壤中流条件下垄向坡度对氮和磷流失的影响

Impact of row grade on losses of nitrogen and phosphorus under seepage condition

横坡垄作系统中因垄向坡度的存在,雨水会在位置较低的垄沟内汇集,当横垄土壤达到饱和后可导致壤中流的产生,进而引发横垄垮塌。以棕壤横垄为研究对象,采用可同时调节垄向和坡面坡度的土槽进行模拟降雨,研究壤中流条件下垄向坡度对不同侵蚀阶段氮、磷流失的影响。结果表明:1)壤中流侵蚀阶段,NO3-N、NH4-N和PO4-P的流失量均表现为垄向坡度2°>10°>6°,而垄向坡度间其浓度差异的大小顺序为10°>6°>2°;细沟间和细沟侵蚀阶段,不同垄向坡度下NO3-N浓度和流失量的差异均为10°>2°>6°,垄向坡度间NH4-N和PO4-P浓度和流失量的差异分别为6°>10°>2°和2°>6°>10°。2)壤中流侵蚀阶段,径流量是导致垄向坡度间氮、磷流失差异的关键因子,而细沟间阶段则为养分浓度。3)垄向坡度的变化仅导致细沟间和细沟侵蚀阶段NH4-N流失机制的改变。研究结果可为横坡垄作的水土保持效益评价及合理利用提供依据。

The existence of row grade in the contour ridge system results in that runoff from side slopes accumulates in the low areas along furrows. When the collected rainfall exceeds the storage capacity of soil,that is,when soil becomes saturated,seepage flows through ridges and then leads to the collapse of the contour ridge system. In this study,we conducted rainfall simulation experiments to evaluate effects of row grade on nitrogen and phosphorus losses in runoff for brown soil during different erosion stages（ seepage erosion,inter-rill and rill erosion） under seepage condition,using the runoff box by which row grade and field slope can be adjusted simultaneously. Results showed that： 1） During seepage erosion stage,NO3-N,NH4-N and PO4-P losses under different row grades were in the order of 2°〉 10°〉 6°,while differences in their concentrations ranked in the sequence of 10°〉 6°〉 2°; for inter-rill and rill erosion stages,the sequence of NO3-N loss under different row grades was 10°〉 2° 〉6°,while the order of NH4-N and PO4-P losses among row grades was 6°〉 10°〉 2° and 2°〉 6°〉 10°,respectively. 2） For seepage erosion stage,difference in runoff was the dominant factor that induced the variation of nutrient loss among rowgrades,while for inter-rill stage it was concentration. 3） The variation of row grade only altered NH4-N loss mechanism during inter-rill and rill erosion stages. These findings in our study would provide scientific guidance for evaluating soil conservation benefit and for implementing the contour ridge system.