RATE OF NITROGEN MINERALIZED FROM INCORPORATED CROP RESIDUES AS INFLUENCED BY TEMPERATURE

Methods are needed to predict seasonal mineralization of N when crop r esidues are added to soils in order to assess N availability to crops, The objective of this investigation was to evaluate and develop metho ds for predicting the effect of temperature on the rate of N mineraliz ation (N-min) from crop-residue-amended soils maintained at near-optim um soil water content, Unamended and crop-residue-amended soils were i ncubated at temperatures between 5 and 35 degrees C to obtain N-min, r ates for calculation of Q(10) values, defined as the ratio of reaction rates at a temperature interval of 10 degrees C. Measured Q(10) depen ded on the C/N ratio of the residue and incubation time, indicating th at for predictive purposes a single Q(10) value is inadequate for desc ribing the effect of temperature on crop-residue N-min. Temperature fu nctions were developed from N-min data collected from unamended soils incubated at four temperatures under laboratory conditions, These func tions were then tested in the MINIMO model (a subroutine of CERES-MAIZ E) for residue-amended soils at four temperatures for up to 160 d. Mod el-predicted mineralizations was close to measured N-min for most crop -residue-soil mixtures tested. The use of the new temperature equation s improved the precision of the model, reducing the residual sum of sq uares (RSS) from 9797 to 5286, However, the modified model was not abl e to accurately predict N-min for crop residues with a C/N ratio of 10 and 28. Inadequate prediction at these C/N ratios may be related to h ow the model allocates the pool sizes for soluble and insoluble plant N and the cellulose-hemicellulose pool size of the crop residues.