Nitrogen leaching and denitrification in continuous corn as related to residue management and nitrogen fertilization

Maintaining crop production levels with reductions in terrestrial greenhouse gases requires strategic residue and nitrogen (N) fertilizer management. Our objectives were to: (1) quantify the effect of nitrogen N application rate on N losses; (2) examine the role of residue returned on N transformation and losses; and (3) verify the capability of the NCSWAP/NCSOIL model to simulate the dynamics of N and N-15 in the soil-plant system. Data obtained from a long-term continuous corn study on a silt loam soil, with two N levels (20 and 200 kg N/ha), with two types of residue management (residue harvested, -R; and residue returned, +R) was used to calibrate the model. The model accurately predicted N-15 in the plant and soil organic matter (SOM) at the 0- to 15-cm and 15- to 30-cm depths for both fertilizer rates and residue managements. Concentrations of N-15 in the corn and SOM were higher for the 20 than 200 kg N/ha treatments. Greater dilution of the N-15 with nontracer fertilizer added at the higher fertilizer rate was responsible for differences in N-15 concentrations in the plant. The predicted cumulative N loss during a 30-year simulation indicates more nitrate leaching past the 1-m depth for -R than +R treatments, while higher denitrification rates were predicted for the +R than -R. The simulated cumulative effect of residue returned on denitrification over 30 years predicted increased cumulative N losses from 1320 to 1705 kg N/ha and 1333 to 2574 kg N/ha for the low and high N application rates, respectively. Better synchronization of N release from residue and addition of N fertilizer with plant-N uptake would minimize leaching and denitrification.