不同降雨强度对农田土壤氮素淋失的影响及LEACHM模型验证

Nitrogen Leaching Under Different Rainfall Intensities for Agricultural Soils-Laboratory Experiments and Numerical Modeling Using LEACHM

云南抚仙湖北岸农田平原区地下水埋深较浅,约0.6m,农田土壤氮素的淋失易对地下水和湖泊造成污染。采自抚仙湖北岸典型农田-蔬菜地土壤,应用3组不同降雨强度作用下室内土柱实验方法,通过测定土壤中铵态氮、硝态氮的含量以及渗漏液流量及其氮素浓度来探讨氮在土壤中的淋失规律。选用土壤营养物淋失模型(LEACHM模型),模拟了实验条件下水分运移和铵态氮、硝态氮浓度变化过程,并对实验数据作了拟合分析。结果表明,在不出现地表径流的情况下,降雨强度越大,水分下渗速率、铵态氮和硝态氮淋失速率也越快,总氮的淋失量也越大。实验中渗漏液铵态氮、硝态氮含量分别达10和120mg·L-1,说明地下径流是营养盐损失的途径之一,硝态氮是氮素淋失的主要形态。营养盐淋失是地下水氮素污染的原因之一。模拟结果与实验数据较为吻合,表明该模型适用于研究区农田氮素淋失的模拟,为评估氮素淋失提供有效工具,同时也为现场模拟工作提供研究基础。

The depth of groundwater in the north agricultural region of Fuxianhu Lake watershed, Yunnan Province is as shallow as 0.6 m. Nitrogen leaching in farmland can easily pollute the groundwater and consequently the lake. One-dimensional soil column laboratory experiments were performed for soils from the agricultural land of Fuxianhu Lake watershed under three different rainfall intensities. Concentrations of ammonia-N and nitrate-N were measured for the tested soils as well as the leaching water at different experimental times. The numerical model of LEACHM was used to simulate the processes of water leaching and the temporal changes of concentrations of ammonia-N, nitrate-N in the leaching water for the experimental conditions. Results indicated that an increase in the rainfall intensity applied would result in an increase in the leaching rate of ammonia-N and nitrate-N, which ultimately resulted in an increase in the leaching loss of total-N. The concentrations of ammonia-N and nitrate-N in leaching water were 10 mg·L^-1 and 120 mg·L^-1, respectively. It is concluded that that groundwater is the one of the runoffs that transports nutrients for the study area, and nitrate-N is the main form of N leaching to groundwater. Nutrient leaching is becoming the major cause of groundwater pollution. Modeling results from LEACHM were found to he agreeable with the experimental data, which implies that the model is suitable to simulate nitrogen leaching for the study area. This study forms the basis for further field simulation work for the study area.