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

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 NO 3 was accumulated in the dry season and leached in the rainy season. No spatial dependence of soil NO 3 distribution could be distinguished along the hillslope due to complex water flow. The soil interflow was the major driver of NO 3 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 NO 3 –N concentrations. The highest NO 3 –N concentration and loss flux were detected in storm runoff after a long drought in 2006. The NO 3 –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 NO 3 –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 NO 3 leaching. The interflow discharge monitoring method together with effluent NO 3 content analysis used in this study proved to be useful and effective for quantifying NO 3 leaching losses at the field scale in hillslope areas.