NLEAP simulation of residual soil nitrate for irrigated and nonirrigated corn

ABSTRACT:

Evaluation of the Nitrate Leaching and Economic Analysis Package (NLEAP) model is needed to determine its utility for assessment of N-management options. Data from a 3-year field experiment of continuous corn (Zea mays L.) consisting of two blocks of plots, Site A' and ‘<Site B’ were used. Half of the plots at each site were randomly chosen to be either nonirrgated or irrgated (based upon calculated potential evapotranspiration). Three replications of nitrogen (N) fertility (56, 112, and 224 kg ha⁻¹; 50, 100, and 200 Lbs ac⁻¹) were used. Soil was a Hecla sandy loam to loamy sand soil (Pachic Udic Haploborall). Soil and climate data were from the North Dakota portion of the upper Midwest database for NLEAP. On-site data were used when available. NLEAP was calibrated using Site A and validated using Site B. When otherwise unavailable or impractical to obtain, required model parameters were determined using Site A experimental data.

For corn grain yields, an irrigation by year interaction was highly significant at both sites; at Site B, response to N was significant. The N-uptake index (NUl), a 'sink' term, was significantly different from the default when low grain yields resulted from dry conditions. Such deviations of NUI must be identified during calibration to optimize NLEAP output. Residual soil nitrate (RSN) levels following har-vest were influenced by N-treatment and year. High N rates resulted in high RSN levels following hawest. Correlations of predicted and observed amounts of RSN for all years and treatments were high at Site A. For year 1, nonirrigated treatments, use of Site A NU-calibration values resulted in calculated RSN values for Site B that were too low. However, predicted and observed values of RSN for the other years and treatments were highly correlated. This study shows that NLEAP is adaptable to data collected for nonirrgated and irrigated conditions on sandy soil for a wide range of N-treatments. Its output should be valuable to users as a decision making aid. Additional work is needed with NEAP for other soils, climatic conditions, N-sources, and economic crops to further evaluate its capabilities and limitations for assessing imgation- and N-management to decrease N-leaching.