土石山区不同农作方式下坡面径流氮素流失过程

Characteristics of Nitrogen Loss Under Different Farming Practices of Slope in Mountain Areas

采用人工模拟降雨方法研究裸地（BL）、花生（PL）、50%裸地＋50%花生（BP）、50%玉米＋50%花生（CP）和秸秆覆盖（SC）5种农作方式下,丹江鹦鹉沟小流域坡面小区径流氮素流失规律。结果表明：地表径流总量表现为裸地BL〉SC〉CP〉BP〉PL;随降雨时间延续,地表径流均呈不同程度增加趋势,其中BL小区增长速度最快,BP措施下出流时间最长（降雨后第6min）,花生立地条件下每5min地表径流变化稳定在0.30-3.46L之间。径流中氮素流失浓度表现为BP〉CP〉PL〉BL〉SC,随时间呈波动增加趋势,沿坡面由上至下表现为先减小后增加。受农作方式的影响,氮素流失在时间、空间上变化规律不同;总氮、硝态氮流失浓度最大增幅分别可达45.54%和55.79%,流失量分别在15.90-110.81mg/m2和15.58-90.33mg/m2之间;径流中氮素浓度的变异性略大于对应的地表径流。农作方式与硝态氮呈正相关,与总氮相关性不显著。在鹦鹉沟小流域农田养分流失不容忽视,需进一步采取有效的水土保持措施。秸秆覆盖措施既能有效保持土壤养分,又可保证入河径流量,是值得推荐的水保措施。

In this study,the loss of nitrogen（N）with different agricultural practices（AP）was studied by field simulated rainfall in Yingwugou watershed,Dan River.Results indicated that the order of amount of surface runoff was that bare land（BL）〉straw cover（SC）〉50% corn＋50% peanut（CP）〉50% bare land ＋ 50%peanut（BP）〉peanut land（PL）.The initial runoff-yielding time was different between five kinds of AP and had no significant effects on the volume of surface runoff.With the increase of rainfall time,surface runoff under different coverage increased with different trends.In the beginning,the surface runoff increased stably.At the mid-to late of the rainfall,the fluctuation of surface runoff became bigger.The surface runoff increased under different stocking rates with the rainfall time and the runoff per 5min ranged from 1.48Lto20.66 Lon bare land which had the highest growth rate.The nitrogen concentration in surface runoff with different AP increased in fluctuation with rainfall time,and followed the order of BP〉CP〉PL〉BL〉SC.Analysis of variance revealed significant differences among the five kinds of AP.As a soil and water conservation measures in water source area,straw mulching not only ensure abundant water but also conserve soil nutrient effectively.The concentration of N loss increased in fluctuation with rainfall time which the largest range for total N and nitrate N were 45.54%,55.79%,respectively.From top to bottom of the slope,the N lossdecreased firstly,and then increased.For all the sampling points of the slope,the concentration of N loss increased at the early and middle stage of rainfall.But the stabilization had been gradually achieved at the later stage.Under the five kinds of conditions,the amounts of TN and nitrate N loss were in the 15.90-110.81mg/m2 and 15.58-90.33 mg/m2 respectively.Even though the straw mulching could reduce the runoff,the nutrient loss under the straw mulching was not the least.Therefore,only combing with other measures of soil and water conservation can improve the capacity of holding water and soil nutrient.The variability of nutrient loss was higher than that of surface runoff which indicated that the nutrient loss was more likely to be affected by environmental factors.According to the correlation analysis,the AP was positively related with nitrate N and had no obvious correlation with total N.This indicated that more attention should be paid to the nutrient loss on farmland in Yingwugou watershed,and effective measures must be adopted.As a soil and water conservation measures in water source area,straw mulching not only ensure abundant water but also conserve soil nutrient effectively in Yingwugou watershed.For reasonable and targeted watershed management,various measures should be combined.