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SOIL PHYSICS

Estimating the Influence of Nitrogen Transformations on Nitrate Leaching in Soils

^a Dep. of Soil and Water Sciences, China Agricultural Univ., Key Lab. of Plant–Soil Interactions, MOE, Beijing 100094, P.R. China
^b State Key Lab. of Water Resources and Hydropower Engineering Science, Wuhan Univ., Wuhan 430072, School of Environmental Science and Engineering, Sun Yat-Sen Univ., Guangzhou 510275, P.R. China

^* Corresponding author (zhangrd{at}mail.sysu.edu.cn).

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.

Abbreviations: pdf, probability density function • TFM, transfer function model