Modeling in situ N mineralization in conservation tillage fields: comparison of two versions of the CERES nitrogen submodel

Knowing the amount of N available from crop residues and soil is important for determining the amount of fertilizer N needed by a crop. Nitrogen availability in conservation tillage systems is often difficult to assess because of uncertain interactions of surface residues with N mineralization processes. Estimates of residual N availability in cotton systems are more critical because both over- and underfertilization can reduce lint yields. The CERES plant growth models use a moderately complex N submodel to simulate many interacting factors influencing net N mineralization and could be useful as a tool to estimate N needs. Simulations of in situ net N mineralization under two cotton (Gossypium hirsutum L.) cover crop systems were conducted with the original N submodel (CERES-N) and a version modified to allow user input of soluble carbohydrate, cellulose, and lignin pool sizes (CERES-NP) and were then compared to field data. Both model versions indicated greater in situ net N mineralization following crimson clover (Trifolium incarnatum L.) than following rye (Secale cereale L.) cover crops. This agreed with results measured in a field study during 1997 and 1998. Simulations of in situ N mineralization were better with CERES-NP than for CERES-N and were improved for both versions when using decomposition parameters determined from data of a previous field study. Simulations of residue biomass and N loss from bagged residues in 1998 indicate that the original model tends to overpredict in situ net N mineralization which is most likely related to the overestimation of soil organic matter N mineralization. Results with CERES-NP indicate that it can be a better tool for estimating N needs for cotton in conservation tillage cover crop systems than the original CERES-N.