Measurements of Nitrate Leaching from a Hillslope Cropland in the Central Sichuan Basin, China

摘要

Nitrate losses through leaching were studied in a crop field in the central Sichuan Basin, southwestern China, during 2003 to 2006. Nitrate accumulations and losses via leaching were measured using two methods: a simulation with sampled soil profiles and field monitoring in situ at a 7% slope. The results showed that NO₃ was accumulated in the dry season and leached in the rainy season. No spatial dependence of soil NO₃ distribution could be distinguished along the hillslope due to complex water flow. The soil interflow was the major driver of NO₃ leaching losses from the experimental plots. The average annual discharge of the interflows was 148 mm, accounting for 63% of total runoff in the rainy season in 2003 to 2006. The interflow water contained high NO₃–N concentrations. The highest NO₃–N concentration and loss flux were detected in storm runoff after a long drought in 2006. The NO₃–N leaching through interflow showed clear annual and seasonal patterns, and largely occurred in the stages from stamen elongation to maturity of maize (Zea mays L.) with a flux of 2.2 g m–2, about 69% of the total annual loss flux. Annual estimated losses of NO₃–N through interflow ranged from 20 to 53, with an average of 36 kg ha–1 yr–1. This study indicates that croplands on hillslopes with regosols are vulnerable to NO₃ leaching. The interflow discharge monitoring method together with effluent NO₃ content analysis used in this study proved to be useful and effective for quantifying NO₃ leaching losses at the field scale in hillslope areas.