Roger Lawes

Determinants of the proportion of break crops on Western Australian broadacre farms

Break crops (e.g. pulses, lupins, canola, oats) underpin the continued profitability of cereal (wheat or barley) based cropping sequences. The area sown on farms to break crops varies widely across geographical regions according to climate, soil type mix, enterprise mix (crop v. livestock), and other constraints such as the prevalence of soil-borne disease. Given recent fluctuations in the area of established break crops in Western Australia, there are concerns about their long-term prospects in the farming system. A survey of the area and grain yield of break crops on-farm was combined with whole-farm bio-economic modelling to determine the upper limit to the area of break crops on representative farms in 4 agro-climatic regions. Sensitivity analysis was conducted to ascertain the potential effects of varying commodity prices (sheep and grain), costs of production, and assumptions on the yield of break crops and the boost to the yield of following cereals. The survey revealed that the two dominant break crops, lupins and canola, occupied 8–12% and 8–9%, respectively, of farm area on those farms that grew them in the medium-rainfall zone and this declined to 6–8% and 7–10% in the drier region. Nevertheless, the modelling results show that break crops are an important component of the farming system, even where the area is small, and the response of whole-farm profit to percent of the farm allocated to break crops is relatively flat near the optimum of 23–38%. The modelled area of break crops at maximum profit is higher than that found in farm surveys. The discrepancy could possibly be explained by the lower break crop yields realised by farmers and a reduced boost to cereal yields following break crops than assumed in models. Also, deterministic models do not account for risk, which is an important consideration in the decision to grow break crops. However, the yield difference does not explain the discrepancy entirely and raises questions about farmer motivations for adoption of break crops. The scope for increased area of break crops beyond 23–38% of the farm is limited, even with increases in the yield enhancements in subsequent cereal crops, higher break crop prices, and higher fertiliser costs. Further research is required to better quantify costs and benefits of break crops in Western Australian farming systems.

Seeking simultaneous improvements in farm profit and natural resource indicators: a modelling analysis

Natural resource indicators are used by catchment management organisations as targets for land use management. However, the nature of the trade-off function between natural resource management (NRM) outcomes and whole-farm profit is ill-defined, and varies between regions and according to the particular NRM indicator considered. Defining this function will assist catchment management organisations and farmers to evaluate the achievability of particular targets, and help determine the size of economic incentives required to offset any expected loss in farm profit associated with meeting targets. We addressed this issue by modelling representative farm businesses in two mixed farming regions (southern New South Wales and the central wheatbelt of Western Australia). The Agricultural Production Systems Simulator (APSIM) and GRAZPLAN farming systems models were linked and used to generate values of four NRM indicators (water leakage, nitrate leaching, groundcover and soil organic carbon change) for a wide range of crop–pasture rotations. The NRM indicator values were then incorporated into the Model of an Integrated Dryland System (MIDAS) whole-farm economic model to define the relationship with farm profit and farm cropping percentage. For some circumstances and indicators, the resulting trade-off functions were relatively flat; a wide range of enterprise mixes can lead to the same NRM outcomes but significant gains in the indicators may not be possible using current rotation options. For others, significant improvements could be achieved but at a substantial loss in whole-farm profit (through the selection of less profitable rotations). There were also examples where simultaneous gains in indicators and farm profit were possible. This analysis demonstrates an approach by which biophysical simulation models of the farming system can be linked to linear-programming representations of farming enterprises, and provides a method for deriving relationships between NRM targets and economic performance.

Evaluation of the Australian Branched Broomrape (Orobanche ramosa) Eradication Program

Abstract Because weed eradication programs commonly take 10 or more years to complete, there is a need to evaluate progress toward the eradication objective. We present a simple model, based on information that is readily obtainable, that assesses conformity to the delimitation and extirpation criteria for eradication. It is applied to the program currently targeting the annual parasitic weed, branched broomrape, in South Australia. The model consists of delimitation and extirpation (E) measures plotted against each other to form an ‘eradograph.’ Deviations from the ‘ideal’ eradograph plot can inform tactical responses, e.g., increases in survey and/or control effort. Infestations progress from the active phase to the monitoring phase when no plants have been detected for at least 12 mo. They revert to the active phase upon further detection of plants. We summarize this process for the invasion as a whole in a state-and-transition model. Using this model we demonstrate that the invasion is unlikely to be delimited unless the amount of newly detected infested area decreases, on average, by at least 50% per annum. As a result of control activities implemented, on average approximately 70% (range, 44 to 86%) of active infestations progressed to the monitoring phase in the year following their detection. Simulations suggest that increasing this rate of transition will not increase E to a significant extent. The rate of reversion of infestations from the monitoring phase to the active phase decreased logarithmically with time since last detection, but it is likely that lower rates of reversion would accelerate the trend toward extirpation. Program performance with respect to the delimitation criterion has been variable; performance with respect to the extirpation criterion would be improved considerably by the development and application of cost-effective methods for eliminating branched broomrape soil seed populations. Nomenclature: branched broomrape, Orobanche ramosa L. ORARA

The Land Use Sequence Optimiser (LUSO): A theoretical framework for analysing crop sequences in response to nitrogen, disease and weed populations

The break crop effect, where a non-cereal crop provides relief from soil pathogens, may increase soil nitrogen reserves for a cereal and help minimise populations of herbicide resistant weeds. It is widely used in agriculture to maximise the economic return and yield of cereal crops. In Western Australia, cereal crops are being grown with increasing frequency, at the expense of less profitable break crops and we have developed a land use sequence optimiser (LUSO) to analyse strategic break crop decisions across a suite of price, yield, nitrogen fertiliser cost, soil borne disease load and weed load thresholds. The model is flexible and can easily be parameterised for a wide range of economic, edaphic and biotic parameters. We demonstrate its use in a strategic sense to determine economic and biotic thresholds that force a rotation change in a typical Western Australian cropping system.

Sacrificial grazing of wheat crops: identifying tactics and opportunities in Western Australia’s grainbelt using simulation approaches

Failing grain crops are sometimes sacrificed for grazing by mixed farmers, a decision involving a complex range of factors. This simulation study used two APSIM (Agricultural Production Systems Simulator)-based approaches to investigate the circumstances under which more revenue might be obtained by sacrificing a wheat crop for grazing rather than harvesting it for grain in Western Australia’s grainbelt. First, we developed a simple partial budget calculation to estimate and compare revenue from grain or grazing alternatives using data for grain yield and standing biomass at flowering. This was simulated for a factorial of soil types and locations varying in mean annual rainfall. We then simulated wheat quality and livestock production on spring wheat grazed at different stages of crop development and at a range of stocking rates. Dynamic simulations of grazing showed that livestock production increased as grazing was delayed; stocking rate had little impact at this time. Grazing earlier necessitated lighter stocking rates but surprisingly had little benefit for animal performance. Partial budgets showed that under average commodity prices, grazing a wheat crop could be more profitable 40–75% of the time on poorer soil types in lower rainfall environments. In these situations, by tactically grazing when grain yield is below a critical level economic returns could be increased by more than A

Pasture cropping with C4 grasses in a barley-lupin rotation can increase production

50/ha in 30–40% of years and over the long term average revenues could be increased by A

Comparing agglomerative clustering and three weed classification frameworks to assess the invasiveness of alien species across spatial scales.

30/ha.year. This critical grain yield ranged from 1.3 to 1.7 t/ha on shallow gravel soil and 1.9 to 2.2 t/ha on a deep sand. In higher rainfall environments and on better soil types grazing was rarely a better option unless livestock prices were high relative to grain. This approach, combining crop simulation with partial budgets, was useful for developing simple management rules for a complex system. Overall, the findings of this study suggest that making tactical use of a wheat crop for forage in situations with low grain yield prospects is a major opportunity to increase profitability and help respond to climate variability in mixed farms in many areas of the Western Australian wheatbelt.

Dynamic crop sequencing in Western Australian cropping systems

Abstract. In southern Australia, intercropping, pasture cropping and overcropping have evolved as techniques to address environmental problems such as dryland salinity and wind erosion and to utilise soil water outside the conventional winter-dominant growing season. We paired three winter-dormant pastures, including two subtropical C4 perennial species (Rhodes grass, Chloris gayana; Gatton panic, Megathyrsus maximus) and the summer-active perennial C3 legume siratro (Macroptilium atropurpureum), with a conventional barley (Hordeum vulgare)–lupin (Lupinus angustifolius) rotation to explore the extent to which different summer-active species reduced crop yields. We also examined whether the competition for resources could be altered by supplying increased nitrogen to the crop and changing the row spacing of the pasture. Under high-input conditions, pasture reduced cereal crop yields by up to 26% and lupin yields by up to 29%. Under low-input conditions, pasture cropping did not significantly reduce crop yield, and frequently increased crop yields. With low inputs, barley yield increases in 2011 ranged from 23% to 31%. In lupins under low-input conditions, yield increases ranged from 91% to 106% in 2010 and from –6% to +39% in 2012. The impact of the crop on the pasture was less pronounced, where the timing of pasture growth was delayed by the crop, but absolute levels of production were not influenced by the crop. Row spacing altered the temporal dynamic of pasture production; initially, the pasture produced less than the narrow spaced equivalent, but after 2 years, production exceeded that in the narrow row. Across all pasture species in 2009 and 2012, winter pasture production reduced crop yield by 0.32 and 0.4 t grain/ha pasture biomass produced, implying that moderate yield losses occurred because pasture production was also moderate. In the other two years, winter pasture production did not affect crop yield, suggesting that the pasture was able to utilise resources surplus to crop requirements. In this environment, with this combination of crops and summer-active pastures, higher levels of inputs did not enhance crop yield in a pasture-cropping system. We suggest that grain yield losses are lower in the low-input system and this implies that, at some level, competition between the species was reduced in a nitrogen-limited environment and the extent of the competition depended on season.

Evaluating the contribution of take-all control to the break-crop effect in wheat

ABSTRACT To prioritize weed management at the catchment scale, information is required on the species present, their relatively frequency, abundance, and likely spread and impact. The objective of this study was to classify the invasiveness of alien species that have invaded the Upper Burdekin Catchment in Queensland, Australia, at three spatial scales. A combination of three published weed classification frameworks and multivariate techniques were employed to classify species based on their frequency and cover at a range of spatial scales. We surveyed the Upper Burdekin Catchment for alien species, and for each species determined the following distribution indices — site frequency, total cover, transect frequency per site frequency and quadrat frequency per site frequency, cover per quadrat when present, cover per transect when present, and cover per site when present. These indices capture the effect of species abundance and frequency between sites (site frequency and total cover), within sites (transect frequency per site and cover per transect when present), and within transects (quadrat frequency per site frequency and cover per site). They were used to classify the species into seven groups using a hierarchical cluster analysis. The relationship between the indices was explored to determine how effective the small scale, site‐specific indices were at predicting the broader, landscape‐scale patterns. Strong correlations were observed between transect frequency per site and frequency (r 2 = 0.89) and cover per transect when present and total cover (r 2 = 0.62). This suggests that if a weed is abundant at the site level, it has the potential to occupy large areas of the catchment. The species groupings derived from the application of the three published weed classification frameworks were compared graphically to the groupings derived from the cluster analysis. One of the frameworks classified species into three groups. The other two frameworks classified species into four groups. There was a high degree of subjectivity in applying the frameworks to the survey data. Some of the data were of no relevance to the classification frameworks and were therefore ignored. We suggest that the weed classification frameworks should be used in conjunction with existing multivariate techniques to ensure that classifications capture important natural variations in observed data that may reflect invasion processes. The combined use of the frameworks and multivariate techniques enabled us to aggregate species into categories appropriate for management.

Capturing the in-field spatial-temporal dynamic of yield variation

Abstract. During the last two decades in Western Australia, the traditional mixed farming system has been increasingly displaced by intensive crop sequences dominated by wheat. Intensive wheat sequences are usually maintained by using suitable breaks, including pasture, fallow, or alternative cereal, oilseed and legume crops, to control weeds and disease, or maintain the supply of nitrogen to crops. New cereal fungicide options may also assist to maintain intensive cereal systems by suppressing soilborne cereal diseases. To guide the successful diversification of intensive cereal systems, we evaluated the effect of a 2-year experimental matrix of 10 different sequence options. Wheat in the sequence was treated with the fluquinconazole fungicide Jockey (wheat + J) to control soilborne pathogens, or with the usual seed dressing of flutriafol fungicide (wheat – J), used for control of bunts and smuts only. The sequences were wheat + J, wheat – J, barley, grain oats, oaten hay, canola, lupin, field pea, oat–vetch green manure, bare fallow) in which all treatment combinations were grown in year 2 following the same 10 treatments in year 1. In year 3, wheat + J was grown across the entire area as the test crop. In year 2, grain yields of all crops were reduced when crops were grown on their own residues, including wheat (22% reduction), canola (46%), lupin (40%) and field pea (51%). Wheat + J significantly outyielded wheat – J by 300 kg ha–1 in year 1 (14% increase) and 535 kg ha–1 in year 2 (26% increase). Wheat + J was more responsive to break crops than wheat – J in both year 1 and year 2. Break crops sown in year 1, such as canola, fallow, field pea, lupin and oaten hay, continued to have a positive effect on year 3 wheat + J yields. This study has highlighted the importance of break crops to following cereal crops, and provided an example in which a seed-dressing fungicide fluquinconazole in the presence of low levels of disease consistently improved wheat yields.