Estimating the Influence of Nitrogen Transformations on Nitrate Leaching in Soils

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 NO 3 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 NO 3 –N leaching process. The N transformations in the model included immobilization, mineralization, volatilization, and plant uptake. In the probability density function of NO 3 –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 NO 3 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.