Long‐Term Effects of Crop Management in Wheat‐Fallow: II. CENTURY Model Simulations

There is increasing need to develop models to assess the long‐term effects of management practices on soil and environmental quality, and to test these models across a wide range of environments. The CENTURY model was used to simulated long‐term management practices for wheat ( Triticum aestivum L.)‐fallow agriculture. The objectives were to compare the accuracy of predicted vs. observed data and use the model to help interpret observed data and to determine the long‐term impact of crop management on C and N stabilization in soil. The model simulated grain and straw yield and grain N uptake within ±10% of the observed data, and 0‐ to 30‐cm soil C and N within ±5%. Improvement in performance requires addition of a dynamic plant growth submodel to represent the effect of soil N on C and N allocation to roots, straw, and grain. Soil C changes were a linear function of aboveground C inputs; an input of 200 g C m −2 yr −1 (4650 kg straw ha −1 ) was required to stabilize soil C at its present level. Estimates of soil C stabilization efficiency ranged from 12 to 27% and was highest for the high N fertilizer treatment. Soil N stabilization efficiency was higher for organic N additions (37–46%) than for inorganic additions (18–26%). Inorganic N treatments had similar N removal in grain, higher other nonidentifiable N losses, but lower N stabilization in soil than organic N treatments. Soil N data suggest that mineralization of N from the 30‐ to 60‐cm layer needs to be considered in the N budget, as nearly 39 g m 2 were mineralized between 1931 and 1986.