PERFORMANCE OF THE APSIM-WHEAT MODEL IN WESTERN-AUSTRALIA

APSIM-wheat is a crop system simulation model, consisting of modules t hat incorporate aspects of soil water, nitrogen (N), residues, and cro p development. The model was used to simulate above- and belowground g rowth, grain yield, water and N uptake, and soil water and soil N in w heat crops in Western Australia. Model outputs were compared with deta iled 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 a nd irrigation. The overall APSIM model predictions of shoot growth, ro ot depth, water and N uptake, soil water, soil N, drainage and nitrate leaching were found to be acceptable. Grain yields were well predicte d with a coefficient of determination r(2)(1:1) = 0.77, despite some u nderestimation during severe terminal droughts. Yields tended to be un derestimated during terminal droughts due to insufficient pre-anthesis stored carbohydrates being remobilised to the grain. Simulation of gr ain protein, and depth to the perched water table showed limited accur acy when compared with field measurements. In particular, grain protei n tended to be overpredicted at high protein levels and underpredicted at low levels. However, specific simulation studies to predict biomas s, yield, drainage and nitrate leaching are now possible for wheat cro ps on the tested soil types and rainfall zones in Western Australia. ( C) 1998 Elsevier Science B.V. All rights reserved.