Study on nitrate leaching characteristics in arable soils in subtropical region

To study the nitrate leaching dynamics and the impacts of soil nitrogen accumulation, ten soil samples belonging to Orthox, Agrudalf, Fluvents, Udalfs, and Orthents were selected from subtropical area of China and soil column experiment was conducted. A quantitative evaluation and prediction of nitrate leaching risk were performed on the ten arable soils investigated. Results showed that the dynamics of nitrate leaching could be divided into two phases: rapidly decreasing phase with high nitrate concentration and slow decreasing phase with low nitrate concentration. An obvious change point between these two phases was observed. The cumulative infiltration amount opposite to the change point, called critical infiltration amount (Dc), ranged from 38.1 mm to 219.7 mm. The values of Dc tended to increase in a power function pattern with the increasing soil nitrate contents, suggesting that the increment of nitrate leaching risk is accelerated with nitrate accumulation. The nitrate leaching intensity (LI) linearly increased with soil nitrate contents for a given soil. Based on the primary prediction, the annual average nitrate leaching amounts for the ten soils was 484.9 kg N/ha, while the coefficients of variance (CV) was 26.5% with annual rainfall infiltration 700 mm and soil nitrate contents 20 mg N/kg. Consequently, controlling soil nitrogen accumulation and fertilizer application amount is the key approach in reducing nitrate leaching risk in the subtropical area of China.