Impact of nitrogen application on nitrate nitrogen leaching in winter wheat and summer maize rotation system based on a literature analysis

Nitrogen (N) leaching is one of the main routes of N loss in farmlands. The entry of nitrate N into water can cause human poisoning and water eutrophication, resulting in serious damage to human health and ecological environments. This study was carried out to explore the effects of different N fertilization rates, crop types, and monitoring methods on nitrate N leaching in the winter wheat and summer maize rotation system, which is the main cropping system used in China. To this end, the China National Knowledge Infrastructure (CNKI) database and Web of Science (WoS) Core Collection database were used to collect publications on nitrate N leaching in winter wheat and summer maize rotation systems from 1980 to 2020. Data from these papers on the effects of N application rates, crop types, and monitoring methods on nitrate N leaching from winter wheat and summer maize rotation systems were then analyzed using regression and Ttests. It was found that an increase in the N fertilization rate exponentially increased the nitrate N leaching amount in this cropping system. The fitted equations for the relationship between nitrate N leaching amount and N fertilization rate in the winter wheat and summer maize seasons were y= 0.4633e ^{0.0109 x}and y= 1.1011e ^0.0103x, respectively. Although there was no significant difference between the N fertilization rates in the winter wheat (218 kg∙hm ⁻²) and summer maize seasons (190 kg∙hm ⁻²), the nitrate N leaching amount (8.8 kg∙hm ⁻²) and rate (3.5%) in the winter wheat season was lower than those (amount: 13.9 kg∙hm ⁻²; rate: 6.4%) in the summer maize season. In both the winter wheat and summer maize seasons, there was a significant exponential correlation between the N fertilization rate and nitrate N leaching amount, as measured using two different methods — lysimeter and solution collection, resulted in fitted equations of y= 0.2448e ^{0.0143 x}and y= 0.6108e ^{0.0098 x}in the winter wheat season, respectively, and y= 1.0284e ^{0.0102 x}and y= 0.972e ^{0.011 x}in the summer maize season, respectively. Thus, both methods can be used to measure nitrate N leaching reliably. The fitting accuracy of the regression equation for the N application rate and nitrate N leaching amount was better when the N application rate was less than 300 kg∙hm ⁻², but the accuracy decreased with a further increase in the N application rate. In conclusion, because more nitrate N leaching occurs in the summer maize season than in the winter wheat season, the leaching problem in the summer maize season necessitates greater attention.