Characteristic of soil micro-aggregates loss on slopes with different surface water drainage patterns

Abstract: No matter on non-continuous slopes formed from natural terrace or on continuous slopes formed in process of excavation, water loss and soil erosion are inevitable. During the process of rainfall, under a certain rainfall intensity, there will be different patterns of slope water and soil loss response mechanism in different land use types, which have different soil infiltration rates and aggregate structures affected by soil particles fractal characteristics. It will cause the soil particle and sediment to transport, and affect soil nitrogen and phosphorus nutrient output. Soil micro-aggregates are an important indicator from which we can estimate how a measure changes soil properties. There are always 2 kinds of runoff outflow modes in natural hydrological systems. Considering the cost of projects, only level trenches parallel to the contour line are used on the slope land of Southwest China. In order to know if there is a better way to control slope runoff and protect surface soil, 2 different layout modes of level trenches were designed to change effluent process of surface runoff on the slopes. And in contrast with slopes without any drainage layout (CK), the rainfall simulation experiments were performed to study the different characteristics of runoff and soil micro-aggregates losses under 2 different slope drainage layout measures, which were respectively designed to lead the water flow to converge in a form of "V" (T1) and to shunt in a form of inverted "V" (T2). The result shows that the layout of drainage T1 and T2 can significantly enrich micro-aggregate particles less than 5 μm in the sediment lost from the slops with different gradients and land use types. Compared with CK treatment, T1 and T2 both can bring a more stable distribution of micro-aggregates on cultivated land slopes, but T2 has a more obvious effect on micro-aggregate particles less than 5 μm on the slopes. However, when the slope is 5° or 10°, T1 mode can better alleviate the trend of "soil coarseness" phenomenon on the cultivated land slopes. Due to the new drainage measures arranged on the forest land slope, we also noticed that T1 mode can decrease the volatility of micro-aggregates' enrichment significantly and decrease the erosion degree of micro-aggregate particles with smaller size. Moreover, T1 mode plays a stronger role on controlling micro-aggregates losses on the grassland slope than T2 and CK. Nevertheless, each kind of slope drainage layout measure has its own focus, and can help change the process of slope runoff and make different size of soil particles deposited on the slope in different ways so as to achieve the control of dewatering and maintain soil quality, which can also reduce non-point source pollution. So it's necessary to choose an appropriate slope drainage layout measure according to soil properties, gradient and land use type of a slope. This study provides a possibility of finding a new level trench which may be valuable to apply in reality.