Success of diagnostic approach to rainfed, wheat-based cropping systems in Western Australia

• Underperforming paddocks is a common problem of cropping systems worldwide.
• We experimentally tested the diagnostic approach in two rainfed cropping systems.
• The success was often contingent on the interactions among remedial treatments.
• We suggest the development of a constraint prioritisation decision tool.
• The tool must consider hierarchy of constraints and temporal consequences of the respective remedial treatments.

Deterioration of crop yields due to exploitive cropping systems (CS) is a worldwide problem reducing profitability for farmers, food availability for consumers and inducing poor utilisation of rainfall. Following a diagnostic approach, likely constraints were identified and corresponding remedies tested in factorial experiments over three years at two sites in the central grain belt of Western Australia. The constraints at the first site (York, sandy clay loam soil) were high cereal cyst nematode (CCN), low cation exchange capacity (CEC) and soil compaction; and the remedies tested were CCN resistant cultivar, green manuring and deep ripping (DR). The constraints at the second site (Beverley, leaching prone sandy duplex soil) were high weed burden (ryegrass, Lolium rigidum L.), soil compaction, low pH and low CEC; and the remedies tested were repeated hay crops, deep ripping including lime application, and green manuring. Nitrogen applications on the cereal crops were split between sowing and after heavy rainfall events at the Beverley site.The crop and variety choice was important at both sites, deep ripping was sometimes useful at Beverley but clearly detrimental at York. CEC was not increased using green manuring. Tactical N showed potential at the leaching site at Beverley where it often assisted in reducing the weed burden. We infer that a diagnostic approach can be successfully used to increase grain yield once constraints have been diagnosed and addressed. Constraints to yield at these sites were related and often interactive implying that addressing only one limiting factor may not be effective in improving yield in the short term. We found that the solution to CS problems can sometimes be as simple as variety replacement (for example, CCN resistant cultivar at York) but can often be complex as seen at the Beverley site.It is concluded that where cropping systems in rainfed areas are not producing yields that approach the limits set by the rainfall, there is a need to devise a system of constraint prioritisation based on yield loss, causal hierarchy and hierarchy of consequences over time. It is suggested that farmers should test the diagnosed remedies on reference paddocks before they commit to heavy costs. Decisions about expensive remedies would ultimately lie in the balance between the costs of lost opportunity and implementation of the remedies.