Perry Poulton

Re-inventing model-based decision support with Australian dryland farmers. 4. Yield Prophet® helps farmers monitor and manage crops in a variable climate.

In Australia, a land subject to high annual variation in grain yields, farmers find it challenging to adjust crop production inputs to yield prospects. Scientists have responded to this problem by developing Decision Support Systems, yet the scientists’ enthusiasm for developing these tools has not been reciprocated by farm managers or their advisers, who mostly continue to avoid their use. Preceding papers in this series described the FARMSCAPE intervention: a new paradigm for decision support that had significant effects on farmers and their advisers. These effects were achieved in large measure because of the intensive effort which scientists invested in engaging with their clients. However, such intensive effort is time consuming and economically unsustainable and there remained a need for a more cost-effective tool. In this paper, we report on the evolution, structure, and performance of Yield Prophet®: an internet service designed to move on from the FARMSCAPE model to a less intensive, yet high quality, service to reduce farmer uncertainty about yield prospects and the potential effects of alternative management practices on crop production and income. Compared with conventional Decision Support Systems, Yield Prophet offers flexibility in problem definition and allows farmers to more realistically specify the problems in their fields. Yield Prophet also uniquely provides a means for virtual monitoring of the progress of a crop throughout the season. This is particularly important for in-season decision support and for frequent reviewing, in real time, of the consequences of past decisions and past events on likely future outcomes. The Yield Prophet approach to decision support is consistent with two important, but often ignored, lessons from decision science: that managers make their decisions by satisficing rather than optimising and that managers’ fluid approach to decision making requires ongoing monitoring of the consequences of past decisions.

Re-inventing model-based decision support with Australian dryland farmers. 3. Relevance of APSIM to commercial crops

Crop simulation models relevant to real-world agriculture have been a rationale for model development over many years. However, as crop models are generally developed and tested against experimental data and with large systematic gaps often reported between experimental and farmer yields, the relevance of simulated yields to the commercial yields of field crops may be questioned. This is the third paper in a series which describes a substantial effort to deliver model-based decision support to Australian farmers. First, the performance of the cropping systems simulator, APSIM, in simulating commercial crop yields is reported across a range of field crops and agricultural regions. Second, how APSIM is used in gaining farmer credibility for their planning and decision making is described using actual case studies. Information was collated on APSIM performance in simulating the yields of over 700 commercial crops of barley, canola, chickpea, cotton, maize, mungbean, sorghum, sugarcane, and wheat monitored over the period 1992 to 2007 in all cropping regions of Australia. This evidence indicated that APSIM can predict the performance of commercial crops at a level close to that reported for its performance against experimental yields. Importantly, an essential requirement for simulating commercial yields across the Australian dryland cropping regions is to accurately describe the resources available to the crop being simulated, particularly soil water and nitrogen. Five case studies of using APSIM with farmers are described in order to demonstrate how model credibility was gained in the context of each circumstance. The proposed process for creating mutual understanding and credibility involved dealing with immediate questions of the involved farmers, contextualising the simulations to the specific situation in question, providing simulation outputs in an iterative process, and together reviewing the ensuing seasonal results against provided simulations. This paper is distinct from many other reports testing the performance and utility of cropping systems models. Here, the measured yields are from commercial crops not experimental plots and the described applications were from real-life situations identified by farmers. A key conclusion, from 17 years of effort, is the proven ability of APSIM to simulate yields from commercial crops provided soil properties are well characterised. Thus, the ambition of models being relevant to real-world agriculture is indeed attainable, at least in situations where biotic stresses are manageable.

A framework for simulating agroforestry options for the low rainfall areas of Australia using APSIM

The long-term benefits of retaining or planting trees on farms to rehabilitate land and protect the soil from erosion or salinity problems has to be traded off against the impact of tree competition on commercial crops, especially in the medium to low rainfall regions of Australia. The incentive to plant trees would increase if tree competition could be offset by economic returns gained from farm forestry products and by the beneficial impacts of tree windbreaks on crop yields and resource sustainability. The Agricultural Production Systems Simulator (APSIM) has a well-established capability to simulate cropping systems and this paper reports on progress in applying APSIM to agroforestry systems in order to quantify the potential benefits and risks of planting trees as windbreaks to cropping land in Australia. A simple case study indicating one possible model configuration is used to demonstrate this emergent capability for simulating tree and crop productivity and their interactions. The simulated agroforestry system consisted of the growth of a belt of trees (Eucalyptus argophloia) positioned as a windbreak on the edge of a field where a crop of winter chickpea (Cicer arietinum L.) is grown over a 30-year period. The example simulations quantify the yield and economic returns of annual chickpea crops in addition to the discounted economic return from timber production after 30 years of tree growth. This example demonstrates how APSIM can be used to quantify the economic tradeoffs in planting trees as windbreaks on a commercial farm in a low rainfall region of Australia.

Regional differences in tree–crop competition due to soil, climate and management

Large areas of trees are being planted in Australian agricultural lands for a range of environmental, ecological and economic reasons. In the medium to low rainfall zones, these plantings can negatively impact upon adjacent agricultural production through competition for soil moisture. The nature of the tree–crop competition zone and the means of managing it have been studied in the main southern cropping zones. However, the differences in soil, climate and agronomic systems in Australia’s northern dryland cropping zones could lead to differences in the competition processes and the management options needed to minimise them. In this study, the competition for soil moisture and resultant impacts on crop production were studied for a Eucalyptus argophloia windbreak on a farm near Warra, Queensland (26.93°S, 150.93°E). The results indicate well defined inner and outer competition zones, the extents of which agree with those found elsewhere in Australia and overseas. However, while the extent of the competition is comparable with other regions, local agronomic practices developed for variable climatic conditions and deep clay soils allow trees to extract soil water stored during fallow periods resulting in relatively higher production losses.

A farm-scale, bio-economic model for assessing investments in recycled water for irrigation

Demand for water in Australia is increasing along with growing pressure to maximise the efficiency of irrigation water use and seek additional and alternative irrigation supplies. The scarcity of water supplies coupled with the need for urban communities to dispose of large quantities of treated recycled water from sewage treatment plants has led to increasing interest from urban and rural communities in the reticulation of this water for irrigating adjacent crop-production areas. Proposals to use recycled water inevitably lead to a complex range of issues that need to be addressed, including: • costs and benefits of supplying an additional source of water to current or new cropping systems; • optimum irrigation design and management, particularly where there are multiple sources of irrigation water; • management of overflow from on-farm water storages; and • environmental implications with regard to salinity, runoff, drainage, nitrate leaching, and environmental flows. Simulation models can capture many of the key factors and processes influencing irrigated crop production systems, and can play a useful role in exploring these issues. In this paper, we have described an approach that couples agricultural production system and economic models in a way that enables analysis of the likely benefits and risks of investing in recycled water, although the analysis is equally relevant to any assessment of the value of an additional source of irrigation water, particularly saline water. The approach has been illustrated with a case study of a mixed-crop farm in the Darling Downs region of Queensland, Australia, in which the farm-scale crop production, economic, and environmental implications of investing in recycled water were considered.

Second harvest-is there sufficient stubble for biofuel production in Australia?

Identifying the location and amount of grain crop residues (stubble) in Australia is necessary for determining the viability of potential biofuel plant locations. We combined 22 years of crop statistics with harvest indices and land use to arrive at spatially explicit stubble productivity figures. Stubble quantities using different focal radii and from different seasons provide an insight into the feasibility of its use for bioenergy. We focus on areas where the stubble concentrations within a 50 km radius were at least 500 kt per year; the amount suggested for a viable lignocellolosic bioethanol facility. The outcome of this study has been to show, for the first time, where there are large amounts of stubble in Australia. Whether the supply of stubble is sufficiently constant over time and indeed available at a price that is economic for a biofuel plant must be subject to future work.

Use of simulation in assessing cropping system strategies for minimising salinity risk in brigalow landscapes

Areas of brigalow (Acacia harpophylla) dominated landscapes in north-eastern Australia have declined drastically due to major clearing and agricultural expansion during the late 1940s and early 1960s. The inherently high salt content of the soils of this region present a potential downstream salinity hazard from groundwater recharge. Chronosequence analysis using paired chloride profiles from soil cores taken beneath brigalow remnants and adjacent pasture or cropping lands provide a tracer for quantifying historic recharge rates as a consequence of vegetation management and agricultural practice. Present day chloride levels are the direct result of past land management. In this paper we present the results of simulation studies used to benchmark historic management practice since clearing in terms of chloride leaching and drainage. These simulations estimated that 15.3 t/ha of chloride leached from the top 150 cm in 7 major drainage events (>15 mm) over a 34-year period, and that these leaching events corresponded with peaks in rainfall cycles. Use of virtual experiments to investigate alternative cropping systems found significant increases in the frequency and magnitude of drainage events of no-tillage wheat compared with sorghum grown in a summer-rainfall region. Systems simulation can provide guidelines for designing cropping systems which best balance production with drainage objectives in dryland farming systems.

Design and evaluation of an irrigation system for creating water gradients under an automatic rain shelter.

SummaryThis paper reports on the design and performance of an irrigation system associated with a rain shelter. The shelter is used in the closed position as a platform for multiple spray lines. This system automatically supplies, at a specified time, water of specified depth and delivery rate, either uniformly or on a specified gradient across the sheltered area. Variations in crop water deficits and yields have conformed closely to imposed water gradients.

A Method for comprehensively Assessing Economic Trade-Offs of New Irrigation Developments

To meet the anticipated increase in global demand for food and fibre products, large areas of land around the world are being cleared and infrastructure constructed to enable irrigation, referred to herein as ‘greenfield irrigation’. One of the challenges in assessing the profitability of a greenfield irrigation development is understanding the impact of variability in climate and water availability and the trade-offs with scheme size, cost and the sensitivity of crop yield to water stress. For example, is it more profitable to irrigate a small area of land most years or a large area once every few years? And, is it more profitable to partially or fully water the crop? This paper presents a new method for efficiently linking a river system model and an agricultural production model to explore the financial trade-offs of different management choices, thereby enabling the optimal scheme area and most appropriate level of farmer risk to be identified. The method is demonstrated for a hypothetical but plausible greenfield irrigation development based around a large dam in the Flinders catchment, northern Australia. It was found that a dam and irrigation development paid for and operated by the same entity is not, under the conditions examined in this analysis, economically sustainable. The method could also be used to explore the impact of different management strategies on the agricultural production and profitability of existing irrigation schemes within a whole of river system context.