三峡库区小流域旱坡地氮磷流失特征研究

Study on the Nitrogen and Phosphorus Loss Characteristics from Sloping Uplands in Small Watershed of Three Gorges Reservoir Region

为探讨三峡库区小流域旱坡地氮磷流失特征,采用标准径流小区对重庆市涪陵区珍溪镇王家沟小流域常规耕作方式(顺坡耕作)以及水土保持耕作方式(常规顺坡耕作+PAM土壤调节剂、免耕+顺坡种植+稻草覆盖、常规顺坡耕作+植物篱、免耕+横坡垄作、常规横坡耕作)下土壤氮素和磷素的流失量及形态特征进行分析。结果表明:(1)就旱坡地土壤氮素的流失特征而言,径流中氮素的流失量相对较小,最大值仅为53.63mg/m2;而泥沙中所携带的氮素流失量相对较大,其最大值达131.25mg/m2;整个观测期内,氮素的流失主要以颗粒态为主,颗粒态氮的流失量占总氮流失量的53.0%～62.0%。(2)就旱坡地土壤磷素的流失特征而言,各处理径流中磷素的总体规律基本表现为:常规顺坡耕作>常规横坡耕作>免耕+顺坡种植+稻草覆盖>常规顺坡耕作+PAM土壤调节剂>免耕+横坡垄作>常规顺坡耕作+植物篱;泥沙中所携带的磷素流失量相对于径流中的磷素流失量而言较大,最大值为58.14mg/m2;整个观测期内,颗粒态总磷流失量为水溶态总磷流失量的1.75～2.15倍,流失方式同样以颗粒态为主。总体而言,水土保持耕作方式下的氮磷流失量均小于常规耕作处理,能有效减少径流及泥沙中各形态氮磷的流失。

For understanding the characteristics of nitrogen（N） and phosphorus（P） losses from sloping uplands in small watershed of Three Gorges Reservoir Region,standard runoff plots were used to analyze respectively the losses amount and speciation characteristics of N and P through investigation of conventional tillage measure（downslope cultivation,DC） and tillage measures based on water and soil conservation including five methods,which respectively were DC＋polyacrylamide（PAM）,no-tillage＋DC＋straw overlay,DC＋hedgerow,no-tillage＋contour ridge tillage and conventional contour cultivation,in Wangjiagou of Zhenxi town,Fulin district of Chongqing.The results indicated that in terms of the N loss characteristics from surface sloping uplands,loss amount of N via runoff was relatively less,the maximum was only 53.63 mg/m2.But the loss amount of N carried by sediments was higher than runoff,the highest value reached 131.25 mg/m2.Across the whole observation period,the loss of N was mainly in the forms of particulate,the loss amount of particulate N takes up of 53.0%~62.0% in total loss amount of N.In terms of the P loss characteristics from surface sloping uplands,the loss amount of P via runoff under different tillage measures was in the decreasing order,i.e.DC,conventional contour cultivation,no-tillage＋DC＋straw overlay,DC＋PAM,no-tillage＋contour ridge tillage and DC＋hedgerow.The loss amount of P carried by sediments was higher than runoff,the maximum was 58.14 mg/m2.During the whole observation period,the loss amount of particulate P was 1.75~2.15 times than water-soluble P,the loss of P was still in the forms of particulate mainly.Overall,the loss amounts of N and P under water and soil conservation tillage measures were all less than the conventional tillage measure,and the loss amount of N and P in runoff and sediments could be reduced significantly based on the water and soil conservation tillage measures.