Sensitivity of LEACHN Model Predictions to Changes in Nitrogen Transformation Rate Constants and Bulk Density
LEACHN is a deterministic model that could be used as a decision support tool to simulate NO 3 -N (nitrate-N) movement through the soil profile in order to make management decisions (i.e., when and how much effluent to apply on land) at effluent-irrigated land disposal sites. However, using this model as a â€œblack boxâ€ is not satisfactory, and an in-depth understanding of how the model works is essential before the model is used by the operators and managers of land treatment systems. This article provides a brief description of LEACHN, the N (nitrogen) cycle and soil hydrological properties in LEACHN, and an assessment of LEACHN. This article also provides the key findings of a previous study as background knowledge for the current study. The main focus of this article is to investigate the sensitivity of LEACHN predictions to changes in N transformation rate constants, i.e., K min (mineralization), K nit (nitrification), and K den (denitrification), at field scale, and also to explore the effect of changes in soil bulk density on leachate NO 3 -N concentrations and amount of N leached. This study shows that LEACHN was sensitive to K min values, and this parameter had a significant impact on soil humus-N and the amount of NO 3 -N leached. The total amount of NO 3 -N leached was slightly affected by K nit values. However, the K den value had no significant impact on the total amount of NO 3 -N leached. This analysis also highlighted the need for accurate measurements of bulk density as inputs to the LEACHN model. The optimized LEACHN model (using the best N transformation rate constants values) was tested successfully for two field data sets.