浙江红壤区经济林坡地氮素径流流失特征研究

以浙江省永康市方山柿经济林坡地为试验区，依据不同地形条件及林下管理措施，设置7个径流小区和沉砂池，定期采集沉砂池水样，测定径流中不同形态氮素浓度。通过为期一年的监测分析，得到如下结论：（1）试验区氮素流失与水文年内降水具有明显的同步性，氮素流失多发生在降水集中的梅雨和台风季节。这两个季节的降水量占全年降水的66．2％，TN、NO；-N和NH4＋ -N流失量分别占全年总流失量的80．3％、78．2％和83．0％。（2）坡顶、凸坡和凹坡径流小区的氮素流失符合养分流失的“临界坡度”规律，临界坡度在坡顶（10．22°）与凹坡（18．55°）之间。水文年内TN和NO33^- -N流失量关系为坡顶〉凹坡〉凸坡，NH4^＋ -N流失量关系为凹坡〉坡顶〉凸坡。三种地形径流小区的年内氮素累积流失量均呈幂函数型增加。（3）对照林下管理措施不同的6号（林下除草）和7号（林下不除草）径流小区，发现草被覆盖对减少经济林坡地氮素径流流失具有明显效果。保留草被覆盖的7号小区比除草的6号小区的TN、NO3^- -N和NH4^＋ -N径流流失分别减少了22．1％、36．2％和44．1％。

Characteristics of Nitrogen Runoff Losses from Economic Forest Lands in Hilly Red Soil Area of Zhejiang Province,China

Nitrogen loss in sloping forest lands is not only an important source of non-point source pollution, but also reduces use efficiency of nitrogen fertilizer. An experiment was conducted to monitor nitrogen losses in persimmon economic forests in hilly red soil area in Yongkang, Zhejiang. Total 7 runoff plots were set up under different terrains and forest managements. Grit chambers were established to collect water samples monthly. Different forms of nitrogen in water samples were then measured. Nitrogen losses were obviously synchronous with precipitation in a hydrological year. Most of nitrogen losses occurred in rainy and typhoon seasons, which accounted for 66.2% of the annum precipitation. During these two seasons, TN, NO~-N and NH~-N losses were 80.3%, 78.2% and 83.0% of the annual total N loss, re- spectively. In the hydrological year, the rates of TN and NO3^- -N losses were crest〉concave slope〉convex slope, while the rate of NH4^＋-N losses was concave slope〉crest〉convex slope. The cumulative nitrogen losses under three terrains had power function relationship with time. Grass coverage,e reduced runoff losses of TN, NO3^- -N and NH4^＋ -N bv 22.1%, 36.2% and 44.1%. resoectivelv.