南方典型灌区农田地表径流氮磷流失特性

Characteristics of nitrogen and phosphorus losses in surface runoff from farmland in a typical irrigation district in southern China

农田地表径流氮磷流失与土地利用、土壤和灌溉方式有着极为重要的联系，而且具有十分明显的地域特点。本文选取我国南方丘陵地区典型灌区——湖北省漳河灌区的水旱作物（分别为水稻和玉米）作为研究对象，开展了农田地表径流N素和P素流失特性及其影响因素的试验研究。结果表明：土地利用类型对地表N素流失量的影响显著，地表TN流失量表现为旱地〉水田；土地利用类型对地表P素的流失量有较大影响，但差异性未达到显著水平，地表TP流失量表现为水田〉旱地。随着降雨强度的增大，铵态氮和硝态氮浓度均呈减小的趋势，有机氮的比例由3．2％增至69．7％，无机氮比例由96．8％降至30．3％，更多的有机氮随地表径流流失；随着降雨强度的增大，农田排水总磷和磷酸磷也呈增加的趋势。采用节水灌溉方式，降雨利用率提高了14％～23％，节水率达15％，降雨排水量减少20～25mm左右，能够有效降低农田氮、磷等养分流失对地表水的污染。作物生育期和地形地势差异也会影响降雨径流特征和农田养分流失。

In order to reveal the mechanisms of agricultural non-point source pollution, the Zhanghe Irrigation District in Hubei Province, a typical irrigation district in hilly areas in central China, is selected to conduct field experiments on the influencing factors ariel characteristics of nitrogen and phosphorus losses in surface runoff from farmland. On the basis of field observation in Tuanlin Experiment Station in the irrigation district in May-September, 2007, the influencing factors and laws of nitrogen and phosphorus losses in surface runoff from paddy rice and corn fields are analyzed. In the experiment station, observations on 10 plots of three kinds of typical terrain are conducted for field-scale experiment. Observations include surface runoff and water leakage monitoring under different land-use types and different irrigation activities. Water sample analysis indicators in surface runoff from the fields include total nitrogen, nitrate-nitrogen, ammonium-nitrogen, total phosphorus and phosphate-phosphorus, and the chemical analyses are conducted according to the national standards. The results show that land-use types have a significant effect on the concentration of the nitrogen, and the total nitrogen losses in surface runoff are in the order of corn 〉 paddy rice. Land-use types have greater impact on the losses of total phosphorus but not at a significant level. With the increase of rainfall intensity from 6.0 mm· d-1 to 52 mm · d 1, ammonium-nitrogen and nitrate-nitrogen concentration decreased remarkably, organic nitrogen increased from 3.2% to 69.7%, inorganic nitrogen decreased from 96.8% to 30.3%, which means that the proportion of organic nitrogen lost in the surface runoff increased; while the total phosphorus and phosphate-phosphorus concentrations increased gradually. Through using the water-saving irrigation technique, rainfall use efficiency was increased by about 14% ~23%, irrigation water was saved up to 25%, and surface drainage was decreased by about 20~25 mm, thus, water pollution caused by the losses of nitrogen, phosphorus and other nutrients in surface runoff can be reduced effectively. Crop growing stages and topography and landscape also have impacts on rain- fall-runoff characteristics and farmland nutrient losses.