agriculture group symposium: agriculture with reduced inputs

J Sci Food Agric 1990,53, 111-121

Agriculture Group Symposium: Agriculture with Reduced Inputs

The following are summaries of papers presented at a meeting of the Agriculture Group of the Society of Chemical Industry held on 24 October 1989 at the Society of Chemical Industry, 14-15 Belgrave Square, London S W l X 8PS. The papers published here have not been refereed and do not necessarily reflect the views of the Editorial Board of the Journal of the Science of Food and Agriculture.

Plant Strategies for Maximising Nutrient Uptake: The Potential Role in Increasing Efficiency

John E Hooker, David Atkinson

School of Agriculture, University of Aberdeen, 581 King Street, Aberdeen AB9 IUD, UK

and

Elizabeth Lavender

Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2QJ, UK

Traditionally breeders have selected plants which produce maximum yields under economic management and fertiliser regimes. However, increased public and political awareness of the need to reduce fertiliser input and/or losses from agricultural systems makes it necessary to select plants that will permit a reduction in nutrient inputs. Strategies utilised by plants to occupy different habitats include variation in root structure and formation of symbiotic associations. There is only little information on potential variation in root structure within individual species and on the importance of specific root parameters in nutrient acquisition. Furthermore, although the value of symbiotic associations in natural systems is clearly established, their value in agricultural systems (except for Rhizobium) is less clear, although clearly this would be enhanced in reduced input agriculture.

Root systems of several barley cultivars were examined. Significant differences in

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J Sci Food Agric (53) (1990)-0 1990 SCI. Printed in Great Britain

112 Agriculture Group Symposium

root structure were observed and increases in root length were correlated with increased P uptake. In a further experiment micropropagation systems were used to generate plantlets of several Betula pendula genotypes and the root systems of the plantlets were compared. Preliminary results indicate wide variation between different genotypes in root structure. The precise effects of differences in structure on nutrient acquisition under different conditions of availability will be determined in future experiments. The potential for optimising the FrankialAlnus symbiosis was investigated. Strains of the nitrogen-fixing actinomycete Frankia were isolated from Alnus spp growing on a range of sites throughout Britain and characterised, both in uitro and in symbiosis with A rubra. Variability in morphology, C nutrition and ability to fix N, in symbiosis was observed. Tests in nursery experiments with a superior strain showed that yields could be obtained significantly above that using N fertiliser.

The results clearly indicate a potential for manipulating existing variation in plant root systems and associated symbiotic associations in order to maximise plant yields under lower input regimes.

Organic Production Systems: A Means of Reducing Chemical Inputs

James M Mackay

Crop Production Department, North of Scotland College of Agriculture, 581 King Street, Aberdeen AB9 IUD. UK

Insoluble sources of P205 and K,O and a limited and only partially effective range of pesticides are the only chemical inputs permitted in organic systems.

A rotational trial was set up near Aberdeen in 1986, one of its aims is to establish the yield loss associated with converting to organic production. The rotation chosen consists of three years of grass/clover, winter wheat, potatoes, spring oats, swedes and undersown spring barley. The soil is a freedraining sandy loam of the Countesswells Series.

The trial includes an organic system, in which the only manurial input in 1987 was 30 t ha-' farmyard manure applied to the potato and swede course. In 1988 and 1989 an additional top dressing of 6.25 t ha-' chicken manure supplying 32 kg ha- N was applied to the cereal courses. Ground mineral phosphate (GMP) is applied to each course each year at a rate supplying 50 kg ha-' P205. The trial also includes a conventional system in which fertiliser and pesticides are applied according to current Scottish Agricultural Colleges' recommendations.

All organic cereal yields were unacceptably low in 1987, being approximately half that of the conventional, and hence a spring top dressing of chicken manure was applied thereafter to organic cereals, thereby raising barley and oats yields to 15- 25 % below the conventional. Organic winter wheat yields were again halved in 1988, however, due to poor winter survival and lack of tillering, but were only reduced by 30% in 1989 following a mild winter. Organic swede and potato yields were reduced by 6 % and 24% respectively in 1987, but in 1988, following aphid

Agriculture with reduced inputs 113

damage on the swedes and late blight on the potatoes, were reduced by 31 % and

A rotational trial was set up adjacent to the site of the previously described trial in 1922, in order to examine the effects on yield of six fertiliser treatments, three of which are considered here: none (organic), complete NPK with phosphate as single superphosphate, and complete NPK with phosphate as GMP. The rotation consists of three years of grass/clover, spring oats, a mixed course of potatoes, swedes and turnips, and undersown spring barley.

To maintain continuity the plane of nutrition has been maintained at the original level, although in modern terms the level of 26.25 kg ha-' N (applied as sulphate of ammonia to the cereal, hay and root courses) is very low. The cereals and hay receive 47.5 kg ha-' P205 as superphosphate or 75 kg ha-' as GMP, while the roots receive 95 kg ha-' as superphosphate or 150 kg ha-' as GMP. The cereals and hay receive 39 kg ha-' and the roots 75 kg ha-' K 2 0 as muriate of potash. The root course of every treatment also receives 30 t ha-' field-stored farmyard manure. From standard figures, 30 t 12-month field-stored farmyard manure supplies 9-2490 kg ha-' N-P-K.

Results from this trial indicate that GMP, which is permitted as an organic input, has not been as effective as superphosphate on the cereal crops over the 67-year period. This is despite the fact that relatively more P205 as GMP is applied, and the fact that the trial site is maintained at an arable pH of 6.2. The nil chemical input treatment, which receives farmyard manure once in the 6-year rotation, suffered yield depressions of 21 % for barley, 29 % for hay, 27 % for oats, 22 % for potatoes, 14% for swedes and 10% for turnips compared with the complete NPK with superphosphate treatment. Given modern higher levels of nitrogen inputs, even greater yield depressions might be anticipated. Yields of cereals and potatoes have risen over the experimental period, even where there have been nil inputs of N, P and K. Yields of hay, swedes and turnips have, however, remained fairly constant, except for a slight decline in yield where there has been nil input of P.

From these two trials it is clear that yield reductions of at least lo%, and perhaps 50%, can be expected when converting to organic production, provided disproportionate amounts of manure are not applied. These lower yields should be sustainable, however, and reductions can be offset by reduced costs of chemical inputs and current premiums for organic produce.

35 %.

Tree Crop Production Systems: A Change in Land Use with the Potential to Reduce Inputs

D R Williamson and A J Moffat

Forestry Commission, 23 1 Corstorphine Road, Edinburgh EH12 7AT, UK.

Britain has a little over 2 million ha of productive woodland, but imports almost 90% of the timber and timber products it needs. Extension of forestry into land previously under agricultural use has the potential to produce inputs and reduce the


surpluses of some food commodities, and is supported by the Government under the Woodland Grant Scheme (1988) and the Farm Woodland Scheme (1988). Forestry may also serve to reduce the amount of fertilisers and pesticides applied to the soil at a time when their application is viewed with concern for the protection of soil and water quality.

At present, only 2.7 % of British productive woodland (56 000 ha) receives fertiliser each year, mainly as unground rock phosphate on upland sites. Potassium is only necessary on some peat soils and nitrogen on deep peats and heathland soils. It is unlikely that sites available for new woodland plantings will substantially increase the need for fertiliser: most lowland farm forestry will not receive it. Forestry is a small user of fertiliser for several reasons. Forests are very efficient in the use of nutrients compared with other land uses. They do this by nutrient recycling and are also effective in capturing atmospheric sources. Leaching losses are usually minor, though can increase during site preparation and at harvest. Denitrification and ammonia volatilisation occur to a much smaller degree than in agricultural systems.

Forestry also uses relatively small quantities of pesticides when compared with agriculture and particularly arable enterprises. A total of approximately 20 000 ha of forest land received herbicide in 1988/89 compared with 3-9 million ha of cereals in 1987/88. Of the 13 300 tonnes of herbicide active ingredient used in the UK in 1988, forestry was responsible for only 15 t.

Forestry Commission research experiments have shown that herbicides are the most cost-effective way of reducing weed competition on trees. This is particularly true when trees are planted into a grassdominated sward. Grass is a very vigorous competitor for nutrients and particularly water, the main limiting factor on most lowland sites.

It is likely that, when farmers decide to take land out of agricultural production, it will be their most difficult sites that will be made available for farm woodlands. Many of these soils will be surface water gleys, the predominant features of which are a fluctuating water table and drying and cracking in a dry summer. Foresters are going to have to develop establishment techniques for dealing with such sites. Most agricultural soils have been heavily limed in the past, and their pH is now above optimum for many tree species. Agricultural sites also have a higher level of fertility and a greater and more diverse weed seed population than traditional forest sites. These two factors are a recipe for disaster if proper management is lacking, and it must be accepted that bare land cannot be maintained within farm forestry plantings. The farmer must therefore set out with the knowledge that the ground flora will need managing and design a system to accommodate this.

When deciding to establish a farm woodland on agricultural land, a grass sward should be regarded as the simplest and preferred starting point. The technology already exists to control grass within tree plantings, and in many respects this situation is similar to many afforestation sites. Trees should be planted to allow tractor access. Inter-row strip or spot weeding should then take place to relieve the trees from the competitive effects of the grass, and the sward can be mown as necessary inter-row.

The problems of establishing trees are much greater when faced with bare ground


such as arable stubble or cultivated soil. The lack of ground cover means that arable weeds are free from competition and can germinate and grow very quickly. The fertility of these sites and the vigour of some arable weeds means that the planted trees can be seriously damaged if the ground flora is not managed. Trees must therefore be planted to allow tractor access inter-row. A cheap and simple management option is to establish a low-productivity grass cover crop prior to planting. This can be controlled with herbicides down the planted row by either strip or spot weeding and mown as necessary inter-row. An alternative course of action is to use residual herbicides down the planted tree row and to mow the weeds which develop inter-row as necessary.

The systems for establishing farm woodlands on ex-agricultural sites are still evolving. The Forestry Commission is heavily committed to carrying out research on this topic, and under a joint venture with MAFF has established farm woodland experiments on a number of ADAS experimental husbandry farms. In 1990 the Forestry Commission in co-operation with Tilhill Forestry and Willmots Crop Protection will set up a series of farm woodland demonstrations with the aim of showing various methods of managing the ground flora within tree planting schemes.

Opportunities for Reduced Pesticide Inputs (with Particular Emphasis on Reduced Herbicide Use)

S R Moss

Department of Agricultural Sciences, University of Bristol, AFRC Institute of Arable Crops Research, Long Ashton Research Station, Long Ashton, Bristol ES18 9AF, UK

Reducing the use of pesticides is a desirable objective for several reasons: limiting agricultural output, lowering production costs, reducing environmental contamination and effects on non-target organisms, minimising pesticide residues in food, delaying the development of resistant pest biotypes.

Worldwide, the proportional usage of agrochemicals by product type is : herbicides 44 %; insecticides, 31 %; fungicides 19 %; plant growth regulators and other products 6 %. The world market for agrochemicals was worth about $20 450 million in 1988. What is the scope for reducing this vast expenditure?

Reductions in the amount of pesticide applied could be achieved by:

(1) Better prediction of the efects of pests and weeds. Use of weed thresholds and methods for the early detection of pest and disease attack, coupled with a better understanding of pest epidemiology and the effects of pests and weeds on crops, should lead to more judicious pesticide use and reduce the need for ‘insurance’ applications.

(2) Use of herbicides with greater intrinsic activity. Many newer herbicides are effective at rates of grams, rather than kilograms per hectare.


( 3 ) Increasing herbicide activity. The use of synergists and other adjuvants (eg surfactants) may permit reductions in the amount of active ingredient used.

(4) More efJicient application methods. Usually only a small proportion (often under 10%) of the pesticide applied reaches its target. Thus the development of more efficient delivery systems has great potential.

( 5 ) Developing resistant crop varieties. This has obvious potential in reducing the need for fungicides, and to a lesser extent insecticides. The introduction of herbicide-resistant crop varieties may permit the use of non-selective herbicides such as glyphosate, which could reduce the total amount of herbicide applied.

Alternatives to herbicides comprise:

(1) No control. Avoid treatments applied for ‘cosmetic’ reasons. In most other cases, of course, simply doing nothing is not a realistic strategy.

(2) Fallowing. A traditional method of weed control, although land is taken out of production. The similar policy of ‘set-aside’ makes this concept a realistic alternative again. However, failure to keep weeds under control in set-aside land may lead to an increased weed problem in subsequent crops.

(3) Crop rotations. Many weeds are favoured by restricted cropping systems, eg black-grass in intensive winter cereals. Rotation of different crops can prevent many weeds building up to unacceptable levels.

(4) Mulches. Natural (eg straw, wood chippings) or artificial barriers such as polythene can be used to prevent weed germination.

(5) Cultivations and mechanical control methods. Pre-sowing cultivations can influence subsequent pest and weed problems, eg mouldboard ploughing reduces the severity of annual grass weed infestations. Hoeing and harrowing are other traditional weed control techniques. There is scope for further development using modern machinery.

(6) Crop competition. Use of higher than normal seed rates, more competitive varieties, narrow row spacings and manipulation of sowing dates can increase the competitive ability of a crop to the detriment of weeds.

(7) Physical energy. Flame and high voltage electrical weeders have been used for non-selective weed control. Straw burning is an effective method of destroying weed seeds on the soil surface. Soil solarisation, in which plastic sheeting is used to increase the surface soil temperature, is another method of destroying soil pathogens and weed seeds.

(8) Seed dormancy breaking chemicals. Stimulating weed seeds to germinate in one flush and destroying the emerging plants prior to plantingcrops is an attractive concept. In practice it is difficult to achieve high germination rates.

(a) Classical biological control (eg control of prickly pear by the larvae of the moth Cactoblastis cactorum), in which an exotic host-specific organism is introduced, has limitations in arable cropping systems. The full potential of such biological control agents requires a relatively undisturbed habitat to allow the build-up of the control agent population to effective levels.

(b) Mycoherbicides are natural fungal pathogens which are applied in large

(9) Biological control


(inundative) amounts to a weed-infected crop in the same manner as herbicides. Their use is more specific and controlled than the classical approach as they do not require time for build-up or spread.

(10) Natural chemicals (a) Allelopathy refers to the effects of one plant on another through the

production of chemicals which escape into the environment. There may be potential for exploitation of this phenomenon but practical implementation is limited by lack of selectivity.

(b) Other plant chemicals. A recent review by Grainge and Ahmed (Handbook of Plants with Pest Control Properties) listed 2400 plants which have pest control properties against 800 pest species.

(c) Microtoxins are phytotoxins derived from micro-organisms. They may have potential for use directly as herbicides or as base materials for the production of new herbicides. There is no evidence that microtoxins are intrinsically safer than synthetic herbicides.

Conclusion In most situations in which pesticides are used, the use of any single alternative strategy is unlikely to be an adequate substitute. However, there is considerable scope for reducing pesticide use by using integrated control systems in which several alternative control measures are used and use of pesticides is restricted. The biological principles for nonchemical control have been established for many weeds, pests and diseases. What is often lacking, however, is the detailed knowledge for the implementation of integrated control strategies on the farm. More work is needed in this area if reliable weed and pest control is to be achieved and high output arable cropping is to be maintained.

Agriculture with Reduced Inputs

D Atkinson

School of Agriculture, University of Aberdeen, 581 King Street, Aberdeen AB9 lUD, UK.

Agriculture, which for many years has been the predominant user of rural land, is now experiencing a range of conflicting pressures. This relates in part to current food surpluses in the EEC but also to public concerns about the types and quality of food being produced. Together these concerns have caused the current level of inputs being used in agriculture to be questioned and have led to demands for farming systems which are more extensive in style and have fewer agrochemical inputs. It is clearly important for agricultural scientists to reassess why we use the levels and types of inputs that are being used, what methods are available to extensify agriculture and what are the financial, environmental and health implications of these changes. Changes can come about by altering what we grow


on the land, eg by switching from cereals to tree crops; by altering the ways in which we grow current crops, eg by moving from systems maintained with synthetic organic chemicals and readily available nutrient sources to ones that do not use these (‘organic farming’); or by changing the genetics of the crop plants we use so as to reduce dependency on immediately available nutrients. All of these changes must be seen against the need to maintain plant health, to allow and encourage financially viable farming systems and to sustain European food supply.

The Economics of Reduced-Input Agriculture

Graham E Dalton and Kenneth J Thomson

Aberdeen School of Agriculture, 581 King Street, Aberdeen AB9 IUD, UK

The paper rehearses some economic principles to be borne in mind when considering the reduction of inputs in UK agriculture. At the field and enterprise level a less intensive agriculture can be encouraged by changes in relative prices or through direct control. Analysis of dairy-farm incomes shows strong economies of scale in feed and labour use, with milk quotas having brought about significant reductions in both groups of inputs since 1984. Lower product prices will discourage intensive ‘low margin per unit of output’ systems of production-for example, winter wheat compared with spring barley-given their greater sensitivity to price changes. Expensive capital will speed up reorganisation in the use of buildings and machinery to secure greater efficiency. Output restrictions will discourage the use of variable inputs until longer term structural changes take place. However, government policy to secure reduced input use directly is subject to a number of problems of efficiency and distribution. For example, set-aside raises land prices, discouraging input reduction, and also displaces farm workers.

At sector level, the UK has had remarkably stable input/output ratios and food consumption patterns over the last ten years, and is not out of line with comparable EC member states. Main concerns for input suppliers are consequently the overall size of the sector in the face of price pressure, enhanced European competition and direct controls on land and input use.

Breeding Barley for Agriculture with Fewer Inputs

R P Ellis

Scottish Crop Research Institute, Dundee DD2 SDA, UK

Intensive agriculture emphasises reduced cultivation and maximum inputs of fertiliser, fungicides, pesticides and herbicides. The pursuit of maximum production at maximum profit can lead to problems such as fungicide tolerance in pathogens,


Side effects Tolerance in the Overuse causes pathogen after ecological problems widespread use I

Diseases = Pests = Fungicides Pesticides

1 P R o m E M s

/ \ High levels of Reduced cultivation

N-P-Kgive economic yield response I 1

I More weeds especially

grasses in cereals

Dificult to achieve low nitrogen winter

malting barley

Fig 1. Potential problems of intensive agriculture.

Greater use of herbicides

Enhanced natural

organic sprays GENETIC RESISTANCE resistance with Use predators

I VARIETY \ / Diseases

\ MIXTURES

Solutions

Weeds Soil nutrients

i MAKE CROPS MORE COMPETITIVE

1 BREED BETTER ROOTS

Fig 2. Possible solutions to the problems of intensive agriculture. Areas of continuing or future work on genetically based solutions are indicated in capitals.

the need for expensive grass-killing herbicides and the indiscriminate destruction of all insects. At the same time economic improvements in yield can be obtained with current fertiliser application rates but at the expense of malting premiums (Fig 1).

Plant breeders work within the constraints of prevailing agricultural practice, particularly in the management of advanced trials. If new systems are sought, then any necessary changes in crop performance should be carefully examined before redefining breeding objectives.

Diseases have traditionally been combated with genetic resistance, with current emphasis placed on more sophisticated mechanisms such as partial resistance of the use of cultivar mixtures (Fig 2). Current research at the Scottish Crop Research


TABLE 1 Genetic control of root characters has been demonstrated in a number of crop species. Breeding targets are most readily achieved by

manipulating relatively few characters

Target Character to be manipulated

Nutrient uptake Lodging resistance Drought resistance

Root weight, number and surface area Root diameter and angle Root depth and length

Institute, funded by the Home Grown Cereals Authority, seeks to enhance natural plant resistance by priming the system with an application of a yeast extract.

Success in breeding depends on the characterisation of genetic variation and its manipulation to produce new cultivars that are well adapted to a range of environmental stresses. Many studies have explored the performance of the above- ground parts of crop plants, but root systems are poorly understood.

Characters that are controlled by a single gene, such as tolerance of acidic soils in barley, can be easily incorporated into existing breeding programmes. However, work on more complex traits, such as efficiency of mineral use or drought tolerance, is a longer term objective which requires collaboration between breeders and plant physiologists (Table 1). Success will depend on the understanding of nutrient uptake and utilisation, plant development and growth, and the production of economically useful yield.

New developments in breeding technology and improvement in knowledge of the genetics of crop species will lead to new opportunities for the plant breeder. Recent work at SCRI has shown linkage between genes for greater yield and a-amylase in spring barley. This offers the prospect of associating quantitatively control traits with simple markers that can more readily be selected in a breeding programme. In turn this would enable breeders, for the first time, to select for complex root traits.

The Consequences for Nutrient Uptake Efficiency of Farm Practices Such as Cr$ Rotation

Anthony C Edwards," Peter Dysonb and Jim A M Rossa

Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 245, UK East of Scotland College of Agriculture, Penicuik, Midlothian EH26 OPH, UK

Agriculture is frequently blamed for the decline in water quality (river/groundwater) and in particular for increased nitrate levels. The actual reasons are more difficult to explain. It is easily shown that recent decades have seen substantial increases in


amounts of fertiliser used, but this is difficult to separate from the background of substantial changes in farming practice which have occurred over the same period.

Nitrogen uptake for various crop varieties is compared with the seasonal pattern of soil N availability. Later developing species such as swedes and potatoes suffered much lower yield reductions in field experiments when no nitrogen fertiliser was applied than did cereals, particularly winter-sown crops.

The nutrient balance for a crop rotation/fertiliser experiment (barley, grass/ clover, winter wheat and potatoes) has provided figures of uptake efficiencies. Crop removal of nitrogen for the whole rotation (at fertiliser rates equivalent to advisory recommendations) accounted for 70 % of that applied, while the efficiency of individual crops ranged from 50% for potatoes to 80% for spring barley. Reduced rates of nitrogen fertiliser application resulted in a very close input/output balance with some but not excessive yield penalties. Fertiliser interactions (particularly N and P) also significantly affected nutrient balances.

Data from various sources, which include field experiments and Scottish advisory soil fertility information system land-use maps, are combined to help explain observed differences in river nitrate levels. The northeast of Scotland possesses various attributes which makes it ideal for a study of this type. Two main rivers (Dee and Don) and their tributaries show substantial differences in the type and intensity of agricultural land use. In addition dramatic changes in land use occur as we progress the 60 miles from their source areas in the uplands to the relatively productive region around Aberdeen.

While it is appreciated that the straightforward input/output balance calculated is an oversimplification, estimates of potential nitrate losses to the rivers were highly correlated with nitrate loads in the local major river systems. Losses vary from less than 2 kg ha-' NOJ-N for moorland sites to amounts in excess of 40 kg ha-' for predominantly arable catchment areas.

agriculture group symposium: agriculture with reduced inputs

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