Estimating the Influence of Nitrogen Transformations on Nitrate Leaching in Soils

Abstract

It is challenging to estimate N leaching in soils attributable to complicated physical, chemical, and biological processes. In this study, a transfer function model was developed to simulate the outflow concentration of NO3 in the field, considering the influence of transient water flow, input of applied N, initial residual N in the soil, and main N transformations on the NO3–N leaching process. The N transformations in the model included immobilization, mineralization, volatilization, and plant uptake. In the probability density function of NO3–N, a weighting factor was introduced to quantify the leaching contributions from applied and residual N. A field experiment was conducted for 196 d during the growing seasons of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.). Soil water potential and NO3 concentrations were measured during the study period along two soil profiles to a depth of 2 m: at 0.10‐m intervals from the soil surface to the 1‐m depth, and at 0.20‐m intervals from 1 to 2 m. A comparison between the experimental data and simulated results with the transfer function showed that the model provided reasonable predictions of the N leaching process as well as the total amount leached at the 2‐m depth. Results also indicated that by considering the transient water condition and N transformations, the transfer function significantly increased the estimation accuracy. Compared with the measured data, relative errors of the estimated total N leached were 1 and 20% with and without considering the transient water condition and the N transformations, respectively. The transfer function with the weighting factor can be useful to estimate the contributions from the applied and residual N to the leaching process in the field.