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 groundwater 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.