A mechanistic model simulating the decomposition of surface-managed winter wheat residues was developed and model predictions were compared to results from field studies of decomposition rates. The model consists of two submodels. The first simulates decomposition of the various components of wheat residues (straw, leaves, and chaff) under constant conditions. This submodel requires input on the N content of the residue, and is based on results of laboratory experiments in which respiration was measured. The second submodel uses meteorological data to simulate environmental conditions in the residue layer. This information is combined with laboratory derived estimates of the effects of temperature and moisture to calculate the cumulative decomposition days. To apply the model to field situations, the relationships between respiration and mass loss were estimated experimentally. The effects of added microarthropods and nematodes were also measured, but no effects on respiration were observed in either case. Model predictions agreed well with data from field experiments in which bundled straw was used, but decomposition of straw in litter bags was slower than predicted. When grab samples were used to measure the loss of residues containing leaves, chaff, and straw, the model performed well even across climatic regions until early summer (32-36 wk after residue placement in the field), when residues began to disappear more rapidly than predicted.
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