亚热带主要耕作土壤硝态氮淋失特征试验研究

Study on nitrate leaching characteristics in arable soils in subtropical region

本文选取红壤、水稻土、潮土、黄棕壤和紫色土等我国亚热带地区的主要耕作土壤为研究对象,采用土柱模拟试验,研究了土壤氮素累积与硝态氮迁移的动态特征,并对氮素的淋失风险进行了定量评价和预测。结果表明,硝态氮在土壤中的淋失过程可分为两个明显阶段,即高浓度快速降低阶段和低浓度缓慢降低阶段。硝态氮淋失过程存在明显的拐点,该点对应的累积入渗量(拐点入渗量)变化范围为38.1～219.7 mm,且随土壤硝态氮含量的增加呈幂函数关系增加,表明随硝态氮含量的增高,其淋失风险呈加速增大的趋势。硝态氮淋失强度随土壤硝态氮含量的增加呈显著的线性变化趋势。初步估测,我国亚热带地区在年降水入渗量700 mm和土壤硝态氮累积水平为N 20 mg/kg的条件下,表层土壤(0—20 cm)的硝态氮年平均淋失量为N 484.9 kg/hm2,土壤间的变异系数(CV%)为26.5%。土壤硝态氮含量是影响硝态氮淋失强度的决定因素,其它土壤性质的影响均相对较小,因此,控制土壤氮素累积和化肥施用水平是降低其淋失风险的关键环节。

To study the nitrate leaching dynamics and the impacts of soil nitrogen accumulation, ten soil samples belonging to Ortbox, 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 Dctended 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 N 484. 9 kg/ha, while the coefficients of variance （CV） was 26.5% with annual rainfall infiltration 700 mm and soil nitrate contents N 20 mg/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.