Characteristics of Nitrogen Losses in Surface Runoff from Farmland

Abstract：In order to understand the characteristics of nitrogen losses in surface runoff from upland field and paddy field under different irrigation condition,field experiments were conducted on the nitrogen losses in surface runoff from paddy fields and maize plots under water-saving irrigation and conventional irrigation.The results showed that crop types have significant impacts on nitrogen losses through influencing the plant cover,soil and water conditions in the field.Ammonium nitrogen in dryland is lower than in paddy,but nitrate nitrogen is in contrary;irrigation also affects the losses of nitrogen from farmland by means of influencing the processes of infiltration and retention.Although the concentration of nitrogen under the condition of water-saving irrigation is higher than those of traditional irrigation,the total nitrogen losses in surface runoff from farmlands is reduced significantly by reducing the total surface drainage;rainfall is the most important factor and driving forces for the losses of nitrogen from farmland.The losses of total nitrogen and nitrate nitrogen increase with rainfall intensity;topography and location of field have impacts on rainfall-runoff characteristics,soil erosion and nitrogen losses from farmland.Ammonium nitrogen from the paddy fields in the downstream is higher than that in the upstream,but the total nitrogen and nitrate nitrogen are in contrary.Moreover,the influence of different growing stages on nitrogen losses in surface runoff from farmlands is not obvious.