Modeling field-scale N mineralization in Coastal Plain soils (USA)

A tool to estimate the amount of net N mineralized under field conditions would be useful to adjust N fertilizer rates. A simulation model of soil N may be useful to develop such estimates, but must first be evaluated under the conditions in which it will be used. In this work, we implemented the N subroutine of CERES-N in Stella 6.0 modeling software to simulate net N mineralized from soil organic matter and cotton residues at three locations in a Coastal Plain field of south Georgia. The model was first calibrated with laboratory data of net N mineralized from an incubation study of cotton leaves and stems, and then used to simulate net N mineralized at three field locations. The calibrated model underestimated net N mineralized at two of the field locations by 45% and 56%, respectively. This underestimation was apparently caused by an underestimation of N mineralized from soil organic matter. To explore possible reasons for the underestimation, we collected soil samples monthly for 1 year to measure potentially mineralizable N at the three field locations, and used the data to modify the rate of soil organic matter mineralization throughout the year according to a sinusoidal wave. Simulated values of net N mineralized with this modification were within the 95% confidence interval for field-measured values. These results suggest that further research should be conducted to study the dynamics of the microbial population and microfauna present in soil, which may be partially responsible for seasonal changes in N mineralization rates.