Optimising the yield and economic potential of high input cropping systems in the High Rainfall Zone

In the southern cropping regions of Australia, grain yield potentials are high due to relatively high rainfall and long growing seasons. However, current management practices including variety selection, sowing times and nutrient management are all derived from areas of lower yield potential. This research is part of an integrated project to move paddock yields closer to their potentials by identifying the impacts of improved practices. The project is supported by state and federal agricultural agencies, the Grains Research and Development Corporation, local farming systems groups and IPNI.

A report released by the project last year identified significant crop nutrient limitations across the region, particularly with N and possibly K and S. In general, soil P concentrations are adequate, although soils in the region are generally acid. To investigate the potential nutrient responses, four nutrient omission trials were established, two for canola and two for wheat in the high rainfall zone. The design aimed to omit P, K, S or Cu/Zn from a full nutrient treatment, and then manage those to different yield potentials by supplying N to 75% or 100% of the water-limited yield potential. Part of the logic behind this approach is to see if current soil test values derived in low rainfall/low yield potential areas were applicable under high yields. Using omission plots has been well received by growers and researchers and this approach gives a basis for deciding on the relative impact of different nutrients and their potential interactions.

The experiments in 2015 showed some differential yield response, but the seasonal conditions were very dry, with spring rainfall approximately half of normal As a result, yields were about 40% below expectation and were in the range of 3 to 5 t/ha for wheat and 2 to 3 t/ha for canola across the four sites. There were yield increases to added N on three of the four experiments, but there were no interactions among N and the omission of particular nutrients. Soil test values were near to the critical values from previous research, and this allied with the poor spring conditions contributed to this lack of response. Full results from the experimental sites are yet to be fully analyzed, but will be posted at http://research.ipni.net/project/IPNI-2014-AUS-022.