John Kirkegaard, Julianne Lilley
CSIRO Agriculture and Food, GPO Box 1700, Canberra ACT 2614, www.csiro.au, firstname.lastname@example.org
Integrating long-season wheat and canola crops in a crop sequence can significantly increase farm productivity and profitability through higher yield potential, improved timing of the whole-farm sowing program, and through grazing. However deep soil water use of higher-yielding crops can leave a legacy of dry or N-depleted soil that may impact subsequent crops, and reduce the expected yield benefits across the crop sequence. We used the APSIM model, validated against 30 years of measured data from a long-term field experiment at Harden in NSW to explore the legacy effects and overall impact of incorporating long-season wheat and canola crops into the cropping system at Harden in southern NSW. APSIM predicted dynamics of water, mineral N, biomass and yield adequately across the continuous 30-year sequence, providing confidence in the ability to explore modified management scenarios. At Harden, we predicted opportunities to increase mean wheat yield (22%) and canola yield (14%) using early-sown, long-season varieties compared to faster-maturing spring varieties sown in May, in seasons where early sowing (from March 1) was possible. The yield improvements increased to 33% for wheat and 72% for canola when an extra 50 kg N/ha was top-dressed each season demonstrating the importance of matching N supply to the higher yield potential of the crops. The continuous simulation revealed legacy effects were evident in some seasons, but were small overall, at least in this high rainfall environment. The approach can be applied elsewhere, but relies on well-validated, continuous simulation of the crop sequence, which are rare.