Performance and application of the APSIM Nwheat model in the Netherlands

APSIM Nwheat is a crop system simulation model, consisting of modules that incorporate aspects of soil water, nitrogen (N), crop residues, and crop gr owth and development. The model was applied to simulate above- and below-gr ound growth, grain yield, water and N uptake, and soil water and soil N of wheat crops in the Netherlands. Model outputs were compared with detailed m easurements of held experiments from three locations with two different soi l types. The experiments covered two seasons and a range of N-fertiliser ap plications. The overall APSIM Nwheat model simulations of soil mineral N, N uptake, shoot growth, phenology, kernels m(-2), specific grain weight and grain N were acceptable. Grain yields (dry weight) and grain protein concen trations were well simulated with a root mean square deviation (RMSD) of 0. 8 t ha(-1) and 1.6 protein%, respectively. Additionally, the model simulati ons were compared with grain yields from a long-term winter wheat experimen t with different N applications, two additional N experiments and regional grain yield records. The model reproduced the general effects of N treatmen ts on yields. Simulations showed a good consistency with the higher yields of the long-term experiment, but overpredicted the lower yields. Simulation s and earlier regional yields differed, but they showed uniformity for the last decade. In a simulation experiment, the APSIM Nwheat model was used with historical weather data to study the relationship between rate and timing of N fertil iser and grain yield, grain protein and soil residual N. A median grain yie ld of 4.5 t ha(-1) was achieved without applying fertiliser, utilising mine ral soil N from previous seasons, from mineralisation and N deposition. App lication of N fertiliser in February to increase soil mineral N to 140 kg N ha(-1) improved the median yield to 7.8 t ha(-1) but had little effect on grain protein concentration with a range of 8-10%. Nitrogen applications at tillering and the beginning of stem elongation further increased grain yie ld and in particular grain protein, but did not affect soil residual N, exc ept in a year with low rainfall during stem elongation. A late N applicatio n at flag leaf stage increased grain protein content by several per cent. T his increase had only a small effect on grain yield and did not increase so il residual N with up to 40 kg N ha(-1) applied, except when N uptake was l imited by low rainfall in the period after the flag leaf stage. The economi c and environmental optima in winter wheat were identified with up to 140 k g N ha(-1) in February, 90 kg N ha(-1) between tillering and beginning of s tem elongation and 40 kg N ha(-1) at flag leaf stage resulting in a median of 8.5 t ha(-1) grain yield, 14.0% grain protein and 13 kg N ha(-1) soil re sidual N after the harvest. The maximum simulated yield with maximum N inpu t from two locations in the Netherlands was 9.9 t ha(-1). (C) 2000 Elsevier Science B.V. All rights reserved.