conservation agriculture || conservation agriculture in australia and new zealand

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Chapter 14Conservation Agriculture in Australia and New Zealand

P. R. Ward and Kadambot H. M. Siddique

© Springer International Publishing Switzerland 2015M. Farooq, K. H. M. Siddique (eds.), Conservation Agriculture, DOI 10.1007/978-3-319-11620-4_14

P. R. Ward ()CSIRO Agriculture Flagship, Private Bag No 5, Wembley, WA 6913, Australiae-mail: [email protected]

K. H. M. SiddiqueThe UWA Institute of Agriculture, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia

Abstract The adoption and implementation of conservation farming principles have followed very different paths in Australia and New Zealand. In Australia, severe erosion events, and the obvious advantages of conservation farming prac-tices, led to rapid adoption, and currently around 90 % of farmers use some form of conservation agriculture. In New Zealand, advantages of conservation farming practices are not so obvious, and the perceived risks have resulted in adoption rates of less than 10 %. In this chapter, we briefly review the adoption in both Australia and New Zealand, and then look in greater detail at how the principles of conser-vation agriculture are currently being applied in Australia. Because agriculture in Australia is largely non-irrigated and reliant on rainfall, we have a specific focus on impacts of conservation farming practices on soil water balance. We also look at the future of conservation farming in Australia and New Zealand, and discuss recent advances in weed control strategies.

Keywords Conservation farming · Water balance · No-till · Zero-till · Reduced tillage · Residue retention · Stubble retention

14.1 Introduction

Conservation farming as a term was defined in 1959 as ‘making the most efficient use of the land over a long period of time’ (Kohnke and Bertrand 1959). Subsequent definitions have focused on various aspects of profitability and environmental protection, but all definitions come back to the simple principles of profitable agricultural production while protecting the environmental resource base. Core com-ponents of conservation farming tend to revolve around three main areas: reducing soil disturbance, increasing vegetative ground cover, and increasing the diversity of crops. Within each of these areas, there is plenty of scope for local adaptation of

336 P. R. Ward and K. H. M. Siddique

suitable techniques. Therefore, conservation farming is not a well-defined sequence of processes or technologies, but is rather an attitude in which the long-term stability of production is as important as the short-term profitability.

Of course, ‘conservation farming’ as a philosophy was in evidence long before 1959, in Oceania and all around the world. Australian farmers proved themselves to be adaptable and innovative, and rapidly responded to challenges as they adapted European farming knowledge to the more fragile Australian conditions.

Farming in the conventional sense commenced in Australia and New Zealand in the late eighteenth century, with the arrival of European settlers. Initially, farming used techniques directly imported from the UK, but these techniques quickly proved unsuitable for Antipodean conditions (Cornish and Pratley 1987). Because of the ready availability of land, a form of ‘shifting’ farming became normal, in which land was cleared, and wheat was grown for a few years until yield declined. The decline in yield was caused by decline in soil fertility and encroachment of weeds. After a few years of crop production, the cycle was repeated on new land, and the previous land was abandoned. Often, the abandoned land was returned to cropping after a period of several years, during which organic matter, nutrients, and weed populations recovered to reasonable levels. In this way, a form of rudimentary crop rotation was established very early in the history of agriculture in Oceania.

Over the past 200 years, innovative Australian farmers have solved many of the problems associated with early agriculture. Inventions including the stump-jump plough in 1876, and the Ridley Stripper in 1843, made major contributions to the development of productive and sustainable farming systems. However, the main factor pushing farmers in southern Australia towards a modern conservation farm-ing system was major erosion events in the 1930s. Erosion was associated with the practice of long fallowing, an idea borrowed from farming systems prevalent in the USA at the time. In this system, soils were kept bare from January in one year until seeding in June of the next year, a period of up to 18 months. Frequent cultivation ensured a weed-free soil surface, but also left a soil with poor structural stability. This proved to be particularly damaging on soils of sandy texture, as is common throughout southern Australia. By 1940, Hore (1940) demonstrated the value of surface cover in reducing the erosion risk, and other research (Callaghan and Mil-lington 1957) showed that a 16-month fallow was no more effective than fallows of 11–12 months. The lessons learned during this time have resulted in a farming system with retained residue, and minimum cultivation, in line with worldwide un-derstanding of conservation farming principles.

More recently, the decline in wool prices during the 1980s resulted in increased cropping intensity, with an associated increase in the need for timely farming op-erations (Llewellyn et al. 2012). At the same time, the price of glyphosate and tri-fluralin also declined, further increasing the appeal of reduced tillage in favour of herbicide options for weed control (D’Emden et al. 2008). The ability of farmers to plant crops over larger areas in a more timely manner resulted in increased average farm size (Kirkegaard et al. 2014). In Western Australia, the average farm size in the wheat belt region (excluding farms with gross production values of less than Australian $ 150,000 per year, which account for less than 4 % of the total value of production) in 2011 was 3300 ha (Trestrail et al. 2013).

14 Conservation Agriculture in Australia and New Zealand 337

Farmers in Australia and New Zealand are now looking towards international best practice, as they strive to improve their conservation farming systems even further. In 2005, Rolf Derpsch, a conservation farming specialist from Paraguay, was invited to Australia. During his visit, he observed that in Australia, ‘…no till has reached a plateau and it appears difficult to advance the system to a higher level…’ (Derpsch 2005). For Australian farming, he recommended full year-round stubble retention, diverse rotations including cover crops, and integrated weed management.

A major factor in the development and extension of conservation farming prac-tices in Australia and New Zealand was the establishment of farmer groups. Groups such as the Western Australian No-Till Farmers Association (WANTFA), South Australian No-Till Farmers Association (SANTFA), Victorian No-Till Farmers Association (VNTFA), Conservation Agriculture and No-till Farming Association (CANFA), Conservation Farmers Inc (CFI), and the New Zealand No-Tillage Asso-ciation (NZNTA) assisted farmers at local and regional level to adopt conservation farming practices. These groups have been instrumental in encouraging farmers to test and refine practices to suit local conditions.

14.2 Climatic Conditions and Conservation agriculture

There are three main climatic zones represented in the cropping regions of Australia and New Zealand (Fig. 14.1), and each has developed slightly different forms of conservation agriculture (CA).

Fig. 14.1 Major climatic zones in Australia and New Zealand


14.2.1 Mediterranean

The Mediterranean region encompasses the south-west and portions of the south coast of mainland Australia, and the western coast of Tasmania. These areas are characterised by hot, dry summers, and because of the general lack of suitable ir-rigation sources, crop growth is only possible during winter and spring. Large parts of this region also have sandy-textured top soils, and these factors to a large degree have shaped the evolution of agriculture.

Conservation agriculture, encompassing minimum tillage and residue retention, has been widely adopted throughout the region (D’Emden et al. 2006), particularly in the west. Currently about 90 % of farmers in the western region use no-tillage (defined in Sect. 14.3; Llewellyn et al. 2012). The initial key driver for large-scale adoption was prevention of wind erosion, and the development of suitable herbicides, machinery, and a sharp decrease in the wool price lead to the high adoption rate.

14.2.2 Temperate

The temperate region includes New Zealand and the southeastern parts of Australia. In this region, rainfall is roughly equally distributed throughout the year. In warmer parts of the region, reliable crop production is restricted to the winter and spring months, as evaporation increases markedly during summer. In cooler parts, the best time for crop production is summer, as it is too cold during winter. The soils tend to be fine textured and more productive than those of the Mediterranean region, particularly in New Zealand.

Conservation farming practices have been readily adopted in the temperate re-gions in Australia (D’Emden et al. 2006; Llewellyn et al. 2012), for similar rea-sons as experienced in the Mediterranean region. For example, average adoption in southern New South Wales was recently estimated at 89 % (Llewellyn et al. 2012). However, adoption has been less extensive in New Zealand, with rates of less than 10 %. Low adoption in New Zealand was attributed largely to the better soils (Baker et al. 2003, 2007), because the benefits of conservation farming practices were not as evident as in Australia. With recent advances in machinery, particularly for seed-ing, and increases in the fuel price, adoption may be increasing (Safa et al. 2010).

14.2.3 Subtropical

The subtropical agricultural region extends along the east coast of Australia, and is characterised by summer dominant rainfall. In this region, either summer or winter crops can be grown reliably, due to the rainfall patterns and good soil-water-holding capacity, but growing two crops in a 12-month period is rare. Intense rainfall associ-ated with summer thunderstorms caused major erosion, and by the 1950s, farmers were encouraged to retain residue to reduce the erosion risk (McFarlane 1952).


As a result of an effective extension programme, residue retention was adopted during the 1950s in this region (Cornish and Pratley 1987). No-tillage was adopted later, and by 2011, no-tillage was used by 72–82 % of farmers (Llewellyn et al. 2012).

14.3 Experiences of Conservation Farming

14.3.1 Reduced Tillage

No-till farming in Australia arose mostly in response to the threat posed by soil ero-sion, and there is no doubt that erosion was substantially controlled by the changes implemented. Additional advantages of a reduced-tillage system, such as allowing earlier seeding, also allowed for better crop production. For these reasons, no-till, or some form of reduced soil disturbance, was enthusiastically adopted by farmers right across southern Australia (D’Emden et al. 2006).

The continuing evolution of reduced tillage in farming systems has seen the in-troduction of the disc seeder (Fig. 14.2), resulting in even less soil disturbance, and this also allows seeding machinery to cope with larger residue quantities (Fig. 14.3). Disc seeding technology was seen by Derpsch (2005) to be a core component of ad-vanced conservation farming systems in the Australian context.

More recently, there has been considerable interest in ‘strategic’ tillage, in which a general no-till farming system is occasionally tilled for various benefits includ-ing weed control and lime or phosphorus incorporation (Kirkegaard et al. 2014). Preliminary evidence under Australian conditions suggests that occasional strategic tillage does not cause damage to the soil, or impact negatively on crop yields.

Fig. 14.2 Disc seeders cause minimal soil disturbance and can cope with large residue loads


14.3.2 Residue Management

In a conservation farming system, residue provides a number of important benefits. Principally, residue protects the soil surface during rainfall so that the impact of droplets does not dislodge soil particles, resulting in potential for surface sealing, increased run-off, and the associated increased erosion risk (Hunt and Kirkegaard 2011). The presence of residue on the soil surface also slows down the rate of water movement across the soil, which helps to restrict soil erosion (Fig. 14.4).

In some situations, residue can also decrease evaporation from the soil surface. By shading the soil surface and lowering the average wind speed at the soil surface, residue can absorb or deflect some of the energy, which would otherwise be used to evaporate water (Ji and Unger 2001). However, research under Australian conditions

Fig. 14.3 A wheat crop growing through canola stubble

Fig. 14.4 A good reason for residue retention


shows that impacts of residue on evaporation are generally minor (Ward et al. 2009, 2012; Hunt and Kirkegaard 2011; Hunt et al. 2013). Where residue retention may have a large positive impact is in slowing down evaporation at the time of crop seeding, which may extend the sowing window to allow more crop to be sown in a timely manner (Ward et al. 2012).

Residue retention can also have an impact on soil temperature, through shading the soil surface and protecting it from direct sunlight (Swella et al. unpublished data). During the hot and dry summer, soil temperatures at the surface can rise above 70°C, and lower soil temperatures are thought to be positive for maintaining diverse soil biology. However, in cooler parts of Australia and New Zealand, lower soil temperatures during periods of crop growth can slow growth and potentially restrict crop yield.

Residue retention also plays a direct role in increasing biological activity in the soil. While residue can harbour crop diseases (see the section on crop diversity), residue also encourages other soil organisms, many of which are beneficial to crop production. Earthworms are encouraged by residue retention, and generally have a positive impact on crop yield (Buckerfield et al. 1997), particularly in the temperate and cooler parts of the Mediterranean zones. Earthworms are less suited to hotter and drier parts of Australia, but in a recent study near Geraldton, the exclusion of ants and termites and other soil insects was associated with a 30 % decline in crop production (Evans et al. 2011). Residue provides a key food source for termites, so residue retention is likely to increase termite numbers, with potential long-term benefits for crop production.

14.3.3 Cover Crops

Cover crops, crops grown specifically to generate ground cover, have been proposed as a means of increasing the quantity of residue. In the subtropical zone, and wetter parts of the temperate zone, there is a scope to plant a summer cover crop between two conventional winter/spring crops. In this way, cover can be maintained year-round without losing a year of production. However, in the Mediterranean zone and drier parts of the temperate zone, cover crops will normally be grown during winter and spring, replacing a conventional crop. Therefore, winter cover crops must pro-vide considerable benefits to subsequent crops, and the whole farming system, in order to be financially attractive.

Some of the benefits that cover crops may provide are in weed control, subsoil amelioration, and for leguminous cover crops, nitrogen fixation (Flower et al. 2012). Because cover crops are not grown for grain, they can be killed at maximum biomass, which gives good options for weed control. One of the options for killing the cover crop is knife-rolling (Fig. 14.5). The blades on the roller damage the stems, which kills the plants (and any weeds) and also prevents re-sprouting (Flower et al. 2012). In South America, knife-rolling alone has been effective, which reduces pressure on herbicides. However, under Australian conditions, herbicide application prior to rolling is usually required to ensure a good crop and weed kill.


In an experiment at Wellington, NSW, summer cover crops of pigeon pea or millet were effective in increasing residue quantity by around 1 t/ha. Water use by the crops resulted in lower soil water contents at the time of cover crop termination, but if the cover crops were terminated early (February or March), impacts on crop production were small (see the section on infiltration, below; M. McNee, unpub-lished data).

Winter cover crops, sprayed at anthesis in trials in southwestern Australia at Mingenew and Cunderdin, did not result in greater levels of residue when compared with residue after traditional grain crops (Fig. 14.6; Ward et al. 2012). However, there was a significant increase in ground cover following a cover crop (Fig. 14.7).

Fig. 14.5 Knife-rolling a Saia oat cover crop. (Photo: N. Cordingley)

Fig. 14.6 The inclusion of a winter cover crop on its own is not enough to increase residue quantity. (Ward et al. 2012)


14.3.4 Diverse Rotations

The benefits of rotation in crop production have been known nearly since the dawn of agriculture. Ancient Egyptians and Romans quickly discovered that crops grown without rotation were subject to disease and yielded poorly. In modern agriculture with greater emphasis on residue retention, rotation and crop diversity become even more important. The residue from a crop can act as a refuge for pathogens, enabling them to react quickly if another susceptible crop is grown (Watt et al. 2006; Gupta et al. 2011).

Diversity in the crop rotation also allows for different weed control options, which reduces the risk and impacts of resistance to any specific form of weed con-trol. Herbicide resistance is becoming a real problem in reduced-till farming, and so the use of a diverse range of crops will help to overcome this.

A key benefit of cover crops is that they do not need to be traditional crops such as wheat, barley, canola, or lupins. This can add considerable diversity to the crop rotation and offer farmers additional weed control options. In Australia, many cover crops are killed chemically prior to seed set, enabling good control of weed seed numbers (Flower et al. 2012).

14.4 Water Balance

Because most of the agricultural areas in Australia and New Zealand are rain-fed, knowledge of the water balance, and the influence that conservation farming has on components of the water balance, can be critical.

The soil water balance (Fig. 14.8) is a simple equation that states that the inputs of water into the soil (in southern Australia, usually just rainfall, P) must equal the outputs from the soil, plus any change in soil water storage (∆S). Outputs are either upwards (evaporation E or transpiration T), sideways (run-off or lateral flow through the soil L), or downwards (deep drainage D).

Fig. 14.7 Despite not increasing residue quantity in the rotation, cover crops increased ground cover for the summer immediately fol-lowing. (Ward et al. 2012)


Because it is a ‘balance’, if one of the components changes, others must also change. For example, if evaporation decreases, one or more of transpiration, lateral flow or drainage to groundwater must increase to maintain the balance.

14.4.1 Infiltration and Soil Water Storage

One of the biggest impacts that conservation farming practices has on water bal-ance is to increase infiltration. Soil is comprised of solid particles and the spaces, or pores, between them. For most soils, total porosity is about 40–50 % by vol-ume, and so in theory, the total amount of water that can be stored in the soil var-ies between 0 (dry) and 50 % v/v (saturated). In practice, the lower limit (LL) of soil water content is largely determined by the ability of plants to extract water from the soil, and the upper limit of soil water storage is determined by the ability of the soil to hold water against the force of gravity. Both the upper limit and LL are strongly influenced by soil texture (Fig. 14.9). The term drained upper limit (DUL), or field capacity, denotes the practical upper limit of soil water storage, and the LL is sometimes called the permanent wilting point. Water in the soil be-tween the DUL and LL is called plant available water (PAW), because this is the water that can be used by plants.

Numerous studies conducted in the 1980s and 1990s in Western Australia, South Australia, Victoria, New South Wales, and Queensland, using rainfall simulators and models, demonstrated that both stubble retention and reduced tillage lead to faster rainfall infiltration, and consequently, increased levels of soil water stor-age, via a reduction in losses due to run-off. Differences such as the one shown in Fig. 14.10 are seasonally dependent, but can happen if summer rainfall conditions are favourable (Hamblin 1984).

A recent study in Western Australia (Evans et al. 2011) also found that the tunnels created by ants and termites encourage infiltration of water away from the soil surface. Deep soil water is less prone to evaporation from the soil sur-face, so ants and termites (encouraged by conservation farming practices) could

Fig. 14.8 Components of the water balance


also lead to higher levels of soil water storage, but this has not yet been widely demonstrated.

In other trials in the Mediterranean region of Western Australia, no consistent differences in soil water storage were observed between the different residue man-agement treatments (Ward et al. 2012) in terms of soil water storage during summer. As indicated earlier, the cover crop treatments did not consistently leave more resi-due than the ‘district practice’ treatments, but within any specific growing season, there was considerable variation in residue quantity depending on crop type. For ex-ample, after the 2009 growing season, residue loads ranged between 6.2 and 9.0 for barley crops at the Cunderdin site. In 2010 and 2011, differences between residue

Fig. 14.10 Zero-till can increase soil water in some situations. (Hamblin 1984)

Fig. 14.9 Plant available soil water varies with soil type. DUL is the drained upper limit, and LL is the lower limit for plant water extraction


levels were enhanced by stubble removal from the ‘district practice’ treatment, so that residue levels in the trial ranged between 1.7 and 7.7 t/ha after the 2010 season, and 3.5 and 9.0 t/ha after the 2011 season. Despite these differences, there were no clear differences between the treatments in average soil water over the summer pe-riod (Fig. 14.11) in both wet (e.g. 2011–2012) and dry (e.g. 2009–2010) summers.

However, as rainfall increases during late autumn and winter, the presence of residue can increase infiltration into the soil. For example, at two sites in the Medi-terranean region of southern Australia (near the towns of Maitland and Wirrabara), soil below a depth of 20 cm wet up considerably more at the start of the 2009 season in the plots where residue was retained (Figs. 14.12; 14.13) (G. Butler, unpublished data). Here, the residue protected the soil surface, allowing greater infiltration to deeper in the soil. At both sites, soil water storage below a soil depth of 20 cm increased by about 20 mm due to the presence of retained stubble on the soil surface.

Fig. 14.12 Residue retention increased soil water early in the growing season (late June and July) compared with residue removal at the Mai-tland (SA) trial. (G. Butler, unpublished data)

Fig. 14.11 Residue quantity has little impact on average summer soil water storage. (Ward et al. 2012)


In the longer term, changes in soil organic carbon can lead to changes in soil structure and infiltration. In the Maitland and Wirrabara sites, after 4 years of residues being either retained or removed, soil organic carbon differed by about 2 t/ha in the top 10 cm of soil. Organic carbon is pivotal in maintaining good soil structure, and a difference of this magnitude could have significant impacts on in-filtration rate.

In the temperate region of eastern Australia, plots with a short-season summer cover crop were drier during the 2009 autumn and early winter than traditional ‘fal-low’ plots (M. McNee, unpublished data). However, soil water storage in the plots with the cover crop responded more to rainfall at the start of the winter growing season, indicating that the cover crop was protecting the soil surface and allowing more rainfall to infiltrate (Fig. 14.14). By the time flowering commenced, there was little difference between the treatments in terms of soil water.

In other years of the trial, there was little difference between the early-season summer cover crop treatments and the ‘summer fallow’ treatments, thanks largely to good autumn rains and increased infiltration due to the summer cover crop resi-due. However, the ‘late season’ and ‘long season’ summer crops used soil water dur-ing autumn, and soil water contents were lower in these treatments at wheat sowing, which impacted crop yield.

Fig. 14.14 Although soil was drier after a summer cover crop in the temperate region of New South Wales, it responded more to winter rainfall (M. McNee, unpub-lished data)

Fig. 14.13 Residue retention also increased infiltration in June and July at the Wirrabara (southern Australia) trial. (G. Butler, unpublished data)


14.4.2 Run-off

A major benefit of stubble retention is that it protects the soil surface. Raindrop impact can lead to a break down in surface soil structure, which leads to reduced rates of infiltration and increased run-off. Residue intercepts the raindrops and prevents damage to the soil structure (Hillel 1971), thereby ensuring good infil-tration. Reduced tillage also has a direct effect on soil structure, with soils gen-erally having a much more stable structure when physical disturbance is mini-mised. Through these two effects, conservation farming practices generally lead to decreased run-off compared with systems, where tillage and residue removal are practised. For example, at a trial on a red-brown earth in the Mediterranean zone of southern Australia, soil loss under simulated rainfall was reduced from 0.8 to 0.4 t/ha, when residue was increased from 0.5 to 5.0 t/ha (Malinda 1995). Earlier trials in the subtropical areas of southern Queensland undertaken by Freebairn and colleagues showed similar results (e.g. Freebairn and Boughton (1980). In other trials in the subtropical zone, Lang (1979) found that run-off and erosion increased markedly when ground cover fell below 75 %. This promoted the idea of ‘threshold’ values for ground cover, and it is generally accepted now that a value of 2 t/ha of residue is adequate to minimise the erosion risk (Scott et al. 2010).

14.4.3 Evaporation

14.4.3.1 Evaporation Rate

Evaporation involves the transport of water to the soil surface, and its conversion into water vapour. This conversion requires energy, which in southern Australia and New Zealand mostly comes from sunlight, with a minor contribution from wind.

Evaporation from an initially saturated soil can be broken down into three stages (Fig. 14.15). In stage 1, there is plenty of water at the soil surface, and evaporation

Fig. 14.15 The three stages of evaporation. For soil mois-ture deficit, 0 is a wet soil, and 1 is a dry soil


is limited only by the amount of available energy. However, as the soil dries, the ability of the soil to transmit water to the soil surface starts to diminish, and the evaporation rate rapidly falls (stage 2). In stage 2, the evaporation rate is related to the surface soil water content. When the surface soil is air dry, the only way that water from deeper soil layers can reach the soil surface is by diffusion of water va-pour (stage 3), which is a slow process. In stage 3, the rate of relative evaporation is roughly constant.

Many studies around the world have demonstrated that residue can slow the rate of evaporation from a wet soil, and it does this by restricting energy available for the evaporation process. Initially, residue shades the soil surface, which instantly reduces the amount of available energy for evaporation. Residue also reduces wind speed at the soil surface, which reduces the input of energy to the soil.

Therefore, while evaporation from the soil is limited by energy availability (that is stage 1 evaporation), residue is likely to reduce the rate of evaporation. However, as a general rule, stage 1 evaporation usually only happens for, at most, a few days. During stage 2 and stage 3 evaporation, residue has little impact on evaporation rate.

For example, Ward et al. (2012) measured evaporation rate at midday a few hours after 18.6 mm of rainfall in January 2009 at a site in southwestern Australia. Evaporation rate from plots with a cover crop averaged 0.28 mm/h, but evaporation from wheat stubble was 0.35 mm/h. However, a few days after rainfall, the evapora-tion rate had fallen to 0.065 mm/h, and there was no difference between plots with high and low residue loads.

After extended dry periods, as is common during summer in zones with a Medi-terranean climate, evaporation rates were even lower, and once again, there was little difference between treatments with high and low residue loads. In three trials in southern Australia, the evaporation rate was measured at midday in March 2010, and at all three sites, evapotranspiration (ET) was slightly faster from the plots with the retained stubble (Table 14.1; G. Butler, unpublished data). This has also been observed at a trial in Western Australia (Ward et al. 2009). Although ET appeared to be faster from plots with retained stubble, the difference was small, and only amounted to a few millimetres if summed over a period of 5 months.

For the Wirrabara (SA) trial, evaporation rate was also measured at the same time on plots newly raked to remove the stubble, and evaporation from these plots was 0.075 mm/h (about three times faster than from the undisturbed plots). This demonstrates the immediate impact that soil disturbance can have on evaporation rate simply by exposing different soil surfaces to direct sunlight. Although evapora-tion rate was not measured at this trial on the next day, we expect that the increase in ET caused by soil disturbance would have been temporary.

Table 14.1 Midday evaporation rate for three trials in southern Australia in March 2010. (G.Butler, unpublished data)Site Soil type Evaporation rate (mm/h)

Stubble retained Stubble removedBuckleboo Sand 0.041 0.031Ardrossan Clay 0.083 0.075Wirrabara Clay 0.033 0.018


14.4.3.2 Total Evaporation over Summer

As discussed in Sect. 14.3.1, there can be differences in evaporation due to residue retention, depending on the time elapsed since the last rainfall. However, over a longer time period, such as the period between harvest of one crop and sowing the next, differences tend to even out. If the ET rate is reduced for a few days after rain by residue retention, then after a few days, the soil is wetter than the soil where residue was not retained. The wetter soil under the residue then loses water faster than the drier soil without the residue, and the total soil water storage tends to even out regardless of residue quantity (Fig. 14.11).

For example, the total evaporation over a whole summer in response to different cereal residue management was studied in trials at Cunderdin and Mingenew in the Mediterranean zone in Western Australia. In both trials, there were substantial differences in residue generated by either retaining or windrow-ing residue, but differences in summer evaporation were not related to residue levels (Ward et al. 2012). Similar results were observed for the trials in Buckleboo, Wirrabara, and Ardrossan (SA), and also in trials in the temperate region of NSW (Hunt and Kirkegaard 2011).

The exception to this rule could be for rainfall received close to seeding time. Evaporation rates at this time of the year are generally much lower than during the height of summer, and so rainfall received at this time is likely to stay in the soil for longer. Therefore, a reduction in evaporation rate, induced by residue, could lead to higher soil water contents for up to a week. In combination with the impacts of residue on infiltration discussed above, this could have large impacts on extending the sowing opportunity for crops.

14.4.3.3 Evaporation During Crop Growth

The presence of large quantities of residue on the soil surface may reduce evap-oration, leaving more water in the soil available for transpiration through crop leaves (Yunusa et al. 1994). Evaporation rates at midday were measured in the tri-als in Western Australia at Mingenew and Cunderdin during the early crop growth stage in June or July. On a sandy soil at Mingenew, total ET rate at midday was 0.17 mm/h from both the ‘residue retained’ and ‘residue burned’ plots, suggesting that on this soil type, residue did not influence evaporation rate. However, at the loamy Cunderdin site, midday ET rate was 0.21 mm/h where residue was removed, and 0.15 mm/h where residue was retained. This suggests that residue retention on a loamy soil reduced evaporation from the soil surface, which could potentially allow more water to be transpired.


14.4.4 Deep Drainage

The water balance component of deep drainage is of crucial importance in south-ern Australia through its link with groundwater recharge, and associated dry land salinity (Peck and Williamson 1987). Although deep drainage is generally a small component of the overall annual water balance (Ward 2006), an increase of just a few millimetres per year (caused by clearing native perennial vegetation, and replacing it with annual crops and pastures) has lead to a substantial increase in the area affected by dry land salinity (Ferdowsian et al. 1996). Any farming practice that increases soil water storage could also increase deep drainage, and so conservation farming prac-tices need careful scrutiny to ensure that the risk of dry land salinity is not increased.

14.4.4.1 Residue Retention

Very few studies have quantified the impact that conservation farming practices have on deep drainage and groundwater recharge. In trials across southern Australia (Ward et al. 2012), impacts of increased residue retention on soil water storage were minimal at all times of the year. Calculations of deep drainage from measurements of the water balance concluded that there was no significant impact of residue re-tention on deep drainage. Although this was only a few trials, all indications at this stage are that increased residue retention will not change the risk of deep drainage and associated dry land salinity.

14.4.4.2 Early Termination of Cover Crops, Crops, or Pastures

At a trial on a sandy soil near Mingenew in Western Australia, there were several instances where crops or pastures were terminated early, around anthesis in August or September. Some of these were planned as a part of the cover crop inclusion, designed to increase residue levels quickly. On other occasions, crops and pastures were terminated early to assist with weed control or to simulate grazing. On all these occasions, extra water was conserved in the soil, and some of this water was car-ried over until sowing of the next crop. Averaged over three summers (2008–2009, 2009–2010, and 2010–2011), the extra water stored in the soil at sowing following early termination was around 20 mm.

This extra water at sowing did not lead to increased crop yield at the Mingenew trial, but increased the quantity of deep drainage by around 10 mm in the 2009 and 2011 seasons (Fig. 14.16). Seasonal conditions were particularly dry in 2010, and deep drainage was zero from all treatments. However, on a loamy soil in West-ern Australia where early crop termination was also practised, there was no clear link between early crop termination and deep drainage, suggesting that increased groundwater recharge is most likely on sandy soils.


14.5 Weed Control

In Australia, one of the principal technologies enabling widespread adoption of conservation agriculture was the introduction of herbicides for weed control. In particular, glyphosate proved successful in killing weeds without cultivation, allow-ing earlier sowing and crop establishment (D’Emden et al. 2006; Llewellyn et al. 2012). However, the frequent use of glyphosate, and lack of equally efficacious alternatives, resulted in the development of weed populations resistant to glypho-sate (Walsh and Powles 2007; Farooq et al. 2011). In Australia, resistant populations of annual ryegrass ( Lolium rigidum) and wild radish ( Raphanus raphanistrum) are widespread throughout the cereal-producing regions. Furthermore, some herbicides (e.g. trifluralin) need to be incorporated into the soil, and so conservation agri-culture practices with minimal soil disturbance and residue retention can reduce their effectiveness. For these reasons, weed control in conservation agriculture in Australia is becoming a major issue, leading to farmers following a more pragmatic line of strategic tillage (Kirkegaard et al. 2014).

Obviously, an integrated approach to weed control is a core component of con-servation farming strategies (Derpsch 2005). With this in mind, an opportunity for weed seed control was highlighted by Walsh and Powles (2007), with the observa-tion that many weed seeds went through the harvester with regular grain harvest op-erations. Collection and destruction of the chaff fraction was effective in reducing ryegrass seed numbers, but less effective for wild radish control. Alternatively, con-centration of chaff in a windrow behind the harvester, followed by burning of the windrow, could control weed seed numbers. However, neither of these operations is consistent with conservation agriculture principles of maximising residue retention.

More recently, a Western Australian farmer, Ray Harrington, developed and test-ed an attachment for a harvester that physically damages weed seeds in the chaff fraction before returning the entire residue fraction to the soil surface. The Har-rington Seed Destructor (Walsh 2012) has proved as effective as windrow burning and chaff removal in reducing ryegrass emergence in the subsequent year.

Fig. 14.16 Early crop or pas-ture termination can increase the deep drainage risk in the subsequent year. (P. Ward, unpublished data)


14.6 Future Outlook

In most of Australia, adoption of conservation farming has nearly reached its maxi-mum level. The biggest threat to a continued high level of adoption is suitable weed control methods. Clearly, an integrated approach to weed control, reducing the reli-ance on herbicides or any other single control strategy, will be necessary to maintain the current use of conservation farming practices.

In New Zealand, current adoption of conservation farming is still relatively low. Greater adoption will rely on demonstration of the advantages of conservation farming principles over current practices. One of these advantages is likely to come from the increased price of fuel, with the lower fuel requirements of reduced tillage likely to prove attractive. With recent developments in seeding machinery making crop and pasture establishment less risky, adoption of conservation farming prac-tices is likely to increase.

In terms of water balance, there is a scope for long-term changes in soil-water-holding capacity, associated with long-term residue retention and potential organic matter accumulation. Increases in soil-water-holding capacity could prove enor-mously beneficial to crop growers, especially in the southern and western parts of Australia where many soils currently have low water-holding capacity. Several research trials around the world have demonstrated improvements in soil-water-holding capacity and soil structure after 5–10 years of conservation tillage practices, and these benefits need to be quantified under Australian conditions.

The current research has also highlighted the role that residue might play in reducing evaporation during early crop growth. This has the potential to increase transpiration, which should flow through to increased water use efficiency and crop yield. However, this has not yet been demonstrated under Australian conditions, and needs further research.

14.7 Conclusions

Farmers in cereal-producing regions of Australia have enthusiastically adopted no-till farming systems, with excellent outcomes from the reduced soil erosion. Local and regional farmer groups have been instrumental in encouraging adoption and developing systems suitable for local conditions. Adoption has been slower in New Zealand, due to the perceived risks of crop and pasture establishment, and lack of clear advantages with a conservation farming system.

In terms of water balance:

• Residue retention, on its own, has little impact on soil water storage, when mea-sured over periods of several months. However, over periods of days or weeks, residue retention can increase infiltration and reduce evaporation, which can be particularly beneficial in extending the sowing window.

• Winter cover crops do not have much impact on residue quantity, but do increase ground cover when residues are ‘rolled’.


• In regions or years with adequate early summer rainfall, summer cover crops increase residue quantity and infiltration of autumn rains. Early termination of summer cover crops (e.g. February) is desirable to maximise storage of autumn rains for subsequent crop production.

• Increased residue during early crop growth has the potential to reduce evapora-tive losses of water, with a complementary increase in transpiration. This should increase water-use efficiency, but has not yet been demonstrated.

• Increased residue retention does not increase the risk of deep drainage and as-sociated dry land salinity. However, early termination of crops or pastures can lead to increased risk, particularly in soils of low water-holding capacity, and in wet years or regions.

An integrated approach to weed control is essential to maintain the current high level of conservation farming use in Australia, and to encourage adoption in New Zealand. The Harrington Seed Destructor, in combination with other weed control mechanisms, may be beneficial in this regard.

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