不同雨型下反坡台阶减少红壤坡耕地氮磷流失的效果

为研究自然降雨条件下反坡台阶对坡耕地氮、磷流失的影响,该文基于滇中红壤坡耕地标准径流小区45场典型降雨观测资料,根据降雨量、最大30 min雨强和降雨侵蚀力,综合采用快速聚类和判别聚类,划分确定出A(高雨量、大雨强、高侵蚀力)、B(低雨量、小雨强、低侵蚀力)、C(中低雨量、中小雨强、中低侵蚀力)、D(中高雨量、中雨强、中高侵蚀力)4种降雨类型。研究发现,反坡台阶减流率和减沙率达到52.11%和71.30%,减沙率显著大于减流率(P0.01);不同降雨类型下反坡台阶的减流率表现为:C雨型B雨型D雨型A雨型,减沙率表现为:D雨型A雨型C雨型B雨型,C雨型和B雨型下反坡台阶减流率显著高于D雨型和A雨型(P0.05),减沙率则显著低于D雨型和A雨型(P0.05)。反坡台阶对径流中总氮(WTN)、硝态氮(NO_3~--N)、铵态氮(NH_4~+-N)削减率分别达到68.10%、69.81%、50.14%,对径流中总磷(WTP)、溶解无机磷(DIP,dissolved inorganic phosphate)的削减率分别达到71.52%和72.77%,不同自然降雨类型下反坡台阶对径流中WTN、NO_3~--N、NH_4~+-N、WTP、DIP的削减率均呈现出随着雨量和雨强增大而降低的趋势。反坡台阶对泥沙中全氮(STN)、水解性氮(HN,hydrolyzable nitrogen)的削减率分别达到57.32%和54.22%,对泥沙中全磷(STP)、速效磷(AP)的削减率分别为67.38%和63.69%,不同自然降雨类型下反坡台阶对泥沙中STN、HN、STP、AP的削减率呈现出削减率随着雨量和雨强增大而提高的趋势。该研究可以深入地揭示反坡台阶控制坡耕地面源污染的机理,以及对于控制坡耕地氮磷流失的效果,为源头控制山区水土流失和农业面源污染提供理论支撑。

Effects of reverse-slope terrace on nitrogen and phosphorus loss in sloping farmland of red loam under different rainfall patterns

In order to reveal the different effects and benefits of reverse-slope terrace on controlling nitrogen and phosphorus loss on sloping farmland, the loss of runoff, sediment, nitrogen and phosphorus after rainfall was observed in 2 sloping farmland standard runoff plots (1# and 2#) in central Yunnan Province from 2011 to 2016. The 1# plot is the original sloping farmland, and the 2# plot is the sloping farmland with reverse-slope terrace. The effects of early rainfall were eliminated; finally the data of 45 typical rainfalls were selected. Based on these data, 4 rainfall patterns were classified according to the amount, intensity and erosivity of rainfall with 2 methods including quick clustering and discriminant clustering: Type A (great amount, strong intensity and high erosivity of rainfall), Type B (low amount, minor intensity, small erosivity of rainfall), Type C (low amount, low medium intensity and erosivity of rainfall), Type D (high medium amount, intensity and erosivity of rainfall). Type B was the most frequent rainfall type in the study area, but soil and water loss in the red soil sloping farmland was mainly caused by Type A and Type D. Moreover, the reduction effect for runoff and sediment of reverse-slope terrace was extremely significant (P<0.01), the reduction rate of runoff was 52.11% and the reduction rate of sediment was 71.30%, and the reduction rate of sediment was significantly greater than that of runoff (P<0.01); the reduction rate of runoff was presented as Type C > Type B > Type D > Type A, and the reduction rate of sediment was presented as Type D > Type A > Type C > Type B; the reduction rate of runoff by reverse-slope terrace in Type C and Type B was significantly higher than that of Type D and Type A (P<0.05), while the sediment reduction rate was significantly lower than that of Type D and Type A (P<0.05). The reduction rates of reverse-slope terrace for total nitrogen, NO3?-N, NH4+-N in runoff were 68.10%, 69.81% and 69.81%, respectively, and the reduction rates of total phosphorus, dissolved inorganic phosphate (DIP )in runoff were 71.52% and 72.77%, respectively. It was presented that the reduction rates of reverse-slope terrace for total nitrogen, NO3?-N, NH4+-N, total phosphorus, and DIP in runoff were reduced with the increase of the rainfall amount and intensity in different rainfall patterns. In addition, reverse-slope terrace could cut 57.32% of total nitrogen, 54.22% of hydrolyzable nitrogen (HN), 67.38% of total phosphorus total phosphorus and 63.69% of available phosphorus (AP), and the reduction rates of total nitrogen, HN, total phosphorus, and AP in sediment were increased as the rainfall amount and intensity rose under different rainfall patterns. In conclusion, this study is very helpful both in revealing the mechanism and evaluating the efficiency of reverse-slope terrace to control non-point source pollution in sloping farmland. It also provides technical support for water and soil conservation and controlling agricultural non-point source pollution in mountainous areas from the source.