Nitrate nitrogen accumulation and leaching pattern at a winter wheat: summer maize cropping field in the North China Plain

Excess application of nitrogen has proved to be one of the detrimental impact factors on soil and ground-water quality in the North China Plain (NCP). A 4-year (from October 2008 to September 2012) field experiment was carried out to investigate the impact of N application rate on NO3-N dynamics in soils, its leaching pattern, and movement in deep soils under different nitrogen (N) application rates in a sprinkler irrigated winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) field in the NCP. The N application rates were 0, 110, 220, and 330 kg N ha(-1) per wheat or maize planting season, referred to as CK, N1, N2, and N3 treatments, respectively. The results indicate that in winter wheat season, the applied water and fertilizer N mostly accumulated in the 0-60 cm soil layer and NO3-N leaching out of the root zone (0-100 cm) was negligible under the sprinkler irrigation scheduling, while water and NO3-N leached out of the root zone during summer maize season mainly due to high rainfall event. A relatively constant NO3-N concentration in soil profile was maintained and NO3-N leaching was negligible when N application rate was 110 kg N ha(-1) per crop season. While about 70 % of the applied N accumulated in 0-500 cm soil layer and about 50 % of the applied N leached out of the root zone when N application rate lager than 110 kg N ha(-1) per crop season, and the NO3-N downward movement was observed to the depth of 300 cm at the end of the 4-year experiment with an average migration rate of about 50 cm year(-1). Considering the potential risk of groundwater pollution, an N application rate of 110 kg ha(-1) per crop season was recommend for winter wheat and summer maize under the conditions of sprinkler irrigation in the NCP and those areas with similar conditions.