Modeling nitrate leaching on a cropped Andosol

Abstract

The nitrate transfer model in Andosol using the multipurpose solver was developed using meteorological characteristics, three-species nitrification and/or denitrification chain (NH4 → NO3 → N2), and a cropping system to evaluate the behavior of nitrate leaching from a cropped Andosol. Its validity was then tested by comparing results calculated by proposed model with results from a capillary lysimeter experiment. The measured values of cumulative water flux and cumulative nitrate nitrogen (NO3-N) flux were compared with those of simulated values, and the accuracy of proposed model was verified by using test statistics of the root mean square error (RMSE) and t-value. The calculated results using the proposed model were accurate despite the small numbers of parameters (e.g. denitrification rate, immobilization rate etc.) and simple mechanistic sub-models were adopted. To understand the behavior of NO3-N concentration visually and qualitatively in the soil horizon, we used colored isopleths of NO3-N concentration in pore water at a cropped Andosol. From the validated results and isopleths results, the leaching risk of nitrate is likely to increase when (1) the agricultural land has high permeability and low capability of adsorption of nitrate, and when (2) heavy rains fall soon after application of nitrogen fertilizer. The results of RMSE and t-test, it was demonstrated that relationship between FlexPDE and observed data is in more agreement than the Hydrus-1D model.