Performance of the APSIM-wheat model in Western Australia

APSIM-wheat is a crop system simulation model, consisting of modules that incorporate aspects of soil water, nitrogen (N), residues, and crop development. The model was used to simulate above- and belowground growth, grain yield, water and N uptake, and soil water and soil N in wheat crops in Western Australia. Model outputs were compared with detailed field experiments from four rainfall zones, three soil types, and five wheat genotypes. The field experiments covered 10 seasons, with variations in sowing date, plant density, N fertiliser, deep ripping and irrigation. The overall APSIM model predictions of shoot growth, root depth, water and N uptake, soil water, soil N, drainage and nitrate leaching were found to be acceptable. Grain yields were well predicted with a coefficient of determination r²(1:1) = 0.77, despite some underestimation during severe terminal droughts. Yields tended to be underestimated during terminal droughts due to insufficient pre-anthesis stored carbohydrates being remobilised to the grain. Simulation of grain protein, and depth to the perched water table showed limited accuracy when compared with field measurements. In particular, grain protein tended to be overpredicted at high protein levels and underpredicted at low levels. However, specific simulation studies to predict biomass, yield, drainage and nitrate leaching are now possible for wheat crops on the tested soil types and rainfall zones in Western Australia.