In many regions, livestock are allowed to graze grain crops during their vegetative development, before grain is harvested at crop maturity. Little is known of the effects of grazing on crop microclimate, particularly the effects of defoliation on crown temperatures. Knowledge of such effects is important because temperature is the main factor underpinning crop ontogeny, and ontogeny drives dry matter allocation, leaf appearance rates and the timing of anthesis, which are key determinants of grain yield. The primary aim of this study was to examine the influence of grazing intensity and duration on the crown temperatures of winter wheat crops grown at Canberra, Australia. A secondary aim was to examine the association between crown temperature and phenology. In 2007, wheat cv. Mackellar was grazed at intensity–duration combinations of low–short (LS, 33 sheep/ha for 31 days), heavy–short (HS, 67 sheep/ha for 31 days) or low–long (LL, 33 sheep/ha for 62 days). In 2008, cvv. Mackellar and Naparoo were grazed at the HS intensity-duration. Cubic smoothing splines were fitted to crown temperature data measured between the end of grazing and anthesis to facilitate identification of long-term trends and statistical differences caused by the effects of defoliation on crown temperature. Grazing treatments with greater intensity or longer duration significantly elevated maximum daily crown temperature; differences of 6–7°C were common in the month following grazing. Cubic-spline analysis showed that long-term trends in maximum crown temperature of the HS and LL treatments were significantly greater than corresponding temperatures of controls for the entire post-grazing duration. By contrast, effects of grazing on minimum diurnal crown temperature were small. Increasing biomass removal significantly delayed stem elongation and anthesis. We demonstrate that although initial phenological delays caused by defoliation are large, greater diurnal crown temperature fluctuation in grazed crops leads to greater growing degree-day accumulation between the end of grazing and anthesis. This increases the rate of thermal time accumulation during the post-grazing–anthesis period and is likely prominent in driving greater development rates of grazed crops. We further demonstrate that delays in phenology associated with grazing can be largely accounted for by a thermal time constant, with the LS, HS and LL treatments delaying stem elongation by ∼52, 141 and 214 degree-days, respectively, above a base temperature of 0°C. Results from these experiments and interpretations herein will be of use in designing crop-grazing regimes, and in studies examining implications of defoliation on vegetative microclimate and on physiological feedback effects caused by elevated temperature.

Dual-purpose crops for grazing and grain production can be highly profitable, provided grazing does not cause significant loss of grain yield. In many plants, defoliation causes a transient reduction in the allocation of resources to stem and root growth and remobilisation of soluble resources to re-establish leaf area rapidly. In Australia, the usual autumn and winter period of defoliation for grazed crops, May–July, coincides with a phase of near-linear root depth penetration in ungrazed crops, and the crop recovery period after grazing occurs during stem elongation, when grain number and yield potential are determined. However, few studies have investigated the potential impact of crop defoliation through grazing on root growth of wheat in the field. We investigated the effect of defoliation by grazing or shoot removal on the root growth of wheat crops in four field experiments in south-eastern Australia in which the timing, frequency and intensity of defoliation varied. Despite significant impacts of defoliation on aboveground biomass (50–90% reduction) and grain yield (10–43% reduction) in all experiments, we found little evidence of effects on the rate of root penetration or final rooting depth. A notable exception was observed in one experiment when defoliation commenced very early (four-leaf stage, Zadoks growth stage Z14) in a repeatedly defoliated crop, reducing rooting depth from 1.65 to 1.35 m. The only other measured impact on roots was in an early-sown winter wheat crop grazed by sheep for 3 months (6 June–3 September), in which root length density was reduced by ∼50% in surface layers above 1.0 m depth, but there was no impact on maximum root depth or root length density at 1.0–2.0 m depth. Our results suggest that grazing has little impact on the rooting depth of wheat unless it occurs very early and repeatedly, when plants are allocating significant resources to establish the primary roots. However, there may be some reduction in the density of roots in surface layers during recovery after long-term grazing, presumably associated with reduced proliferation of the nodal root system. We conclude that most significant yield penalties due to grazing relate to impacts on the assimilation of aboveground resources, rather than to reduced water or nutrient acquisition by roots.

Cropping has recently expanded into arable areas of the high rainfall zone (HRZ) of Australia. We assessed the suitability of canola varieties of winter, winter × spring and spring-maturity at six sites across the south-eastern, northern and western HRZ of Australia for their suitability for dual-purpose production. Experiments measured potential forage production and the effect of defoliation or grazing on grain yield of crops sown from mid-March to mid-May. Overall, these experiments demonstrated the potential for dual-purpose canola across a wide area of the HRZ. In the south-eastern HRZ where winter conditions were sufficient for vernalisation and spring conditions were mild, winter and winter × spring types outperformed spring types as they provided an extended vegetative period for ‘safe’ grazing (prior to stem elongation), producing 3.0–6.8 t dry matter (DM) ha^–1 of forage and recovered to produce 2.5–4.9 t ha^–1 of grain yield. In the south-eastern region, early-sown winter types produced more forage than other canola types for grazing in late autumn and winter. In one experiment with four sowing times, consecutive delays in sowing of 2 weeks reduced forage available for grazing by 58%, 72% and 95% compared with the earliest sowing time of 10 March (6.1 t DM ha^–1). Although spring types in this region provided some potential for grazing, the phenology was unsuitable for early sowing as the rapid onset of flowering reduced the period of safe grazing. Winter types were not suited to the western region, but the winter × spring and spring types produced >1.0 t DM ha^–1 of forage and grain yield of 2.3 t ha^–1. In the northern region, spring types produced the highest grain yield (>3.0 t ha^–1) but suffered significant yield penalties associated with grazing. In other regions there was generally little or no effect of grazing on grain yield when crops were grazed or defoliated before stem elongation. These experimental studies confirm the potential for dual-purpose canola across all regions of the HRZ when suitable maturity types are sown, managed and grazed appropriately.

European winter canola (Brassica napus L.) varieties adapted to the long, cool seasons in high-rainfall areas of southern Australia have recently been adopted as autumn-sown, grain-only and dual-purpose crops. A spring-sown winter canola could be used as a biennial dual-purpose crop, to provide additional forage for summer and autumn grazing before recovery to produce an oilseed crop. We report a series of field experiments demonstrating that European winter canola types have suitable phenological characteristics to allow for their use as biennial, spring-sown crops, providing significant forage (2.5–4 t ha^–1) for grazing while remaining vegetative through summer and autumn, and recovering following vernalisation in winter to produce high seed yield (2.5–5.0 t ha^–1). Sowing too early (September) in colder inland areas risked exposure of the crop to vernalising temperatures, causing the crop to bolt to flower in summer, whereas all crops sown from mid-October remained vegetative through summer. Crop stands thinned by 20–30% during summer, and this was exacerbated by grazing, but surviving stands of ∼30 plants m^–2 were sufficient to support high yields. Grazing had no effect on grain yield at one site, but reduced yield by 0.5 t ha^–1 at a second site, although this was more than offset by the value of the grazed forage. The spring-sowing approach has potential to replace the existing forage rape–spring cereal sequence, or to add a further option to the existing autumn-sown winter canola in areas such as southern Victoria, where early autumn establishment can be problematic and spring-sown crops can better withstand pests and winter waterlogging, which limit yield of autumn-sown crops. Because these are the first known studies in Australia to investigate the use of spring-sown winter canola, further work is warranted to refine further the crop and grazing strategies to maximise productivity and profitability from this option.

Winter cropping in Western Australia (WA) is dominated by spring-type cereals and canola (Brassica napus L.) with no vernalisation requirement that are sown in late autumn (late April and May). With limited earlier sowing opportunities for later maturing winter-type crops in early autumn, farmers aiming to obtain some benefit from the grazing of crops (i.e. dual-purpose) must consider the grazing potential of spring types sown in late autumn. The aim of this study was to develop grazing guidelines for spring-type crops in WA that will limit the potential for grain yield losses. In order to determine the recovery response of spring-type crops to grazing intensity and timing, 59 time-of-cutting × height-of-cutting experiments were conducted throughout the south-western region of WA in 2012. Experiments were conducted on spring types of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), canola and oats (Avena sativa L.). Multi-site analysis showed that treatments simulating high-intensity ‘crash’ grazing to ground level or to a height of 5 cm reduced grain yield unless conducted early in vegetative growth before reproductive stages. Treatments simulating ‘clip’ grazing by removing only the top 5–10 cm of crop foliage reduced grain yield to a lesser extent than crash grazing, and in several instances could extend the safe cutting period past hollow stem (Zadoks growth stage 30) and/or the end of July for cereals, or past mid-July for spring canola, provided the developing reproductive parts of all crops were not damaged. On average, the amounts of biomass removed by clip grazing without yield penalty were 0.4, 0.3, 0.5 and 0.3 t ha^–1 for barley, wheat, oats and canola and were similar to those removed by earlier, safe crash grazing. These represent significant amounts of forage and suggest that clip grazing of spring-type crops may be an approach suited to WA cropping and grazing systems.

In mixed cropping and livestock dryland farming systems in southern Australia, grazing of cereals during their vegetative growth stages (typically during winter) can provide a valuable contribution of high-quality feed during a period of low pasture growth. This paper reports results from a series of experiments investigating the impact of defoliation on the grain production of cereals in the Eyre Peninsula region of South Australia. The comparative dry matter production and grain yield of wheat, barley and oats cultivars, with and without defoliation, at a range of growth stages were measured in four experiments over three growing seasons, two of which were water-deficient. The barley varieties evaluated produced up to twice the dry matter of the wheat or oats cultivars to the time of defoliation. Mowing following stem elongation more than halved grain yield (1.9 to 0.9 t ha^–1) relative to no defoliation in an early-maturing variety, but with less reduction in later maturing varieties. Defoliation before stem elongation in two seasons of very low growing-season rainfall (<100 mm) caused no or very little loss in grain yields, which were generally <1 t ha^–1. A long-season winter wheat produced similar grain yields irrespective of defoliation and timing, but with no yield advantage over the defoliated spring cereals. The results suggest opportunities to incorporate the grazing of cereals to fill a winter feed-gap in the low-rainfall zone of southern Australia.

In the Mallee region of north-western Victoria, Australia, there is very little grazing of crops that are intended for grain production. The success of dual-purpose crops in other regions in south-eastern Australia with higher and more evenly distributed rainfall has driven interest in assessing the performance of dual-purpose cereals in the region. Five experiments were established in five consecutive years (2009–13) in the southern Mallee to measure the forage production and grain yield and quality response in wheat and barley to grazing by sheep or mechanical defoliation. The first three experiments focused on spring cultivars sown from late April to June, and the last two on winter cultivars planted from late February to early March. Cereal crops provided early and nutritious feed for livestock, with earlier sowing increasing the amount of dry matter available for winter grazing, and barley consistently produced more dry matter at the time of grazing or defoliation than wheat. However, the grain-production response of cereals to grazing or defoliation was variable and unpredictable. Effects on yield varied from –0.7 to 0.6 t/ha, with most site × year × cultivar combinations neutral (23) or negative (14), and few positive (2). Changes in grain protein were generally consistent with yield dilution effects. Defoliation increased the percentage of screenings (grains passing a 2-mm sieve) in three of five experiments. Given the risk of reduced grain yield and quality found in this study, and the importance of grain income in determining farm profitability in the region, it is unlikely that dual-purpose use of current cereal cultivars will become widespread under existing grazing management guidelines for dual-purpose crops (i.e. that cereal crops can be safely grazed once anchored, until Zadoks growth stage Z30, without grain yield penalty). It was demonstrated that early-sown winter wheat cultivars could produce more dry matter for grazing (0.4–0.5 t/ha) than later sown spring wheat and barley cultivars popular in the region (0.03–0.21 t/ha), and development of regionally adapted winter cultivars may facilitate adoption of dual-purpose cereals on mixed farms.

Canola (Brassica napus L.) has recently been adopted as a dual-purpose crop (graze and grain) in the higher rainfall areas (>550 mm) of eastern Australia, but the feasibility in drier inland areas with a shorter growing season is uncertain. We modified the APSIM-Canola model by using observations from an irrigated grazing experiment, with the aim of using a simulation approach to investigate various aspects of dual-purpose canola production. Sowing opportunities, forage production for grazing and grain production were considered in the simulations, and effects of variables such as sowing date, cultivar type, plant density and nitrogen supply were investigated in simulations for 109 years of climate data from Wagga Wagga, NSW. APSIM-Canola predictions of vegetative growth and grain yield for recent varieties were inadequate when using existing parameters, but were improved by increasing the maximum leaf area parameter to reflect those of modern hybrid types. For grazed crops, APSIM-Canola overestimated the initial rate of regrowth, but accurately simulated biomass at flowering. Simulations of a range of management options to generate different pre-grazing biomass predicted that sowing before 15 May, using vigorous (hybrid) cultivars, high plant density (60–80 plants m^–2) and adequate soil nitrogen, maximised biomass production. Assuming a rainfall-based sowing opportunity of 25 mm over 3 days and a minimum pre-grazing biomass of 1000 kg ha^–1, grazing was possible in 53% of years, with 50% of those years providing grazing opportunities before 7 June at Wagga Wagga. Depending on stocking rate, crops could be grazed until early to mid-July, providing 400–1000 dry sheep equivalent days ha^–1 of grazing, and allow regrowth to achieve a target biomass of 5000 kg ha^–1 at flowering, which was required to maximise potential yield. The simulation analysis confirms significant opportunities to achieve valuable livestock grazing from canola crops sown in an early window (before May) without compromising potential yield, and the simulation framework developed can be readily applied to other regions.

Interest is growing in the potential to expand cropping into Australia’s high-rainfall zone (HRZ). Dual-purpose crops are suited to the longer growing seasons in these environments to provide both early grazing for livestock and later regrow to produce grain. Grain yield and grazing potential of wheats of four different maturity types were simulated over 50 years at 13 locations across Australia’s HRZ, and sowing date, nitrogen (N) availability and crop density effects were explored. Potential grazing days on wheat were obtained by simulating sheep grazing crops to Zadoks growth stage Z30 at 25 dry sheep equivalents (DSE)/ha. Optimal sowing dates for each maturity type at each location were matched to the flowering window during which risk of frost and heat stress was lowest. Overall, we found significant national potential for dual-purpose use of winter wheat cultivars across Australia’s HRZ, with opportunities identified in all regions. Simulated mean wheat yields exceeded 6 t/ha at most locations, with highest mean grain yields (8–10 t/ha) in southern Victoria, and lower yields (5–7 t/ha) in the south-west of Western Australia (WA) and central and northern New South Wales (NSW). Highest grazing days were from winter cultivars sown early (March–mid-April), which could provide 1700–3000 DSE-days/ha of grazing across HRZ locations; this was 2–3 times higher than could be obtained from grazing spring cultivars (200–800 DSE-days/ha). Sowing date was critical to maximise both grazing and grain yield potential from winter cultivars; each 1-week delay in sowing after 8 March reduced grazing by 200–250 DSE-days/ha and grain yield by 0.45 t/ha. However, in Mediterranean climates, a lower frequency of early sowing opportunities before mid-April (<30% of years) is likely to limit the potential to use winter cultivars. Prospects to graze shorter season spring cultivars that fit later sowing windows require further examination in south-west WA, the slopes of NSW and southern Queensland.

Recent expansion of cropping into Australia’s high-rainfall zone (HRZ) has involved dual-purpose crops suited to long growing seasons that produce both forage and grain. Early adoption of dual-purpose cropping involved cereals; however, dual-purpose canola (Brassica napus) can provide grazing and grain and a break crop for cereals and grass-based pastures. Grain yield and grazing potential of canola (up until bud-visible stage) were simulated, using APSIM, for four canola cultivars at 13 locations across Australia’s HRZ over 50 years. The influence of sowing date (2-weekly sowing dates from early March to late June), nitrogen (N) availability at sowing (50, 150 and 250 kg N/ha), and crop density (20, 40, 60, 80 plants/m²) on forage and grain production was explored in a factorial combination with the four canola cultivars. The cultivars represented winter, winter × spring intermediate, slow spring, and fast spring cultivars, which differed in response to vernalisation and photoperiod.

Overall, there was significant potential for dual-purpose use of winter and winter × spring cultivars in all regions across Australia’s HRZ. Mean simulated potential yields exceeded 4.0 t/ha at most locations, with highest mean simulated grain yields (4.5–5.0 t/ha) in southern Victoria and lower yields (3.3–4.0 t/ha) in central and northern New South Wales. Winter cultivars sown early (March–mid-April) provided most forage (>2000 dry sheep equivalent (DSE) grazing days/ha) at most locations because of the extended vegetative stage linked to the high vernalisation requirement. At locations with Mediterranean climates, the low frequency (<30% of years) of early sowing opportunities before mid-April limited the utility of winter cultivars. Winter × spring cultivars (not yet commercially available), which have an intermediate phenology, had a longer, more reliable sowing window, high grazing potential (up to 1800 DSE-days/ha) and high grain-yield potential. Spring cultivars provided less, but had commercially useful grazing opportunities (300–700 DSE-days/ha) and similar yields to early-sown cultivars. Significant unrealised potential for dual-purpose canola crops of winter × spring and slow spring cultivars was suggested in the south-west of Western Australia, on the Northern Tablelands and Slopes of New South Wales and in southern Queensland. The simulations emphasised the importance of early sowing, adequate N supply and sowing density to maximise grazing potential from dual-purpose crops.

The development of guidelines for successful dual-purpose (graze and grain) use of wheat and canola in Australia’s high-rainfall zones (HRZ) has mostly emerged from separate wheat- and canola-focused research. Less attention has been placed on the benefits of integrating dual-purpose wheat and canola into pasture-based grazing enterprises. We conducted a farming systems experiment during 2010–11 to evaluate the benefits of integrating wheat and canola as dual-purpose crops into a pasture-based grazing system in Australia’s south-eastern tablelands. We compared forage production and grain yield in three separate crop–livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these. Initial growth rates were higher in early-autumn-sown canola than wheat in 2010, but were much lower although similar in both crops in 2011. Significant forage was available from both canola (3.1–3.4 t ha^–1) and wheat (2.3–2.4 t ha^–1) at the onset of grazing, but winter growth rates of wheat were higher than those of canola, leading to increased sheep grazing days (SGD). In the favourable 2010 season, dual-purpose wheat and canola separately provided 2393 and 2095 SGD ha^–1, and yielded 5.0 and 1.9 t ha^–1 grain, respectively, with an apparent nitrogen limitation in canola. In the drier season of 2011, grazing was reduced to 1455 and 735 SGD ha^–1 in wheat and canola, respectively. Wheat yield was reduced from 5.9 to 5.4 t ha^–1 grain by grazing, whereas canola yield was unaffected (3.6 t ha^–1). In both years, grazing did not affect harvest index or oil content of canola, but harvest index was higher in grazed wheat crops. The yield of wheat and canola crops grazed in sequence did not differ from yield in treatments where animals grazed only a single crop, but the total overall grazing window when crops were grazed sequentially increased by 1054 and 618 SGD ha^–1 in wheat, and by 1352 and 1338 SGD ha^–1 in canola in 2010 and 2011, respectively. The major benefits of including crops that can be grazed sequentially were the widening of the grazing window and other operational windows (sowing, harvest), along with the rotational benefits for wheat by including canola in the system. Additional benefits to pastures may include eliminating the need to re-sow, because a more productive pasture composition is maintained under lower grazing pressure while stock are on crops, and reduced weed invasion. The commercial availability of new, herbicide-tolerant winter canola varieties provides significant opportunities to underpin the performance of dual-purpose crop sequences on mixed farms in the high-rainfall zone.

In south-eastern Australia, low winter temperatures often reduce pasture growth and thus winter herbage supply relative to livestock requirements. Grazing of vegetative grain crops in winter is one strategy that might overcome this feed gap. In a study with young sheep over two seasons near Canberra, ACT, we compared pasture-only grazing with three separate crop–livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these, for intervals over the period May–August. We measured forage biomass, sheep grazing days (SGD) and liveweight accumulated per ha. Crop-grazing treatments resulted in much more winter forage for grazing sheep (t DM ha^–1): in 2010, one crop 2.5–3.0, two crops 3.5 v. pasture only 1; in 2011, one crop 2, two crops 3 v. pasture only 1.4. In the first season, grazing one crop resulted in ∼2000 extra SGD ha^–1 and the accumulation of more liveweight per ha than in the pasture-only treatment; grazing of two crops resulted in >3500 extra SGD ha^–1. Equivalent values in the second, drier season were: one crop, ∼1000 extra SGD ha^–1; two crops, 2600 extra SGD ha^–1. Spelling of pastures during crop grazing led to extra pasture growth, such that in each of the two seasons, 40% of the total benefit in extra SGD per ha came from the extra pasture.

The results indicate that, like grazed wheat, grazed canola can provide valuable winter forage, especially when used together with wheat. The data also provide the first quantification of the effect of crop grazing on pasture spelling and subsequent pasture supply, and suggest value in the incorporation of grazing wheat and canola into grazing systems in the high-rainfall zone.

Dual-purpose crops can provide valuable winter forage in livestock production systems and increase subsequent pasture availability. Using experimental measurements of sheep grazing on pasture only or dual-purpose crops of wheat, canola, and wheat and canola in combination, and their associated effects on subsequent pasture grazing, we estimated for two different years the whole-farm changes in whole-farm sheep grazing days (SGD), relative farm production and farm economic impact. The increased winter feed supply and higher grazing intensity on dual-purpose crops allowed 2–3 times the area of pasture to be spelled, which together enabled increases in potential year-round pasture stocking rate. Up to 20% of farm area could be allocated to dual-purpose crops while still obtaining the same number of SGD per farm ha with additional grain production (5.0–5.4 t wheat ha^–1 and 1.9–3.6 t canola ha^–1) adding significantly to farm profitability and production. Allocating 10–20% of the farm to a combination of dual-purpose wheat and canola grazed in sequence could increase whole-farm SGD by 10–15%, increase farm output by >25% and increase estimated farm profit margin by >AU$150 farm ha^–1 compared with pasture-only livestock systems. The long crop-grazing period from wheat and canola in combination providing a large pasture-spelling benefit was a key factor enabling these economic and productivity increases. Introducing wheat or canola alone on up to 30% of the farm is likely to reduce SGD per farm ha, but still significantly increase whole-farm productivity (10–20%) and estimated profit margin ($50–100 farm ha^–1). Over the two very different experimental growing seasons, the estimated relative changes in whole-farm productivity and estimated profit margin were similar, indicating that these benefits are likely to be consistent over a range of years. Together, these findings suggest that once whole-farm livestock feed-base effects are considered, large economic and productivity benefits can be attributed to dual-purpose crops when integrated into livestock production systems in Australia’s southern high-rainfall zone.

In Mediterranean-type environments, livestock productivity in mixed livestock and cropping enterprises often is limited by a period of feed scarcity that extends from late autumn, when dry residues of crops and pastures from the previous growing season are being exhausted, through to early winter when green feed is just commencing. Dual-purpose crops have been developed as a source of winter green feed, while still being a source of grain at harvest. These crops increase feed availability and boost livestock productivity. This study evaluates the role and value of dual-purpose wheat and canola crops, in combination with lucerne, in mixed-enterprise farming systems that experience a Mediterranean-type climate. Using bioeconomic modelling, the value of dual-purpose crops is assessed under a range of yield, price and technical assumptions. For an Australian study region, the robust finding is that the joint inclusion of dual-purpose crops and lucerne greatly increases the farming-system profits. Under standard assumptions when the farming system is operated to maximise profit, farm profit increases by AU$68 000 (or 88% over the base case) following the inclusion of both dual-purpose wheat and canola. The increase in profit is attributable to wool and sheep sales rising by 261%, yet the proportions of crop and pasture remain similar with or without the dual-purpose crops. Importantly, the proportion of the pasture area that is lucerne greatly increases to complement the increase in feed availability generated by the dual-purpose crops. The resultant large increase in feed availability in winter and summer allows the stocking rate to increase so sheep numbers and sheep turn-off become the main source of the increase in profit. Sensitivity analysis shows that even with significant commodity price fluctuations and further reduction in grain yield caused by grazing, and exclusion of lucerne, inclusion of dual-purpose crops in these farming systems still increases farm profit.

Grazing sheep on cereal crops in winter has become widely adopted in medium–high-rainfall zones of Australia. Interest in this practice has spread to the lower rainfall parts of the cereal–livestock zone where it is being applied to shorter season crop varieties. A farm-system modelling study was conducted to investigate the value of deferment of annual pastures by grazing spring wheat in their place. The biophysical simulation model, based on a representative wheat and sheep farming system in the wheatbelt of Western Australia, involved two grazing-management scenarios and used climate data for the period 1962–2011 for three locations in Western Australia representing low-, medium- and high-rainfall cropping regions: Merredin, Wickepin and Kojonup. The grazing-management policy of the main scenario, ‘crop grazing’, placed livestock on the crops only until the crop reached Zadoks growth stage 30, provided the green biomass of the farm’s annual pastures was <800 kg/ha. A second ‘shadow-grazing’ scenario was run in which a group of ewes identical to the main ewe flock was used to graze annual pastures simultaneously with the main ewe flock whenever the main flock grazed wheat crops. The difference between the two scenarios represented the pasture deferment value associated with grazing wheat crops.

Pasture deferment had little effect on total pasture production during the period when crops were grazed. However, there was a small benefit to feed supply through the accumulation of pasture during the period of crop grazing. This feed was available at a time of year when feed is scarce. This was reflected in improved animal production, with the weight of lambs at weaning being higher in the crop-grazing scenario than the shadow-grazing scenario. These results suggest that although increases in pasture productivity and feed supply associated with spring crop grazing are only marginal, grazing of spring wheat crops can still lead to changes in lamb production because this enterprise is sensitive to the feed supply in winter.