold: to protect water courses from ecological damage, and to sustain the rural economy. Agriculture has an absolute need to use water to produce crops and livestock and in many horticultural crops product quality and profitability are highly dependent on timing, uniformity and volume of water applied. However, water availability is declining. Where water is “available”, in the sense that its use does not damage the environment, an increase in water use will often improve productivity and the success of agricultural enterprises. Any water saving measures need to be targeted to catchments where water is in short supply and environmental benefits can be realised.

The UK relies heavily on imports of agricultural products and is a major net importer of “virtual water”. For reasons of food security we should seek to maximise our own agriculture outputs using our available water resources and to make significant contributions to the global research effort to increase the efficient and sustainable use of water in agriculture overseas.

The Anglian, Southern and Thames Environment Agency regions are clearly the priority regions where most benefits can be realised from reducing water use in agriculture. The Anglian region is dominant as it is by far the largest abstractor of water for irrigation of field crops, where peak demand for water occurs during periods when water availability is lowest.

In livestock farming In England and Wales most of the water use is for drinking, particularly for dairy cows, with little scope for savings. In addition, although direct water abstractions for agriculture are approximately equally divided between livestock and crop production, the livestock industry is more prominent in the West where rainfall is higher and pressure on water supplies is less than in the East. However, significant water savings can still be made by reducing waste during farm washing procedures as this makes up some 21% of water used for dairy cows, and further savings can be made through good management practices at the farm scale.

Field crops in the UK are either exclusively rain fed, or they receive supplementary irrigation. Abstraction of water for irrigation can clearly reduce levels of ground water and surface flows, but it is also true that changing land use to crops with higher evapotranspiration, such as anticipated with biomass crops, even if they are not irrigated, can also have a big impact on local hydrology; further research is needed to model land use effects. Most water abstractions are applied to potato and vegetable crops, with around half of the water abstractions for field crops being applied to potato. Of this, about half the irrigation for potato crops is used to control common scab, and if non-irrigation-based methods could be developed to this end then large water savings could be achieved. The other half of the water applied to potatoes is required for optimising tuber yield. Breeding research is justified in potato because it is a large, single-species sector; key breeding targets are resistance to common scab, and an improved root system. Agronomy research to promote good soil management and to reduce soil compaction for potato could significantly reduce the need for irrigation. In field vegetables, further research is required to establish the levels of water deficit that are acceptable to maintain quality and yield for each combination of crop and soil type, and irrigation scheduling research could make gains by combining low cost technologies for sensing environmental variables (e.g. thermography, soil sensors, potential evapotranspiration sensors) with mobile communications and automation. Improvements in models for scheduling, particularly for the relationships between soil type, soil water movement and root zone development would be beneficial. Currently, a significant proportion of irrigators do not use scientific methods for irrigation scheduling but rely on personal experience and judgment; significant water savings could be made by improving the uptake of existing technology. Efforts to form networks of

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Farmer-Organised Abstractor Groups should be supported to encourage the spread of best practice and joint investment, for example in on-farm reservoirs.

Intensive soft-fruit production under polythene is an expanding industry that uses significant amounts of irrigation water. There are opportunities for saving water through the use of regulated deficit irrigation, improved scheduling and breeding. In general, although crop production in polytunnels is intensive and can create local problems it does use water more efficiently than open field crops, and as water availability declines, more growers may move to polytunnels or protected cropping to maximise returns from available water.

Hardy nursery stock (HNS) is a major user of water for irrigation and although water costs are a minor consideration in the industry, improvements in irrigation methods and scheduling could reduce labour costs, improve product quality and reduce water inputs. Knowledge transfer activities to promote investment in sub-irrigation systems, rain water harvesting and recycling systems could lead to substantial water savings.

The key to successful breeding programs to increase water use efficiency and drought resistance is the understanding and modelling of the physiological traits that limit productivity in each crop and in each environment where it is grown. This will allow trait selection assays to be developed that are useful to breeders but it will require commercial breeders and scientists to work closely together, supported by public funding. Genetic modification using candidate genes should focus on moving work from model species to crop species and on the evaluation of field performance at an early stage through multidisciplinary collaboration. In addition to potato, breeding efforts are needed for the non-irrigated, large-acreage crops comprising cereals, oilseed rape, sugar beet and biomass crops in order to improve yield stability as drought years become more frequent. Research is also needed to establish if alternative (e.g. Mediterranean) crops could be adapted to Southern England as climate change progresses.

A list of research priorities and estimates of potential water savings are given in Table 8 of the Project Report.

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Contents1._Aim ………………………………………………………………………………………………………

82. Objectives ……………………………………………………………………………………

………… 8

3. Introduction ……………………………………………………………………………………………..

83.1. Pressures on water for agriculture…………………………………………………………………….

83.2. Drivers for water saving: why reduce water use in agriculture? …………………………………..

93.3. A global perspective – water, food security and sustainable agriculture………………………….

93.3.1. Dependence on imported embedded water………………………………………………...

93.3.2. Global research agenda……………………………………………………………………...

103.4. Consumption of water by agriculture in England and Wales: the water cycle and CAMS………

104. Identification of sectors and geographical regions where research and knowledge transfer

activities have the potential to lead to significant reductions in water use………………………12

5. Water use in crop production - generic approaches and issues…………………………………

145.1. Water use efficiency: definitions and scales…………………………………………………………

145.1.1. Catchment scale………………………………………………………………………………

145.1.2. Farm scale……………………………………………………………………………………..

145.1.3. Field scale………………………………………………………………………………………

145.1.4. Plant scale……………………………………………………………………………………..

145.1.5. Leaf scale………………………………………………………………………………………

155.2. Irrigation scheduling…………………………………………………………………………………….

155.2.1. Methods and equipment for applying water………………………………………………..

155.2.2. Approaches to monitoring need for irrigation……………………………………………….

155.2.2.1. Soil water monitoring……………………………………………………………...

155.2.2.2. Direct monitoring of the crop……………………………………………………..

165.2.2.3. Models using meteorological and crop development data and the potential

of remote sensing…………………………………………………………………

165.3. Crop improvement………………………………………………………………………………………

175.3.1. Defining terms: water use, water use efficiency, drought resistance and yield

potential…………………………………………………………………………………………

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175.3.2. Drought resistance can incur a penalty……………………………………………………..

175.3.3. Strategies for improving drought resistance that minimise penalties in yield potential...

185.3.4. Breeding for drought resistance must tailor crop water use to demand based on crop

type, phenology and environment……………………………………………………………

19 5.3.5. Breeding for drought resistance: key points………………………………………………..

196. Specific crop

sectors…………………………………………………………………………………..

206.1. Field crops: Potato (Solanum tuberosum subsp. tuberosum).....................................................

206.1.1. Summary agronomic data…………………………………………………………………….

206.1.2. Physiology and agronomy of water use…………………………………………………….

216.1.3. Irrigation and common scab (Streptomyces spp.)…………………………………………

226.1.4. Irrigation scheduling for potato………………………………………………………………

226.1.5. Agronomy and cultural practices…………………………………………………………….

236.1.6. Conclusions: Water saving in the potato crop through agronomy and physiology…….

246.1.7. Water saving through crop improvement in potato………………………………………..

246.1.7.1. Is crop improvement for water use traits in potato worthwhile? ………………..

246.1.7.2. Introduction to potato genetics……………………………………………………..

246.1.7.3. Genetic diversity……………………………………………………………………..

256.1.7.4. Conventional breeding………………………………………………………………

256.1.7.5. The potential role of Marker Assisted Selection (MAS) in breeding for drought

resistance……………………………………………………………………………..

266.1.7.5.1. Two-parent mapping populations………………………………………

276.1.7.5.2. Association mapping…………………………………………………….

276.1.7.5.3. Current use of molecular markers and potential use to select for

drought resistance……………………………………………………….

276.1.7.5.4. Genome sequencing projects and comparative genomics in

Solanum…………………………………………………………………..

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6.1.7.6. How to assess WUE and drought resistance of cultivars, or within a breeding program……………………………………………………………………………….

286.1.7.6.1. Root traits…………………………………………………………………

286.1.7.6.2. Canopy development……………………………………………………

296.1.7.6.3. Use of stable isotope techniques………………………………………

296.1.7.7. Genetic Manipulation……………………………………………………………..

306.1.7.8. Conclusions: water saving through crop improvement in potato…………….

316.2. Field crops: vegetables ………………………………………………………………………………..

316.2.1. Background information………………………………………………………………………

316.2.2. Irrigation scheduling…………………………………………………………………………..

326.2.3. Mulching………………………………………………………………………………………..

326.2.4. Breeding………………………………………………………………………………………..

326.2.5. Conclusions: water saving in field vegetables……………………………………………..

336.3. Field crops: Sugar beet (Beta vulgaris spp. vulgaris) ………………………………………………


336.3.2. Research opportunities……………………………………………………………………….

336.3.3. Conclusions: water saving for sugar beet…………………………………………………..

346.4. Field crops: Fruit………………………………………………………………………………………..


346.4.2. Water use in strawberries (Fragaria x ananassa)………………………………………….

346.4.3. Strawberry breeding…………………………………………………………………………..

356.4.4. Irrigation scheduling in soft fruit……………………………………………………………...

356.4.5. Rain water collection from polytunnels and water recycling………………………………

356.4.6. Orchard fruit……………………………………………………………………………………

366.4.7. Conclusions: water savings in field-grown fruit ……………………………………………

366.5. Field crops: Cereals…………….……………………………………………………………………...

366.5.1. Conclusions: Water saving for cereals………………………………………………………

376.6. Field crops: Energy crops………………………………………………………………………………

376.6.1. Background…………………………………………………………………………………….

376.6.2. Crops for bioethanol, biobutanol and biodiesel production……………………………….

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6.6.2.1. Production trends………………………………………………………………….37

6.6.2.2. Water use…………………………………………………………………………..37

6.6.3. Biomass crops…………………………………………………………………………………386.6.3.1. Production trends………………………………………………………………….

386.6.3.2. Water use and hydrology…………………………………………………………

386.6.4. Breeding for WUE in energy crops………………………………………………………….

386.6.5. Conclusions: energy crops……………………………………………………………………

396.7. Protected crops (edibles and ornamentals)………………………………………………………….


396.7.2. Which is the best source of irrigation water? ………………………………………………

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6.7.3. Recirculating hydroponics systems………………………………………………………….40

6.7.4. Manipulation of environment and crop to reduce transpiration…………………………...41

6.7.5. Conclusions: water saving in protected crops……………………………………………...41

6.8. Outdoor (hardy) nursery stock…………………………………………………………………………426.8.1. Background information: current status and drivers for change………………………….

426.8.2. Types of growing beds and irrigation systems……………………………………………..

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6.8.2.1. Growing systems employing overhead irrigation or drippers…………………42

6.8.2.2. Sub-irrigation growing systems.………………………………………………….42

6.8.3. Growing media…………………………………………………………………………………43

6.8.4. Irrigation scheduling…………………………………………………………………………..43

6.8.4.1. Scheduling based on estimates of evapotranspiration (ET)………………….44

6.8.4.2. Scheduling based on monitoring soil water content…………………………..44

6.8.4.3. Scheduling based on imaging methods…………………………………………44

6.8.4.4. Regulated deficit irrigation (RDI) ………………………………………………..44

6.8.5. Research facilities in the UK………………………………………………………………….446.8.6. Nursery-scale water management…………………………………………………………..

456.8.7. Knowledge transfer……………………………………………………………………………

456.8.8. Conclusions: water saving in hardy nursery stock…………………………………………

467. Washing of Root Vegetable and Potato Crops …………………………………………………

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7.1. The Washing Process…………………………………………………………………………………..477.1.1. Dry soil removal……………………………………………………………………………..

477.1.2. Dumping into packhouse…………………………………………………………………..

477.1.3. Soak tank and stone separation…………………………………………………………...

477.1.4. Rotary barrel washer……………………………………………………………………….

487.1.5. Brush washers and vegetable polishers (mainly carrots and parsnips)………………

487.1.6. Hydrocooling (mainly carrots, parsnips and turnips)…………………………………….

487.1.7. Final spray rinse…………………………………………………………………………….

487.2. Water recycling and re-circulation……………………..……………………………..……………….

497.2.1. Waste water and solids disposal…………………………………………………………..

497.2.2. Screening…………………………………………………………………………………….

497.2.3. Sedimentation……………………………………………………………………………….

497.2.4. Waste soil/sludge……………………………………………………………………………

497.2.5. Waste water…………………………………………………………………………………

507.2.6. Action Points to Minimise Water use in Washing Vegetable Crops…………………. 50

8. Current and emerging technologies aimed at saving water in livestock farming…………………

518.1. Water requirements of cattle…………………………………………………………………………..

538.1.1. Drinking water requirement………………………………………………………………..

538.1.2. Drinking water supply……………………………………………………………………….

538.1.3. Wash water…………………………………………………………………………………..

558.1.4. Case studies on reduced water use………………………………………………………

568.2. Water requirements of Sheep………………………………………………………………………….

578.3. Water requirements of Pigs ……………………………………………………………………………

588.3.1. Drinking water requirement…………………………………………………………………..

588.3.2. Drinking water supply…………………………………………………………………………

588.3.3. Wash water…………………………………………………………………………………….

598.3.4. Water management on pig units…………………………………………………………….

598.4. Water requirements of poultry ………………………………………………………………………..

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8.4.1. Drinking water requirement…………………………………………………………………..60

8.4.2. Washing water…………………………………………………………………………...........60

8.5. Conclusions – water saving in livestock farming…………………………………………………….61

9. Existing water saving initiatives and case studies………………………………………………………

629.1. Award schemes………………………………………………………………………………………….

629.2. Farmer-organised abstraction groups (FOAGs)……………………………………………………..

629.3. Conclusions and opportunities………………………………………………………………………...

6210. Opportunities to reduce water wastage on farms through auditing and good

practice………...62

11. Summary and conclusions: opportunities for water saving in agriculture……………………….

6811.1. Drivers for water saving………………………………………………………………...………………

6811.2. Water withdrawals, changes in land use and food security…………….………………………..…

6811.3. Reducing water withdrawals in over-abstracted catchments in England and Wales……………

6911.4. Generic research issues………………………………………………………………………………..

7012. Literature

cited………………………………………………………………………………………………..…73

13. Acknowledgements …………………………………………………………………………………………….

82

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FiguresPage

1. The global water cycle……………………………………………………………………………….

10 2. Annual water use by agriculture…………………………………………………………………….

11 3. Annual rainfall in England and Wales………………………………………………………………

11 4. Indicative water availability…………………………………………………………………………..

12 5. Irrigation of outdoor crops……………………………………………………………………………

13 6. Schematic response curve for the relationship between crop yield and water input………….

17 7. When does high WUE give drought resistance?………………………………………………….

17 8. Distribution of the potato crop in England………………………………………………………….

20 9. Water supply for cattle via nose pumps……………………………………………………………

55 10.Specialist livestock pumps…………………………………………………………………………..

55 11.Typical “flat deck” weaner accommodation with nipple drinkers………………………………...

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Tables1. Water availability related to population……………………………………………………………..

82. The water use footprint of the UK…………………………………………………………………..

93: Source of irrigation water used at 50 protected crops sites surveyed by ADAS………………

404. Summary of drinking and wash water requirements for livestock……………………………….

525. Characteristics of the dairy farm case study (CS) and details of the amendments to practice

on the CS farm for each management scenario………………………………………………..

576. Changes to the amounts of slurry produced and sufficiency in storage capacity after

adopting each alternative management strategy. ……………………………………………...

57

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7. Estimates of drinking water requirements for pigs (L pig-1 day-1)………………………………..

588. Research priorities……………………………………………………………………………………

72

AnnexesI. Summary of recent research projects related to water use funded by the UK government or

Levy Boards…………………………………………………………………………………………

83II. Environment Agency Water Efficiency Awards 2001-2007; NFU Agriculture & Horticulture

Category…………………………………………………………………………………………….

89

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1. AimTo identify new and existing areas of research and knowledge transfer that will create opportunities for reducing water use in English and Welsh agriculture

2. Objectives2.1. To identify geographical regions and agricultural sectors where research and knowledge

transfer activities have the potential to lead to significant reductions in water use2.2. To review current and emerging technologies aimed at saving water in agriculture that are

most relevant to the region x sector combinations identified in objective 2.1.2.3. To review existing initiatives and case studies related to saving water in agriculture, with

emphasis on the region x sector combinations identified in objective 2.1.2.4. To identify and prioritise research areas by integrating information from objectives 2.1 to 2.3

and to seek consensus from an expert group

3. Introduction

3.1. Pressures on water for agricultureScenarios for climate change in the UK driven by rising greenhouse gas emissions indicate that on average winters will become wetter, but that summers will become drier; by 2020 in the south and east it is predicted that average summer precipitation will decrease by 20%, and that year-to-year variability will mean that on average one-in-ten summers will be considered very dry, such as the summer of 1995. By 2080, mean summer rainfall may have decreased by up to 50%, and soil water by up to 40% [1]. If this occurs there would be a large impact on agricultural practices and the rural economies in the south and east. In particular, yields of field crops could only be maintained by increasing irrigation, and/or by the adoption of varieties or alternative crops suited to the drier summers.

Following adoption of set-aside policies designed to limit food production in the UK and the EU, a future scenario is of massive expansion in land use for biofuel production to replace fossil fuels and limit further CO2 emissions. Sugar, palm oil and wheat prices have increased on world markets because of use as biofuel rather than food. If biofuel production expands there would be pressure to maximize the area of land in use for agriculture and to increase production efficiency in relation to inputs such as water and nutrients, such that available water is used efficiently and without damaging the environment.

The amount of water available per head of population is low in the UK in comparison to some other countries generally considered to be dry, mainly because of our high population density (Table 1.). This is most extreme in South-east England where rain fall is lower than in the West, and population density is high. Competition for water between agriculture and domestic and industrial users is therefore important, particularly in the South-east. Trading of abstraction licenses to maximize profit from available water will tend to reduce water availability for agriculture.

Table 1. Water availability related to population

Region/Country m3 person-1 year-1

England and Wales 1,334South-east England 921Thames Valley 266Egypt 794Ethiopia 1519Israel 255FAO data taken from Environment Agency website: http://www.environment-agency.gov.uk/subjects/waterres/1014767/1370506/1401671/1407535/?lang=_e

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3.2. Drivers for water saving: why reduce water use in agriculture?There are two key drivers for reducing water inputs in agriculture in England and Wales;

(i) Environmental protection Environmental protection is now regulated by the EU Water Framework Directive (WFD), implemented by the Environment Agency, with all water courses needing to reach good ecological status by 2015 [2]. Abstraction of surface and ground water in the future is unlikely to be permitted if it is shown to cause environmental damage. Excessive use of water also has major impacts on water quality and the flow of nutrients and other pollutants into rivers and lakes.

(ii) Sustainable agricultural production Food and potentially energy crop production needs to be sustained into the future in the face of reducing water availability both to meet the needs of consumers in the UK, but also to maintain a healthy and sustainable rural economy. Efficient use of the water that is available - once the needs of the environment have been taken into account - and the ability to maintain productivity with lower water inputs will be increasingly important in order to ensure the success and profitability of agriculture.

3.3. A global perspective – water, food security and sustainable agriculture

3.3.1. Dependence on imported embedded waterA 3oC global temperature rise would result in major redistribution of global surface water, and cause crop losses due to drought and flooding. Models predict there would be a serious drought every ten years on average in Southern Europe [3]. Larger temperature increases could have serious negative effects on global food production, and a redistribution of production, e.g. from South to North.

The concept of “virtual water” or “embedded water” [4] has been introduced to describe the volume of water required to produce a product or service, and to track the trade of that embedded water around the globe. The UK is the third largest net importer of embedded water, with a net import of 47,000 Mm3 year-1 (million cubic meters per year) [5], of which over half represents agricultural products (Table 2.). The UK is therefore highly dependent on the exploitation of water resources overseas. Water availability is the most important limiting factor in crop production globally [6], and agriculture accounts for approximately 85% of the consumptive water use on our planet. Currently water resources are under threat in many countries because water is mined from non-renewable aquifers, or environmental damage due to over-abstraction goes unchecked. For reasons of food security, and to avoid damaging exploitation of overseas water resources, the UK should maximize production by making the most effective use of our renewable water supplies.

Table 2. The water use footprint of the UK

Category Water used Gm3 year-1

Domestic water

Domestic water withdrawal 2.2Crop evapotranspiration (products consumed within the UK)

12.8

Crop evapotranspiration (products exported) 3.4Industrial water withdrawal (products used within the UK)

6.7

Industrial water withdrawal (products exported)

1.5

Use of foreign water

Importation of agricultural products 34.7Importation of industrial products 16.7Re-exported products 12.8

Total 73Net import 47Data taken from Chapagain and Hoekstra (2004) [5]. Note: crop evapotranspiration includes irrigated and non-irrigated crops.Note: 1 Gm3 = 1000 Mm3 = 1 km3

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3.3.2. Global research agendaThe development of drought resistant crop varieties (see section 5.3.1. for definitions) has been recognized by economists as a potentially very important and economically attractive means to adapt crop production to climate change, and to address current challenges faced by many developing countries; the Stern Review on the Economics of Climate Change [3] recommends that a framework for international collective action of “global public good” should be pursued to allow adaptation to climate change, and this would include, as one of four key points, the development and deployment of drought- and flood-resistant crops. Similarly, in the Copenhagen Consensus a panel of expert economists were asked to answer the hypothetical question; “if the international community had an additional $50 billion to devote to new initiatives (to address major world challenges), how should that money be spent?”. Research to increase water productivity in food production was ranked as the 15 th most important global challenge. Increasing water use efficiency in crops, if this can be achieved, has major economic and humanitarian rewards on a global scale, not just in England and Wales, and any research performed in the UK should ideally contribute to, and gain from, international programs in this area, including those proposed by CGIAR [7] and DFID/BBSRC [8].

3.4. Consumption of water by agriculture in England and Wales: the water cycle and CAMS

In England and Wales irrigation is used to supplement relatively unpredictable rainfall patterns during the growing season, with water being abstracted from both ground water (bore holes) and surface waters. Since a primary driver for saving water is to ensure sufficient is available to the environment to prevent ecological damage, the use of water must be considered in the context of each catchment and its unique hydrology. Irrigation has a major impact on the environment because the need for water is greatest when availability is lowest; water is required in the summer when rain fall is low and surface and ground water resources are already stretched. Use in agriculture is also largely consumptive because water is lost to the atmosphere rather than returned downstream to surface waters as for other sectors such as energy generation and industry.

When considering the need for saving water, care must be taken not to restrict water use unnecessarily; abstraction in many cases will have no environmental impact, and so should be

promoted to maximize agricultural productivity. Water is not consumed in the same sense as energy – it flows through the water cycle (Figure 1) and is a renewable resource in the UK. Catchment Area Management Strategies (CAMS) have been introduced to define catchments where water saving is required to protect the environment, and to provide the geographical units by which water abstraction is managed.

Water withdrawals for agriculture, at around 300 Mm3 year-1 [9] to 500 Mm3 year-1 (see below), are small compared to the calculated UK crop evapotranspiration (16,200 Mm3 year-1, Table 2). As can be seen from Figure 1, the degree of evapotranspiration will affect the runoff and percolation of precipitation into surface and ground waters; protection of water courses must therefore take into account effects of changing land use on catchment hydrology, for example for non-irrigated crops, a

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Figure 1: The Global Water Cycle (taken from United Nations Environmental Program: http://www.unep.org/vitalwater/ )

http://www.unep.org/vitalwater/


shift in land use to crops with higher evapotranspiration (e.g. biomass crops, forestry) could impact on ecology to a similar extent as direct abstraction for irrigated crops [10].

15

0102030405060708090

100W

ater

usa

ge (M

m3 a

-1)

All livestock

Glasshouseand Nurserycrops

Irrigation offield crops

Figure 2: Annual water use by agriculture according to EA regions in England (Mm3 year-1). The proportion of the total contributed by the three largest sector categories of field irrigation, all livestock and glasshouse and nursery crops, are shown. Taken from King et al, 2006 [9].

Figure 3: Annual rainfall in England and Wales. From Environment Agency, using Met Office data 2001


4. Identification of sectors and geographical regions where research and knowledge transfer activities have the potential to lead to significant reductions in water use

The total amount of water withdrawn for use in agriculture, either abstracted from surface or ground waters or taken from mains supplies, is of the order of 300 Mm3 year-1 [9] to 500 Mm3 year-1 [11]. A useful categorisation of water use is into the three categories (i) livestock, (ii) irrigation of field crops, and (iii) irrigation of glasshouse and nursery crops, and water use in these categories can be broken down by Environment Agency (EA) regions [9] (Figure 2).

The water used by the two other activities considered, washing of field vegetables, and spraying of arable crops, is small in comparison to total use, being 0.2 and 3.1 Mm2 year-1 respectively [9]. Mitigation measures for crop spraying are not considered further, but measures for washing field vegetables and potatoes are presented in section 7.

The primary aim of water saving is to prevent depletion of water levels to the point of environmental damage and the impact of regional water use must be assessed in the context of regional rainfall (Figure 3), the amount of water available for abstraction [12] (Figure 4) and patterns of agricultural practice. Rainfall ranges from 2200 mm in the high-ground on the West, to 550 in the East, with a clear gradient from East to West (Figure 3). The Anglian region has low rainfall and good agricultural soils, and is consequently the area with the most irrigated land (Figure 2). Abstraction of summer surface water is currently considered unsustainable in much of the Southern and Anglian Regions. In most of England and Wales, with the notable exceptions of the North East Region, the Peak District, and limited areas of Wales, any increase in summer abstraction from surface waters

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Figure 4: Indicative water availability, 1, summer surface water; 2, winter surface water; 3, ground water. From: Environment Agency.


would lead to environmental damage. If no further water is available now, then the predicted reductions in summer rainfall are likely to make the current levels of summer surface abstraction unsustainable in the future. Additional water is available for abstraction from ground water resources in some scattered areas of England and Wales but the locations where ground waters are currently being used unsustainably are largely restricted to the South and East (Figure 4).

Of the irrigated field crops more than half of abstracted water is used for potato (Figure 5, [13]), and the next biggest use of irrigation is for field vegetables. Other outdoor crops use relatively little abstracted water.

From considering data in Figures 2 to 5 the following points can be made:

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Anglian, Southern and Thames are clearly the key EA regions where water savings would be of the most benefit by reducing the environmental damage that is already occurring.

Irrigation of field crops is by far the biggest agricultural user of abstracted water in the key regions (98 Mm3 year-1), with the Anglian region dominating (72 Mm3 year-1).

More than half of irrigation water for field crops is used for potatoes. In the Midlands, where a significant amount of water is used for irrigation of field crops,

and for glasshouse/nursery production, there is currently only limited scope in localized areas for increasing abstraction without causing environmental damage.

Livestock farming is particularly important in the South West, North East, North West and Midlands where in most areas summer abstraction would only reach damaging levels if future summer rainfall declines.

The Midlands, North West and Southern regions use the most water for glasshouse crops and nurseries, with the Southern region being the key area requiring reduced water use in this sector on environmental grounds.

0

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1980 1985 1990 1995 2000 2005Year

Irrig

atio

n ap

plie

d (M

m3 ye

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Orchard fruit

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Potatoes

Sugar beet

Orchard fruit

Small fruit

Vegetables

Grass

Cereals

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Figure 5: Irrigation of outdoor crops (plotted from Weatherhead and Danert 2002 [13]).


5. Water use in crop production - generic approaches and issues

In this section generic issues related to water use, irrigation and breeding are covered. More specific details related to particular crop sectors are presented in section 6.

5.1. Water use efficiency: definitions and scales

Where water use is likely to cause environmental damage crop water use efficiency (WUE) becomes important so that maximum benefit can be obtained from the limited amount of water available. WUE can be considered at many levels, from catchment to farm scale, and, in the case of crops, from field to plant to single leaf scale, but the key practical definition of water use efficiency relevant to farmers and growers is the amount of agricultural product produced per unit of water consumed.

5.1.1. Catchment scaleThe consumptive use of water can be considered as water that is used and then lost from the catchment in such a way that is no longer available to the environment or abstractors, and includes evaporation and transpiration. Withdrawals per se do not necessarily represent consumptive use; where withdrawals are excessive one possible scenario is that excess water is returned by run-off or percolation for the benefit of the environment and other abstractors. However, operating this high flux by having both high withdrawals and high return flow rates has other negative consequences such as unnecessarily high labour and energy inputs, and nutrient leaching. Excessive abstraction from ground waters may result in depletion of ground water reserves in favour of surface flow which then may be lost to the sea. Excessive abstraction from surface waters followed by percolation to ground waters may lead to water-logging and salinity problems because of a rising water table.

5.1.2. Farm scaleAt the farm or nursery scale, withdrawals can be minimized, for example by recycling of water, by harvesting and using rainwater, by avoiding wastage due to leakage, and by careful irrigation scheduling. Water saved in this way may benefit the individual farm or nursery by reducing costs and ensuring EA abstraction licences are not exceeded, but could still have little impact on efficiency at the catchment scale if the reduction in withdrawals was offset by a reduction in the run-off or percolation of rainfall back into the catchment. Local hydrology will determine whether savings at the farm scale will be translated into benefits for the wider catchment.

5.1.3. Field scaleAt the field scale WUE can be defined as either the yield per unit of water lost by evapotranspiration, or alternatively, as the yield per unit of water received by the crop as rainfall and irrigation, e.g. as kg ha -1 mm H2O-1. It is affected by all the factors discussed below for plant and leaf scale WUE but in addition is affected by irrigation efficiency and uniformity (see section 5.2), climate, canopy structure and soil type. Evapotranspiration is higher at higher temperatures, wind speeds and intensities of solar radiation, but is reduced by increasing CO2 and relative humidity (see section 5.2.2.3). Ground cover by the crop canopy affects the ratio of productive transpiration to non-productive evaporation from the soil, and surface roughness of the canopy influences the boundary layer resistance to transpiration; a crop with a smooth canopy surface as in cereals will tend to have a humid layer of air above the canopy because of low air turbulence and this can limit loss of water from the leaves. The water holding capacity and hydraulic conductivity of the soil influences the time period during which irrigation or rain water is held in the root zone and so is available to the crop.

5.1.4. Plant scaleAt the whole plant scale, WUE can be defined as the total biomass (or biomass of harvestable material) gained per unit of water lost from the plant as transpiration. It is influenced by leaf scale factors (see below), but also specific factors that operate at the whole plant level, including:

partitioning of assimilate between root, shoot and reproductive tissues (including flowering time and harvest index)

metabolic, physiological and developmental responses to the environment that operate at the plant level, for example root-to-shoot signalling

5.1.5. Leaf scale

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Two fundamental processes that influence biomass accumulation and water loss occur primarily in leaves; (i) net diffusion of CO2 into the leaf through stomata and into sub-stomatal airspaces followed by assimilation of CO2 by photosynthesis, largely in the palisade cells, and (ii) transpiration whereby evaporation occurring mostly at the cell surfaces in the sub-stomatal spaces is followed by a net diffusion of water vapour out of the leaf through the stomatal pores.

At the leaf scale WUE can be defined as the ratio between rate of CO2 assimilation (A) and rate of transpiration (E), but, because transpiration rate is highly dependent on temperature and relative humidity (encapsulated in the term VPD, the vapour pressure deficit for H2O between leaf and atmosphere), it is often defined as the ratio between A and stomatal conductance (gs), and described as intrinsic WUE - a measure that is independent of VPD.

In leaves, instantaneous A/E and A/gs ratios can be measured using infrared gas-exchange equipment, and surrogate measures of A/gs that are time-integrated over leaf development can be obtained by measuring carbon isotope discrimination (Δ13C), a relatively high-throughput method (see also sections 6.1, 6.2 and 6.5 for application in specific crops).

5.2. Irrigation scheduling

5.2.1. Methods and equipment for applying waterIrrigation application efficiency can be defined as the ratio of the average amount of water stored in the root zone to the average amount of water applied [14]. Irrigation uniformity is a further important consideration and can be expressed as Christiansen’s coefficient of uniformity (CU) (see section 6.8).

In 2001 around 88% of the irrigated land in England was irrigated using hose reels, either connected to rainguns (72%) or booms (16%), with the remaining area irrigated by drip or sprinklers [13]. Rainguns, as the most popular method because of simplicity and low investment costs, also have the lowest application efficiency and uniformity because of evaporative losses from droplets, wind-drift and inherently poor uniformity. Research aimed at improving raingun uniformity in England has been initiated [15]. Increased uptake of alternative equipment (e.g. drip (trickle), boom or sprinklers) may provide increased uniformity and application efficiency provided that they are adequately managed (see also section 6.1.4 for discussion of drip irrigation in potatoes).

Maximising the water held in the root zone requires that application rates and frequencies are in step with water movement in the soil profile, to minimize run-off and percolation. Research to model water movement in soils could help optimise this aspect of scheduling.

5.2.2. Approaches to monitoring need for irrigationProductive scheduling requires an estimate of how much water should be applied to match the demands of the crop and to prevent the yield or quality losses that would result from insufficient water being available in the root-zone. Accurate scheduling should minimise both the amount of water applied, and the associated labour and energy inputs. There are three approaches to scheduling that can be used independently or in combination, outlined below. A good understanding of the minimum water requirements for a particular combination of crop and soil-type is needed to avoid excessive or unnecessary irrigation. At the time of the last survey of irrigation of outdoor crops 48% of irrigators used non-scientific (i.e. visual assessment, experience and judgement) methods to schedule irrigation [13] and it is possible that water savings could be made by increasing the use of more objective monitoring and scheduling approaches.

5.2.2.1. Soil water monitoringMeasurement of soil water content or soil water potential can be achieved with a range of instruments placed in the root-zone. The data can then be used to calculate the volume of irrigation required to bring the soil to the desired level. Instruments include neutron probes, sensors of soil capacitance or electrical conductivity, tensiometers and psychrometers. However, in many field situations heterogeneity of soil properties means that measurement of soil water status at only a few positions as is possible with current technology has limited value and is not adequate to accurately evaluate the need for irrigation [16]. Despite this, 29% of irrigators in the UK used soil moisture sensors to schedule irrigation [13]. An ideal solution would be a high density network of soil sensors combined with an irrigation system that was capable of delivering water differentially over the field at relatively high spatial resolution [17]. Such a system is not practical or economic with current technology, however there is a trend for sensor costs to decline and there are rapid technological developments in “wireless sensor networks” for many applications including environmental monitoring, for example monitoring salinity intrusion [18], and early prototype systems are being employed to control irrigation [19, 20]; in

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the medium term it is conceivable that a system consisting of a network of low cost sensors transmitting data to a system controlling a network of solid set sprinklers or drip tape could be developed. This would require close collaboration between engineers and agronomists for its development. Some practical progress has been made in the UK through development of closed-loop irrigation control systems based on a small number of relatively expensive soil sensors, including the use of mobile phone data transmission (see sections 6.4.4. and 6.8.4.2. for applications in soft fruit and hardy nursery stock respectively), but future developments in low-cost, highly distributed sensor networks would provide a major advance.

At the field to catchment scale, soil water content in the surface layer (0 to 5 cm) can be estimated and mapped from microwave remote sensing (e.g. from satellite, air-craft or cherry picker) [21, 22], although this approach is not yet fully developed for scheduling it was able to remotely identify leaking farm pipework [22].

5.2.2.2. Direct monitoring of the cropRather than monitoring soil water content, the response of the crop to soil water availability can be monitored and irrigation applied when a response is detected. Direct measurements of plant water status such as leaf water potential and relative water content have been evaluated for scheduling purposes [23] and generally do not provide practical approaches. A more indirect method of monitoring the crop is the use of infrared thermography (IRT) to create a 2-dimensional map of canopy temperature. Transpiration results in evaporative cooling, thus an increase in canopy temperature, relative to suitable references, can indicate stomatal closure and crop stress [24]. Energy balance calculations can be used to map evapotranspiration at the farm and catchment scale using thermal image data collected by satellite, and can also be use to calculate the crop coefficients used in scheduling [25, 26] (see below). Catchment scale IRT is more suited to arid regions with higher VPDs and predictable cloud cover so it is not clear that it will be well suited to field crops grown in the current UK climate [23]. However, IRT is being investigated at a practical level to schedule irrigation in UK nurseries, i.e. for monitoring protected crops using gantry mounted cameras (see section 6.8.4.3).

5.2.2.3. Models using meteorological and crop development data The most common method of irrigation scheduling is to use a model to calculate evapotranspiration from a reference crop (EO) using meteorological data (temperature, humidity, wind-speed, solar radiation), and then to determine evapotranspiration from a specific crop (ET) by multiplying EO by a crop coefficient (Kc) [27]. Kc is dependent on crop attributes and developmental stage (e.g. albedo, leaf area index and height). Irrigation need is then determined with a simple water-balance model, i.e. the difference between calculated ET and water inputs (rain fall and irrigation), taking into account the soil type and the water stored in the root zone. Models need to be calibrated and checked against actual soil water availability data collected from soil moisture sensors as errors are cumulative throughout the season.

Values for Kc can be taken from tables, or from observations taken in the field by the farmer, however more recently they can be obtained from remote sensing (“earth observation”), either by IRT, or using hyperspectral image data from satellites to calculate normalized difference vegetative index (NDVI), a parameter that has been shown to have a fairly linear relationship to Kc [28]. An ideal situation could be where an irrigation advisory service was able to provide irrigation recommendations based on field-by-field Kc and EO values calculated from satellite and meteorological data, taking into account past and predicted rainfall, and using internet or mobile phone technologies to rapidly provide specific information to each farm. Currently it is not clear if use of satellite data for providing ET and Kc values is viable in the UK climate where rainfall and cloud cover is sporadic during the growing season, and irrigation is only supplementary and on selected crops; this situation may change as climate change progresses. However, there are real opportunities to provide growers with high resolution meteorological data at an affordable price suited for calculation of EO. Currently the most suitable data from the Meteorological Office is not affordable to most growers.

Commercially available scheduling packages that use ET and water-balance models are commonly used in England, for example IRRIGUIDE developed by ADAS, is used on at least 300 farms [29]. Consultants often work together with growers and farmers using these models, and in 2001 23% of irrigators used water balance calculations to schedule irrigation [13].

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5.3. Crop improvement5.3.1. Defining terms: water use, water use efficiency, drought resistance and yield

potentialWhen considering how to reduce water inputs through crop improvement it is important to define the terms used to describe the productivity of crops in relation to water use. The concept paper of Blum [30] provides robust terminology, using the terms yield potential, drought resistance, and WUE. This section explains the use of these terms before we discuss crop improvement for specific crops. In particular, drought resistance and WUE are overlapping and complementary terms with subtly different meanings and applications.

Yield potential (YP) is the maximum yield of a cultivar under optimal conditions. A drought resistant cultivar can simply be defined as one that produces a higher yield than a standard cultivar when under drought stress (YDS) [31] (Figure 6). Drought stress is defined as conditions where demand for water by the crop is not met by supply such that crop water status declines. The term “drought tolerance” is often used in the literature but it is poorly defined, or defined in many different ways. It is not used further here, as it can be confused with the terms dehydration avoidance and dehydration tolerance (see section 5.3.4.).

WUE has already been defined in various ways in section 5.1, but here it is most usefully considered as the ratio between the crop yield and the water used by the crop, or between crop yield and water input (irrigation and precipitation). The value of the WUE ratio can be increased by reducing water use or input (the denominator) or by increasing yield (the numerator).

5.3.2. Drought resistance can incur a penaltyIn theory, a cultivar could be produced that has both higher YP and YDS, but drought resistance often comes with a penalty in YP such that a crossover point between two cultivars is observed, with the drought resistant cultivar only out performing the standard cultivar below the crossover point in water input [30] (Figure 6). If could be said that the drought resistant cultivar is better adapted to low water

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Figure 6: Schematic response curves for the relationship between crop yield to water input. Curves are given for a drought resistant (red) and a standard (green) cultivar differing in yield potential (YP) and yield under drought stress (YDS). Non-productive water use (NPWU) for each cultivar is indicated on the x-axis. Difference in yield potential (ΔYp) when water is not limiting (at water input B), and difference in yield under drought stress (ΔYDS) at water input A are given.

Figure 7: When does high WUE give drought resistance? A schematic plot of yield against the water used over a season (seasonal transpiration) for cultivars of a theoretical crop of high (H), medium (M) and low (L) WUE. It is assumed that yield is proportional to water used and that yield potential (Yp) is suppressed as WUE increases. WUE is given by the slopes of the lines; horizontal dotted lines represent yield potential. Crossover points are the levels of water use at which one cultivar becomes more productive than another.


input environments, and the standard cultivar is better adapted to environments where water inputs are higher, or non-limiting.

The relationship between WUE and drought resistance can be counter-intuitive because yield itself has a strong positive relationship with water use: the more water a crop uses the higher its yield. And, at least at the leaf level, the relationship is non-linear; for a given reduction in transpiration the reduction in CO2 assimilation is initially small and then becomes greater, and so WUE increases as transpiration is reduced. So, if a cultivar is bred to have lower transpiration it is likely to have higher WUE, but lower total water use over a season and therefore lower yield potential. The consequence is that high WUE does not always equate to drought resistance. This is illustrated in Figure 7 where yield is plotted as a function of water used for cultivars of differing WUE: in this example if environmental conditions restrict seasonal water use to less than 280 mm then the high-WUE cultivar has the highest yield, but if more water is available and is used, the medium-WUE and then low-WUE cultivars provide a higher yield, even though they are less productive per unit of water consumed. If crop water use was restricted to 350 mm because of environmental conditions, and these conditions met the definition of a drought stress, then from Figure 7 it can be seen that the medium-WUE cultivar would give the highest yield and would, under the definition given above, be considered as the most “drought resistant”.

From this it is clear that a pitfall of selecting for high WUE (based on the ratio of yield to water used) is that total water use may be reduced, and that this will be associated with a drop in yield potential, and possibly even a drop in yield under moderate drought. The challenge for breeders is to increase yield stability (yield integrated over a number of seasons) in water-limited environments, but care must be taken not to depress yield potential to the point where the grower will lose out in the longer term by having low yields in years with higher than average rainfall. Breeding for improved leaf level WUE has been successful in Australia: wheat varieties were selected using carbon isotope discrimination that now provide yield advantages in semi-arid environments where total water use is restricted due to lack of late-season rainfall [32].

5.3.3. Strategies for improving drought resistance that minimise penalties in yield potential

The discussion above about the relationship between water use and yield is an over simplification because it is assumed that reducing water use will reduce yield potential by limiting CO2 assimilation. However CO2 assimilation is not the only factor that can limit yield potential. Indeed, most crops will experience some water deficit stress even when soil water is not limiting, for example, because of imbalance between water uptake and transpiration at midday. Under these circumstances a cultivar with reduced transpiration may have an increased yield potential because turgor-driven growth is improved by the higher water status. Growth and development can also be controlled through hormonal or other developmental signals that depend on the water status of the plant and soil, and such signals may limit growth before assimilation becomes limiting. In addition, although the majority of crop water loss occurs through the stomatal pores where water loss and CO2 uptake go hand-in-hand, there are also components of water loss that are non-productive because they are not necessary for CO2 uptake (see NPWU in Figure 6). Traits that reduce non-productive water loss include greater cuticular resistance, more rapid crop establishment to prevent evaporation from bare soil, and deeper roots to capture soil water before it is lost by percolation. Both deeper roots and greater canopy cover could result in a crop using more water from the soil. This would improve yield per unit of water input because more of the water available could be used productively (better WUE at the field level), but because of greater transpiration it would actually reduce WUE at the leaf level, and could also have knock-on effects by reducing return-flow of water to surface and ground waters in the catchment, so reducing water availability to others in the catchment. It is important to consider WUE at all levels, as each may have different significance in particular situations.

In theory, increases in WUE without a penalty in YP could also be achieved by selecting for an increased rate of CO2 assimilation or by reducing the rate of carbon lost through respiration, provided that corresponding increases in water use did not occur. Cultivars with higher WUE and no reduction in YP would perform better at all levels of water use.

It remains to be seen the extent to which yield and WUE can be improved in parallel, but a screen for high WUE combined with high yield potential, provided these two traits are not always physiologically mutually exclusive [30], could provide the best of both worlds. In Defra project HH3608TX, by placing QTL for both biomass and WUE on the same genetic map it has become possible to determine which WUE QTL are associated with suppression of biomass, and which are not.

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5.3.4. Breeding for drought resistance must tailor crop water use to demand based on crop type, phenology and environment

As alluded to above, drought resistance and WUE mechanisms can be various, and include different strategies, but can broadly be broken down into dehydration avoidance and dehydration tolerance [31]. Dehydration avoidance is where plant water status is maintained as soil water availability is reduced, e.g. by osmotic adjustment to maintain turgor, reduced evapotranspiration to conserve water, increased rooting depth to access more soil water, and optimised phenology such that canopy development and sensitive reproductive phases of growth occur when water availability is greatest, i.e. matching crop development to predictable seasonal variation. Dehydration tolerance mechanisms allow growth to continue even when plant water status declines; they include production of metabolites and proteins that protect cellular functions and so maintain photosynthesis as cellular water potentials decline. The tolerance of severe dehydration that can allow plant recovery during episodic extreme drought is a mechanism that has evolved in some xerophytes, but, despite a great deal of activity by molecular biologists in this area, it is generally accepted that such mechanisms are unlikely to have any bearing on agricultural systems where a quiescent phase would clearly not be compatible with high yield [30].

In some cases, including potato and field vegetables, irrigation is used to enhance economic yield by controlling quality, rather than enhancing biomass and growth, and breeding for high quality with low inputs is an important consideration.

When breeding for drought resistance two possibilities are available: breeders could select for yield, and/or field level WUE in the specific environments where the crops will be grown. However, such high-level traits exhibit low heritability because of the strong environmental interaction, and complex, quantitative genetics. Alternatively, if a good understanding of the specific physiological traits that will influence drought resistance or WUE for a specific crop x environment combination can be reached, then those more highly heritable traits can be selected for directly and then breeding lines tested in those environments. It is likely that some traits will be more widely applicable than others, for example selecting directly for leaf level WUE, whereas other traits (e.g. root development and phenology) will be highly specific to rainfall patterns, soils and crop types.

5.3.5. Breeding for drought resistance: key points In terms of reducing water input in agriculture, by definition drought resistant cultivars will give

a higher yield where water inputs are low enough to create stress in the crop, and cultivars with higher WUE will give a higher return for each unit of water consumed, and will also give a higher yield per se provided that the total water use does not go beyond any crossover point that might occur (Figure 7).

Drought resistance and WUE are highly complex traits that depend on many interacting genetic and environmental factors, and although the potential gains from breeding are significant, the task is challenging, with the greatest challenge being the understanding of which traits limit productivity in water-limited environments.

Molecular genetics, including identification of quantitative trait loci has become routine and can be applied to most crops providing the physiology and agronomy is in place to put genetic analysis in the right context, and this should allow more rapid progress in reaching breeding goals. Molecular genetics and the contribution of genetic modification approaches are explored in more detail in the context of potato, a key target crop (section 6.1.7).

Commercial breeding tends to focus on traits that are currently more tractable such as disease resistance and quality. It will therefore be important to maintain public funding in the area of drought resistance, aimed at adapting UK crops and contributing to a global effort that will enhance our food security in the long term.

It is increasingly recognised that progress in crop improvement for water-limited environments will only come from multidisciplinary teams with a deep understanding of the physiological and agronomical factors that limit productivity.

Key targets for breeding in England are the most heavily irrigated field crops (potato and field vegetables). Potato potentially provides the best returns from research investment because it is a large sector and a single species, although both quality and yield issues related to water must be considered of equal importance in this crop. Other key targets are the energy crops that are water-hungry and threatening a rapid expansion in cultivated area that could impact on the catchment scale (section 6.6).

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6. Specific crop sectors

6.1. Field crops: Potato (Solanum tuberosum subsp. tuberosum)

6.1.1. Summary agronomic dataGlobally, potato is the fourth most important crop behind the cereals rice, wheat and maize, and has significantly more nutritional value than these cereal crops. As discussed below potato is particularly sensitive to soil water deficits, is a large acreage crop in the UK (149,000 ha in 2004 [33]) with an annual farm gate value averaging £500-600 million [34]. The market value of the UK potato crop doubled to £1 billion in 1995 because hot, dry conditions reduced availability of good-quality tubers on global markets [34], demonstrating how climate change could have major impacts on the economics of potato production in the UK. In 1975/76 yields were reduced by around 32% compared with mean yields because of severe summer drought [35]. Since this time, irrigation has been increasingly employed to curtail effects of drought such that the area of the potato crop in England and Wales that is irrigated has increased from 15% in 1982 to 48% in 2001 [33]. In 2001, 76 Mm3 of irrigation was applied to the potato crop in England and Wales, representing over 50% of irrigation applied to field crops [13], and around 25% of the total volume of water (300 Mm3 [9]) used in agriculture. It has been estimated that for pre-pack (supply of fresh potatoes packed in bags for supermarket sales), growers apply between four and eight irrigations of 12 - 18 mm per season to avoid common scab symptoms in the period following tuber initiation [37]. Taking into account that only 48% of the total crop was irrigated in 2001, and that pre-pack crops occupied 48,000 ha in 2005, the volume of water used to prevent common scab is in the range 11 to 33 Mm3 per year, although the figure maybe higher considering the reducing tolerance for severe common scab in the processing markets [38]. It is estimated that for pre-pack typically about half the irrigation is applied to avoid scab during a critical four week period, and the other half is applied in the following 8 weeks to improve bulking and yield [39].

The potato crop is mainly grown in the East of England, with 47% of the acreage being in Lincolnshire, East Anglia, Cambridgeshire and the East Midlands [35] (Figure 8, [40]), where rainfall (Figure 3) and water availability (Figure 4) are relatively low. There is also significant production in eastern Yorkshire and Humberside and the West Midlands [35].

Between 1960 and the present day there has been a 50% reduction in acreage of the potato crop, but annual production has remained fairly steady at around 6 million tonnes because over the same period yield has improved from 23 to 49 t ha-1[35]. Recent yield increases are due mainly to improvements in cultural practices, particularly the increased use of irrigation, although new cultivars may also have played a major role, and it is claimed that 50% of the four-fold yield increases in the period 1930 to 1980 were due to genetic improvement [41], although Russet Burbank is an example of an old variety (selected in 1875 in the USA), that continues to be grown and provides high yields in the USA. The export of home potato crops is insignificant, but around a million tons of processed potatoes were imported in 2004. Thus the potato crop is grown mainly for the home market and is consumed at a rate of 100 kg (head of population)-1 year-1, a figure that has remained steady over the last 15 years, although during this time there has been a shift from consumption of fresh to processed potato [35].

One attractive means of reducing the volume of irrigation water for potato production would be to further increase yield, such that the 6 million t year-1 required by UK consumers could be produced on a smaller acreage, thereby reducing the area of irrigated land. Current average fresh weight yields

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Figure 8: Distribution of potato crop in England


are around 49 t ha-1, whereas yield potential is in the region of 75 t ha-1, but is greatly dependent on soil type and tuber dry matter content of the cultivar grown [42]. Yield may be limited by factors such as disease and nutrition rather than by water availability and if these factors can be overcome yield increases may well result in improved WUE (i.e. increased yield with the same water input). Even if such yield increases required greater water input, the resulting smaller area of production could be focused more in the West where summer rainfall is more reliable, and the need for supplementary irrigation is lower, and the availability of water for irrigation is greater. A shift to the West would need to take into consideration the heavier soils requiring higher energy inputs, and the need to provide infrastructure such as packing stations.

6.1.2. Physiology and agronomy of water useThe absolute WUE in fully irrigated potato crops in the USA was reported to vary from 0.5-1.2 t FW ha-

1 cm-1 (tuber fresh weight yield per unit of evapotranspiration), this is equivalent to 83 to 185 tons of water consumed per ton of tubers produced [43]. On a dry weight basis, assuming a dry matter content of 20%, WUE is 0.11-0.24 t DW ha-1 cm-1. These values are similar to other irrigated crops grown in comparable environments, for example in irrigated spring wheat WUE ranged from 0.10 to 0.19 t DW ha-1 cm-1 [44]. For the UK crop, where solar radiation and evaporative demand are lower than typical conditions in the USA, the WUE is much greater, with typical values ranging from 1.9 t FW ha-1 cm-1 [45] to 2.7 t FW ha-1 cm-1 [46] and an eleven year mean (1987-1998) at Cambridge University Farm of 2.4 t FW ha-1 cm-1 [39], equivalent to 42 tons of water required to produce 1 ton of tubers. The high harvest index of potato contributes to its relatively high WUE (a high proportion of the fixed carbon is partitioned to the tuber). The response of potato fresh weight yield to irrigation has been reported to be in the range 0.5 to 2.5 t ha-1 cm-1 depending on environment and cultivar [47].

Climate change predicts increased atmospheric CO2 concentrations, and the effects of this on the WUE of irrigated potato crops have been investigated in free air CO2 experiments. In this case up to 70% increases in WUE were recorded – CO2 assimilation increased due to the higher CO2 concentration, whereas water loss was restricted due to CO2 -induced stomatal closure [48, 49]. In one case it was proposed that reduced transpiration also led to increased leaf temperature which stimulated growth rate [48], however, beneficial effects on WUE may not be maintained to the end of the season due to gradual acclimation to high CO2 [50]. Thus although climate change will reduce water availability and increase evaporative demand through temperature and irradiance effects, this will be mitigated to some extent by the effects of elevated CO2. Indeed on a global scale it appears continental run-off (run-off of rivers into oceans) has been increasing during the last century despite greater human demands on water, and models indicate that this increase in run-off is best explained by a reduction in transpiration brought about by elevated CO2 [51]. It is anticipated that in the future these beneficial effects on water courses will be reversed by the reduction in rainfall, increasing temperatures and even greater demands on land use.

The dependence of potato production in the UK on irrigation arises from the steep yield response to soil water deficit and the need to maintain soil water content above a particular threshold to avoid yield losses, physiological disorders and tuber diseases, especially common scab. The unusual feature of the potato crop is not its WUE per se, but rather the very steep response of economic yield to water inputs in many varieties (although less responsive cultivars such as Hermes have been identified [39]), and thus there are large returns for investment in irrigation. Both yield and quality are more sensitive to soil water deficits than other common crops, and therefore irrigation is justifiable for economic production in nearly all environments. Even in Ireland where rainfall is high (750-1000 mm annually in production areas), and where in most seasons yield is not limited by water availability, irrigation has an economic benefit by preventing development of common scab [52], although even in this climate reductions in rainfall are predicted to make potato production non-viable in the east of Ireland within 50-70 years [53].

The high sensitivity of tuber biomass to soil water deficit can be explained in two ways: Firstly potato is generally regarded as having a shallow root system, and this is largely believed to be due to the inability to penetrate restrictive layers, such as plough pans [43, 54, 55], since rooting depth in some cultivars of potato in good soils can reach depths of up to 1.4 m [56]. It is considered that the potato root system, irrespective of the distribution of roots in the soil, is poor at extracting soil water at depth, and that the fine and fibrous nature of the root system contributes to this [47, 57, 58]. Potato crops can often be seen to wilt at times of high evaporative demand for water even when the soil is irrigated to field capacity, presumably because of resistance to water flow, most likely in the root system. Features of the root system that are likely to be responsible for the high sensitivity to soil water deficit are:

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limited access to water in the deeper soil profile a tendency of the shallow root system to dry-out the upper soil layers containing the bulk of the

nitrogen fertilizer more quickly, leading to growth becoming limited by lack of nitrogen uptake possible accentuation of root-to-shoot signaling pathways where a large proportion of the

shallow root system is in contact with drying soil, resulting in stomatal closure and inhibition of leaf growth.

because of the low root length density and narrow root diameters, the hydraulic conductivity of roots may be too low to supply sufficient water at times of peak transpiration, leading to a drop in leaf water status.

sensitivity to soil compaction which causes a more rapid decrease in root elongation rate with increase in soil resistance in comparison with many other crop species [55]

Secondly, independently of root characteristics, stomatal closure in potato is triggered at a threshold level of leaf water potential of approximately -0.8 to -1.0 MPa, whereas a more severe leaf water deficit is required to close stomata to the same extent in other crops such as wheat, cotton and soybean [43, 58]. This early stomatal closure limits photosynthetic assimilation and explains, at least in part, the high sensitivity of potato yield to water deficit, although the extent to which assimilation declines as stomata close differs between cultivars [59]. There is also evidence that potato leaf, stem and tuber expansion is very sensitive to a very small decrease (-0.3 to -0.5 MPa) in leaf water status [60]. Further, once stomata close in potato due to stress they take longer to reopen than more drought resistant crops, resulting in further yield depressions [43].

In conclusion, any attempts to reduce the need for irrigation of potato, either through cultural practices or breeding, should concentrate on the following objectives:

6.1.3. Irrigation and common scab (Streptomyces spp.)Around 70% of potato crops employ irrigation to control common scab and about half of the total water used for potato production is to avoid this disease, thus common scab control is one of the largest single factors consuming water in agriculture (see section 6.1.1.), and should be a priority of further research. Cultivars vary in their susceptibility to common scab, with russetted cultivars tending to be more resistant, but no cultivar is 100% resistant to common scab; this remains an important breeding target. Different soil locations can contain complex populations of different strains of Streptomyces, and strains can be transmitted via seed because up to 25% surface coverage with scab is currently deemed acceptable in the seed industry. Previous work has established biocontrol agents by the use of bacteriophage to kill Streptomyces spp. on seed tubers [61] but in practice these are only likely to be effective where the soil populations are low.

A LINK project (LK0989, see annex I) is currently investigating the population dynamics of pathogenic and non-pathogenic Streptomyces strains and how this can be influenced by precision irrigation, soil types, pH, nutrient status and other microflora. This should allow improve predictions on the likely benefits of irrigating to prevent common scab in different scenarios, will help to understand the mechanism by which incidence of scab is controlled by irrigation, and possibly allow development of non-irrigation based control methods.

6.1.4. Irrigation scheduling for potatoResearch at Cambridge University Farm has evaluated approaches to irrigation scheduling in the UK [62], and various models for irrigation scheduling have been developed overseas [63]. Requirements of the potato crop are well defined in terms of optimised frequency and soil moisture deficits when irrigation should be applied for optimum yield, and for prevention of common scab. Water balance models (see section 5.2.2.3.) for irrigation scheduling that calculate evapotranspiration (ET) from the crop based on climatic data, crop cover and rooting depth, balanced against stored soil water, rainfall and irrigation applied are generally good at predicting irrigation need for potato, although there is some

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reducing the sensitivity of growth and stomatal closure to small changes in soil and leaf water potential so that crop productivity can be maintained with less frequent irrigation

optimizing the root system for recovery of soil water at a greater depth in the soil profile optimizing hydraulic conductivity of the root system to ensure adequate supply of water from

the root to shoot under conditions of high atmospheric evaporative demand. reducing the requirement to control common scab through irrigation


scope to improve this further. The biggest uncertainties appear to be obtaining accurate values for irrigation applied, water held in the soil after recharge by rain and crop rooting depth [63].

Access to accurate local meteorological data to predict future rainfall before committing to applying irrigation is an issue for growers particularly in the UK with sporadic rainfall patterns; the data is available from the Met. Office but is expensive. An affordable, web-based forecast that is accurate at sufficiently high resolution, linked to scheduling computer programs, in a form that was sufficiently user-friendly to be readily taken up by a high proportion of growers has the potential to significantly reduce wasted irrigation in many crops, including potato. ET-based irrigation scheduling for the potato crop in Wisconsin, as compared with typical experience-based grower scheduling, resulted in a 40% decrease in irrigation volume while maintaining yield and quality, and often prevented yield losses and nutrient leaching due to excessive irrigation [64].

Drip (a.k.a. trickle) irrigation in principle provides the most accurate and controllable delivery method with minimal losses to the atmosphere of interception by the canopy and potentially provides the most efficient use of water, however in 2001 only 2% and 1.5% of the potato crop was irrigated by drip for earlies and maincrop respectively [65]. Drip irrigation is expensive to install but is steadily increasing, although since the introduction of the WFD drip irrigation now requires an abstraction license and is less attractive. Increasing the proportion of the potato crop irrigated by drip could possibly provide significant water savings, but a significant increase in water costs, or reduced investment costs due to technical advances may be required before the costs of installation can be justified. Additional research is also required to establish that drip really does provide practical gains in WUE, as at least in one study no WUE differences between sprinkler and drip irrigation were apparent [66]. There are however two case studies in the UK where water savings of 20% and 24% were achieved in irrigation of potatoes by moving from rainguns to solid-set sprinklers and drip respectively (see Annex II, Osberton Grange Farm and Farmcare Ltd). Management of drip irrigation frequency and amount is often poor, leading to over-watering and so improved training of farm staff in irrigation practices, such as offered by the UK Irrigation Association and others, could have a large impact on reducing water use. Because of the localized nature of water applied by drip tape, lateral movement of water in the soil is a key issue, and this may be affected by soil water content itself. It is possible that the need to maintain high soil water potentials to promote lateral movement would be a factor that would reduce the irrigation efficiency relative to overhead irrigation.

There is currently much interest in the finding that partial root drying in grape vine provides advantages in WUE and quality [67] and in the possibility that this approach could be applied to other crops, including potato. Irrigation of alternate rows provides an easy method for applying PRD to the potato crop when drip irrigation is employed. There is now some promising evidence that use of PRD in the field can lead to water savings of up to 30% by restricting leaf expansion and reducing stomatal conductance (gs) in potato, however impacts on quality have not yet been evaluated [68]. Defra project HH3609TX addresses this research area (see Annex I).

6.1.5. Agronomy and cultural practicesThe system of growing potatoes in ridges is far from ideal in terms of water use efficiency:

The ridge increases soil surface area and so increases direct evaporation from the soil before canopy cover is achieved

The ridge creates a free draining volume of soil with a large drying surface that may stimulate root-to-shoot signaling and increase sensitivity of stomatal closure

The slope of the ridge and soil texture may cause overhead irrigation to bypass the ridge thereby limiting access of the crop to the water applied [69].

Ridging involves increased cultivation traffic and so sub-soil compaction.

There are opportunities for re-addressing the best cultural practices for improved water use efficiency, globally there has been considerable agronomic research and this could be evaluated in the context of production in England. Alternative innovative cultural practices that have been evaluated include:

ridge verses bed production use of tied ridging, or dyked furrows [70], or in the case of beds, the use of reservoir tillage

systems (e.g. use of the Aqueel [Simba International Ltd]) to improve infiltration of water and reduce run-off.

Planting density [47] and arrangements such as single versus double rows [71] can influence water use by reducing non-productive water loss from soil before canopy cover

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Planting in furrows rather than ridges to direct irrigation water toward instead of away from the crop can reduce sensitivity to drought [72] but there is an inherent risk of tuber rotting attached to this practice if rainfall is high

Subsoiling, including inter-row or zone subsoiling to break-up compacted soil and increase the volume of soil accessible to the root system [73, 74]. This may also have benefits in reducing emissions of N2O [75]

Conservation tillage (no tillage or zone tillage) may have some advantages but can make compaction problems worse [76, 77]

Predictions of wetter winters, and higher temperatures are likely to advance planting times to earlier in the season when soils are wetter and more prone to compaction. Careful scheduling of tillage to avoid creating compaction by passage over wet soils is vital, and knowledge transfer activities are needed to ensure that growers understand the importance of this.

Design and evaluation of such cultural practices will require a good understanding of the movement of water in soil, depending on soil structure, type and methods of applying irrigation water. Research is required to model the movement of water in such systems.

Note that changes to cultural practices would have knock-on effects on many other processes including energy consumption in tillage, and harvest, and in fertilizer application. Also greening of tubers is a major issue for processors and alterations in cultural practices should avoid causing additional greening. However, as water use becomes a more important factor, practices will need to be designed with a greater focus on water use issues.

6.1.6. Conclusions: Water saving in the potato crop through agronomy and physiology

6.1.7. Water saving through crop improvement in potato

6.1.7.1. Is crop improvement for water use traits in potato worthwhile?The potato crop is a large single-species sector where investment in crop improvement has potentially high returns in reducing water use. In contrast, the other main sectors such as field vegetables, outdoor nursery stock and ornamentals are more fragmented from a crop improvement perspective, with a diverse range of species and crop types. As breeding efforts are generally specific to each crop, efforts in individual species in these smaller sectors would have relatively little impact on water use. However, it is possible in the longer term that if individual genes can be identified for drought resistance traits in one crop, some of these genes may be applicable between crop types in some circumstances (but see discussion above on matching drought resistance traits to development and environment, section 5.3.4.).

6.1.7.2. Introduction to potato geneticsCultivated potato is a member of the Solanum genus, and although classification schemes are constantly being updated, it can be considered that the sub-genus Potatoe contains the three very closely related sections potato, pepino and tomato [78]. The potato section contains all of the tuberising Solanum species of which there are around 200. Cultivated potato in the UK is exclusively in the form of Solanum tuberosum ssp. tuberosum, a self-incompatible autotetraploid that displays tetrasomic inheritance, whereby each locus is represented by four chromosomes with potentially between one and four different alleles at each locus. Tetrasomic segregation patterns are far more

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Potato WUE is not much different from other crops when fully irrigated Economic yield declines sharply when water inputs are reduced – mainly because of poor water

capture, sensitivity to leaf water deficit and susceptibility to common scab. Increasing atmospheric CO2 due to climate change will increase crop WUE and offset to some

extent predictions of reduced summer rainfall. Simple yield improvements through excellence in general agronomic practice would increase WUE

by eliminating other limits to yield (such as disease, nutrient deficiency) and so reduce the irrigated land area required to produce a static UK production need.

Preparing soil for good root development, particularly avoiding compaction, would reduce the need for irrigation by making more soil water available to the crop. Compaction is believed to be one of the most important factors responsible for reducing yield and increasing the need for irrigation.

Alternative growing systems (avoiding ridges) and irrigation systems (increasing use of drip) need to be evaluated as availability and cost of water alters the economics of production.


complex than those in the diploid genetic systems, and can involve both chromatid and chromosome segregation, and the self-incompatibility in potato ensures that loci often exist in a heterozygous state. This genetic complexity slows the progress of both traditional breeding and molecular genetics in cultivated potato, but significant ground has been made in recent years, as described in the following sections.

6.1.7.3. Genetic diversityAs mentioned above there are currently around 200 tuber-bearing potato species recognized, most of which are self-incompatible diploid species. They have been collected from a wide range of habitats and include many accessions that could be described as xerophytic, colonizing dry environments. About 50% of the accessions currently present in potato germplasm collections worldwide are wild species, with the other half consisting of potato cultivars, and it is estimated that more than 95% of primitive species have already been collected, with large amounts of duplication between collections [41]. In Scotland the Commonwealth Potato Collection (CPC) [79, 80] provides around 1500 accessions, mostly wild-species, and the Scottish Agricultural Science Agency (SASA) [81] maintains a collection of heritage and current potato cultivars, with information listed at The European Cultivated Potato Database [82]. These are the two primary collections that can support research efforts in the UK that may require breeding lines and/or the identification of germplasm with desirable phenotypic traits. Other collections and resources are available in Europe but quarantine regulations potentially make import of material to UK institutions a time consuming process.

Despite this embarrassment of riches in genetic resources it is estimated that only 5% of the genetic diversity available is represented in the cultivated potato [41], thus there remains enormous potential to use previously unexplored germplasm in potato crop improvement.

6.1.7.4. Conventional breedingDevelopment of new commercial cultivars through traditional breeding typically takes around 10 to 13 years to make the appropriate crosses, and go through various rounds of selection and field trials, including the final two years for national list trials for the UK [83]. Breeding efforts in the UK remain competitive, and successful breeding programs are underway e.g. in partnership between SCRI and commercial breeding companies, and independently within several breeding companies. The difficulties in developing successful new cultivars are illustrated by the continued success of many cultivars that have been bred many decades ago, although this is undoubtedly in part due to inertia following development of cultural and processing protocols tailored to particular established cultivars, and customer loyalty to familiar cultivars.

Initial crosses for breeding programs may be between existing commercial cultivars, or may include breeding lines hosting genetic material from wild-species possibly in the form of limited introgressions. Alternatively some dramatic yield increases have been achieved in the US by simply selecting spontaneous mutant lines with favourable canopy development from many hundreds of thousands of plants growing in commercial monocultures of elite cultivars [84].

The primary trait targets of breeders are currently largely limited to disease resistance and tuber quality. Potato is a unique crop in the sense that it has many pest and disease problems that impact on both tuber yield and quality, and also in comparison to cereals, there are a great many more quality traits that need to be considered in a breeding program, such as tuber size, shape, colour, eye depth, skin finish, dormancy, processing and cooking quality, and flavour. Currently the main focus for breeding disease resistance for cultivars destined for the UK are late blight (Phytophthora infestans), and potato cyst nematode (PCN, Globodera rostochiensis and G. pallida), and all breeding programs include screens for a range of tuber quality traits, depending on whether cultivars were destined for the fresh or processing markets.

Currently potato breeders do not appear to consider water use efficiency or drought resistance traits in their breeding programs, probably for the following reasons:

Genuine economic pressures for reducing water inputs are still some way off, and this trait has not yet come high enough on the breeding agenda, although awareness is increasing following the introduction of the Water Bill, technology transfer events, e.g. events organised by the UK Irrigation Association, and popular articles [85, 86]. Breeding for resource-use efficiency was highlighted as a future target in discussions at a recent potato breeding conference [87].

The complexities of breeding for disease and quality traits limit the scope for adding additional complex traits to conventional breeding programs.

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Water use efficiency and drought resistance are quantitative traits that are difficult to measure – there is a lack of suitable economically viable assays or molecular markers for these traits (see section 6.1.7.6.).

However, once cultivars are released, they are often given a drought resistance score by the breeding company, but this trait has never been scored as part of the national trials stage [88, 89]. The British Potato Council (BPC) provide a British Seed Variety Online Handbook that includes tolerance tables with “drought tolerance” scores [90], and has funded independent variety trials where differences between irrigated and non-irrigated crops was scored in a range of yield, quality and disease traits [91], and the European Cultivated Potato database [82] also includes a “drought resistance” score. In the period leading up to and including 1999, the annually published NIAB Potato Variety Handbook [92] included a drought tolerance score for the majority of cultivars. However in the year 2000, drought tolerance data was only provided for earlies, and not for second earlies or main crop cultivars, and then from 2003 to 2006 no drought tolerance scores were given except as notes in the text where a cultivar was considered to be particularly sensitive or tolerant.

The value of drought tolerance scores is perhaps questionable as they may not in many cases be based on well replicated scientific trials, and water input in such trials is usually rain-fed with or without supplementary irrigation, such that there will be large trial-to-trial variation in water inputs, and large interactions between environment and genotypes. These scores in some cases are likely to be based on anecdotal evidence alone (e.g. based on visual observation by the trialist or breeder in a dry season), or on insufficiently replicated yield trials. Drought resistance scores may also be specific to one environment and not be robust across soil types, or may only apply at particular growth stages. Generally there is believed to be a large genetic x environment interaction for drought resistance. If meaningful and standardized drought resistance data could be accumulated for large number of cultivars over a period of time, similar to the information available for disease resistance traits, not only would this provide growers with better information for cultivar choice but would also allow association mapping as an approach to identifying genetic loci for drought resistance (see section 6.1.7.5.2.).Recently some breeding programs have focussed on breeding and marketing cultivars for the organic sector where low pesticide and fertilizer inputs are desirable, e.g. Lady Balfour is a cultivar produced at SCRI, now marketed by GreenvaleAP for the organic sector, which combines good disease resistance with high yields on “poor soils”. The mind-set that led to this development could profitably be extended to issues of water input also.

There are significant opportunities for developing new potato cultivars that will produce high yields with reduced water inputs through conventional breeding. The key points are:

6.1.7.5. The potential role of Marker Assisted Selection (MAS) in breeding for drought resistance

MAS relies upon establishing a robust association between a specific molecular genetic marker and the trait of interest, and allows progeny to be selected rapidly at relatively low cost in young plants, independently of environment. There are two basic approaches for establishing association between a genetic locus and a quantitative trait;

a mapping population based on recombination and segregation in a cross between two parents

association mapping, based on association of marker and trait data in germplasm populations where individuals are related to each other over 10s to 1000s of generations.

6.1.7.5.1. Two-parent mapping populations The theoretical frameworks for quantitative genetic analysis in autotetraploids have been developed [93], and much practical progress has been made in recent years. Many diploid and tetraploid mapping

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to develop robust and cost-effective screening methods for drought resistance, based on a sound understanding of the physiological reasons for the high degree of sensitivity of potato to soil water deficit

for researchers in drought resistance to engage with commercial potato breeders, none of whom currently include drought resistance as a trait in breeding programs

to bring drought resistance higher up the agenda of breeders and growers, and to provide trait data for genetic studies by including this trait in the national list trails, or equivalent.


populations having been created and in the last few years have been used successfully to identify QTL for disease resistance traits [94-100], and to a lesser extent traits related to tuber quality [101], and cold tolerance [102]. Such studies are facilitated by the ultradense molecular marker genetic map in potato [103], however the QTL obtained are often imprecise due to limitations of the recombination frequency within a single generation, such that molecular markers may often be some distance from the target locus.

Currently the author knows of no published studies where QTLs for drought resistance traits have been investigated or discovered in such potato mapping populations. In a pilot study, measurements of carbon isotope discrimination (Δ13C), the surrogate measure for water use efficiency, were made in a few genotypes of a diploid potato mapping population [104], and further investigations of the use of Δ13C are currently being made on a complete tetraploid mapping population produced at SCRI (unpublished, A. Thompson, Warwick HRI; P. White and J Bradshaw, SCRI) [105].

6.1.7.5.2. Association mappingAssociation mapping (AM), also known as association analysis or linkage disequilibrium mapping, is a relatively new approach in plant genetics that has much promise [106, 107], and has been used successfully to find QTL in model species and crops, e.g.[108]. Large collections of germplasm need to be assessed for phenotype, and then genotyping allows tests for association between phenotype and candidate genes, or with markers in the vicinity of known, but broad QTL. Genotyping also allows the population structure of the germplasm collection to be determined, a prerequisite in interpretation of AM data. Genome-wide AM can also be performed if genotyping can be done at sufficient density, and this allows an unbiased search for QTL [108]. The key advantages of AM over two-parent mapping are that much greater allelic diversity is sampled, and any identified marker will tend to be more closely linked to the target gene and so will be more reliable as a marker.

Several AM studies have now been carried out in potato: this approach, by testing association of particular alleles of candidate genes with phenotype, allowed the discovery that invertase genes underlie known QTL for tuber sugar content (affecting fry-colour), and that an orthologous locus in tomato controls fruit sugar content [109]. In another study, 415 potato cultivars with existing passport data on late blight resistance and maturity type were genotyped, and AM performed using the passport phenotype data and markers in the region of a known gene for late blight, R1. In this case, it was possible to demonstrate association with markers that were 0.2 cM or less from the R1 gene, but not with more distant markers, thus proving the utility of the approach for improving QTL resolution [110]. It has also been suggested that in some potato germplasm collections AM may work up to 5 cM from the target gene and that collections can be designed depending on contrasting degrees of resolution needed between the processes of QTL discovery or fine mapping [111]. Genome-wide AM studies have also recently been presented using a diversity set of tetraploid genotypes mapped at 149 loci using AFLP markers, and it is claimed that loci can be associated with a range of tuber quality attributes [112], although it is far from clear whether the correct theoretical framework for allelic association has been established for tetrasomic inheritance (John Bradshaw, SCRI, pers comm.).

Both two-parent mapping and AM approaches to finding molecular markers can only succeed if drought resistance can be assessed in a meaningful way, and there is to date little agreement among physiologists, agronomists and molecular biologists about how to best to assess drought resistance and passport phenotype data for drought resistance is questionable or non-existent (see section 6.1.7.6.). The use of AM, particularly the testing of candidate genes, has great potential in identifying suitable molecular genetic markers provided that robust phenotype screens, with relevance to field production, can be established.

6.1.7.5.3. Current use of molecular markers and potential use to select for drought resistance

Loci important for disease resistance and quality traits have now been identified, using QTL and candidate gene approaches, and MAS is currently being used commercially by some breeders in the mid-stages of selection, on hundreds to thousands of lines (rather than at the earlier stages where typically 50,000 to 100,000 lines may be screened). For example in the Agrico breeding program up to eight disease resistance molecular markers are used routinely [113], and others have combined four loci for disease resistance using PCR based markers [114]. Progress has been made in developing molecular markers for tuber quality traits [101] but these are apparently not yet used in commercial breeding programs.

Molecular markers are valuable for traits that are difficult or expensive to assay at the phenotype level, and also where multiple loci need to be combined for quantitative traits. Under these circumstances marker screening will be cheaper and faster than phenotype screening. However,

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difficult to measure, genetically complex traits (such as drought resistance) are also the most difficult traits to identify markers for, and indeed reliable molecular markers suitable for breeding of drought resistance have yet to be identified in any crop. This remains a major challenge, but if robust markers were developed this would greatly improve the prospects for combining traits for sustainable agriculture, such as reduced water use, with the more classical disease resistance and tuber quality traits.

6.1.7.5.4. Genome sequencing projects and comparative genomics in Solanum

The tomato (Solanum lycopersicum L.) genome sequencing project is at the time of writing 17% complete [115], and the beginning of the sequencing of the potato genome is imminent (Potato Genome Sequencing Consortium). Looking further ahead the Sol-100 project aims to sequence 100 genomes from within the 3000 members of the Solanaceae [116]. Genomics data on this scale will increase the understanding of gene function in processes specific to potato, such as tuber traits, and ultimately, by combining genomics data and trait data, MAS will be based on the combination of advantageous alleles of individual genes, rather than ill-defined QTL. For some traits that are common between tuberising and non-tuberising Solanum species, there are advantages in establishing molecular markers in the simpler genetic system offered by the diploid, self-compatible wild species of tomato. Markers can then be transferred to the highly syntenic potato genome.

The advances in genomics and genetics in Solanum will undoubtedly provide the technical platform necessary for MAS of drought resistance traits, the limitation is currently in understanding drought resistance, and knowing how to measure it.

6.1.7.6. How to assess WUE and drought resistance of cultivars, or within a breeding program

Ultimately breeders or geneticists would like simple assays for drought resistance that can be readily applied to many thousands of potato clones. The baseline measurement of drought resistance is the economic yield under limited water inputs, or the yield response to water input, but such measurements require large replicated field trials, and interactions with environmental variables (soil type, climate, timing of precipitation etc) are expected. Large scale field trials for drought resistance in the UK are hampered because sporadic rainfall may negate differential irrigation treatments, or crops need to be protected by large areas of expensive rain-cover facilities. Trials at Mediterranean or North African sites where rainfall is lower and more predictable are attractive for large-scale breeding trials.

Ideally, simple physiological measurements would be discovered that show good correlation with baseline drought resistance measurements and these could be used as the basis for a screen. However, such correlations within cultivars are generally found to be weak, presumably because drought resistance is a complex quantitative trait with many physiological processes contributing to different extents in each cultivar. However, lack of correlation between an individual trait and drought resistance does not necessarily imply that selection for that trait will not lead to improvement in drought resistance. This is because a genuine functional relationship may be masked by confounding traits. Good physiological models of crop performance when water is limiting are required, taking into account a range of possible environments, so that the effects of changing one trait can be predicted in terms of yield. The desired trait can then be selected for directly, or molecular markers identified for QTL for that trait and then used as a screen. QTL mapping of multiple traits related to drought resistance can help by identifying traits that co-localise, so that the overall effect of a locus on crop performance can be predicted [117]. Selection for root traits is a successful example, given below, of using a physiological trait to improve overall drought resistance through conventional breeding. Attempts to screen using root and other physiological traits for screening are summarised below (see also section 6.1.2.).

6.1.7.6.1. Root traitsMassive differences in root-to-shoot ratio were observed within potato cultivars [118], wild relatives [119] and breeding populations [120]. Of all the traits measured in one study root biomass showed the highest variation between clones [104]. Passioura (2006) suggested that capturing more of the water supply and reducing deep drainage and runoff, for example by improving the root system, could potentially have a larger impact on crop water productivity than the approach of restricting crop transpiration [32]. Progress has been made in Japan in a long-term research program aimed at improving potato root traits through linking physiology and conventional breeding; this has resulted in potato clones that are able to maintain higher gs, assimilation rates and tuber yields in drying soil [120, 121]. Screening for root traits by excavation in the field is expensive and time consuming, but some

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simpler pot-based approaches may also be useful [122,123]. There is an opportunity to initiate a program of research involving breeders and root physiologists, but now also incorporating molecular genetics, to improve potato root traits in cultivars suitable for the European markets. Existing Defra research seeks to provide molecular markers for root traits in Solanceous crops [124].

6.1.7.6.2. Canopy developmentFor six cultivars grown under irrigated and mild drought conditions it was found that the response of intercepted radiation to drought correlated well with the response of tuber yield (although it was also true that intercepted radiation in irrigated plants was just as good a section criteria for yield under drought) [125]. Thus the extent of canopy cover could possibly be used as a surrogate for tuber yield in a given environment, however there is also likely to be genetic variation in partitioning between tuber and shoot under drought. Canopy development is influenced by flowering time, longevity and senescence, and can be closely related to root development [56]. Such traits influences the rate and period of water use at each point in the growing season, and also the ratio of productively transpired water to water lost by evaporation from the soil, and thus are important considerations in selecting for high WUE [32].

6.1.7.6.3. Use of stable isotope techniquesCarbon isotope discrimination (Δ13C) is relatively easy and cheap to determine and has been shown to be negatively correlated in theory and in practice with WUE at the leaf scale [126]. In potato it was found to correlate strongly with gravimetric WUE in pots [127]. In a subsequent study [128] Δ13C was measured in 19 genotypes under irrigated or droughted conditions in the field and compared to biomass accumulation. Using data from both irrigated and droughted plants and from early and late varieties there was a weak positive correlation between Δ13C and biomass accumulation, indicating a negative correlation between WUE and biomass accumulation. If data was restricted to main crop varieties under drought conditions there was a weak negative correlation between Δ13C and biomass accumulation, suggesting a positive correlation between WUE and biomass accumulation under these conditions. There were significant differences between cultivars in the Δ13C response to treatment. The authors concluded that biomass accumulation has a strong association with leaf area duration, but that WUE may contribute to biomass accumulation in droughted conditions by conserving soil water, thereby delaying canopy senescence. This study also reported that Δ13C did not vary with leaf position in irrigated plants, but progressive drought was reflected in the Δ13C of leaves at different positions. Another study by these authors using field grown Cara and Desiree demonstrated a weak negative correlation between WUE (calculated from biomass accumulation and SMDs in the field) and Δ13C [129].

Δ13C was measured in a diploid cross between Solanum tuberosum and Solanum vernei. Clones from this cross showed significant differences in gs, Δ13C, stomatal density, root growth and total dry matter production in well-watered conditions [104]. Biomass accumulation was positively associated with Δ13C under well-watered conditions when a model taking into account differences in time of plant emergence was used. This means that high WUE was associated with low yield potential, probably because reduced gs was the main factor responsible for increasing WUE. Indeed Δ13C correlated well with gs and not at all with assimilation in well-watered conditions. It is possible that the desired negative correlation between Δ13C and yield under drought (drought resistance) might be found under drought conditions. Selection for both Δ13C and Δ18O (the latter being a surrogate measure of transpiration) may provide a method for identifying clones that have high WUE AND high transpiration, and so possibly a maintained yield potential, and this approach is under investigation in Defra project HH3608TX. In another study, tuber Δ13C appeared more sensitive to drought than leaf Δ13C and was proposed as a better integrative measure of Δ13C as it reflected the assimilate produced in many leaves, and all those that contribute to final economic yield [130]. Δ13C in tubers was constant in the tuber radially, but did vary a little longitudinally. In this study the authors pointed out that biomass production was largely determined by time of plant emergence, rate of canopy development, and timing and rate of canopy senescence, i.e. canopy duration and light interception. It is likely that Δ13C and canopy duration would affect biomass accumulation independently so selection for both Δ13C and particular growth strategies may provide a means to select cultivars with high yield under limiting water availability.

Conclusions regarding use of stable isotopes in crop improvement:

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6.1.7.7. Genetic ManipulationThe genetic transformation of clonally propagated, elite potato cultivars offers a much more rapid route to drought resistance than attempting to combine multiple traits through protracted breeding programs. The approach relies on availability of genes that provide the desired trait (and knowing how to define the trait be begin with), a regulatory framework that can approve safe GM cultivars, and of course acceptance from consumers.

The poorly defined trait “drought tolerance” (see section 5.3.1. for definitions of terms), has been claimed for a number of transgenes in various crop species [131, 134] and a number of such genes are being pursued commercially e.g. Performance Plants Inc. are marketing technology based on genetic modifications that increase sensitivity to abscisic acid (the era1 gene and the Yield Protection TechnologyTM technology [132]), also research programs for engineering drought resistance are believed to be underway in other Biotechnology companies such as Dupont [32], Mendel Biotechnology, Monsanto, Bayer, Syngenta, Dow and BASF; despite this there are no current GM varieties marketed for drought resistance. There remains scepticism among many that single gene approaches can provide genuine drought resistance (maintained yields with lower water input), as there are hundreds of patents for drought resistance genes, but as yet no GM products on the market for this trait [32]. Some argue that the genetic complexity of the trait, and the need to tailor genetic modifications to specific combinations of crop type x environment x phenological development make simple, single gene solutions unlikely [30]. However, in principle there is no reason why single transgene effects could not make a major contribution if such transgenes are incorporated into existing breeding programs alongside coherent drought resistance selection protocols albeit on the same time scale of cultivar development as conventional breeding.

Recent work in tomato has demonstrated complex physiological consequences of over expressing a candidate gene that increases abscisic acid (ABA) biosynthesis [208]. In this example, high ABA content increases water use efficiency and drought resistance dramatically when the level of additional ABA is increased moderately, but this is accompanied by changes in reproductive development, leaf growth, plant establishment and seed germination. Some of these secondary changes can be predicted to be beneficial, others not. It is therefore critical to empirically establish the pleiotropic transgene effects on whole plant and crop physiology since these are often too complex to predict in advance. Transgene expression may then be adjusted in its level, tissue-specificity or developmental timing to achieve the desired affects. A common issue with many transgenic approaches is that transgenes, particularly those that have been identified because they are involved in the drought response of a plant, tend to suppress yield potential (yield under ideal conditions) by effectively creating a phenotype that is constitutively drought-adapted (see section 5.3.2.). Although they would hopefully increase yield when water availability is low a balance is needed between yield stability (average yield over many seasons, some of which may be dry), and maximising yield in good years. Modelling approaches for example have been able to demonstrate that capping transpiration (through genetic changes, say) in a Sorghum crop, would actually tend to increase average yield over 115 seasons in Australia [135]. Some progress has been claimed in modifying transgene expression with stress-induced promoters such that transgene effects on yield potential are reduced, while effects on drought resistance are enhanced [133].

To successfully make use of the many candidate genes that are claimed to impact on drought resistance the following are required:

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it appears that Δ13C, particularly in tubers, does provide a sensitive and practical measure of plant response to drought, i.e. the Δ13C signal will inform on whether the crop has closed stomata in response to soil drying.

the selection of clones just based on low Δ13C will probably lead to loss of yield potential because of association with lower gs. Parallel selection for yield/canopy development or Δ18O could be used to counteract this trend.

clones with the smallest response of tuber Δ13C or leaf Δ18O to soil water deficit could be selected. Such clones would be predicted to remain productive in drying soil, so reducing the need for frequent irrigation.


6.1.7.8. Conclusions: water saving through crop improvement in potato

6.2. Field crops: vegetables

6.2.1. Background informationField vegetables are a diverse collection of crops, mostly herbaceous annual crops, where the harvested part of the crop plant can be the leaf, stem (bulbs), root or fruit. This diversity makes it difficult of offer generalizations concerning water use, irrigation scheduling, or breeding. One common factor within the field vegetable crops is that they tend to be high value crops, intensively grown, where a good economic yield is highly dependent on producing a crop with the quality attributes demanded by supermarket buyers. As such, investment in irrigation to optimize the yield of high quality produce is often justified, and, in recent years, irrigation has been directed more to vegetables than to other crops such as sugar beet and cereals [13, 138]. The added value from irrigation of field vegetables is high, for example estimated at 6.92 £ m-3 for celery and 4.48 £ m-3 for lettuce, compared to 1.56 £ m-3 for maincrop potatoes in 2001 using drip irrigation [65]. Also many UK vegetable crops, for example lettuce, celery, vegetable Brassicas, onions and leek are relatively shallow rooted, as is the case with potato, and therefore tend to require more frequent irrigations of lower volume to maintain the appropriate soil water content in the root zone [139]. In many situations good quality field vegetables acceptable to UK consumers cannot be produced without carefully scheduled supplementary irrigation.

In 2006 in the UK there were 121,691 ha of field vegetables grown (including legumes) [140]. The crop types with the largest areas were legumes (74,635 ha in the UK) [140], followed by (from a survey of vegetable production in England [141]) vegetable Brassicas (31471 ha), salads and leafy vegetables (12455 ha, 48% lettuce), carrots (9952 ha), onions (9184 ha) and parsnips (3968 ha); all other crop types had areas of less than 2000 ha.

In 2001 it was estimated that there were 39,180 ha of irrigated field vegetables [13], equating to 29% of the total vegetable area (including legumes), using 34 Mm3 of water; there was also a trend for an increasing proportion of field vegetable crops to be irrigated [140]. Field vegetables make up 27% of the area of irrigated crops [13], however data does not appear to be available regarding which of the vegetable crops are the most irrigated. It was estimated that 6% of the irrigated field vegetable crops were irrigated by drip in 2001, with the remainder irrigated by overhead, mostly spray guns [65].

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an improved understanding of drought resistance traits at the whole plant and crop level, and the genetic control of such traits.

multidisciplinary projects between genetic engineers, physiologists and agronomists, to create and assess transgenic genotypes, an aim shared with the recent BBSRC Crop Science initiative where a key aim is to translate information gathered in model crop species into applications in crop species.

public acceptance, an aim that would likely be advanced by the successful demonstration of GM products that promote sustainable agriculture with environmental benefits, for example, through reduced input of water and/or nutrients.

The potato sector represents a good target for breeding for drought resistance as it consumes approximately 25% of the total water used by agriculture, and is a single-species sector where new cultivars could have a major impact on overall water use.

There is a need to further understand and model the crop physiology of drought resistance and water use efficiency in potato so that meaningful and robust genetic screens can be designed and performed.

It is already well-established that potato cultivars are poor at capturing soil water, and in Japan conventional breeding has led to improvements in root traits and drought resistance. Concerted effort from consortia of breeders, root physiologist and molecular geneticists is required to apply this approach to European cultivars.

Quality traits, mainly tuber disorders and common scab, are often the drivers for irrigation, and therefore resistance to these when water inputs are lower is an important breeding objective.

Advances in genetic and genomics in both tomato and potato, including association mapping, will facilitate the discovery of molecular marker for drought resistance in potato, provided that suitable phenotypic screens can be established and included in passport phenotype data for cultivars.


6.2.2. Irrigation schedulingHDC-funded research (see Annex I) has focused on scheduling irrigation of field vegetables to improve quality and uniformity rather than to reduce water use per se; for example irrigation of carrot can be scheduled to reduce cracking (FV46a), or common scab (FV195), and at the establishment phase uniformity can be improved by modified irrigation scheduling (FV 39/a). Effect of irrigation on postharvest quality of broccoli has also been investigated in Defra project HH2602, and it was found that quite severe soil moisture deficits were needed before improvements in broccoli shelf life were observed.

A survey indicated that most field vegetable growers who shifted from overhead to drip irrigation of field vegetables did perceive improvements in quality presumably because of greater uniformity and control, but experiments did not indicate water savings (FV187). In the case of lettuce and other “ready to eat” crops, microbiological safety is a key topic, and an increasing need to treat irrigation water to reduce potential human pathogen risks (FV248) [142] also increases the cost of irrigation and provides an additional pressure to minimize water use.

The recently completed PINT project (HL0165) has investigated the use of fertigation for field vegetable production in England and has found that considerable water savings can be made by scheduling irrigation using drip tape and a closed-loop automated irrigation system based on sensing soil water content. Weather forecast data could also be included in the automated scheduling programs and could lead to further savings. Similar technical advances are under investigation for use in irrigation of fruit and hardy nursery stock (see section 6.4.4. and 6.8.4.2.). The PINT project has also enabled modeling of the movement of water from drip tape through the soil profile using an array of soil moisture sensors [143]. Given the diverse nature of field vegetables, and the likely gradual increase in uptake of drip irrigation it will be important to understand the extent of the rooting zone of each crop in each soil type and to model the movement of water in such systems; for example rooting depth is highly dependent on soil type and degree of compaction for potato (see section 6.1.2) and this is likely to be true for most vegetable crops and is certainly true in the case of onion. Such models will enable scientifically based decisions for defining suitable dripper positioning and scheduling of irrigation events so that water is delivered to the root zone while minimizing loss of water to surface evaporation and/or deep percolation. For example, in Israel it is common practice to place drip tapes underground to restrict surface evaporation. Also further research is needed to define the demand for water of each crop, especially the minimum irrigation requirement needed to deliver the desired yield and quality; currently many field vegetable crops are likely to be over-irrigated to be “on the safe side” because of a lack of knowledge about crop needs and the high value of the crops.

6.2.3. MulchingMulches are a good method for increasing WUE as they reduce non-productive evaporation from soils, ensuring that more water is lost productively through the plant, with no physiological trade-offs. Mulching is more suited to high value, intensively produced crops such as field vegetables because of the additional costs involved, and has greater potential benefits for wide row crops, or situations where the soil is exposed (not covered by crop canopy) for a significant period. Vitacress, in the production of baby leaf salads in Hampshire, use a green waste mulch primarily to suppress weeds and to condition soils [144], and it is likely that use of such mulches would have the further benefit of reducing water inputs. For soils with low water holding capacity such as sandy soils the use of green waste mulches, through the incorporation of organic matter into soils, will increase water holding capacity and thereby hold water in the root zone rather than allow loss through percolation. The recycling of green waste has increased 10-fold in the last 10 years; in 2005/6, 9.6% of household green waste was recycled in England, equivalent to 2.4 million tonnes [145]. A limiting factor in the use of green waste is the EU Nitrates directive which limits the amount of nitrogen which can be applied in any year to 170 kg N/ha in nitrate vulnerable zones (NVZs). Assuming a compost N content of about 0.8% of fresh weight, and a bulk density of 0.6 tonne m-3, a typical mulch of 2.5 cm could be applied to 14% of the land area of a farm.

Increased use of black polythene or waste materials for mulching could result in significant water savings, but research is required to assess the extent of potential water savings and to establish cost-benefit analysis, and viable sources of novel mulching materials.

6.2.4. BreedingVery little research has been carried out aimed at breeding field vegetables for improved water use traits with the exception of the vegetable brassicas, Brassica oleracea. In the latter group of crops, QTL for δ13C (a surrogate measure of WUE), δ18O (a surrogate measure of transpiration) and “biomass

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response to irrigation” have been identified in two doubled-haploid mapping populations [117, 146]. By combined analysis of these QTL it is hoped to find molecular markers for WUE that are not associated simply with low transpiration and low yield [146]. The closely related model species Arabidopsis thaliana is being used to define and validate further QTL, that are likely to also be relevant in Brassica species [146-149] and in one case the gene underlying a QTL has been identified [149].

As already mentioned, shallow rooting is a feature of many vegetable crops, and thus identification of QTL and genes for increasing rooting depth and density and so the volume of soil water available to the crop, could have beneficial effects on yield in water-limited environments (see also section 6.1.7.6.1. on root traits in potatoes). A great deal is now known about the genetic control of root development, particularly in Arabidopsis [150] and rice [151]; root QTL research has also been initiated in Defra project HH3615SPC in tomato.

Despite a strong interaction between crop-types, genes and environments for the complex WUE trait, some genes will possibly have wide applicability and thus research to identify QTL and the underlying genes for WUE in a dicotyledonous species may be applicable to many field vegetable crops (all are dicots apart from Allium species). Given the diversity of field vegetable crops, a search for such robust, “generic” WUE genes in model species, followed by validation in several crop types may provide the most cost-effective research strategy.

6.2.5. Conclusions: water saving in field vegetables

6.3. Field crops: Sugar beet (Beta vulgaris spp. vulgaris)

6.3.1. Background informationSugar beet production is focused in eastern England in areas of lowest rainfall and sandy soils, and sugar beet is generally considered to be a drought resistant crop. However, it was estimated that 10.5% of sugar beet production was lost to drought, representing an annual average loss of 1.4 million tonnes [138]. The area of the sugar beet crop in 2005 was 148,000 ha, and the irrigated area peaked at 17% in 1990 [138], but fell to only 6% in 2002, representing 4.6 Mm3 of water withdrawals [13]. The decrease occurred apparently because growers switched irrigation priority to higher value field vegetable crops where returns on irrigation were higher [152]. This situation is unlikely to change in the future as abstraction licensing increases the pressure to obtain the highest returns from water use. When comparing irrigated and non-irrigated crops in simulations over the last 30 years, irrigation increased sugar yields by an average of 3.5 t ha-1 at Brooms Barn [152] over and above the non-irrigated sugar yields which ranged from about 8 to 11.5 t ha-1 over this period. There are few or no quality issues related to irrigation of sugar beet in stark contrast to the situation in field vegetables, fruit and potatoes.

6.3.2. Research opportunitiesIssues related to irrigation scheduling are similar to those discussed for potato yield (ignoring irrigation for common scab), and generic research in improving scheduling and soil and environmental monitoring will be of benefit. However, as sugar beet is not a major irrigated crop, and irrigation is unlikely to increase for this crop, research efforts in breeding increased WUE and drought resistance so that yields can be maintained in the future should be a priority. Research in the UK at Brooms Barn [153-155] has begun to address the genetic control of WUE in sugar beet and further work is needed in

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Field vegetables use a significant amount of irrigation water nationally (34 Mm3 in 2001) and demand is increasing, however field vegetables are a highly diverse collection of crops, reducing the impact of crop-specific research

Effects of irrigation scheduling on quality are very important for economic viability. Research is needed to define the extent that irrigation can be reduced without negative effects on quality, and to provide more precise, automated scheduling systems that take into account soil properties that influence water movement and the extent of the root zone.

The possibility that increased use of mulches could be used to save water needs to be evaluated.

Breeding research aimed at increasing WUE in field vegetables is required but will be most productive if genes can be identified that are applicable to a range of crop types and environments


this area to progress to successful breeding programs. Currently home grown sugar beet provides 70% of UK sugar consumption and, noting the increasing sugar prices due to bioethanol and biobutanol production, it will be important to maintain this supply in the face of increasing frequency and severity of summer droughts (see also section 6.6.2. on bioethanol).

6.3.3. Conclusions: water saving for sugar beet

6.4. Field crops: Fruit

6.4.1. Background informationFruit production occupied 33751 ha in 1995/6 and has declined to 26031 ha in 2005/6 [140], with most of the decline attributed to a steady decline in orchard fruit. Soft fruit declined from 10446 ha in 1995/6 to 7681 ha in 1999/00, but is now showing rapid growth with 8943 ha in 2005/6, and an increase in soft fruit production from 78100 t in 1995 to 100500 t in 2005 (provisional) [140]. Soft fruit production has increased mainly due to the increased yields per hectare from the use of polytunnels; in 2006 there were 8943 ha soft fruit of which 42% was strawberries [140] and 65% was in polytunnels [156], and soft fruit sales have been increasing since 2003 on average by about 20% per year [156]. 105 ha of glass was used for strawberry production in 2006 [157]. Strawberries represented 64% and 60% of soft fruit production in 2005 by weight and by value, respectively [140] and as an irrigated crop and an expanding sector strawberries are clearly the key target crop for water saving in the fruit sector. The irrigation survey indicated that 3.3 Mm3 of water was used for soft fruit irrigation in 2001 [13], although this figure is likely to be much greater now (see below). Although total water use is relatively small, the intensive nature of polytunnel production could have local impact on water courses/ground water particularly in the South east, and this could limit the further expansion or viability of the industry if abstraction licenses were not renewed on environmental grounds. The high value of soft-fruit crops (e.g. mean crop value for strawberries is £33.7 k ha-1) means that financial returns from limited water resources are high, raising the possibility that abstraction licence trading could reallocate water to high value crops such as soft fruit.

A new HortLINK proposal (HL0187) “Improving WUE and fruit quality in field-grown strawberry” includes a survey to gather more detailed information on water use, scheduling, sources of water and WUE. This is likely to be completed in 2008 [158].

6.4.2. Water use in strawberries (Fragaria x ananassa)

Many systems of growing are currently used [159], but crops are either everbearers (long season under protection) or Junebearer crops. Most growers apply around 2500 m3 ha-1 (250 mm) to protected crops per season, depending on soil type and growing system, and such crops where soil is fumigated tend to have the greatest yield of class I fruit and so have the largest water use efficiency purely based on high yield [159]. With an estimated 2400 ha of strawberries grown in polytunnels in 2005, the water use for strawberries alone must now exceed 6 Mm3 year-1.

WUE (in terms of fresh weight (FW) of class I fruit per volume of irrigation applied) ranges from 1.7 t FW ha-1 cm-1 for non-protected crops in fumigated soil (rain-fed), to 1.2 t FW ha-1 cm-1 for protected crops in peat, to 0.83 t FW ha-1 cm-1 for protected crops in fumigated soil, to 0.41 t FW ha-1 cm-1 for non-fumigated, non-protected crops [159]. A similar value of 1.5 t FW ha-1 cm-1 was reported for non-stressed plants grown in Spain [160]. Peak water demand for field-grown strawberry crops has also been estimated at 500 ml day-1 plant-1 [161] although this will clearly depend on planting densities and growing system etc. Compared to production in soil, peat container crops used 33% less water to produce a tonne of first class fruit, and this is possibly due to the greater water-holding capacity of the

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Current water use is 4.6 Mm3 but declining, and only 6% of the area is irrigated Where the crop is irrigated accurate scheduling is likely to reduce water inputs Research should be focused on breeding for drought resistance and WUE


peat [159]. Organic production compared to non-organic production used 60% more water to produce a tonne of class I fruit mainly because of lower yields [159].

Clearly large differences in yield due to different growing systems largely account for the differences in WUE, but protection in polytunnels also will tend to reduce crop transpiration and increase WUE due to the higher humidity and lower air movement. Crops are typically irrigated with drip tape, an efficient method, and soil is usually covered by plastic or straw mulch to protect berries but this has the additional advantage of reducing soil evaporation and has been shown to improve yield where water is limiting [162].

6.4.3. Strawberry breedingAs a major, water-hungry crop with an expanding market strawberry is a justifiable target for breeding to improve WUE. Very little is currently known about which traits are important for WUE specifically in strawberry crops and research is required to identify target traits. Mapping populations between diploid wild species of strawberry have been created [163-165] and can now be exploited for a variety of traits including WUE, although application of molecular markers for complex quantitative traits in octoploid cultivated strawberry will be highly complex. Genomic resources in the Rosaceae are rapidly becoming available through sequencing of apple and peach genomes, and this provides an opportunity to progress marker and mapping work in the related Fragaria [166].

Like potato, strawberry has a shallow root system, with an effective rooting depth of only 30 cm [167] and thus improving root traits may be an advantage under some growing systems. Leaf transpiration efficiency and resource allocation (vegetative versus fruit) are likely to be important traits for WUE. The relationship between WUE and quality will be an important consideration.

6.4.4. Irrigation scheduling in soft fruitMany growers do not use scientific methods to schedule irrigation to match the demands of the crop, but clearly adequate irrigation is needed to produce class I fruit; poor irrigation practice is often the cause of downgrading the value of a crop such that it can only be used for processing. Current Defra project HH3609 includes experiments to establish scheduling methods for both strawberries and raspberries, including use of partial root drying and regulated deficit irrigation (RDI). In strawberry water savings of 30% have been claimed over typical grower practices by the use of RDI without loss of fruit yield or quality [161], although experiments performed in Spain indicated that even a mild water deficit (soil water potential of -0.03 MPa) had a negative impact in fruit yield [160]. RDI at 80% of potential evapotranspiration (ETp) has the possible advantage of limiting vegetative growth, helping to limit disease by reducing incidence of humid air under canopies, and allows sunlight to penetrate to ripening fruit but without reducing yield of class I fruit. Further research is needed to establish if RDI can also actually improve nutritional value of fruit as the concentration of some metabolites is likely to rise in RDI treatments. Scheduling irrigation using the Evaposensor/evapometer (Sky Instruments, Ltd, see also section 6.8.4.1.) so that irrigation was applied at no more than 100% of ETp could also result in substantial water savings relative to ad hoc irrigation that tends to be excessive [161]. Scheduling based on soil monitoring with tensiometers has also been reported for strawberry [168]. Because of the promise of these approaches they are now likely to be taken forward with industry support as part of a HortLINK project (HL0187) [158].

6.4.5. Rain water collection from polytunnels and water recyclingThe move of soft fruit production to polytunnels is driven by the ability to extend the growing season, to protect crops from rain damage, to reduce disease associated with wet conditions and to maximise quality. In terms of water use, the trend towards polytunnels is positive because, although production is intensive, it is potentially more water use efficient provided that run-off of precipitation can be managed productively and used for irrigation locally, or directed to ground or surface water for downstream abstractors. In positioning polytunnels, growers will need to increasingly take into consideration the likelihood of future abstraction restrictions. By constructing suitable drainage and reservoir systems, taking into account local hydrology, growers could make good use of tunnel run-off water.

Estimates of irrigation requirement for Strawberries grown in polytunnels in raised beds in the West Midlands indicated that if rain falling on the tunnels could be collected, stored and used for irrigation, then the collected water would be sufficient, at least in the case of everbearers, to provide over 90% of the irrigation requirement of the crop [169]. The recent introduction of effective guttering systems to commercial polytunnels, mainly driven by the need to control flooding problems, provides the opportunity to collect clean rainwater, although significant investment by growers is clearly also needed to store the collected water. Polytunnels are often moved each season to avoid soil diseases and so flexible systems for rain water collection are needed. In one example of current practice a

39


grower who had moved from potato to strawberry production now irrigates his strawberry crop using rainwater and irrigation run-off that has been collected via drainage ditches and stored in a farm reservoir [170]. Most growers use untreated borehole or on-farm reservoir water to irrigate strawberries [159].

Strawberry is sensitive to high salinity and one use of excess irrigation is to flush accumulated salts originating in irrigation water out of growing media. Use of collected rain water with low electroconductivity for irrigation would reduce the need for this practice.

6.4.6. Orchard fruitOrchard fruit occupies a greater area than soft fruit although this is in decline, but only 10% of orchard fruit is currently irrigated. Consequently water withdrawals for irrigation of orchard fruit are insignificant (0.9 Mm3 in 2001) [13]. Declining summer rainfall in the South east where most orchard fruit production occurs could result in increased demand for irrigation; if the current total area of orchard fruit was irrigated to maintain production in drier summers the water use would become significant at around 9 Mm3 year-1. The predicted higher temperatures could stimulate further growth of novel high value crops that are well adapted to lower water inputs; apricots produced in Kent are already on the market, and olive trees have been planted although are not yet cropping [171].

Rootstock genotypes can strongly influence drought resistance [172, 173] and dwarfing root stocks may work by hydraulic restriction [174], thus increasing susceptibility to drought. Reduced risk of frost damage due to climate change may make expansion of cherry production viable, and, although cherry crops are generally not currently irrigated, cherry trees on dwarfing root stocks are relatively drought sensitive and may become an irrigated crop in the future. Research for development of alternative rootstocks that could impose drought resistance on many cultivars of a particular crop may help to maintain a viable industry as summers become drier.

Orchards are an attractive cropping system for the use of mulches as the soil surface is largely unprotected from evaporation, unlike other field crops where a full, low canopy develops. The use of green waste for mulching has been piloted in orchards [175], to reduce non-productive evaporation from the soil and thereby increasing fruit yield and size where soil water is limiting.

6.4.7. Conclusions: water savings in field-grown fruit

6.5. Field crops: CerealsOf the approximately 2.5 million ha of cereals grown in England in 2001 only 0.2% were irrigated [13]. In an average year evapotranspiration from wheat throughout spring and summer exceeds rainfall by 130 mm, and this soil moisture deficit (SMD) is easily recharged by winter rainfall [176]. For deep soils with a reasonable water holding capacity this 130 mm SMD is not sufficient to limit yield in an average year [176], but clearly yield would become water limited in drier than average summers and these are expected to become more frequent. It is estimated that 250,000 ha of wheat is grown on shallow soil and 220,000 ha on sandy soils and in both cases the average SMD of 130 mm is sufficient to limit yield because less soil water is available to the crop [176]. For example, in a trial of irrigated versus non-irrigated wheat on sandy soils at Gleadthorpe, non-irrigated wheat had a lower yield by 17, 34 and 44% in 1994, 1995, and 1996 respectively [177]. In 1996 the non-irrigated plots experienced 46 days with an SMD greater than 100 mm, and had an SMD of 139 mm in mid-July [177]. Thus drought resistance is an important trait in UK wheat both because of poor soils and because of the likely

40

Recent rapid changes in the soft fruit industry make it difficult to estimate current total water use for fruit, but it is likely to be in the range 6 to 10 Mm3 year.

Strawberry is the key fruit crop to target for water saving. Rainwater harvesting from polytunnels is an ideal way to provide irrigation water for soft fruit to

minimise environmental impact. There are many strawberry growing systems with widely differing water use efficiencies; more

research is needed to evaluate the best growing system for low water inputs. Research and knowledge transfer is needed to provide growers with accurate and user-

friendly irrigation scheduling protocols, including the introduction of RDI. This could lead to water savings of around 30%

Breeding for WUE in strawberry could reduce water inputs; advances in genomics and molecular marker work in the Rosaceae provide new opportunities in this area.

Orchard crops currently use little water but changes to crop types, introduction of root stocks for drought resistance, or mulching will help to sustain the sector as summer rainfall declines.


increasing frequency of dry years. Research is required to define the relevant traits and genetic loci for breeding drought resistance in wheat. Progress has been made in defining the physiology and genetics and gene x environment interactions in European germplasm of winter wheat [178], and breeding programs for drought resistance in Australia are well advanced with some successful releases of new cultivars [32].

An increase in irrigated area for cereals seems unlikely given that up to 2001 there was a decline in irrigated area as growers switched irrigation resources to higher value crops [13]. However, cereal production in England has received a recent boost by use of surplus wheat for bioethanol production (see section 6.6.2.). It is likely that more set-aside land could be used for this non-food use in the future; this change in land use could reduce both run-off and the recharge of ground waters [179] and could have local hydrological consequences for abstractors and the environment.

6.5.1. Conclusions: Water saving for cereals

6.6. Field crops: Energy crops

6.6.1. BackgroundThe need to reduce net CO2 emissions by finding alternative energy sources to fossil fuels has focused much attention and investment on energy crops. It was estimated that 1 million ha are available for non-food use in the UK and such an area would be able to produce 8 million tonnes of energy crops [180]. In 2007 it was stated that 76,000 ha (21%) of the set aside land is currently used for non-food crop production, with the majority of this for energy crops, particularly oilseed rape [181, 182].

Thus there is considerable scope for a large expansion of energy crop production in England and Wales, and indeed government provides grants for establishing short rotation coppice (SRC) and miscanthus crops to encourage this expansion [183]. The rise of energy crops combined with possible yield reductions for food crops due to climate change, and continuing population growth, is likely to lead to ever-increasing pressures to maximise land use and crop productivity in the medium to long term. Changes in land use from say pasture or set-aside to energy crop production are likely to have a negative impact on hydrology and ecology of water courses because of higher evapotranspiration, however energy crops are very unlikely to be irrigated due to the low financial return for the effort and cost of irrigation in comparison to higher value food crops such as potato, fruit and vegetables.

6.6.2. Crops for bioethanol, biobutanol and biodiesel production6.6.2.1. Production trends

Bioethanol and biobutanol can be used as transport fuel and in the last two years production of these fuels from wheat and sugar beet has been initiated in the UK; a £20m plant at Wissington in Norfolk aims to produce 30,000 tonnes of biobutanol per year from sugar beet grown by farmers in Norfolk, Cambridgeshire and Suffolk, with a planned input of 600,000 tonnes of sugar beet per year grown on around 10,000 ha [184], whereas in Teeside a plant for production of bioethanol from wheat is under construction where it is planned for 1.2 million tonnes of soft wheat grown on 150,000 ha (5% of total cereals production) to be converted to around 400 million litres of bioethanol each year beginning in 2008 [185]. Two further wheat-to-bioethanol plants are planned by company Green Spirit Fuels sited in Somerset and Humberside [186]. Oilseed rape is used for biodiesel production, with, in 2006, 575,000 ha of production, of which 75,000 ha was on set-aside land for non-food use only [182].

6.6.2.2. Water useAn increased area of non-irrigated sugar beet, wheat and oilseed crops, perhaps increasing the area of cultivated land and use of set-aside, would potentially have some impact on local hydrology through reductions in run-off and percolation if evapotranspiration exceeded that from the previous land use.

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Little water is used for irrigating cereals and this is unlikely to change Cereal yields are water-limited on poor soils and will increasingly become water-limited on good

soils in dry years Increased use of set-aside land for cereal production for bioethanol could reduce local water

availability by reducing run-off and deep-percolation. Modelling work is required to assess the significance of this

Increasing water use efficiency of wheat by breeding could help to maintain yields and minimise hydrological impacts


Crop yields may decline due to future reductions in summer rainfall in the south and east and therefore breeding for drought resistance traits (i.e. for high biomass production in water-limited environments) will become increasingly important. For example, it was estimated that 10.5% of sugar beet yield is currently lost to drought each year on average (see section 6.3.1.).

6.6.3. Biomass crops6.6.3.1. Production trends

Biomass crops are essentially those burnt to generate electricity or produce heat. In the UK currently these include short rotation coppice (SRC) of willow (Salix spp.), the perennial grass miscanthus (elephant grass) and forestry. Other potential crops for the UK include SRC of poplar (Populus spp.), and growth of other grasses such as reed canary grass (Phalaris arundinacea) and switchgrass (Panicum virgantum). In 2005 the contribution of biomass fuel in the UK was 2% to electricity and 1% to heat [180], and there were around 2500 ha of SRC plus miscanthus [180]. Bical have claimed in 2007 that the Drax power station “planned to triple its purchases of miscanthus from 100,000 tonnes to 300,000 tonnes each year and that much of the grass would be grown by farmers in Yorkshire” within a 50 mile radius of the power station [187]. This represents an increased production area of around 13,000 to 17,000 ha (typical yields are 12 to 15 t ha-1). Further expansion of biomass crop areas is anticipated, depending on the economic success of the current expansion phase.

6.6.3.2. Water use and hydrologyBiomass crops are rapid-growing, develop a large leaf area and have a long season. As a consequence they use larger amounts of water than the crops they are likely to replace (e.g. wheat and grass). The hydrological impact of the expansion of biomass crop production is the main area of concern for water use in the context of energy crops. This issue is currently being addressed as part of the current “RELU-Biomass” project [188]. An earlier comprehensive report [10] calculated that replacing wheat and grass with energy crops would reduce hydrologically effective rainfall (HER; the rainfall that reaches water courses and ground water through run-off and deep percolation) by 120 mm for miscanthus and 140-180 mm for willow. If energy crops occupied 100,000 ha this would reduce the total freshwater resource by 150 Mm3 year-1, equivalent to 12% of annual fresh water withdrawals [10]. If we consider the example given above whereby the Drax power station is fed 300,000 tonnes year-1 of miscanthus, grown on approximately 25,000 ha within a 50 mile radius of the power station (total area of this zone of 2 million ha), then the relatively small proportion of the land area converted to energy crops means that large effects on hydrology are unlikely at the catchment scale. However, at the sub-catchment scale, in the local area of a growing crop, observable effects on stream flow, recharge of ground waters, and so aquatic ecology are possible [10]. Addition hydrological assessments have also concluded that SRC of willow would reduce HER, depending on soil type, by approximately 100 mm, 173 mm and 184 mm compared to sugar beet, potato and barley respectively [189]. These figures can be reduced by 40 to 100 mm in the case of miscanthus which has lower water use than SRC [190]. Where non-irrigated crops greatly reduce HER the knock-on effect may be restrictions on neighbouring abstraction licences for irrigated food crops because of reduced flow rates. A study funded by the Forestry Commission and Defra reported on the hydrological impacts of changing land use to short rotation forestry, and further modelling work in this area will report in 2007 [191].

In the east it is suggested that deep-rooted energy crops could lead to soil water deficits so large that the soil would not be brought back to field capacity in the winter, leading to zero deep percolation and potentially progressive year-on-year depletion of aquifers and decline in soil water [10]. Yield of biomass crops is likely to be limited in many cases by rainfall, particularly where root depth is restricted so that crops do not have access to water stored in the soil at depth.

6.6.4. Breeding for WUE in energy cropsGiven that energy crop production will often be water limited and that large cropping areas are likely to cause localized ecological damage due to reductions in HER, it is important to include WUE as a key trait in energy crop breeding programs.

The National Willow collection is held at Rothamsted Research and comprises 1,300 accessions, representing more than 100 species from around the world. Genetic resources for poplar, including mapping populations, are available at the University of Southampton and the BEGIN project (2003-2008) [192] aims to improve yield of both willow and popular. The National Miscanthus Germplasm Collection is held at The ADAS Arthur Rickwood Research Centre, although this is no longer maintained, and a crop improvement program for miscanthus, including an actively growing Miscanthus germplasm collection, has been funded by Defra at the Institute of Grassland and

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Environmental Research (2004-2009, NF0426). These national resources and skills provide a suitable base for future breeding for WUE in biomass crops.

As a C4 crop, miscanthus has a nearly two-fold greater WUE than C3 biomass crops such as willow and poplar and so is more suited to water-limited environments [193], however genetic variation in miscanthus WUE has been reported [194] suggesting that breeding has the potential to improve WUE in miscanthus still further, although the need for improvement of WUE may be greater in C3 crops, particularly willow.

Germplasm collections of oilseed rape (Brassica napus), consisting of 188 lines, have been assembled from international collections as part of the Defra-funded OREGIN project [195], and are held at Warwick HRI. Also at Warwick HRI are a range of other Brassica oleracea mapping populations and diversity sets that are being used to define the genetics of WUE in the vegetable Brassicas and in the Brassicaceae family more widely [105]; results from this work would be expected to be highly relevant to breeding for WUE in oilseed rape.

Alterative crops for dryland production could also be considered; for example Cardoon (Cynara cardunculus) is a high-yielding perennial thistle-like crop adapted to dry conditions that can yield 16-30 t dry matter ha-1 year-1 with only 450 mm winter rain in the Mediterranean regions, producing both biomass for burning and a high yield of seed oil (13% of dry matter is partitioned to seed, and seeds are 25% oil) [196-198]. Such crops may provide higher yields with less environmental impact as climate becomes more Mediterranean in character.

6.6.5. Conclusions: energy crops

6.7. Protected crops (edibles and ornamentals)

6.7.1. Background informationThe water used in production of edible protected crops is estimated to be 10.4 Mm3 year-1 [9], with the largest area of production (25% of the total) in the South East where solar radiation is greatest, and summer droughts are most likely to affect water availability. Protected ornamental crops, including cut flowers are estimated to use only 2.5 Mm3 year-1 of irrigation water [9], and thus this is of little significance nationally, being between 0.5% and 0.8% of the total water used in agriculture in England and Wales.

Water used is either mains water, roof water, or water abstracted from bore holes, with nearly half of growers surveyed relying exclusively on mains water (see Table 3.). The survey was of 20 edible and 30 ornamental protected crop growers, and mains water was more prevalent with ornamental growers although 4 of the 10 tomato growers surveyed relied exclusively on mains water. It is however likely that larger growers use mainly borehole and/or roof water rather than mains water [199]. Abstraction from rivers is avoided due to potential disease problems, for example Ralstonia solanacearum (brown rot) that has been known to be spread from wild Solanum dulcamara to tomato crops.

Tomato is the largest single protected crop by area (206 ha) and uses between approximately 1.1 m3 water m-2 year-1 (open irrigation system flowing to run-off) [9] and 0.75 m3 water m-2 year-1 (recirculating systems [199]), giving a total water use for tomato of approximately 1.9 Mm3 year-1.Avoiding or reducing the use of mains water in protected crops would have economic benefits for growers; for example the typical gross income from a tomato crop is around £44 m-2 year-1 [199, 200] and the mains water cost is around 77p m-2 year-1, assuming a water cost of 70p m-3.

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Energy crops are generally not irrigated but by definition produce a large biomass and will generally use more water than food crops. This will reduce the run-off and deep-percolation of rain water by up to 150 Mm3 per 100,000 ha, with potential impact on both ecology and also water availability for irrigated crops within the catchment.

The potential huge expansion of the area of energy crop production is a major environmental threat that needs to be managed at the sub-catchment scale.

Research is required to model and directly assess crop water use and its impact on local hydrology. This will improve predictions of environmental impact and also yields under scenarios of reducing summer rainfall.

Energy crop breeding programs should be expanded to include WUE as a key trait and should consider alternative crops suited to drier conditions.


Table 3: Source of irrigation water used at 50 protected crops sites surveyed by ADAS [201]

Source %age of sitesMains 46Mains + roof/reservoir 22Mains + borehole 12Borehole 12Roof/reservoir 4Other sources 4

Protected crops have a very high WUE compared to field crops; intensive production ensures high yields, and high humidity and relatively still air limits ET. For example, typical WUE for potato is 2.4 t FW ha-1 cm-1 (see section 6.1.2.), whereas for tomato under glass, assuming 60 kg m-2 year-1 and water use at 0.75 m year-1, the WUE is 8.0 t FW ha-1 cm-1. Generally protected crops command a higher price and a have higher WUE than field crops and they provide a greater return for the volume of water consumed. Reductions in water availability, increases in water costs and abstraction licence trading may stimulate a shift from field crops to crops protected under glass or plastic, as has been seen in Spain [202]; where water is a key economic driver crops are chosen the maximise profit per unit of water.

6.7.2. Which is the best source of irrigation water?The average water use for protected crops is 0.96 m3 m-2 year-1 (960 mm year-1) and average annual rainfall in the South East currently ranges from 600-800 mm year-1, thus a large proportion of the water required could be obtained from roof water. For newly built glasshouses it is usually a requirement for local planning purposes that roof water is captured to prevent flooding due to run-off and thus storage capacity for roof water will increasingly be the norm [199]. Although only 26% of growers in a recent survey collected roof water (Table 3.) it is believed that most of the larger commercial growers that dominate the sector in terms of area already collect roof water. Under global climate change scenarios average annual rain fall is not predicted to decline markedly, rather the long-term trend will be for more winter and less summer rainfall. So, provided there is sufficient investment in reservoir storage, roof water should be adequate to cover crop requirements, with the possible exception of the east of England where rainfall currently averages 550 mm (Figure 3.). Collected rainwater is also of high quality because of the low levels of dissolved minerals and so issues with borehole and mains water with hard water deposits and the need to remove unwanted ions, e.g. through acidification, are avoided.

Borehole abstraction may become less reliable with global climate change (see Figure 4.) due to restrictions on abstraction imposed by the EA to protect the environment. Since borehole (ground) water is recharged from precipitation via run-off or deep percolation, the collection of roof water may be just as consumptive of water resources because, depending on local hydrology, it may reduce recharge of ground water or flow to other water courses. The coastal location of much of the glasshouse industry will limit the impact of capturing roof water because there are less likely to be competing downstream abstractors before rivers run to the sea.

Irrespective of any environmental impact, collection of roof water is purely under the control of the grower and cannot be restricted by the EA whereas direct abstraction is licensed and may not be allowed at times of drought. Encouraging growers to use roof water is likely to improve economic sustainability by reducing costs and providing a reliable water supply in the face of restriction on borehole abstraction.

6.7.3. Recirculating hydroponics systems.Growing systems for protected edibles in existing glass are estimated to be approximately evenly split between non-recirculating (open systems) and recirculating (closed) systems. In open systems it is estimated that 20% to 50% of nutrient solution flows to run-off. Closed systems include Nutrient Film Technique (NFT), popular with some tomato and lettuce growers, but the most prevalent closed system used in much of the newly built glass in recent years is a recirculating rockwool block system. It is anticipated that a gradual move from open to closed systems will occur through new build (glasshouse area turns over at about 2% each year [140]), but that investment to convert open to closed systems in existing glass may be slow due to investment costs. EU research aims to optimise and automate closed systems, by modelling and scheduling water use, by monitoring individual nutrient ions with ion-selective electrodes and also by optimising the hydraulic properties of the

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rockwool growing media [203]. Such approaches will minimise waste of water and discharge of nutrients whilst maximising production. Currently nutrient is replenished in closed systems based on monitoring of electroconductivity, and can lead to imbalance of specific nutrients, or a build up of the salts that are input from the source water; development of reliable ion-specific monitoring and replacement technology would be a major advance as it could reduce the need to bleed and refill closed systems. The intensive protected crop industry in the Netherlands (10,500 ha of glass) has led to stringent environmental legislation and a drive towards complete use of closed systems to limit run-off of nutrients. Knowledge transfer to the UK from such developments may be possible.

One barrier to the uptake of recirculating systems is the fear of spreading root diseases, thus a good understanding of microbial ecology [204] and/or effective sterilization techniques is needed [205] to encourage the uptake of recirculating systems. Several HDC projects have addressed these issues (see Annex I). The British Tomato Growers Association has in its research plan of 2003 the target “Operation of closed irrigation systems without risk to yield or fruit quality”.

Some crops cannot be sustained in recirculating systems for long periods because of exudation from roots of autotoxic compounds, such as benzoic acid in the case of cucumbers [206], that accumulate in the closed system. Crop-specific growing protocols and systems for removal of organic acids (e.g. ion exchange resins) are needed in this case.

Assuming that half of the area of protected crops currently uses open systems, and 20 to 50% of nutrient solution in open systems runs to waste, then between 1.3 and 3.2 Mm3 year-1 water could be saved by converting all open systems to closed systems.

6.7.4. Manipulation of environment and crop to reduce transpirationCrop evapotranspiration (ET) is strongly influenced by vapour pressure deficit (VPD), and so relative humidity. Venting in glasshouses is used to control temperature and humidity and research is ongoing to establish the most energy-efficient venting practices (Defra Project HH3611SPC, Annex I). Reduced venting can reduce energy requirements but will increase humidity and may lead to problems with diseases such as botrytis, however high humidity will have the beneficial effect of reducing ET from the crop and improving crop WUE. Transpiration can also be reduced by removal of lower shaded leaves from the crop that do not contribute assimilate to the plant [207].

Breeding, including GM approaches, could be used to limit crop transpiration and this could have benefits to both water use and energy use (reduced venting, and increased leaf temperature) and would be beneficial provided that impacts on yield were minimal; profitability and survival of growers depends to a large extent on maximising economic yield, and a small drop in yield would negate any economic gains from saving on energy and/or water costs. GM tomato plants with increased abscisic acid production have greater WUE by up to 79% in glasshouse trials with no significant impact on vegetative biomass production [208], although effects on economic yield are not yet known. Many tomato crops are grafted using disease resistant root stocks, and one attractive approach to reduce crop transpiration would be the use of root stocks (created by conventional breeding or GM) that limit canopy transpiration through root-to-shoot signalling. Attempts to limit transpiration by applying high salt concentrations to half of the root system in soil-less culture have met with limited success in tomato [209] and pepper [210].

6.7.5. Conclusions: water saving in protected crops:

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Water use in protected crops is approximately 13 Mm3 year-1 and so is not a large user of water in England and Wales, however reducing the use of mains water could have economic benefits for growers.

Protected cropping provides high economic returns per unit of water and could be favoured over field crops as water availability declines.

Collection and storage of roof water could be promoted; this may have benefits in conserving mains water for other users, and providing a reliable source of water, but may impact on downstream abstractors, depending on local hydrology.

Increased use of recirculating systems with appropriate disinfection methods, could reduce water use by 20-50% for individual growers.

Optimising venting for reduced energy use may also reduce water use. Breeding could have a role in limiting crop transpiration in the major crops such as tomato.


6.8.Outdoor (hardy) nursery stock

6.8.1. Background information: current status and drivers for changeThe hardy nursery stock (HNS) sector occupies 9519 ha in the UK and is estimated to have a total water use of 50.5 Mm3 year-1 [9]. In terms of water use, HNS is the largest single sector for plant-based agriculture after irrigation of potatoes, using marginally more water than irrigation of field vegetables. 60% of nursery water use occurs in the Government Office Regions East Midlands, Eastern England and London and the South East, where pressures on water availability are greatest [9]. Most HNS is grown in containers, although trees and roses spend a number of years in the field prior to containerisation.

HNS is a high value crop, making the cost of mains water historically a relatively minor, but not insignificant, consideration; at around 75 p m-3 water costs are usually dwarfed by labour costs. However improvements in control, scheduling and uniformity of irrigation can lead to large gains in profits because of reduced disease, improved crop uniformity and the resulting reduced labour inputs for crop-picking and spot-watering [211].

6.8.2. Types of growing beds and irrigation systemsCrop production in containers outdoors makes poor use of available rainfall because of the limited water storage capacity of the growing media in comparison to field grown crops. Most rain falls between pots, is deflected by the canopy, or, during heavy or prolonged rain, is not useful once the relatively small volume of growing media reaches its water holding capacity, with excess rain being lost as run-off. As a consequence frequent irrigation of pots is needed, and, in the case of overhead irrigation, again a large proportion of this falls between pots or outside the bed and is lost to run-off. Nurseries grow a large range of species that will often have different requirements for water, nutrients, pot sizes, growth rates etc, and thus growing systems need to be flexible, and ideal solutions will tend to be complex. Many different growing systems can be employed on nurseries and each has implications for water use. Three criteria can be used to assess the effectiveness and efficiency of the system used [211-213]:

1. mean application rate (MAR): simply a measure of average water delivery over the bed – ideally MAR should not exceed the rate at which water can be absorbed by the containers, typically should be less than 15 to 25 mm h-1

2. coefficient of uniformity (CU): a measure of the uniformity of irrigation across a bed, that should ideally have a value of 100% for perfect uniformity, or a lower value as irrigation becomes less uniform. Values of 85% or greater are typically acceptable for nursery overhead sprinklers.

3. Scheduling coefficient (SC): gives a measure of the additional irrigation that is required to adequately irrigate the driest areas of an irrigated bed. Ideally SC would have a value of 1, but for beds that are non-uniformly irrigated the value is higher, and growers should aim for values of less than 1.5 for overhead sprinklers, but values of 1.1 to 1.2 are achievable.

Highly uniform irrigation is a prerequisite for efficient use of water and successful irrigation scheduling, and it has been estimated that up to 50% of irrigation water applied in nurseries by sprinklers could be saved by improving uniformity of irrigation [214].

6.8.2.1. Growing systems employing overhead irrigation or drippers: The simplest bed for containers consists of soil covered with a porous ground cover fabric (e.g. Mypex). This does not allow for collection of run-off, and has problems with water-logging in the winter due to a perched water table in the containers and formation of puddles on the ground. Gravel beds, or gravel filled with sand, covered in Mypex reduces the problems of water logging, but still does not allow capture of run-off. Soil at an appropriate angle covered in polythene and then Mypex (and/or gravel) allows for run-off collection and prevents puddle formation.

Overhead irrigation takes the form of sprinklers, microsprinklers or less commonly mobile gantries. Microsprinklers and gantries tend to offer greater flexibility, but with higher investment costs. CU and SC values for overhead irrigation are often poor, leading to wasted water, but improvements can be made by optimum placement of sprinklers, and the HDC Irrigation Calculator allows growers to assess and optimise CU, SC and MAR values for each bed in their nurseries [212]. Drippers give excellent control and uniformity but are expensive to install, and are only practical for larger containers

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(e.g. over 5 to 7.5 litres) and care must be taken to avoid partial wetting in containers by using media that allows good lateral spread of water, or multiple drippers per container.

6.8.2.2. Sub-irrigation growing systems:Water can be delivered to the base of containers by standing pots on sand beds or capillary matting, or by the use of ebb and flow systems; all offer greater efficiency of water use than overhead irrigation because in theory they provide perfect uniformity of irrigation, and irrigation rates are determined by the needs of the crop through capillary uptake. However, overhead irrigation remains by far the most popular system because of the high installation costs of sub-irrigation associated with benching (e.g. ebb and flow) or in creating perfectly level ground.

In sand beds a layer of sand is placed in a level, sealed bed and the water table in the sand bed is controlled with a header tank (or in some cases by drip irrigation). Water is then delivered to the containers by capillary action, with the water potential of the growing media regulated by the tension produced in the sand bed (dependent on the size of sand particles and the water table in the bed). Mixtures of sand and gravel can provide the necessary capillary action, combined with good winter drainage. Because water is taken up by capillary action from sand beds the media in all containers (where plants may vary in species, size, and transpiration rates) tends to be maintained at a similar water potential, and thus sand beds are ideal for production of a wide range of species on a single bed. There are some limitations; low trays and small plugs tend to get water-logged and pots greater than 9 litres (depending on pot height) do not take up sufficient water [213]. Container plants grown on sand beds use approximately 25 to 33% of the water typically applied from well managed overhead systems [211]. Also as irrigation water moves only into the pots from the base, with little or no reverse flow, there is less opportunity for the leaching of nutrients that is often seen with excessive overhead irrigation.

In Australian nurseries floor-based ebb and flood systems use concrete floors with underground piping, or sealed gravel beds and have similar advantages as sand beds, lending themselves to water recycling and good uniformity [213]. Such highly efficient systems are only used to a small extent in England, e.g. Lansen Nursery in Spalding has over 100 ebb and flood beds, but if this system was taken up more widely in England and Wales it could have a large impact on water use in this sector.

6.8.3. Growing mediaType of growing media can be chosen to control rate of water absorption and container run-through and drainage. Pot dimensions (height versus diameter) can be manipulated to influence total water content, water logging, and surface absorption from overhead irrigation. Pot colour can influence temperature of root zone, and so root activity and soil evaporation. Wetting agents can be used to increase water absorption rates, and mulching used to reduce surface evaporation (and suppress weeds). HDC project HNS107a (see Annex I) concluded that mulches could reduce evaporative loss from growing media by nearly 50% and that wetting agents improve surface absorption from overhead irrigation and horizontal water movement in containers (important for drip irrigation), particularly in peat-based media. However, relatively little research has been done to explore the importance of these factors [211].

6.8.4. Irrigation schedulingCurrently is it believed that the majority of nurseries employ non-scientific methods for scheduling irrigation. This is usually based on experience, and visual inspection of the crop, or on rigid timer regimes that do not take into account changing demand for water from the crop due to environment and development. Psychologically there is a tendency for staff to over-irrigate when non-scientific methods are used because the effects of lack of water (wilting) are immediately visible and of greater concern in the short term, whereas longer-term effects of over-irrigation (high cost, poor quality) are less apparent. Science-based scheduling performed by well-trained staff will be a key element to water saving in nurseries.

Irrigation scheduling and water management is more complex in container grown plants than it is in field crops because nurseries are not monocultures, but have a range of different crop species. Irrigation efficiency is inherently lower than in field crops because of the relatively limited capacity of containers to hold water reserves. Container production does have the advantage that water use in pots can be monitored easily by pot weighing so that appropriate scheduling regimes can be readily developed for each situation.

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Accurate matching of irrigation to plant demand for water (scheduling) is most relevant to overhead irrigation because in sub-irrigation capillary uptake from the bed is already determined by plant water use.

6.8.4.1. Scheduling based on estimates of evapotranspiration (ET)Scheduling based on calculation of ET from Penman-Montieth equations can be used, as commonly used in field crops, but this approach requires expensive weather station equipment. In the recent HDC project HNS97 (see Annex I) it was concluded that the combined use of an Evaposensor/Evapometer [215] and a rain gauge could be used to simply and accurately schedule irrigation in nurseries. This equipment costs approximately one tenth of a weather station and provides a time-integrated estimate of the atmospheric evaporative demand experienced by the crop, as influenced by temperature, solar radiation, wind speed and humidity. This information, together with local rainfall, indicates the relative fluctuations in demand for irrigation over time; growers can then calculate the irrigation needed by each crop throughout the season provided that the requirement of each crop is empirically calibrated against the ET data.

6.8.4.2. Scheduling based on monitoring soil water contentRecent research has investigated the use of “closed loop systems” to schedule irrigation in nurseries based on measuring dielectric constant of the growing medium (related to volumetric moisture content) with a probe, and triggering irrigation based on a threshold output from the probe. 30-40% savings were achieved using a prototype closed loop system in comparison to manual irrigation [214, 216]. This system proved highly reliable, operated well for whole beds with just one probe placed in a representative pot, and produced results comparable to the use of the Evaposensor/meter [217] (see above). Inexpensive soil moisture probes and control systems have recently become available to growers (e.g. SM200 probe and GP1 system from Delta-T [218]).

6.8.4.3. Scheduling based on imaging methodsInfra-red imaging to monitor leaf temperature as a surrogate measure for transpiration has been considered for use in scheduling irrigation in a range of systems [23], and is now being evaluated in the context of gantry irrigation systems for nurseries in HDC project HNS97b (“Water link II”, Annex I). Such a system holds promise for producing a closed loop system where canopy temperature is monitored by passage of an IR camera mounted on the gantry, and then irrigation from the same gantry is triggered based on canopy temperature relative to suitable reference surfaces. It has the potential advantage of providing a richer source of data in two dimensions for taking scheduling decisions, rather than just from one or a few pots in a bed as is the case with soil moisture probes. Costs of infra-red cameras are reducing (currently below £4000), so purchase by growers in the future is credible.

6.8.4.4. Regulated deficit irrigation (RDI) RDI is simply sub-optimal irrigation, below the potential ET for the crop. The crop adapts to this level of irrigation for example by altering growth habit and resource allocation (e.g. root-to-shoot ratios or vegetative vigour versus reproductive growth), and effects on leaf morphology and stomatal conductance tend to increasing crop water use efficiency. In the context of HNS, RDI can potentially be used to control crop growth and quality, reducing the labour costs associated with pruning, and improving performance of plants after purchase and transplanting, and generally increasing crop value, whilst reducing water use by up to 50% [214]. It was found that RDI applied by drippers did enhance quality of woody species by producing more compact plants [219], and that control of basal breaking and height in roses could be improved with RDI [158], however some species suffer reduction in quality under RDI [220], so each species needs to be evaluated for its response. RDI is only possible where irrigation systems are highly uniform and readily controllable, and where rainfall is not likely to negate its effects on quality [214], and so it is important to establish whether RDI is a practical approach for the outdoor sprinkler irrigation systems that dominate the industry currently.

6.8.5. Research facilities in the UKMany of the growing and scheduling systems described above are available for demonstration and/or research trials at the East Malling Water Centre (EMWC) facility, including capillary matting, micro-sprinklers, large overhead sprinklers, a gantry system, sand beds and covered gravel beds [217].

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6.8.6. Nursery-scale water managementMany nurseries use mains water, or water abstracted from bore holes, with run-off water running to local water courses. Where this is still current practice, significant savings in water withdrawals can be made by collection and re-use of run-off from rainfall and excess irrigation. The UK region with the lowest rainfall currently receives around 550 mm year-1 (Figure 3.) and as discussed above much of this water is not immediately available to the crop due to the low water capacity of containers, and it is estimated that only 20-50% of rainfall is “useful” to the crop where good irrigation scheduling is practiced [211], and less if the crop is over-irrigated. The area from which run-off can be collected will depend on the nursery but is often considerable and can be made up of sealed beds capable of collecting run-off, areas of hard standing (e.g. car parks and walk-ways etc), or roofs. The average outdoor nursery requirements for supplementary irrigation are 530 mm year-1 [9], thus in many cases it is expected that collection of run-off from the cropping area plus other areas could provide the bulk of the nursery water requirement.

The potential environmental impact of collecting run-off should not be forgotten as this water is clearly no longer available to local water courses or downstream abstractors, or, in some circumstances, the collected run-off may have drained in to the same aquifers that the growers would have used as their borehole supply. However, from the grower’s point of view, where it is the wish to avoid possible future restrictions on abstraction, or to expand the business beyond what is possible on current abstraction licences, the collection and use of run-off water has the advantage of not being considered as licensable abstraction unless it passes through the soil before collection. Collection of run-off can also provide considerable cost savings where mains water is used.

Systems for collection of water typically involve concrete drains, a reservoir for untreated water and then a purification system (e.g. slow-sand filtration, or chlorination), prior to storage of the treated water. The purification is necessary so that the water can be used for irrigation without the fear of spreading disease. Extensive research into adapting long established slow-sand filtration systems to nursery requirements has been carried out in the past [221, 222] supported by HDC (see Annex I, HNS88/a/b).

In 1999 Hilliers nursery were given a “Waste Watchers Award” for achieving savings of up to 80% in their use of mains water by installation of a system for collection, storage and purification of run-off water. In this example the 20.3 ha site originally used mains water at a rate of 104,000 m3 year-1

(514 mm year-1 averaged over the site), but after installation of the system the mains water bill was reduced from £100k year-1 to £15k year-1 and capital investment was recovered within 18 months in this case [223]. Installation costs and availability of space for reservoirs may limit the uptake of this approach but clearly very large savings, in terms of costs and water withdrawals can be made.

6.8.7. Knowledge transferIn HDC project HNS122 the Water use Monitoring Scheme (WUMS) is being carried out. WUMS aims to collect accurate water use, rainfall and potential evapotranspiration data for commercial overhead irrigation systems. The information will allow comparison between systems and growers (“benchmarking”). Initial data indicate that irrigation rates can vary between nurseries by up to 4.5-fold [211], and there is therefore much scope for sharing of good practice. Currently the majority of nurseries no not carefully monitor their water use but in the future they will need to provide information to demonstrate efficient use of water to the EA before abstraction licences can be renewed.

As described above, much information is already available on how to monitor and improve irrigation, and knowledge transfer will be key to delivering real water savings. Growers need to be encouraged to monitor water use of each bed using low cost water meters, and to check and optimise irrigation uniformity using catch can approaches, and to schedule irrigation based on scientific methods. In 2006 HDC ran a series of workshops: “Water workshop for container nursery stock” across England, and have published grower fact-sheets [212, 216]. These activities need to be continued and expanded to ensure that water saving measures are taken up, and best practices shared.

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6.8.8. Conclusions: water saving in hardy nursery stock

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Water use for hardy nursery stock is significant at approximately 50 Mm3 year-1. Overall it was estimated (HNS97b final report, 2003) that a combination of improved irrigation uniformity, scheduling and the introduction of RDI could reduce water use in nurseries by 75%, saving 38 Mm3 year-1, whilst at the same time reducing labour costs and improving crop quality.

Collection, storage, treatment and reuse of run-off from irrigation and rainfall, employing existing technologies, could allow some nurseries to reduce their water withdrawals to close to zero. It would also reduce the impact of poor uniformity and over-watering on total water use (but not on quality) because run-off could be reused.

Further research is needed to improve the uniformity of overhead irrigation systems, possibly by development of novel sprinkler technologies.

Research is needed to further develop effective closed-loop automated irrigation scheduling systems that are simple to use (part of current HDC project HND97a)

Sub-irrigation is far superior to overhead irrigation as it consumes much less water and provides greater uniformity, but is expensive to install. Research is needed to develop lower cost sub-irrigation solutions, or to establish the economic viability under future scenarios of reduced water availability of existing efficient systems such as sand beds.

Continuing knowledge transfer is needed to ensure that nurseries monitor and optimise irrigation systems and use scientifically-based scheduling methods for irrigation. Growers should also be encouraged to consider moving to sub-irrigation.


7. Washing of Root Vegetable and Potato CropsThe volumes of water used in washing of vegetables and potatoes are small compared with the water used in irrigating vegetable crops [9]. For example a 75 t ha-1 carrot crop may be irrigated 6 times with a total water requirement of 150 mm ha-1 ≡ 1500 m3 or 20 m3 t-1 compared with 0.1 m3 t-1 for washing i.e. 200 times more.

Primary producers are fully aware of the need to use water efficiently because of above inflation increases in water supply costs, particularly for mains water, and also higher waste water treatment costs. Efforts have been and continue to be made to minimise water use. In the past, when there was less concern about the cost of water, the questions raised when installing washing plants were cost and reputation of the suppliers but now the considerations uppermost are energy efficiency and volume of water used.

The stages in washing and preparing root vegetable crops for market involve some or all of the following processes. This information gives an indication where water is introduced into the process.

7.1. The Washing ProcessAll systems and procedures for washing root vegetables tend to be custom designed using specialist equipment and procedures to take account of:

crop(s) to be washed obtaining ease of cleaning minimisation crop damage market requirement/outlet scale of operation soil type (e.g. less water required for crops grown on sands than those on heavier clay soils) water use minimisation and re-circulation

No two washing systems are the same though the objective is of course the same i.e. to provide a clean marketable product to the next stage of the supply chain.

There are a number of stages in the washing of root vegetable crops though not all stages will apply to every crop.

dry soil removal dumping into the packhouse stone separation barrel washing brush washing vegetable polishing cooling final rinsing

At all stages handling must be minimised and movement of product should always be in one direction without crossovers. Increasingly water (often under pressure) is used to move the crop from one stage to the next. This technique minimises damage such as bruising (in parsnips) and breaks and splits (particularly in carrots).

7.1.1. Dry soil removalDry soil removal is often considered the best option for the first stage in market preparation or processing, particularly were water volumes are restricted and dirty water cleaning is difficult. There are a number of options available to suit soil type, ranging from web units through to vibratory separation.

7.1.2. Dumping into packhousePreparation for the fresh market starts with dumping onto packinghouse feeding lines. Dumping may be dry or in water to wash/move produce out of the trailers that come from the field. In both cases it is important to minimise drops as well as to control the flow of product. Water systems for moving produce cause less bruising and breakages. Where water is in plentiful supply a trailer wash out system is one of the best ways to ensure reduced crop damage and good pre-soaking abilities for difficult to clean soil types.

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7.1.3. Soak tank and stone separationStone separation is vital to ensure minimum crop damage and longevity of washing equipment, and is therefore placed before crop washing. Most separators use a centrifugal current of water (re-circulated) which floats the crop and allows stones and heavy clods/mud to sink. The crop passes over an inclined water separation grid or is removed by an elevator and the stones and clods fall out of the bottom of the separator and are removed by a chain mechanism going in the opposite direction. Up to 100% stone and clod removal with limited damage can be achieved at work rates of up to 50 t hour-1.

7.1.4. Rotary barrel washerStandard barrel wash systems are available to give a primary clean by removing small stones and particularly ingrained soil. The crop is put in one end (from the soak tank), washed in a rotating barrel, and emerges at the other end up an elevator. Some models rely on jets of re-circulated water with a final fresh water rinse within the final barrel section. The equipment is designed to allow root vegetables to run partially or fully submerged and is self cleaning due to rotary scrapers and an auger system for automatic sludge extraction. After barrel washing, crops are relatively clean for the next part of the washing process. Throughputs range from 1 to 60 t hour-1 and the water requirement could be from 180 to 270 L t-1 of carrots washed.

7.1.5. Brush washers and vegetable polishers (mainly carrots and parsnips)For optimum produce wash results a brush washer may follow the barrel washer in a processing line particularly when more delicate washing/cleaning is required. The vegetable polisher system, which is a combination of a barrel and a brush washer, has revolutionised the quality of pre-pack and fresh market produce. The equipment works by removing the surface membrane from the roots and polishes them to give a quality finish deep glow. It has proved to be very effective in reducing the ‘silvering’ effect seen on carrots and/or diseases such as scab or cavity spot and has considerably increased ‘recovery rates’ on product that would otherwise been out graded.

Since the crop passes through the suspended barrel with a sprinkler spray bar built inside there is no soaking effect of the vegetables with dirty water. A steel tank incorporating a filter system and re-circulation pump delivers water to the spray bars which assist in crop cleaning, fresh water rinsing and keeping the brushes clean.

However this equipment uses more water as there is a sprinkler bar continuously running and the water has to be replenished more often because of the accumulation of carrot tissue removed in the washing/polishing process.

7.1.6. Hydrocooling (mainly carrots, parsnips and turnips)An in-line hydrocooler will remove much of the field heat and assist in the preservation of freshness and shelf life. Potable water is introduced at hydrocooling, often each day though some producers only change water every 2 to 3 days and use chlorine to maintain water quality.

The final stage in preparation is cooling, which for crops requiring appreciable field heat removal, is best achieved by hydrocooling. However not all crops can be hydrocooled because they need to be able to tolerate wetting, the possible addition of chlorine and water infiltration. For hydrocooling the refrigerating medium is cold water either achieved by immersion or through means of a chilled water shower. Carrots, parsnips and to a lesser extent turnips are hydrocooled to prevent loss of turgidity and maximise shelf-life. Capacity of hydrocoolers is typically 5 to 30 t hr-1 (for carrots and parsnips). Mains quality water is used. Water introduced at the hydrocooling stage is re-circulated to dirtier parts of the operation before final discharge.

7.1.7. Final spray rinseOnly potable water should be used either from the mains or if recycled after sediment pre-filter and UV sterilisation. Water is recycled to dirtier parts of the washing process.The processes for washing other vegetable crops such as leeks, celery, salad onions have been described [9] but the important point is that potable water is often a requirement of the customer because of microbial risk, and hence the opportunities for re-circulation may be more limited.

Most root vegetable crops follow some or all of the above procedures. However on a very small scale some crops may be harvested direct from the field into nets or may only go through a small capacity barrel washer.

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7.2. Water recycling and re-circulationAwareness of the environmental and the financial need to reduce water usage is high, particularly in areas where water is already an increasingly scarce resource.

In the past, producers have used freshwater for vegetable washing and then let it go to waste. However most vegetable washing water is now extensively recycled for use in wash cycles such as stone separation and barrel washing that do not need such a high quality. Alternatively the water can be cleaned by settlement and filtration and recycled for higher quality use. If a chlorinating plant or other effective purification treatment is added the recycled water may be used for final wash and rinse purposes. The Crop Assurance Generic Protocol strongly recommends that there is an adequate cleaning and conservation policy for water used for washing and wherever possible water for washing should be reused.

Specialist machinery companies will custom design a complete water recycling system to allow all water to be re-used in the washing process before finally being discharged, possibly for irrigation.

7.2.1. Waste water and solids disposalProvision of an adequate waste water and solids disposal system is as important as a good source of water. Washing water can usually be disposed of more economically on the farm than by creating a discharge to a sewer or watercourse. Disposal systems must cope with:

the volume of liquid waste its fluctuation the quantity of solids the polluting nature of dissolved organic matter large seasonal and day-to-day variations of quantities with rainfall and run-off

The provision of adequate treatment to meet stringent conditions of consent to discharge can be very expensive. There are statutory powers to prevent the pollution of underground water by discharge of effluent and great care is needed to prevent this. Pollution of streams and water supplies derived from wells, springs and boreholes can lead to action by the local water authority (Environment Agency/water company). Screening and sedimentation are the two methods of separating the solids from water.

7.2.2. ScreeningThe solids in washing water consist of several fractions such as large pieces of root and foliage, smaller pieces of tissue, disintegrated cell contents, soil-derived particles of mineral and organic nature. Screening using a screen of c. 150 microns, will remove considerable quantities of solids.

7.2.3. SedimentationSoil particles can be removed by sedimentation following initial coarse screening. Settlement is best provided in the form of a pit or lagoon about 3 m deep or a settling tank, large enough to hold three days’ water consumption. The solids in the lagoon or tank should not be allowed to accumulate beyond half depth and are best removed at regular and frequent intervals. Sufficient and suitable access for taking out sludge is very important.

7.2.4. Waste soil/sludgeSoil left behind in the bottom is augered-out into trailers and may be returned to the fields where the crops were grown. If not spread immediately, it may be piled in the yard until there is sufficient volume to be worth loading and spreading. However, it may not be practical or desirable to return the recovered soil if there is a risk of disease being present. Alternative uses have been found such as in road construction industry or by combining with local household green waste streams (e.g. with Swanley Council green waste).

Waste vegetable material and soil can contain significant levels of persistent pests and diseases. For example particular attention must be given to the disposal of infected carrot waste, as this can be a major source of Violet Root Rot. Wherever possible, waste must be composted on land that will not be used for crop production. It is imperative that solid pack-house and washer waste is not returned to land that is likely to be cropped with roots.

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7.2.5. Waste waterDisposal of waste water can be a major problem as its suitability for irrigation can be limited. For example water from carrot washing plants may be contaminated with the disease cavity spot and therefore there is a reluctance to spread this on arable land, particularly if the land is rented. Also contamination with disinfectants such as chlorine treatment or low levels of pesticides used to treat the vegetable crops is a perceived concern. However the waste wash water is used for irrigation purposes but only for woodland, grassland or non-cropped land such as set-aside. Ideally these areas need to be in close proximity to the packhouse. This technique gives minimum waste as there is no discharge to watercourses.

7.2.6. Action Points to Minimise Water use in Washing Vegetable Crops

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The primary consideration is to grow and harvest clean vegetables and thus reduce the volume of soil that needs to be washed off.

Choice of soil type will influence amount of washing and hence water required e.g. crops grown on sands will have less soil adhering than those on peats and silts. However other factors need to be considered such as sandy soils not being ideal for all vegetable crops and geographical location in relation to infra-structure, labour, etc.

Time of year will influence the amount of washing required, with more soil adhering in winter month.

Sand soils are in areas where there is already pressure on water use for irrigation and the opportunities for additional production of vegetable crops may be limited due to restrictions on licenses and rotational considerations.

More dry cleaning with efficient soil extraction on harvesters and at the washer intake would reduce the volume of wash water required in subsequent stages and help conserve supplies. For example more baby Chanteney carrots are being grown which can have up to 10% weight of soil rather than an average of 3% for larger roots grown on light sandy soil. This needs to be removed, ideally whilst the crop is still ‘dry’. However there is the potential for increased crop damage. Further development work is required.

It is now universal practice to introduce potable water at the final rinse or hydrocooling stage and then re-circulate the water to the cruder parts of process.

There is little re-circulation of water used for some crops such as potatoes, celery and radish as there is a customer requirement to use a potable supply.

Possibility of collecting rainwater off packhouse roofs, yard surfaces, etc; at present on most sites runs into the drains. Some growers are considering this but the water would have to be filtered and treated before use because of contamination by birds, small rodents and pollution.

The investment in purification treatment may be difficult to justify being influence by the source and cost of water currently used.

Waste water can be used for irrigation but there is the possibility of disinfectant and pesticide residues. Further work is required to ascertain the level of any residues.

Also there is a perceived concern that the waste water may be contaminated with disease organisms, such as cavity spot, and therefore it is used to irrigate non-cropped areas, grassland and woodland rather than higher value arable crops where it would mitigate the need for irrigation. Research work could address these concerns.

However recycled waste water is used for irrigation of vegetable crops around the world including other developed countries such as Australia. There is technology available to produce safe potable (i.e. drinking) water if there is a demand and if it is cost effective. Using recycled water for vegetable crop irrigation would offer substantial environmental benefits but the technique would have to be acceptable to the Environmental Agency and comply with crop protocol and assurance schemes. Research work could address these concerns.

Scope for more water metering and benchmarking to monitor consumption levels, efficiency and identify leakage and wastage.


8. Current and emerging technologies aimed at saving water in livestock farming

Within the baseline review of water use, annual water requirements for both drinking and wash water were estimated from best available industry information and from limited research data. These estimates were combined with the census numbers for livestock in order to derive estimates of total requirements, both on a regional and national basis. The cattle sector is the major consumer, with a total requirement of c. 82 million m3, followed by sheep, at 17 million m3, poultry at 12 million m3 and pigs at c. 8 million m3 – a total of 119 million m3, overall. Although no attempt was made to profile these requirements throughout the year it seems likely that a fairly level demand would be observed for the pig and poultry sector, with production dominated by mostly year-round housing systems. For sheep and cattle, peak demands are likely during the summer months, but drinking water intakes of animals at grass are much affected by the dry matter content of herbage as well as weather conditions and, in the case of dairy cows, milk yields.

Data collected in the baseline study also showed that wash water requirements were relatively small compared with the volumes required for drinking purposes (Table 4.). Expressed as a percentage of total water, drinking water requirements ranged from 79% for dairy cattle, 87-99% for different categories of pigs, >99% for sheep and 96-99% for poultry, respectively.

It should be recognised that the water requirements of livestock (i.e. water needed for metabolism) are met from three sources [136,137]:

water consumed voluntarily (drinking water); water contained in feed; water formed within the body as a result of metabolic oxidation (body tissues, dietary protein,

carbohydrates and fat).

The metabolic water requirements will vary widely according to the losses that occur during body metabolism as well as the amounts of water included in milk or in new tissue formation during growth or pregnancy. Since metabolic water demands represent such a large component of total water requirement in livestock production, any review of water efficiency should include a consideration of the factors that can impact on voluntary intake by the animals.

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Table 4. Summary of drinking and wash water requirements for livestock [9]

Production cycle (weeks)

Drinking water Wash water Other requirements Drinking water Wash water Drinking water proportion5

L animal-1 day-1 L animal-1 day-1 L animal-1 yr-1 L animal-1 yr-1

Cattle

Dairy cow 56 91.8 25 33516 9125 0.79Growers & replacements 52 20.0 0 7300 0 1.00Beef cows & heifers 52 20.0 0 7300 0 1.00Dairy & Beef bulls 52 20.0 0 7300 0 1.00Beef store cattle 52 20.0 0 7300 0 1.00Dairy & Beef calves 9 5.0 0 1825 0 1.00Pigs

Dry sows & gilts 52 6.0 0.086 1708.2 24.5 0.99Boars 52 6.0 0.086 2190.0 31.4 0.99Farrowing sows 5 30.0 5.63 2409.0 452.1 0.84Maiden gilts 10 5.52 0.0863 2007.5 31.4 0.98Barren sows 10 5.52 0.0863 2007.5 31.4 0.98Weaners (<20 kg) 4 2.0 0.286 730.0 104.4 0.87Growers (<50 kg) 5 4.0 0.371 1460.0 135.4 0.92Finishing pigs 11 5.5 0.229 2007.5 83.6 0.96Sheep Dipping

L event-1 head-1Dipping

L animal-1 yr-1

Ewes 52 4.50 0 2.25 1644.3 4.5 0.997Rams & other adult sheep 52 3.30 0 2.25 1204.5 4.5 0.996Lambs under 1 yr 52 1.68 0 2.25 613.5 0.94 0.999Poultry batch –

L m-2 floor areaSt density –

birds m-2

Pullets 16 0.0911 5.0 12.0 33.24 1.1404 0.97Broilers 7 0.2041 5.0 12.0 74.49 2.7083 0.96Laying hens - caged 56 0.2041 6.0 22.0 74.49 0.2445 1.00Laying hens - non-caged 56 0.2219 6.0 11.5 81.01 0.4678 0.99Broiler & layer breeders & cocks 44 0.1948 5.0 6.0 71.10 0.9420 0.99Ducks 7 1.2245 5.0 7.0 446.94 4.1270 0.99Turkeys (m) 20 0.7143 5.0 2.2 260.71 5.3719 0.98Turkeys (f) 16 0.4464 5.0 4.3 162.95 3.3592 0.98

Notes: 1 – census data assumed to represent animal numbers throughout year; occupancy figures used only in pigs where sow farrowing time taken into account 2 – maiden gilts & barren sows for fattening assumed to have similar drinking requirements to growing pigs as both categories are growing3 – maiden gilts & barren sows for fattening assumed to have similar wash water requirements to dry sows kept on straw4 – Approx. 40% of lambs kept as stores to c. 12 months and have a dipping requirement5 – Drinking water requirement per animal as a proportion of total water requirement

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8.1. Water requirements of cattle

8.1.1. Drinking water requirementWater intake varies according to whether the animal is in a state of maintenance, fattening, pregnancy or lactation. There is evidence of significant correlation between weight gain in calves, dry matter intake and water intake [224a]; also of a reduction in weight gain in calves as a result of restricting water intake [224]. For lactating cows the following relationship was derived for water intake [225]:

Iw = 2.15 Id + 0.73 M + 12.3,

where: Iw = water intake, kg day-1

Id = dry matter intake, kg day-1

M = milk yield, kg day-1

Research indicated that a daily supply of 40 kg water cow -1 for dairy cows at grass was sufficient for almost all situations, and that there should be trough space to allow access for 10% of the herd at any one time [226]. A flow rate of 655 L hour-1 has been suggested in a trough for a 100-cow herd at grass and where such a flow rate cannot be maintained, provision for reserve water storage. In studies on autumn calving herds a requirement for 160 cm trough for 30-50 cows was indicated, depending on high or low DM diet; for water bowls, the equivalent requirement was one bowl per 6 or 10 cows, respectively [227]. Mean drinking rate from bowls has been observed at 4.5-5.0 kg min-1, compared to 5.6-14.9 kg min-1 from troughs. It is likely that water bowls could limit water intake in some circumstances.

In the ARC review of water requirements [136], net water intake relative to DM ingested [(water in feed + water drunk – water in milk) (DM intake)-1] varied from 3.1 to 10.2 kg kg-1. The moisture content of the feed, ambient temperatures and animal breed having some impact on water consumed. It was suggested that for temperatures below 10ºC, the water intake of non-pregnant, non-lactating cattle should be 3.5 kg kg -1 DM ingested, increasing to 5.4 kg kg-1 DM ingested, for temperatures of 11-15ºC, 6.1 kg kg -1 for 16-20ºC and 7.0 kg kg-1 for 21-25ºC [136]. Heat stress in dairy cattle is something the industry is already aware of in the UK, and advice was provided on diet, water and stock management during 2006 [228].

It is apparent that water intake is positively related to the %DM content of the feed [229], with a closer relationship for animals fed on dry diets than those on low DM diets, when it is suggested that total water intakes may be in excess of apparent needs. In general, the higher the proportion of minerals in the diet the greater the excretion of urine and, accordingly, the larger the water intake. Cattle also drink more on a high protein, than on a low protein diet, since any increase in N surplus requires a larger volume of urine for excretion. Most natural waters range in pH from 6 to 9, although waters from springs may exceed pH 9.0. It is generally accepted that water within a pH range of 6-9 is satisfactory for cattle [230].

8.1.2. Drinking water supplyWhilst there may be differences in the water demand of cattle, according to the factors outlined, there is very limited scope of achieving any reduction in water requirements, at least within an existing livestock production and feeding system. However, the logistics of water supply must be carefully considered and, with a daily drinking water requirement of almost 100 L day-1 for large dairy cow, i.e. 20 m3 day-1 (4500 gallons day-1) for a 200 cow herd and possibly several km of pipe-work on a large farm, the potential for wastage via leakage must be considerable. A number of measures will help to reduce consumption of water either from mains supply or from abstraction. These involve either reducing water loss or wastage, or water recycling/re-use:

(i) water metering. In view of the large differences in water demand between enterprises on a large mixed farm, separate water meters should be installed to allow independent monitoring of each enterprise. This will allow inefficient water usage or leakage to be quickly identified.

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(ii) leaking or burst pipes. Exposed pipe work should be appropriately lagged to minimise the risk of freezing. Remote troughs should be checked regularly for leakages, especially after freezing weather. Lengths of supply main should be isolated and protected by inspection chambers and stopcocks.

(iii) trough alternatives. Many farmers invest in larger water troughs so that more can be stored. Maintaining high, or even adequate, water quality in these tanks is difficult. Cleaning out can mean wasting up to 500 gallons of water for a large trough. A proposed solution has been that farmers might consider using a large bowser tank fitted with troughs around the sides and back [231]. The tank could be an old milk tanker or other, re-registered for agricultural use. Filling with a cleaned out slurry tanker would allow water to be collected from a natural source and transferred quickly into the bowser. Large herds will need a fast flow into the side troughs, which might be best done using a large bore direct feed from the central holding tank.

(iv) collection and use of rain water. Livestock housing, particularly on dairy farms has large areas of roofing which, according to good practice [232], needs to be provided with guttering and intact downpipes in order minimise surface water access to slurry storage. Advice, however, has been that such water should be discharged to the nearest clean water drainage and it should be no surprise, therefore, that almost no farms collect this water for possible use. Anecdotal evidence has indicated as few as 5 farms in a period of dairy husbandry consultancy in England and Wales have collected any roof water [233]. Even in these latter cases, water was collected into tanks, which then supplied troughs directly via a simple overflow. The potential contribution to total could be significant, based on average space allowances for adult dairy cows – 5-6 m2 animal-1 for housing and, together with dairy and parlour areas, perhaps a total of 9-10 m2 animal-1 of roof area available for water collection. Collection of roof water over a 180 day winter with an average of say, 250 mm rainfall would amount to 10 m2 x 0.25 m x 0.9 (roof runoff coefficient) = 2.25 m3 cow-1 winter-1; or a total of 450 m3 for a 200 cow herd. The estimated drinking water requirement for the 200 cow herd (see above) is 3600 m3, so the collected roof water could supply c. 12% of that total requirement. (v) livestock water pumps. Livestock water pumps provide a number of benefits, in particular:

use of natural water sources, including ground water (via shallow wells); elimination of need for long lengths of piped supply and water troughs; hence, reduced risk of leakages; supply in remote locations; protection of water courses by stock exclusion; low cost compared to pipes and troughs.

For cattle the systems are generally based on a nose pump, as shown in Figure 9. The animal is attracted to the unit by the water retained in a bowl placed below the unit. To access the water, pressure on a broad-ended lever is needed and, in the process, a diaphragm is operated, creating suction and drawing water into the bowl. Practical limits of these pumps (through a 25 mm polyethylene pipe) are typically lifts of 6 m from the water surface and up to 60 m horizontally.

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( a) nose pump with bowl (b) pump in use on a raised mounting

Figure 9. Water supply for cattle via nose pumps

( a) nose pump with catch basin for calves (b) Frost-free pump working in freezing conditions

Figure 10. Specialist livestock pumps

Young calves are not able to operate the pump, however, adding a catch basin for overflow water makes water available to calves (Figure 10a); young stock are able to operate the units at a few months old. Similarly, an adaptation involving the replacement of the lever with a crate, the weight of the animal stepping into the crate operating the diaphragm, allows the system to be adopted for either young stock or sheep.

Recommendations in Canada, state that one water pump is needed per 20-30 beef cows or 10 dairy cows [234]. Specialist units have also been developed capable of operating successfully in severe winter conditions, with the lever operating a piston pump set down a shallow well (Figure 10b).

It can be seen that these pumps offer several benefits, including the very significant advantage of reduced risk of water loss through pipe leakage or broken troughs and, hence, increased efficiency in water use. There is also reduced risk of water contamination through exclusion of stock from the water source.

8.1.3. Wash waterIn the survey of slurry management strategies on commercial dairy farms in England, Wales and Scotland in 2004, water use in the washing of the parlour and associated yards was based on measured hose flow rates and daily usage [235]. Average daily water use was 28 L cow-1 (range, 17 – 40 L cow-1) when high-volume hoses (average flow rate, 97 L min -1) were used in the milking parlour, 22% more than for low volume hoses, at 23 L cow -1 (range, 13 – 30 L cow-1). Previous guidance on dairy, milk tank and pipeline cleaning and collecting yard wash-down was given in the Water Code [232]:

35 L cow-1 day-1 for power hoses 18 L cow-1 day-1 for non-power hoses

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On the basis of the above estimates, daily usage of 30 L cow-1 and 20 L cow-1 were taken as reasonable guidelines for high and low volume hoses, respectively, within the recent PLANET manures inventory [236]. However, the very wide range in water use in the milking parlour between farms in the survey (15-63 L cow-1 day-1) suggest that the use of “standard” values could be seriously misleading and it is recommended that actual water volumes used, should be measured (as outlined [235]). Moreover, consultancy experience has suggested recently that, with larger dairy herds and greater mechanisation, the use of high pressure washing systems is on the increase and, hence, wash water volume cow -1 day-1 [233]. The use of wash water for cleaning purposes is normally confined to cleaning and hygiene around the dairy, the milking parlour, the bulk milk tank, pipelines and the collecting and dispersal yards.

One recent development is the flood-washing system, which has been introduced from the US. This generally confined to use in housing and feed yard areas and is thought to provide a more effective cleaning than is possible via scraping alone. The water is collected and recycled via a lagoon system, with sedimentation and overflow – this allows re-use of the water for washing down, though it is suggested that a daily addition of c. 20% water volume is necessary. Of course, since feeding yards and cubicle passageways would not normally be washed down, this system cannot be seen as a contribution to water economy. Normally, unless there are specific animal disease or health reasons, no cleaning water is used in stock accommodation for both adults and young stock, whether dairy or beef. Periodically, slurry or manure and soiled bedding are cleaned out and fresh litter spread, perhaps after a disinfectant spray. Depending on the condition of the animals, there may be an additional requirement for stock washing in the case of finished beef cattle, for compliance with meat hygiene requirements [237].

8.1.4. Case studies on reduced water useMuch anecdotal information suggests significant opportunity for savings in water use, particularly on dairy farms; however, systematic studies where attempts to monitor reduced wastage or improved efficiency of water use are generally lacking. However, in a study on dairy farms [235], an empirical model based on the measurements and information gathered in the present survey was constructed and used to study the impact of management strategies on water use and slurry management. The model allowed an estimate of the amount of each constituent (excreta, parlour washings, run-off and rainfall capture) in slurry and the total volume of slurry produced on a hypothetical, but typical, dairy farm in SW England. Calculated averages for herd size, housing period and yard area allocated to the cows and standard excretion rates [238] for Holstein x Friesian cows were used. Rainfall intensity and slurry storage practice was selected to represent common practice in this geographical area. Full characteristics of the case study farm (CS) are shown in Table 5. The impact of adopting a range of alternative management strategies, aimed at reducing the amount of slurry produced on CS was investigated under sixteen separate management scenarios. These strategies included changes to the dairy herd (housing period, breed of cow) and twelve strategies examined opportunities to reduce the amount of water entering the slurry store. Of these, four (scenarios 9-12) specifically considered the impact of reducing washing water usage in the parlour. These are outlined in Table 5.

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Table 5. Characteristics of the dairy farm case study (CS) and details of the amendments to practice on the CS farm for each management scenario

Synopsis of management strategies and resources for CS Annual rainfall: 1100 mm with 60% of the annual total falling in the October-March period.Herd: 180 Holstein x Friesian cows, 148 in lactation. Housing period: 180 daysExcretion rate: 64 L of undiluted slurry (dung and urine) produced daily on average for each cow, both lactating and non-lactating.Slurry storage: an earth-banked lagoon (no separation) taking all slurry and dirty water; surface area, 750 m2; depth, 2.5 m; capacity 1875 m3; sufficiency, 69 days (58% of 4 month storage requirement).Yard area and run-off: total farmstead area, 35 m2 cow-1; run-off from 30% of the total farmstead area draining to the slurry store.Parlour washing: high volume hose used for 40 min daily (20 min per milking); flow rate, 80 L min-1; pipeline and milk tank cleaning, 10 L cow-1 daily.Adaptations to management practice on CS for each scenario Scenario 9 Parlour water (low pressure) 50% decrease in hose water usage (40 L min-1)Scenario 10 Parlour water (buckets) Zero hosing; milking parlour washed with water from buckets;

average 5 L cow-1 dailyScenario 11 Parlour water (-10min) High volume hose used for 30 min daily (15 min milking-1)Scenario 12 Parlour water (-20min) High volume hose used for 20 min daily (10 min milking-1)

Thus, it can be seen in Table 6. that, a simple reduction in the volume of wash water use in the parlour by using a low pressure hose supply (scenario 9, reducing water flow by c. 50%) would reduce overall wash water use by >30%. A similar reduction could be achieved by reducing the time of high pressure hose use to only 10 minutes (from 20 minutes) after each milking (scenario 12). The financial savings due to reduced costs of mains water supply would be augmented by reduced slurry application costs as a result of the reduction in slurry volume, these latter savings were estimated at between £1.50 - £4.70 cow-1 yr-1 [235]. Such reductions in the volume of wash water are more easily achieved when used in conjunction with hand scraping of the parlour and collecting yard prior to washing.

In some of the farms in the study, simple low-cost strategies to improve water management, including restricting water use in the milking parlour and preventing clean water ingress into the slurry store, appeared likely to allow a significant increase the slurry storage capacity on the farm. This option can be particularly effective in cases where farms may be marginally below what may be considered adequate capacity (currently 4 months). Otherwise the need for additional construction is likely to incur very substantial extra costs.

Table 6. Changes to the amounts of slurry produced and sufficiency in storage capacity after adopting each alternative management strategy

Scenario Change to CS management

Total slurry volume (m3)

Reduction slurry volume (% CS)

Estimated water use in parlour – L cow-1 day-1

Potential wash water costa

£ yr-1

CS 4849 - 33.8 1277

Scenario 9Parlour water (low pressure) 4561 6 23.0 870

Scenario 10 Parlour water (buckets) 4406 9 17.2 649Scenario 11 Parlour water (-10min) 4705 3 28.4 1073Scenario 12 Parlour water (-20min) 4561 6 23.0 870Note: a assuming purchase costs of mains water @ £0.7 m-3 [239].

8.2. Water requirements of SheepLike cattle, the drinking water requirements for sheep vary enormously according to diet, body weight and the number of lambs reared. On very wet diets like stubble turnips, water intake will be low but on straw-based diets indoors, intakes will be high. Variation in water demands

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for ewes at different stages of pregnancy and for lambs was discussed in the baseline review [9]. Opportunities for savings would appear to be few and confined largely to regular inspection of the water supply system, especially remote troughs. Although nose pumps have not been developed for sheep, the option of a crate mounted pump diaphragm, operated by the weight of the animal was described earlier.

As with adult and young cattle, there is no requirement for washing operations during or following the housing period, which is usually of short duration only. Dipping and foot bathing, however, make a significant demand for water. Foot baths are of various sizes; walk-through ones may hold 100 L but stand-in ones may hold 300 L. Foot bathing is done very regularly on some farms; weekly through the housing period if foot rot is a problem, otherwise perhaps 4 times a year in many flocks. For dipping, baths hold say 500 L, or more, and sheep are dipped once or twice a year, although the number of flocks dipping has fallen dramatically due to concerns over pollution. It was estimated that water requirements for dipping were within a range from 1 L head-1 up to approximately 4 L head-1, depending on the type of bath [239]. The same author makes a general estimate of 2.25 L head -1. With water for dipping representing such a small proportion of total requirement (Table 4.), any reduction in the use of dips through the use of alternative systemic treatments will hardly contribute to water efficiency.

8.3. Water requirements of Pigs

8.3.1. Drinking water requirementAs for ruminant animals, the water requirements of pigs were included within a wide ranging and robust review of nutrient requirements [137]. Many of the same factors impacting on the daily drinking water requirements of cattle also apply. Moreover, because of the number of variables involved, drinking water requirements for pigs cannot be stated with any precision. In the review it was acknowledged that with free access to water there are wide variations in individual consumption. Excluding suckling sows and their offspring, the evidence suggests that the water requirement of pigs is about 2 parts of water for each 1 part of feed (by weight), the ratio perhaps a little wider for recently weaned pigs and narrower for older animals. These relationships are reflected in the research estimates of water requirement in Table 7.

Table 7. Estimates of drinking water requirements for pigs (L pig-1 day-1)

Category Consultancy estimates [240]

Research estimates1

Dry sows & gilts 6.0 10.0Farrowing sows 30.0 21.0Weaners 2.0 1.6Growers 4.0 3.4Finishers 5.5 5.71 Derived from relationships between meal and water intake and slurry output [242]

8.3.2. Drinking water supplyAs in the case of cattle, it is generally clear that access to water should be unrestricted such that pigs are able to drink as and when they need to. However, the logistics of water supply need to be examined and opportunities to prevent water loss or water wastage explored.

Studies on opportunities for minimisation of waste on commercial farms [243] highlighted water use on one of two pig farms included in the study. The enterprise comprised 580 breeding sows, 300 replacement gilts and 26 boars, with weaners reared to 30 kg live weight. Drinking water supply on the farm was via monoflow nipple drinkers (see Figure 11). Large spillages and water loss as a result of recreational play with the drinkers was seen to be a significant problem that led to the wasting of water and an increase in slurry volume. Through the installation of bite type drinkers, these losses were reduced, saving 10% on drinking water usage and reducing slurry spreading costs.

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Figure 11. Typical “flat deck” weaner accommodation with nipple drinkers

The experience on the commercial pig unit replicates consultancy experience, where these drinkers are commonly known to be associated with significant leakage, to the extent that estimations of slurry production in the past have usually included a 10% increase in volume to take account of this additional source.

Alternatives to nipple drinkers include troughs (preferred for sows), shallow bowls with lever-activated valves, as well as the bite type drinkers. Where nipple or bite drinkers are mounted on pen walls, the tendency for pigs to approach the drinker from the side, or at an angle often results in water flowing out from the side of the mouth and this, too can result in significant waste. This latter problem has been addressed by erecting a side bar/rail on either side of the drinker which requires the pig to access the drinker from the front and makes it more likely that the nozzle is fully inside the mouth as the pig drinks.

As discussed with cattle, water metering is a good way of avoiding excessive water demand, either as a result of poor drinker performance or leaking pipes [231].

8.3.3. Wash waterWashing of pens between batches of growing/finishing pigs is an important and substantial requirement, particularly in the case of sows and litters and weaners where wash water represents up to 13-16% of total demand as a result of the more demanding cleaning requirements (Table 4.).

Estimates for wash water use, based on typical production systems and observations of cleaning and washing practices on commercial units [240] were described in detail in the baseline review. The few data available from commercial units of potential value for validation purposes were again outlined in the baseline report and these data have compared well with the proposed wash water volumes (Table 4.). These wash water volumes are therefore recommended as useful guidelines, in the absence of adequate information either in current advisory literature or the Water Code.

8.3.4. Water management on pig unitsWhilst information about farm practices (“farm activity data”), including livestock housing and manure management has improved significantly in recent years, there is little if any information about water use and water management in the pig industry. Information from limited case studies and much anecdotal information suggest that significant savings in water use could be achieved on pig farms in England and Wales. However, no reliable data exist to allow a comparison of industry practice with the guidelines on either drinking water or wash water requirements.

In this context it is of interest to consider the typical analysis of pig slurry found on commercial units in England and Wales, where slurry is commonly found to be of low dry matter content. In the manure analysis database [242] the mean figure for pig slurry DM content is 3.7% and median 2.2% (n = 75) and this replicates common consultancy experience. In fact the high proportion of highly dilute pig slurries is reflected by the still extensive use of irrigation systems, either “rain-guns” or slurry booms, for the application of pig slurry estimated at >20% [244].

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Calculation of the likely slurry and dirty water outputs on a notional pig unit, such as that outlined [9] (400 sow unit with progeny to bacon weight), allows us to estimate the relative volumes of slurry and dirty water from this unit. In this case the dirty water volume added an estimated 22% to the slurry output from the pigs. Adding a further 10% for drinker leakage (as outlined above) would generate a slurry with DM content of c. 8%DM, assuming raw undiluted slurry starts at 10-12%DM. Roof water and surface water draining from precipitation falling on dirty concrete yards and accessing the slurry store will add very significant additional dilution water to the slurry. However, this would not be expected to explain more than an additional 50-80% increase in slurry volume, resulting in a net 1:1 dilution of slurry by water, unless what might be considered very poor management had occurred. Dilution to this extent (1:1) would generate slurry of c. 5-6% DM content, but the typical 2-3% DM slurry suggests a much greater dilution, of perhaps 3:1 or even 4:1, on many pig units. It does seem likely that extra water may gain access to the slurry system, on some units, by ingress of ground water (during the winter months) through imperfectly sealed below ground slurry channels which are a common feature of pig units in England and Wales. However, it does also seem possible (if not probable?) that very substantial volumes of wash water may be commonly used on some pig units and that this may be part of the explanation for the very dilute slurries. By contrast, the DM content of dairy slurry in the MANDE database is reported as 7.8% (mean) and 8.2% (median) (n = 109) [242] where surface water drainage is known often to represent a significant contribution to total slurry production.

Improved understanding of water budgets on typical pig farms is, thus, a serious concern that would indicate the need for further research. This would either confirm what may be considerable potential for reducing water wastage on pig farms or, if the additional water is from surface runoff or ground water sources, to reduce the consequential risk of diffuse pollution as a result of the excessive slurry volumes being generated on these farms.

8.4. Water requirements of poultry

8.4.1. Drinking water requirementAs with other species, the drinking water requirements of poultry are much greater than for washing water. Data on typical drinking water consumption summarised in the baseline review were based on information collected from a number of commercial producers [245]. Nipple and cup drinkers for laying hens and broilers are recognised to be preferable to bell drinkers, in terms of reduced spillage or leakage of water. This is important, not only for cost savings, but also to avoid wet litter or manure, which is associated with much greater odour offensiveness and is known to give rise to increased ammonia (NH3) emissions. For poultry that are in direct contact with wet litter, there are also adverse implications for animal welfare.

Additional, but smaller improvements in water use efficiency may be made according to the particular design of nipple or cup drinker used. It should also be remembered that nipple and cup drinker systems are not suitable for all poultry. Larger species (such as turkeys) require the use of bell drinkers. For ducks, water is often provided to meet behavioural needs in addition to consumption requirements and for this reason, a bell or open trough system may be used. It is accepted that the latter in particular will increase the total use of water by the ducks.

It should be noted that water consumption by poultry will increase in response to increasing environmental temperature. Houses which are well insulated and which have effective environmental control systems are best equipped to minimise any increase in water consumption during hot weather conditions, providing that they are not over-stocked with birds.

Maintenance of the lines and drinkers is important. This should include regular cleaning of the water lines and drinkers with treated water (including acids and disinfectant chemicals) to remove solids, which may include lime deposits in hard water areas. Inspection of the manure collecting in the below-cage pits can quickly highlight the location of water leakages and facilitate remedial action.

8.4.2. Washing waterIn the baseline review washing water requirements were derived from some of the companies that supply the cleaning chemicals (disinfectants etc.) for poultry houses, since these companies produce recommendations for the quantities of water to use and dilution rates for

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their particular products. Some differences in water use between sites are likely to be attributable to the particular products used.

Whilst virtually all broiler, turkey, duck and pullet rearing sites will be wet cleaned at turnaround time, some egg laying houses may be dry-cleaned only. This may be due to the nature of the site (e.g. a multi-age site may have adjoining houses which are still stocked), its management policies (e.g. deep pit manure may be removed according to land spreading requirements, rather than when the house is empty) or because the position and complexity of equipment is such that wet cleaning may cause electrical and/or other damage. Where wet-cleaning of houses is practised, a number of factors will influence the quantity of water used. These include:-

The diligence of the producer or contract cleaner; The extent to which efforts are made to remove as much of the visual contamination as

possible by dry cleaning, so that less water is used in total; High versus low pressure washing systems; Water temperature - steam cleaning may be more effective than cold water cleaning and

also use less water; Building differences e.g. surface absorption, run-off etc. Equipment type – in some cases, equipment such as drinkers, slats and perching

systems can be dismantled and soaked in water to loosen contamination prior to washing. This is likely to reduce the overall use of water.

8.5. Conclusions – water saving in livestock farming

Drinking water requirements represent, by far, the greatest demand for water on livestock units. Hence, because of animal welfare concerns and possible implications for production, scope for reduction in water use is very limited; in the main, attention should be directed towards identifying unnecessary consumption, wastage in water use and leakage or inefficiency in water supply systems. The following requirements and opportunities should be considered:

monitoring of water supply systems – metering to allow rapid identification of inefficiencies in water use, breakages (troughs or burst pipes) and leaks;

consider alternative drinking water designs, including troughs; also management of drinkers, e.g. guard rails adjacent to drinkers in pig pens;

alternative water sources, e.g. collection and storage of roof water and use of livestock water pumps (cattle, sheep);

washing water management – consider low pressure delivery, reduced time (recreational hosing of yards) and hand cleaning options;

farm water inventories with separate budgets for individual enterprises – will allow comparison with guideline advice on water requirements, also changes over time;

industry studies on water management on farms – to address lack of reliable farm level information on water use; will help to identify where significant savings are possible. The need for this information thought to be particularly urgent in the pig sector.

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9. Existing water saving initiatives and case studies

9.1. Award schemesThe Environment Agency Water Efficiency Awards have been held in alternate years from 2001 to 2007 supported by a number of organizations, notably Defra and NFU, and include the NFU-sponsored Agriculture and Horticulture Category where case studies are assessed by experts and organizations given awards for saving water. Annex II provides a list of winners and runners-up. This scheme provides an excellent vehicle for knowledge transfer and for spreading of best practice by publicising successful examples of the economic and environmental benefits of water saving. Most of the awards are made for farm- or nursery-scale water saving measures such as recycling, rainwater harvesting, distribution systems, irrigation systems and introduction of scientific irrigation scheduling methods.

9.2. Farmer-organised abstraction groups (FOAGs)The threat to abstraction licenses has led to the formation of FOAGs, particularly in the most critical regions in the South and East of England, for example BAWAG in the Norfolk Broads, ESWAG in East Suffolk and the Lark Valley Abstractors in West Suffolk [247, 248]. FOAGs were formed to represent the interests of local irrigators where restrictions on abstraction during drought years were a major concern. ESWAG was recognized for their training activities in the 2005 EA Water Efficiency Awards.

An alliance between the NFU, the UK Irrigation Association (UKIA) and the Agricultural Development in the Eastern Region (ADER) has been promoting the formation of additional FOAGs, with the ultimate aim of having at least one FOAG in every CAMS in East Anglia [247]. The East of England Development Agency (EEDA) has more recently funded a project to develop a strategic water programme for the agri-food sector in Eastern England. In the first phase this project aims to assess key issues, and then to develop phase II and III proposals that target support for increasing the efficiency of water use in the region [249]. It is anticipated that this will promote the formation of more FOAGs, possibly in a regional federation; such a structure would be ideally placed for sharing and disseminating information, benchmarking good practice, and sharing of physical resources such as on-farm reservoirs.

9.3. Conclusions and opportunitiesThere is enormous potential for water savings simply by the greater uptake of best practices, even without further technical innovation; funding for knowledge transfer activities and training programs would facilitate this. Networks or federations of FOAGs, possibly organized to mirror the CAMS, would provide an ideal structure to disseminate information, identify and share best practice, and to allow strategic representation of growers within the Environment Agency abstraction licensing process. The work already underway in East Anglia to promote these networks could profitably be extended to other regions with appropriate regional support.

Organisations such as ADAS, the UK Irrigation Association, and a number of Research Institutes and Universities do currently engage with growers and/or FOAGs in knowledge transfer activities and training programmes; in recent years several events have been organized driven by the need for growers to demonstrate to the EA that they use water efficiently, a requirement for abstraction license renewal. If such work was encouraged and expanded, and best practice implemented by growers, significant water savings could be achieved.

10. Opportunities to reduce water wastage on farms through auditing and good practice

Before technical developments are resorted to, there are often a range of checks and maintenance measures that farmers can easily perform to avoid water wastage and thereby lower the overall water use by agriculture. Further savings could be made by specifically carrying out a “water audit“ on-farm and drawing up a “water savings plan” in response.

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ADAS has proposed such ideas in the past and some of the potential is explored below, having been prompted by internal reports on water saving on farm (Stansfield, pers comm.).

What follows is a draft plan of what could be termed a “Good Practice Guide” for water use on farms and is intended to help farmers:

A. To identify what they need to do to prevent unnecessary usage of waterB. To be more conscious of the cost of wasting waterC. To assist them to develop a Water Savings Plan for their premises

These aims are addressed in turn below:

A. To identify what they need to do to prevent unnecessary usage of waterTo be able to make improvements an understanding is necessary of how and when losses occur, and the chief causes are: excessive use, lack of recycling, unknown uses, leaving hose pipes running, and poorly designed systems or facilities.

Regular maintenance checking is vital, as wastage often occurs due to: overflowing tanks and troughs, incorrectly set ball valves, dripping taps and worn washers, leaks in pipelines and joints, and operating systems at too high a pressure.

B. To be more conscious of the cost of wasting waterTo put these issues into context; the quantity of water lost from one tap which is left trickling because of a worn washer will amount to 120 - 150 m3 year-1. A 25 mm hose pipe thrown on the ground and left running will discharge 30-60 L min-1. So in 16 minutes as much as 1 m³ of water could be lost. In addition to the water charges incurred there are also associated costs such as waste disposal. An example from a dairy farm could be: Water wasted will probably end up in the farm’s dirty water system, which increases the quantities of liquid that have to be both stored and spread to land, resulting in increased costs.

Systems fed from mains water supply usually operate at the “mains” pressure. This pressure can be much higher than is needed for day-to-day use, and even the topography of farms can influence operating pressure of the pipe system e.g. water pressure increases downslope of the point at which the mains supply enters the property.

If a leak develops, or a tap starts to drip, then the quantity of water lost is increased at higher pressures. Therefore the quantity of water lost through a leak, a dripping tap or a hose-pipe left running, can be limited by reducing the water pressure or restricting the water flow.

The flow rate can be reduced by restricting the water flow in the pipe by means of an isolation or ball valve set to an optimum flow rate. Fitting a pressure control device at strategic points of the distribution system will allow a steady flow to be delivered, but at reduced pressure. The fitting of such a device is useful on variable pressure supplies. In a field distribution network the reduced flow to a drinking trough can be off-set by increasing the trough capacity.

C. To assist them to develop a Water Savings Plan for their premises.To reduce water use and costs a plan of campaign will enable farmers to assess their own situation, compare it with other similar situations, and then work out an action plan of how to save water.

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Outline of a Water Savings Plan:Step 1. Assessment

SurveyLook at how water is used on premises and who is responsible for using it. Calculate the quantities that should be used based on standard figures. Compare these to the quantities actually used. If on a private water supply, fit a meter if not already fitted.

Step 2. Develop a Plan Draw up a plan which covers four areas:

i. Management - awarenessii. Maintenance programmeiii. Improvementsiv. Monitoring

i. Management- awareness

Encourage staff to be conscious of the need to save water. Is training necessary for staff so that they understand what is required? For example, to be alert about dripping taps and possible leaks, so that necessary repairs can be organised.

ii. Maintenance programme

Establish a routine programme of checking the piped system, repair troughs, replace worn valve seating and make adjustments promptly.

iii. Improvement Programme

Identify opportunities for recycling and storage of rain water and grey water. Can an alternative method be used which uses less water ?

iv. Monitoring Monitor water meter(s) reading on a weekly basis. There may be more than one meter on each premises. Keep a record of the readings, as a jump in consumption may signify that a leak has developed.

Below are the intrinsic steps required to develop an effective plan, but more detailed information and a template to follow to enable a farmer/grower audit their water use, is given in the EA booklet “Waterwise on the farm version 2” [250] . Much of the outline below is given in this booklet together with some worked examples.

Step 1 - Assessment Survey

Farmers and landowners should familiarise themselves with the water distribution system on their property, and make a plan of the location of pipelines, stop taps and meters. Ideally this should be part of the title deeds.

The next step is to calculate the quantity of water expected to be used based on standard figures, which should take into account all types of water, depending on the type of business. Examples would be that:

A livestock farmer would need to take into account all livestock as well as the number of people living/working on the farm

A horticultural business would need to calculate the quantities used by the type of irrigation system it operates

If there is a good understanding of what water consumption should be for the enterprise, then it will be easier to identify whether there is a problem or not.

Once the water usage sheet has been completed it can be used to compare actual consumption with standard figures. If it is found that actual consumption is greater, then there is a clear opportunity to save water. Even if the actual usage is less than the standard figures suggest it should be, there may still be potential to save water.

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Staff on the farm should also be made aware of the implications of wasting water. They should also appreciate the potential savings that could be made (for example, tanks should not be left overflowing during washing down of a milking parlour).

Step 2 - Develop a Plan

Developing a plan is a simple step in creating a policy statement for the farm business to demonstrate ways to save water and it should address the four areas mentioned in step 2 above:

i) Management - awarenessThe very first step is to familiarise all staff with the many ways that water can be saved by simple changes in how tasks are completed. For example:

When washing down walls, floors or yard areas use a brush, scraper and squeegee to remove solid waste before washing down with water

Using a combination of physical means and damping down to loosen the waste rather than relying on water alone to do the task saves water

Training sessions for staff should be considered, so they understand the need to make improvements, and where this can be done. The message can be more easily brought home by fitting a meter in, say, the dairy so that they can see for themselves how much water is being used.

ii) Maintenance programmeA schedule for regular and seasonal maintenance should be drawn up, such as:

Shut off supply lines when not in use Drain troughs to reduce damage by frost If you cannot shut off the supply line, the make sure the riser pipe to the trough is well

lagged When turning the water supply on check each trough and adjust the ball valve so the

water does not overflow

Depending on the type of business this could be daily or weekly, but the important point is that maintenance should be carried out on a regular basis. Further examples of on-going maintenance are:

Ensuring drinkers, troughs, taps and pipe-work are securely fastened to the building/wall or sited on firm foundations

Protecting exposed pipelines against damage from passing machinery Maintaining the ball valve in drinkers and troughs so they do not overflow Lowering the ball valve float so there is less risk of spillage Replacing worn plugs in basins/tanks used for washing down Replacing ball valve seating to ensure watertight closure If a trough has been dislodged then re-site it on a firm base, and fix it so that it cannot

move If troughs are mains fed then there must be a ‘Type A’ air-gap between the lowest

point of the top of the trough and the mains inlet to prevent water being siphoned back

Keep a stock of tap washers and ball valve seats so that repairs can be carried out straight away

iii) Improvement ProgrammeDuring the course of developing the Water Savings Plan possible opportunities to make improvements are likely to have been identified. Many improvements will involve expenditure, but also produce an immediate cost saving. However, other improvements will be more expensive and it will be necessary to calculate the pay back period to justify them. To be

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financially worthwhile, the pay back period needs to be as short as possible, ideally 2 to 3 years.

Examples of improvements may be:

To fit further stop taps to enable sections of the water supply system to be isolated. This is particularly important where parts of the system are isolated geographically, or are only used for short periods of time e.g. for summer grazing.

Where the design of the water drinking system is wrong. It is necessary to select and fit the correct type and size of trough for the purpose, rather than use a loose large old bath tub.

Changing to a dedicated stock drinking system for livestock. Nipple and cup drinkers for poultry rather than bowl type which tend to spill when used.

For hose pipes that are used for washing down, a hand held trigger operated nozzle as spray head to the hose pipe which automatically cuts the flow when left unattended.

If a ‘volume’ washer to clean yard areas etc. is used, then a change to a pressure washer, should be considered.

Fit self-closing taps on sinks and basins. Fit in line pressure reducing valves to avoid excessive pressures

When carrying out improvements, the British Standard Specification 6700:2006 – “Design, Installation, Testing and Maintenance of Services Supplying Water for Domestic Use within Buildings and their Curtilages”, should be borne in mind.

Water RecyclingThe potential for recycling of water for a secondary use such as for stock drinking or washing down should be considered.

Plate coolers are often found in dairy parlours to assist in reducing the temperature of milk before being stored in the bulk milk tank, and the water from this could be re-cycled to storage for stock drinking or washing down. To gain an idea of the quantities of water involved are:

Plate coolers use between 2-3 L water per L of milk cooled.

For a 150 cow herd yielding 30 L milk cow-1 day-1, a plate cooler will use between 9 m3 and 13.5 m3 water day-1. This compares with the drinking requirements of the same herd, which will drink 12 to 16 m3 water day-1, depending on the feeding programme.

iv. MonitoringA regular routine of reading the meter or meters once a week and keeping a record of consumption should be developed so that (at least) a simple graph can be kept and any sudden increase in consumption noticed readily.

If there are doubts about water consumption, then meters should be read last thing at night and first thing in the morning (depending on the type of business). Livestock will drink through the course of the night but comparing the quantity of water that the stock are expected to drink, against standard figures will help ascertain if there is a leak.

In the event of a leak:

Sections of the supply line should be shut off so that the approximate area of the leakage can be located.

A check meter may be necessary to achieve this for long pipe runs. Obvious signs of water such as unexplained wet spots in fields may help locate

problems.

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The use of a ‘listening bar’ on the pipeline at a convenient point, such as the stop tap, may help identify a problem (by hearing running water, the problem is located down line of that point.

If the leak cannot be found, then professional help should be sought.

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11. Summary and conclusions: opportunities for water saving in agriculture

11.1. Drivers for water savingThe aim of reducing water inputs in agriculture is two-fold: to protect water courses from ecological damage resulting from low water flows or levels, and also to sustain the rural economy. Agriculture has an absolute need to use water to produce crops and livestock, and if water supplies are limiting then greater efficiency in water use will be rewarded with improved productivity. In many horticultural crops, product quality and profitability are highly dependent on timing, uniformity and volume of water applied.

Water availability in England and Wales is declining, especially in the East and South East of England where rainfall is lowest, and population densest. The decline is a result of climate change, increased regulation of water abstraction to protect the environment, and increased competition from industrial and domestic users.

11.2. Water withdrawals, changes in land use and food securityDepending on the source of information used, direct withdrawals of water for agriculture are in the range between 300 to 500 Mm3 year-1. Field crops in the UK are either rain fed, or they are rain fed with supplementary irrigation between the typically sporadic episodes of summer precipitation. An alternative way of looking at water use is to consider total evapotranspiration from crops, estimated at 16,200 Mm3 year-1 in the UK. Changes in land use can profoundly affect evapotranspiration and the hydrologically effective rainfall (HER), i.e. the amount of rainfall that reaches ground and surface waters via run-off and percolation, and can potentially have a greater effect on ecology then direct water withdrawals. Despite this, regulatory powers are largely restricted to controlling water abstraction rather than land use. We are entering a phase where major land use changes are anticipated that could present a significant environmental threat to aquatic ecology. These include the introduction and expansion of biomass crops, and the reinstatement of set-aside land for biofuel production. Further research to model water use by energy crops and predict hydrological impact on specific catchments is needed both to provide realistic expectations of energy crop yield in a water limited environments, and to avoid serious environmental impacts. A general appreciation of catchment and sub-catchment hydrology is needed to establish at what level water savings on the farm or nursery will be translated into environmental benefits.

It is important to remember that where water is considered to be “available” on the grounds that its use does not damage the environment, then greater use of water in many cases will improve productivity and the success of agricultural enterprises. Water saving in catchments where water levels and fluxes in the water cycle are in excess of the needs of the environment and abstractors has no benefits. The land area crops receiving irrigation in England has an increasing trend and research and knowledge transfer activities in water use may reinforce this trend by demonstrating the benefits of irrigation to growers who have water available to them within the framework of the EA licenses and CAMS. Water saving measures need to be targeted to catchments where water availability is, or will become with climate change, in short supply.

The UK relies heavily on imports of agricultural products and so is a major net importer of virtual water. Many of these imports are produced with unsustainable water supplies and cannot be relied upon in the long-term, especially given global climate change, population growth and the competition between food and energy crops. For reasons of food security we should seek to:

maximise our own agriculture outputs using our available water resources make significant contributions to the global research effort to increase water use

efficiency in agriculture promote responsible and sustainable use of water in agriculture overseas

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11.3. Reducing water withdrawals in over-abstracted catchments in England and Wales

Table 8 gives water use and research priorities by sector. The key conclusions are summarised below.

LivestockWater withdrawals for use in livestock farming are large, but most of this water is used for drinking, particularly in dairy cows, with little scope for reduction. In addition, the dairy industry is more prominent in the West where rainfall is higher and pressure on water supplies is currently less than in the East. However, significant water savings can still be made in the use of water for washing as this makes up some 21% of water used for dairy cows, and wastage could be eliminated by research and survey activities that examine issues such as monitoring, auditing and optimising distribution systems and water pressures. Embedded water in the fodder eaten by livestock (i.e. the evapotranspiration or irrigation needed to grow the fodder crops, or grass) far exceeds the water needed for drinking and washing and consequently meat and diary products themselves have embedded water values substantially higher than food crops. This needs to be considered in a full life-cycle analysis of livestock water use.

Field cropsIn field crops, water use is dominated by potato and vegetables because irrigation is rewarded with significant yield and quality gains. In potato, about half the irrigation used is to control common scab, and the other half for increasing yield. Breeding research can be justified in potato because it consumes a large amount of water, it is a single species sector, and it is now underpinned by genome sequencing projects in both potato and tomato. Key breeding targets are resistance to common scab, and a root system able to access soil water at a greater depth. Further research, including modelling approaches, is needed to fully understand what other factors limit productivity under water-limited conditions; this would allow trait assays related to drought resistance and water use efficiency to be included in conventional breeding programs and for molecular marker to be developed for use in marker assisted selection. If all new potato cultivars were more fully and systematically characterised in terms of their drought resistance across many environments and seasons, e.g. as part of national trials listing, it would allow more informed cultivar choices by growers, and would facilitate the building up, in the long-term, of a database of more reliable cultivar drought resistance data that could be used to identify genes by association mapping.

Cultural practices for potato need to be re-evaluated in the face of changing rainfall patterns. Soil management will be important because more intensive spells of rain and opportunities for earlier planting times will exacerbate soil compaction, a major factor in the volume of irrigation needed by the crop. Continuing research into soil conditions and microbial populations could establish alternatives to irrigation for the control of common scab.

In field vegetables, the diversity of crop types reduces the impact of breeding efforts, although progress has been made in describing the genetics of water use efficiency in Brassicas and the related Arabidopsis. Many vegetable crops may be excessively irrigated because of fears of loss of quality, and further research if required to establish the levels of water deficit that are acceptable to maintain quality and yield for each combination of crop and soil type. Improved control and scheduling or irrigation is the main route to reducing water inputs in vegetable production. Research into mulching systems could have a role in some circumstances. New approaches to irrigation scheduling are summarised below.

The large acreage crops comprising cereals, oilseed rape, sugar beet and biomass crops are likely to always be nearly exclusively rain-fed rather than irrigated crops in England and Wales. Climate change may reduce yields of our elite cultivars in increasingly frequent dry summers. Breeding efforts are needed in all these crops to maximise yield stability in increasingly water-limited environments, and to improve water use efficiency at catchment scale - this is especially important now that all these crops can contribute to replacing fossil fuels for energy production. As already mentioned, understanding implications for HER is important in large acreage crops, especially long season biomass crops.

If climate change predictions are correct there will be opportunities to expand the introduction of traditionally Mediterranean crops such as olives and apricots to the UK. This could include energy crops such as cardoon.

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Nurseries, protected crops and polytunnelsHardy nursery stock (HNS) is a major user of water, and it has been estimated that 75% of the water used can be saved. The cost of water is currently not significant for HNS but the industry will be receptive to water use research, especially irrigation scheduling and application methods that reduce labour costs, increase product uniformity and quality, and allow industry expansion on current licenses; the by-product of this will be water saving. Investment in sub-irrigation systems, rain water harvesting and recycling/storage/disinfection systems could lead to substantial savings, and this will require continuing support for knowledge transfer and demonstration projects to engage the industry with the issues.

Intensive soft-fruit production under polythene is an expanding industry that uses significant amounts of irrigation water. Quality as influenced by irrigation practices, and water use efficiency are important issues. Advances in genomics and active breeding efforts in the UK for strawberry have opened opportunities for breeding for water use efficiency and drought resistance. Research to apply regulated deficit irrigation methods in soft-fruit production is advanced and well placed to deliver water savings to the industry and has arisen from unpinning basic research on root-to-shoot signalling by whole plant physiologists. In general, although crop production in polytunnels is intensive and can create local problems due to heavy abstraction and nutrient leaching, as has been seen in Spain, it does use water more efficiently (greater economic and yield returns per unit of water) than open field crops, and as water availability declines to the point where it limits production, more growers may move to polytunnels or protected cropping (see below) to maximise returns from their water.

Protected crops provide the highest return for each unit of water used because the tightly controlled growing conditions give high seasonal yields and the high humidity under glass limits transpiration. Further, such crops can potentially receive the majority of their water needs from rain water harvesting. Water costs are currently a minor component of protected crop production. Research or knowledge transfer projects are needed to encourage the industry to move towards closed hydroponic systems rather than open run-to-waste systems. Research to save energy for heating glasshouses by reducing venting has positive implications for water use because of increased humidity; water and energy use could be considered together in such modelling studies. The largest protected crop, tomato, is amenable to breeding efforts to control water use, possibly delivered in the form of root stocks that restrict transpiration and excessive vegetative growth.

11.4. Generic research issuesBreeding The key to successful breeding programs is the understanding and modelling of the physiological traits that limit productivity in each crop and in each environment where it is grown. This will allow trait selection assays to be developed that are useful to breeders but it will require commercial breeders and scientists to work closely together, supported by government funding. Commercial breeders targeting UK markets have shown little interest in breeding for traits related to resource use, partly because other traits are more tractable (e.g. quality and disease resistance), and partly because strong commercial pressures in water and nutrient use are only just beginning to emerge. Public funding is therefore needed to provide the underpinning knowledge for breeding programs that will deliver before the full impacts of climate change become reality.

Transgenic approaches using candidate genes should focus on moving work from model species to crop species and on the evaluation of field performance at an earlier stage than has previously been typical. This could be achieved by closer collaboration between molecular biologists, crop physiologist and agronomists.

Irrigation technology and schedulingIrrigation research is key in the areas of potato, field vegetables, hardy nursery stock and fruit. Scheduling in potato is already good at matching supply with demand for water by the crop, but improvements in irrigation efficiency and uniformity (e.g. by optimising rain gun use or moving to drip or solid set sprinklers) need to be investigated and delivered to the industry through knowledge transfer activities.

In the higher value crops such as salads, fruit and HNS, more sophisticated irrigation control systems can be imagined that make use of crop imaging, and, as sensor technology advances and costs decline, perhaps networks of soil water sensors could be developed. Effective scheduling requires a good understanding of the movement of water in the soil

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profile and root zone; modelling research for water movement in different soil and crop combinations could inform on irrigation methods and rates and frequency of delivery. Automated “closed-loop” control systems are under investigation in HNS, fruit and salads, and could be developed further, but emphasis needs to be placed on making the technology accessible and easy for growers to install and use. The evaposensor/evapometer is an example of a low-cost and simple but effective device that could be integrated into automated control systems.

Improved access to high resolution meteorological data and weather forecasting at low cost, linked to scheduling software, would be a valuable resource to growers.

Knowledge TransferCurrently a significant proportion of irrigators do not use scientific methods for irrigation scheduling but rely on personal experience and judgment; significant water savings or improvements to quality and productivity could be made by improving the uptake of existing scheduling approaches. This will be addressed in a forthcoming Defra/ADAS booklet on the topic of a “water audit toolkit for irrigators”. Investment in the building of on-farm reservoirs, installation of re-cycling and disinfection systems, and rain water harvesting could make a big impact across many sectors.

A network of Farmer-Organised Abstractor Groups, based on the CAMS structure would be an ideal forum for knowledge transfer for irrigation methods, and steps in this direction should continue to be promoted. Water saving award schemes have proven effective at highlighting good practices at the farm scale.

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Table 8: Research priorities

SectorTotal water withdrawals (Mm3 year-1)

Potential savings in water withdrawals(Mm3 year-1)

Potential impact of water use research in environmental protection

Potential impact of water use research towards sustaining rural economy

Research priority Priority Research areas

Crop spraying 0.2 NIL Very low Very low Low None

Field crops: potato 75, increasing 30 (40%) High High High

Breeding for drought resistance and WUE, particularly root traits; breeding for common scab resistance; alternatives to irrigation to control common scab; avoiding compaction and good soil management.

Field crops: vegetables 34, increasing 13 (40%) Medium/High Medium/High High

Irrigation scheduling including knowledge transfer; understanding crop water needs related to quality; mulching; identifying genes for drought resistance or WUE applicable across many species

Field crops:fruit 6-10, increasing 2-4 (40%) Medium/Low Medium Medium Irrigation scheduling including RDI; breeding for drought resistance

and WUEField crops: cereals 1.5 Low Low High Medium Breeding for drought resistance and WUE; understanding effects of

changing land use on HERField crops: sugar beet 4.6, declining Low Low Medium Medium Breeding for drought resistance and WUE

Field crops: energy crops

0, but potentially large effect on HER NIL Low, but could become

very significant High High Breeding for drought resistance and WUE; modelling of catchment hydrology and water-limited productivity

Protected crops 13 5 (40%) Low Low Low Closed hydroponic systems, rain water harvesting, venting control,

breeding of root stocks.

Hardy nursery stock 50 38 (75%) Medium High High

Knowledge transfer for storage/recycling/disinfection systems, rain water harvesting, and sub-irrigation; irrigation uniformity and scheduling including automation

Washing of produce 3.1 < 1 Low Low Low Benchmarking, microbiological and pesticide residue monitoring and

disinfection, rainwater harvestingLivestock:Cattle 82 9 (50% of wash

water) Medium Medium Medium Washing water management for dairy cows; drinker design; leak detection; rainwater harvesting; farm-level water management.

Livestock:Sheep 17 < 1 Low Low Low Little scope for saving as 99% of water is used for drinking

Livestock:Poultry 12 < 1 Low Low Low Little scope for saving at >96% of water is used for drinking

Livestock:Pigs 8 < 1 Low Low Low Wash water management; drinker design; improved understanding of

farm water management practices; rain water harvesting

Estimates of total water use are taken from the body of the report. Potential water savings from research are a rough best-guess of the author based on information presented in the report. HER, hydrologically effective rainfall; RDI, regulated deficit irrigation; WUE, water use efficiency.

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13. Acknowledgements

This report was funded by Defra, project code WU0101. The following are thanked for useful discussions and comments:

Dr Steve Adams (Warwick HRI)Dr Chris Atkinson (East Malling Research)Chris Burgess (Independent Consultant)Dr Mark Else (East Malling Research)Dr Duncan Greenwood (Warwick HRI)Gerry Hayman (Independent Consultant)Dr Jerry Knox (Cranfield University)Dr Orla Grant (East Malling Research)Dr Ralph Noble (Warwick HRI)Matt Smallwood (Harleys Seeds)Anthony Snell (NFU)Graham Moore (Haygrove Tunnels)Dr Mark Stalham (Cambridge University Farm)Chris Stansfield (ex ADAS)Dr Keith Weatherhead (Cranfield University)

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Annex I. Summary of recent research projects related to water use funded by the UK government or Levy Boards.

Project Code Project Title Start year End year

Total Cost (£) Sponsor Contractor

HH3608TXIdentification of genetic markers for water use efficiency in horticultural crops

2004 2008 993771 Defra Warwick - HRI

HH3615SPCGenetic analysis of root traits relevant to water use in horticultural crops


HL0132LHN (HNS97)

Improving the control and efficiency of water use in container-grown hardy ornamental nursery stock (WaterLINK I).

1999 2003 330627 HortLINK(HDC) HRI

HP0218 Dormancy and water use efficiency in potato tubers 2002 2007 926064 Defra University - Nottingham

WU0101 Opportunities for reducing water use in agriculture 2006 2006 69442 Defra Warwick - HRI

WU0102 A study to identify baseline data on water use in agriculture 2006 2006 29741 Defra ADAS UK Ltd.

CC0338 Irrigation monitoring with synthetic aperture radar 1998 2000 4500 Defra University - London,

University College

LK0955

Development of drip irrigation technology as a delivery system for the improved targeting and control of nematode pests in a range of root crops

2004 2007 211764 Defra

British Potato Council, CypherCo Ltd, Du Pont (UK) Ltd, Field (GB) Ltd, Frontier Agriculture Ltd, Q V Foods, Rothamsted Research (BBSRC)

HH3609TXPartial root drying: delivering water saving and sustainable high quality yield into horticulture

2004 2009 1117553 Defra EMR, HRI, U. Dundee, U. Lancaster

HH3607SX

Desk Study: Recent developments in understanding molecular responses of plants to water stress

2003 2004 48386 Defra U. West of England

HL0168LHN (HNS97b)

Enhancing the quality of hardy nursery stock and sustainability of the industry through novel water-saving techniques (WaterLINK II)

2005 2009 744762 HortLINK(HDC)U. Dundee, U. Lancaster, EMR, plus HortLINK consortium

HL0165 Precision Irrigation and Nutrient uptake (PINT) 2003 2007 nd HortLINK Warwick – HRI plus

HortLINK consortium

HH3611SPCEnergy saving through an improved understanding and control of humidity (WG)


HH3606 Sustainability of UK strawberry crop 2003 2005 nd Defra U. Hertfordshire

CC0336 Assessing drought risks for UK crops under climate change 1998 2002 286763 Defra Rothamsted Research

(BBSRC)

CC0368Re-assessing drought risks for UK crops using UKCIP02 climate change scenarios

2003 2004 90649 Defra Rothamsted Research (BBSRC)

CC0370

Maintaining UK wheat performance through improved exploitation of drought-resistance traits

2000 2002 41094 Defra ADAS UK Ltd., John Innes Centre, U. Nottingham

OC9602Maintaining wheat performance through improved resistance to drought

1997 2000 293928 Defra U. Nottingham

WT01011Drought and demand in 2006: consumers, water companies and regulators

2006 2007 4000 Defra U. Lancaster

ES0110 Lowland Catchment Research (LOCAR) 2003 2004 100000 Defra Natural Environment

Research Council

LS3609New developments in near infrared reflectance spectroscopy: a fact finding mission

2000 2001 20037 Defra ADAS UK Ltd.

AC0301 Vulnerability of UK agriculture to extreme events 2006 2007 109104 Defra Rothamsted Research

(BBSRC), Warwick - HRIBD2302 Research into the current and 2006 2007 54138 Defra University - Hertfordshire

87


potential climate change mitigation effects of Environmental Stewardship

HH1945 Environmental auditing for the Hardy Nursery Stock industry 2001 2002 9969 Defra nd

BD2302

Research into the current and potential climate change mitigation effects of Environmental Stewardship

2006 2007 54138 Defra nd

WQ0101

Environmental Footprint and Sustainability of Horticulture (including potatoes) - a comparison with other agricultural sectors


NT2517Scientific and technical revision of IRRIGUIDE water balance model 2005 2005 25981 Defra ADAS UK

LK0989

Integration of precision irrigation and non-water based measures to suppress common scab of potato

2006 2009 134000 Defra/AS-LINKCentral Science Laboratory/Cambridge University Farm

BBD52316X1 Role of the vacuolar SV/TPC1 channel in plant Ca signalling 2005 2008 280038 BBSRC U. York, U. Bristol

C10234 Analysis of voltage-evoked ionic signals in stomata 1999 2004 68280 BBSRC U. Glasgow

G15188Cell cycle dynamics and the specification of cell fate during stomatal patterning in Arabidopsis

2001 2006 237216 BBSRC U. York

GER00618 Genetic control of stomatal distribution in Arabidopsis 1995 1998 149043 BBSRC U. Cambridge, U.

Sheffield

P03912

Can root signals link the effects of soil drying and climatic variation in the control of gas exchange and growth of plants in the field?

1995 1998 127641 BBSRC U. Lancaster

P13274

Positioning oscillations of cytosolic free calcium in the circadian intracellular signalling pathway

2000 2003 218268 BBSRC U. Cambridge

P14501/P14506

A signalling pathway linking CO2 perception with stomatal development


BBC5078371/BBC5099311

What makes rice roots able to penetrate hard layers? An integrated biophysical, modelling, genetic and molecular approach

2005 2007 154585 BBSRC Rothamsted Research (RR), U. Aberdeen

BBD0128211Soil:plant signalling networks: manipulations to sustain plant productivity during drought


D11972

The sfr6 mutation as a tool for investigating cold and drought- stress-induced gene expression in Arabidopsis

2001 2003 234684 BBSRC Royal Holloway

P06568 Regulation of ion channels in maize roots during water stress 1997 2000 138204 BBSRC U. Cambridge

P11790

The development of Near Isogenic Lines at root growth and drought resistance Quantitative Trait Loci in upland rice

1999 2001 28700 BBSRC U. Aberdeen

P08406 Cloning and functional analysis of a putative abscisic acid receptor 1997 2000 177917 BBSRC Imperial College London

P14424Molecular basis for discrimination between drought and cold in Arabidopsis

2001 2004 201800 BBSRC U. Durham, U. Oxford

P15146 The role of specific CDPK isoforms in signal transduction of Arabidopsis thaliana

2001 2004 225792 BBSRC U. Oxford

P15279 Sphingosine-1-phosphate: a new signalling molecule in plants 2001 2006 245360 BBSRC U. Bristol,

U. Lancaster

P16766 Molecular dissection of the jasmonate signal pathway in Arabidopsis

2002 2005 219992 BBSRC U. East Anglia

P18613 The mechanism of action of SFR6, a key regulator of gene 2003 2006 195920 BBSRC U. Oxford,

U. Durham

88


expression and cold acclimation

BBSEC4301Transposon tagging of wheat to isolate new promoters and genes involved in stress tolerance

2003 2005 CSG BBSRC Rothamsted Research (RR)

BBSEC11485

Photosynthetic rate and metabolic regulation of sunflower, wheat and transgenic tobacco leaves in response to water stress

1993 1999 CSG BBSRC Rothamsted Research (RR)

C17932

Abscisic acid and nitric oxide signalling in Arabidopsis thaliana guard cells: cyclic cGMP synthesis and protein kinases activation

2003 2006 219284 BBSRC U. West of England

P19758

Key roles of ABA and hydrogen peroxide in photo-oxidative stress-induced signalling for APX2 gene expression

2004 2007 263319 BBSRC U. Essex

P20194

Functional analysis of the glucosylation of auxin, abscisic acid and their metabolites in Arabidopsis thaliana

2004 2008 290689 BBSRC U. York

BBSEH-00AT0234

515: Regulation of abscisic acid biosynthesis 2005 2006 CSG BBSRC U. Warwick

96B1C02643 Photoaffinity labelling of abscisic acid receptors 1996 1999 Studentship BBSRC Rothamsted Research

(RR)

14902

New genetic tools and new technology to investigate the control of fruit and shoot growth under drought stress

2001 2003 69004 BBSRC Lancaster University

SC040008

Exploration of the Reasonable Needs for New Licenses Brought about by the Water Act 2003 (Trickle Irrigation)

2004 2006 EA Cranfield University

SC040097 The Sustainability of Water Efficiency Measures 2005 2006 EA

SC030022 Lowland Catchment Research (LOCAR) 2004 2006 EA NERC-Programme

Management Group

SC030301Climate Change and the Water Framework Directive Incorporating River Typologies

2004 2006 EA

SC050032The Effect of Social, Industrial and Agricultural Change on the Demand for Water

2005 2007 EA

SC030233Model for Investigating the Impacts of Groundwater Abstraction

2003 2007 EA BGS (Wallingford)

SC050047Water Resources Management in Co-operation with Agriculture (WAgriCo)

2005 2009 EA

Water4All 2 2006 2008 EA

PSR(06)01 Social Science of Encouraging Water Efficiency 2006 2009 EA

Making Information Available for Integrated Catchment Management

2006 2007 EA

Science Policy Interfacing in Support of the WFD 2006 2008 EA

PIC(06)06 Science Policy Interface 2006 2008 EATrickle Irrigation in England and Wales 2001 2003 EA Cranfield University,

Silsoe CollegeTrickle Irrigation Optimum Use Methodology 2004 2004 EA Silsoe Research Institute

Implementation of the EC Water Resources Framework Directive 1997 2002 EA WRc (Medmenham)

Agriculture and Industry Dependent on Direct Abstraction Phase 3

2000 2002 EA Steffan, Robertson & Kirsten (UK) Ltd

Development of a Decision Support Tool for Sustainable Use of Water Resources at the Catchment Scale

2002 2004 EA Silsoe Research Institute

Decision Making Framework for Water Resources Licensing Using 2001 2004 EA JBA

89


Uncertain DataClimate Change Scenarios for Water Resource Planning 2003 2005 EA

Application and Effectiveness of Water Efficiency Measures 2000 2005 EA Hartlepool Water plc

Developing a Catchment Management Template for the Protection of Water Resources: Exploiting Experience from the UK, Eastern USA and Nearby Europe

2007 nd RELU Imperial College London

RELU-Biomass: social, economic and environmental implications of increasing rural land use under energy crops

2006 2009 RELU Rothamsted Research et al

Understanding and Acting Within Loweswater: A Community Approach to Catchment Management

2007 RELU U. Lancaster

Modelling the Impacts of the Water Framework Directive ongoing RELU U. East Anglia

Coping with Uncertainty in River Basin Planning and Management completed RELU U. Lancaster

807/231 Independent Variety Trials and variety selection 2005 BPC NIAB

BPC Research Review - Soil compaction and potato crops 2005 BPC ADAS/TAG

An infra-red thermography (IRT) method for measuring plant water stress

2000 BPC ADAS

Manipulating potato tuber dry matter concentration through soil water status

1999 BPC Cambridge University Farm

Irrigation scheduling and efficient use of water in potato crops 1998 BPC Cambridge University

Farm

PC119

Glasshouse irrigation: a review of R+D and evaluation of current techniques for irrigating edible crops grown in hydroponic systems

1997 HDC

PC116The efficiency of water and fertilizer use in different protected ornamental production systems

2000 HDC

PC23a Tomato: irrigation and recirculation 1991 HDC

PC23b Irrigation requirements of the tomato crop 1992 HDC

PC23d Tomato: evaluation of recirculation systems 1991 HDC

PC56

Hortitrans: a programme for calculating humidity and transpiration in greenhouses and its effects on tomato crops

1991 HDC

PC82 Irrigation regimes for tomatoes grown on rockwool 1993 HDC

PC83 Tomatoes: Irrigation regimes for NFT 1995 HDC

PC142

Tomatoes: comparison of methods of determining irrigation frequency with measured crop use

1999 HDC

PC149

Cucumber and tomato: investigation of the cause, epidemiology and control of root proliferation (“root mat”)

2002 HDC

PC151 Tomatoes: water uptake by NFT and rockwool grown crops 1999 HDC

PC186

Tomato: an assessment of current problems and future risks of Verticillium wilt in hydroponic and soil-grown crops.

2002 HDC

PC186a Tomato: epidemiology and control of Verticillium wilt in hydroponic

2005 HDC

90


and soil-grown crops

PC241

Protected hydroponic tomato: investigating the potential for various novel non-chemical techniques for the suppression or control of root-mat disease

New project HDC

CP4

Disinfection in commercial horticulture: a review of chemical disinfectants, soil treatment with formalin and water treatments for controlling plant pathogens

1992 HDC

PC60

Protected crops: root diseases in recirculating hydroponic systems and the potential for control with disinfection

1993 HDC

PC60a

The development of a sustainable system for the prevention of root diseases in recirculating hydroponic crops

2000 HDC

PC67 Reed beds: treatment of hydroponic run-off 1994 HDC

FV187Evaluation of trickle irrigation on horticultural crops using celery as a model crop

1997 HDC

FV248

Salad crops: assuring the microbiological quality of water used for irrigation – an assessment of the options available

2004 HDC

CP13

Promoting the efficient use of water, and reducing the environmental impacts in horticulture field vegetable irrigation

2003 HDC

FV38a Review of crop covers and mulches for field vegetables 1990 HDC

FV39/a Timing of irrigation during vegetable crop establishment 1994 HDC

FV/SF138

A review of the current knowledge on the use of fertigation of vegetables and trickle irrigation and of its potential application

1994 HDC

FV140 Improving irrigation scheduling using infra-red thermography 1996 HDC

HNS138Manipulation of the root environment in hardy nursery stock production

current HDC

HNS38 Water use under different hardy nursery stock container systems 1995 HDC

HNS38a Estimating irrigation needs for HNS in containers 1994 HDC

HNS122

Container nursery stock irrigation: demonstration and promotion of the best practice and recent developments

2005 HDC

HNS88Monitoring the commercial development of slow sand filtration

1998 HDC

HNS88a

Development of a low cost pilot test procedure for the assessing the efficiency of slow sand filtration on individual nurseries

2000 HDC

HNS88b

Slow sand filtration in HNS production: assessment of pre-filtration treatments of water to reduce the frequency of tilter cleaning operations

2001 HDC

HNS107 Container HNS irrigation: use of capillary matting under protection 2003 HDC

HNS107aContainer HNS: improving water management within growing media

2004 HDC

TF10 Fertigation of orchard trees 1994 HDCTF77 Economic aspects of apple tree 1995 HDC

91


irrigation

Notes: Data collected by key word searches from the following sites and may not be fully comprehensive: BBSRC Oasis: http://oasis.bbsrc.ac.uk/search.html, Defra Science and Research projects: http://www2.defra.gov.uk/research/project_data/default.asp?SCOPE=0 Environment Agency Projects: http://www.environment-agency.gov.uk/science/922300/scienceprojects/?

version=1&lang=_e Rural Economy and Land Use Program (RELU) Research: http://www.relu.ac.uk/research/ British Potato Council Water Research:

http://www.potato.org.uk/department/research_and_development/projects/index.html?cid=Nw== Horticulture Development Council (HDC): http://www.hdc.org.uk/index.asp

92


Annex II. Environment Agency Water Efficiency Awards 2001-2007; NFU Agriculture & Horticulture Category

Farmer/Grower Activity Award Year SavingCA Strawson Farming Limited

Farm Water Management Winner 2001 20% (recycling of water for veg. washing, move from rain guns to booms for irrigation, improved scheduling)

JR & M Weekes & Sons

Dairy Farm Good Housekeeping

Commended 2001 Unknown (improvements to distribution pipework and recycling of cooling water from dairy)

Notcutts Nurseries Water Recycling and Reuse Commended 2001 20% saving in borehole abstraction (collection of run-off and recycling through sand filter, improved irrigation scheduling)

Osberton Grange Farms

Efficient Watering for Pot-grown Rhododendrons and Azaleas

Commended 2001 60% saving (use of pot in pot system to prevent root overheating, move from overhead to drip irrigation, improved scheduling)

Palmstead Nurseries

Recycling and Computer Controlled VPD Watering

Finalist 2001 84% reduction in mains water use (collection of root water, and recycling of run-off, installation of VPD-based irrigation scheduling system)

East Clyffe Farm Water Preservation on the Farm

Joint Winner 2003 > 10% (repair, rerouting of pipework, control of run off, return of water to chalk)

Osberton Grange Farms

Solid Set Sprinkler Irrigation Joint Winner 2003 20% (move from raingun to solid set sprinklers for irrigation of potatoes)

Place UK Recycling Water Commended 2003 38% (recycling system for bean sprout production)

Coolings Nurseries Ltd

Rainwater Capture & Long Term Storage

Finalist 2003 70% reduction in mains water use (rainwater harvesting and long term storage, use of drip irrigation)

Denys E Head Garden Style Pond Finalist 2003 6,700 m3 year-1 reduction in mains use (collection of run-off to pond and re-use)

Unigro Greengro Finalist 2003 50% saving compared to conventional methods by growing produce in tunnels with precise irrigation.

Sheepdrove Organic Farm

Sustainable WaterManagement Project

Winner 2005 10% reduction in abstraction (reed bed and return to aquifer)

Brackenburgh Home Farms

Dairy Modernisation Commended 2005 33% reduction in main water use (rainwater harvesting and recycling); 13% reduction in water used per cow

East SuffolkWater Abstraction Group

ESWAG Training Project Finalist 2005 Water efficiency and spray irrigation training

Farmcare Ltd Goole Potatoes, TrickleIrrigation on Maincrop Potatoes

Finalist 2005 24% reduction in water used for irrigating potatoes (move from rain-gun to trickle irrigation)

L F Papworth Ltd Improving on farm irrigation efficiency

Commended 2007 Company managed 4000 ha of farmland and saved 3355 m3 in 2006 through improved irrigation scheduling and staff training.

Natures Way Foods Ltd

Rain Cloud salad production and washing

Commended 2007 35% saving though improved efficiency of washing (300 m3 week-1) and reuse of wash water for irrigation

Place UK Soft fruit irrigation scheduling

Commended 2007 Installation of soil water monitoring equipment for irrigation scheduling, reduced abstraction by 6%, saving 6000 m3 in 2006. Fruit quality also improved.

Tamar Nurseries Ltd

Water recycling in hardy plant nursery

Commended 2007 Installation of drainage and collection system; 36% saving through recycling of about 700 m3 month-1

Data from EA Web site: http://www.environment-agency.gov.uk/subjects/waterres/

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