NLES5 – An empirical model for estimating nitrate leaching from the root zone of agricultural land

Abstract

NLES5 is the fifth version of an empirical model for predicting annual nitrate leaching from the root zone (1-meter depth), accounting for effects of nitrogen (N) inputs, crop sequences, autumn and winter crop cover, soil types, and weather conditions. It was developed and calibrated based on a comprehensive nitrate leaching dataset, primarily from Denmark. The model is used for quantifying annual nitrate leaching under Danish soil, weather, and field management practice. The model simulates the effects of N application rate, the presence of a cover crop, and the effects of crop management targeting measures to reduce agricultural nitrate leaching for the improvement of the quality of groundwater and surface water systems. The model takes into account crop and N management effects in the year of nitrate leaching and the two previous years, while long-term effects of N inputs are accounted for via total N in topsoil. The model provides estimates of nitrate leaching for the most important crops grown in Denmark and their management at cropping system level considering effects of soil and climate. The prediction of average annual nitrate leaching following the 13 main crop classes in the model varied from 25 to 170 kg N ha−1 with a model performance (independent validation data (856 observations)) of Root Mean Square Error (RMSE) of 30.8 kg N ha−1 and a coefficient of determination (R2) value of 0.40. The RMSE obtained for the calibration data (2053 observations) was 29.6 kg N ha−1 and the R2 was 0.53.