西南干热河谷坡耕地土壤分离及季节动态变化研究

The dry-hot valleys region in southwest China is characterized as the rotation between the extremely dry-hot season and the heavy-rain-concentrated wet season. Meanwhile, steep slope cropping and tillage disturbance is one of the main factors that causing intensive soil loss in this region. It is important to clarify the seasonal dynamic of soil properties as influenced by both the natural rhythm and periodic tillage disturbance. The response of soil resistance to erosion also need to be explored and quantified for soil loss prediction. This research is therefore focus on the slope cropland in the dry-hot valleys region of southwest China. According to the theory of soil erosion process and hillslope hydraulic, soil detachment parameters were chosen to describe soil resistance to concentrated flow erosion. Field plots would be designed with the combination of different influential factors. Field runoff simulation experiments would be conducted to measured soil detachment indexes of different stages. In turn, the seasonal dynamic trend of soil properties and detachment would be explored. The effect of dry-wet rotation, tillage disturbance and plant growth on soil detachment can be therefore quantified. Accordingly, equations can be developed to calculate soil detachment capability and rill erosion parameters in a process-based erosion model. The results would be helpful in the precise prediction of soil erosion on slope cropland of southwest China.

极端干热的旱季与高强度降雨集中的雨季交替是我国西南干热河谷地区最鲜明的环境特征，坡地开垦与耕作扰动是导致该地区强烈水土流失的主要原因之一。那么，在自然节律性和耕作扰动周期性共同作用下的土壤属性变化对抗侵蚀能力有何影响？如何描述土壤抗侵蚀能力的动态变化并用于侵蚀预报？针对以上问题，本申请项目拟以干热河谷典型坡耕地为研究对象，基于土壤侵蚀过程和坡面水动力学理论，采用土壤分离指标表征土壤抵抗水流侵蚀的能力，设置不同影响因素的对照组合，开展野外原位模拟冲刷试验测定不同时期的土壤分离指标，以期阐明干热河谷坡耕地土壤属性和土壤分离的季节变化趋势，揭示干湿交替、翻耕扰动和植物生长等因素对土壤分离的影响机制，构建坡耕地土壤分离能力和细沟侵蚀参数预测方程，为干热河谷坡耕地土壤侵蚀精准预报提供依据。

针对西南干热河谷地区极端干湿交替和人类活动导致的坡耕地土壤抗侵蚀能力动态变化复杂性，本研究选择凉山州德昌县的典型坡耕地，建设了9组不同措施和坡度组合的试验样地，开展了三个季节的原位径流模拟冲刷试验和土壤入渗试验，测定了土壤属性和孔隙结构等指标。通过以上研究阐明了坡耕地休闲、翻耕和种植玉米三种处理在雨季初期、中期和末期的土壤分离能力变化趋势，建立了土壤分离速率与水流剪切力、水流功率、单位水流功率等水动力学参数之间的量化关系，计算了坡耕地土壤细沟可蚀性等因子，在此基础上对比了土壤结皮和农作物对翻耕后基础细沟可蚀性因子的影响，发现农作物生长能够有效提高土壤抗侵蚀能力，在雨季时段对细沟可蚀性的消减作用超过了土壤结皮的作用；与此同时开展的土壤入渗试验和原状土CT孔隙扫描结果表明，坡耕地翻耕扰动和农作物生长均能显著提高土壤孔隙指标和入渗能力，缺少农作物覆盖的翻耕休闲土壤孔隙和入渗速率容易因雨滴打击压实和结皮发育而迅速减小，而生长玉米的样地则能够保持较好的土壤孔隙连通条件和较高的入渗能力；在上述土壤可蚀性和入渗能力参数的基础上运行WEPP模型，得到的坡面土壤侵蚀强度估算值模型有效系数可达0.867，显著优于WEPP默认土壤参数的估算精度，说明本研究获取的土壤抗侵蚀能力指标较为可靠，尤其是对于翻耕扰动和农作物生长条件下的估算精度最优。以上研究从土壤侵蚀过程和微结构角度阐明了西南干热河谷坡耕地土壤抗侵蚀能力的动态变化机制，在大量原位模拟试验的基础上量化了土壤抗侵蚀能力参数，有助于提高坡耕地土壤侵蚀强度的预测精度，同时也有利于深化认识农作物在研究区坡耕地水土保持中的重要意义。