不同农地利用方式下地表径流中氮的输出特征

Nitrogen Exports via Overland Runoff under Different Land Uses and Their Seasonal Pattern

选取太湖流域典型小流域，通过长期观测，研究了自然降雨过程引起不同农地利用方式下的地表径流氮流失特征．坡地上玉米一油菜轮作和蔬菜种植条件下氯的流失途径主要为土壤侵蚀，两种利用方式下的土壤侵蚀和径流氮流失都大大高于竹园和板栗园，土壤侵蚀和氮流失主要发生在6～9月降雨集中分布的梅雨和台风季节．稻田水旱轮作条件下，氮主要随农田排水流失，降雨时间和施肥等农事活动的间隔长短在很大程度上决定了氮的年流失量，37欠最大的流失事件中氮的流失量可达到伞年氮流失的70％以上，总体上稻田水旱轮作方式下氮的径流输出低于坡地旱地．

Sediment and phosphorus losses via overland studied in an agricultural watershed in the Taihu Lake area in eastern China. Much higher runoff, sediment and phosphorus losses were observed under corn/rapeseed rotation and vegetable fields than that under chestnut orchard and bamboo forest. Sediment attached phosphorus accounted most of the P export under corn/rapeseed rotation and vegetable fields, indicating erosion control is the most effective way to reduce phosphorus losses from upland. Distinct seasonal pattern of phosphorus losses was observed, with 80. 9% - 84.7 % of annual phosphorus loss whcih happened during monsoon and typhoon season （from June to September）. For the paddy field under rapeseed/rice rotation, phosphorus was mainly exported with runoff and drainage water. Annual P losses were mainly affected by the amount fertilization of precipitation and its coincidence with fertilization. Three rainfall events immediately following accounted as high as 70% of the annual P export.