不同农艺措施对巢湖沿岸坡耕地不同形态磷径流输出的控制效果

为明确巢湖沿岸坡耕地不同农艺措施对生态保护和水环境治理的影响,以农业面源污染长期定位观测基地为平台,于2014—2015年连续2 a对常规耕作(CK)、植物篱(黄花菜,PH)、植物篱+秸秆覆盖(PHS)和等高垄作(CR)4种农艺措施下的水土及随地表径流迁移的各种形态磷进行了监测。结果表明,与常规耕作相比,PH、PHS和CR能有效地减少径流量和产沙量(P0.05),降低效果依次为:PHSPHCR。与CK相比,PH、PHS和CR可分别减少23.5%、36.5%和19.7%的径流流失和29.5%、45.2%和26.3%的土壤流失,表现出显著的水土保持作用。CK条件下的径流液总磷(TP)浓度是0.612~1.220 mg·L~(-1),其中颗粒态磷(PP)占总磷的71.5%~81.7%,颗粒态磷是磷随地表径流迁移的主要形态。在溶解态总磷(DTP)中,溶解态正磷酸盐(D-Ortho-P)所占比例较大,为87.4%~90.7%;溶解态有机磷(DOP)所占比例较小,仅占9.3%~12.6%。与CK相比,PHS、PH和CR显著降低了径流液PP和TP的浓度(P0.05),但却不同程度地提高了DTP和D-Ortho-P的浓度,而对DOP的浓度无显著影响(P0.05)。CK条件下,磷的年流失负荷平均为0.706 kg·hm~(-2),占当年作物施磷量0.98%。与CK处理相比,PH、PHS和CR处理磷的年流失负荷分别降低38.4%、53.8%和33.4%(P0.05),其对磷素输出的控制效应主要通过减少径流量和降低径流液PP的浓度来实现的。综上可知,植物篱(黄花菜)、植物篱+秸秆还田和等高垄作是控制巢湖沿岸坡耕地水土及磷径流输出的有效措施,其中植物篱配合秸秆覆盖还田效果最佳。该研究可为巢湖流域坡耕地水土流失和面源污染防治提供科学依据。

Effect of agronomic measures on phosphorous loss via runoff in sloping croplands around Chaohu Lake

Eutrophication has been recognized as one of the main global environmental problems in areas with intensive agri-cultural production where there is nutrient export from farmlands to surface water bodies. Phosphorous (P) via runoff from farmland has been found to be one of the main contributors to water-quality degradation in Chaohu Lake. Thus, source control of P loss from farmlands was critical in remediation of eutrophication in Chaohu Lake. In order to test the efficiency and effi-cacy of different agronomic measures on reducing runoff, sediment and P loss, a long-term field runoff experiment was carried out in a sloping cropland around Chaohu Lake. Four treatments of agronomic measure were applied — 1) conventional tillage (CK), 2) plant hedgerow ofHemerocallis citrina (PH), 3) plant hedgerow with straw mulching (PHS) and 4) contour ridge (CR). Runoff volume, soil loss, concentrations of TP (total phosphorus), PP (particulate phosphorus), DTP (dissolved total phosphorus), D-Ortho-P (dissolved orthophosphate phosphorus) and DOP (dissolved organic phosphorus) as well as P loss via runoff were determined. The results for 2014–2015 showed that PH, PHS and CR treatments significantly reduced soil and water loss in the order as follows: PHS > PH > CR (P< 0.05). Also the reduction in sediment was great than that in runoff. Compared with CK, agronomic measures of PH, PHS and CR decreased runoff, respectively, by 23.5%, 36.5% and 19.7%, and reduced sediment, respectively, by 29.5%, 45.2% and 26.3%, showing significant effect on soil and water conservation (P< 0.05). The concentration of TP in runoff under CK was 0.612–1.220 mg·L-1, in which PP was the predominant form, account-ing for 71.5%–81.7% of the TP. In DTP, D-Ortho-P was the main form, accounting for 87.4%–90.7%, while DOP remained in low concentration. It was found that the three agronomic measures (PH, PHS and CR) significantly reduced PP and TP con-centrations in runoff (P< 0.05), concurrently increased the concentrations of DTP and D-Ortho-P, but had no obvious effect on DOP concentration (P> 0.05). Obviously, TP concentrations in the current study were higher than 0.4 mg·L-1, exceeding Class V level of the national environmental quality standards for surface water (GB3838—2002). The results implied that P loss via runoff from farmlands in Chaohu Lake region posed pollution risk if allowed to drain directly into the lake. Besides, annual P runoff loss from sloping croplands under CK was 0.706 kg·hm-2, the equivalent of 0.98% of applied P fertilizer in the experi-ment. Compared with CK, PH, PHS and CR reduced annual P loss respectively by 38.4%, 53.8% and 33.4%. Another finding in the study was that the reduction in runoff volume and that in PP concentration were mainly responsible for the decline in P loss. In conclusion therefore, PH, PHS and CR significantly reduced soil, water and P loss via runoff in sloping farmlands in Chaohu Lake region. Among the treatments, PHS was the most effective. The results of this study provided more insight into the need for strategies to reduce agricultural non-point source pollution in Chaohu Lake region and other similar regions.