喀斯特区典型石漠化坡耕地覆盖措施水土流失调控效应

Soil and water loss on slope farmland is an important driving factor of rocky desertification aggravation in Karst area, while the harnessing scope of National Soil & Water Conservation Key Project is still limited. Therefore, it has important realistic meaning to carry out the relevant experiments of soil & water conservation tillage measures such as mulch on rocky desertification slope farmland. Straw application, forage intercropping and so forth have been verified to be effective measures on soil & water conservation on sloping farmland; however, the reports about straw mulching effect on soil structure and soil & water loss have not been retrieved in Karst area, and the effective minimum straw mulch rate based on soil & water conservation in med-and-long term has not been ascertained. To exploring the scientific problem, the experiment of straw application and forage intercropping would be carried out by using field runoff plots, in which the straw would be mulched on the soil surface in current year and ploughed into plough layer in following year. Basing on above experiment, mulch influence on soil environment factors such as soil structure, nutrient and so on, soil erodibility, soil moisture, runoff and soil erosion would be studied. The regulating effect and its soil mechanism of mid-and-long term mulch on soil & water loss would be illuminated; the minimum straw mulch rate would be ascertained. Meanwhile, to the existing problems of observation method of runoff and sediment, we would improve the collection and sampling methods, and then make the monitoring values of soil & water loss a better accuracy. Basing on this study, the key technologies of mulching tillage on rocky desertification slope farmland would be refined, and the results would contribute to further studies on soil environment improvement and soil & water conservation. Those results are also useful for basic data accumulation of the application of Universal Soil Loss Equation in karst area.

坡耕地水土流失是喀斯特区石漠化加剧的重要驱动因子，而目前国家治理专项治理范围较为有限，因此，开展覆盖等水土保持耕作措施研究具有重要的现实意义。已开展的研究证实了秸秆还田及牧草间作等覆盖措施防治水土流失的有效性，但暂未见喀斯特区秸秆还田对土壤结构及水土流失的调控效应相关试验报道，同时，基于水土保持的中长期最小秸秆覆盖率尚未探明。为探讨上述问题，采用径流小区野外定位观测法，开展秸秆还田（当年覆于表土层，次年翻入耕作层）及牧草间作种植试验，研究中长期覆盖措施对典型石漠化坡耕地土壤结构及养分等土壤环境因子、土壤可蚀性、土壤水分、径流及土壤侵蚀的影响，阐明其水土流失调控效应及土壤学机制，探明基于水土保持的中长期最小秸秆覆盖率，提炼覆盖耕作措施关键技术，同时，改进径流泥沙常规观测方法，提高观测精度，为石漠化坡耕地土壤环境改善及水土流失防治奠定研究基础，为通用土壤流失方程在喀斯特区的应用积累基础资料。

坡耕地水土流失是岩溶区石漠化发展及土地退化的重要驱动因子，严重制约了区域农业可持续发展。为探究秸秆等有机覆盖措施对岩溶区坡耕地水土流失调控效应的有效性，项目采取野外径流小区原位观测法，持续开展了为期4年的原位覆盖种植试验，观测天然降雨条件下，中长期有机覆盖措施对土壤养分、土壤水分，以及坡面产流产沙等水土保持功能的影响，证实了秸秆等有机覆盖措施调控岩溶区坡耕地水土流失的有效性，探明了基于水土保持功能的中长期适宜秸秆覆盖率范围，并对有机覆盖耕作措施关键技术环节进行了总结和凝练。结果显示，有机覆盖措施不同程度降低了土壤侵蚀风险，提高了土壤水分和养分，改善了土壤环境，并在一定程度上提高了作物产量。但随着秸秆覆盖率的增加，前述指标并不是一直增加，例如当秸秆覆盖率从5556kg/hm2增加至6944kg/hm2后，水土保持效果不再明显加强。基于坡耕地秸秆覆盖下土壤肥力、土壤水分、产流产沙等水土保持功能的综合分析和评价，结合经济有效原则，我们建议在西南喀斯特坡耕地覆盖6000kg/hm2左右的秸秆，并适当添加钾肥以维持土壤钾素平衡，以促进农田生态系统的恢复，从而取得较好的水土保持功能，同时促进作物增产；牧草间作覆盖在玉米苗期对坡面产流产沙的调控效果不够理想，较玉米单作并未显著提高，但随着玉米生育期的推进，牧草间作措施水土流失防治效果逐渐提升。各牧草间作处理之间，紫花苜蓿间作处理在增加土壤有机质、全氮、全磷等方面较为显著，且保墒效果也相对较好。因此，紫花苜蓿可能是一种较为合理的坡耕地间作牧草，可作适当推广。研究结果可为西南喀斯特区坡耕地水土流失综合治理提供理论参考，同时为农艺耕作措施在喀斯特区的推广提供一定的技术支撑。