The Relation between Stability of Aggregates on Surface and SOM of Red Bare Soil in the Karst Area of East Yunnan, China

Abstract

Red bare soil is a kind of soil remained on plateau from ancient ages. Researchs toward better understanding of the relationship between stability of surface aggregate and SOM (Soil Organic Matter) based on 14 typical samples indicate that red bare soil clay (<0.002mm) contents between 12.18% and 64.02% which belongs to poor cultivation performance soil. The number of macro-soil aggregates after dry sieving were far more than the number after wet sieving. Water-stable aggregate content (WSAC) informed the feature of red bare soil. The WSAC were between 28.77% ~ 52.87% at the size >0.25mm and the aggregates destruction rate (PAD0.25) were 34.28% to 68.10%, mean weight diameter (MWD) were at the size of 0.53 to 1mm, geometric mean diameter (GMD) were between 0.37 and 0.58mm, fractal dimension (FD) were between 2.79 and 2.92. The 5 index above indicated the structural stability, anti erodibility and physical property were both poor when compared with other typical soil samples in southwest karst area of China. The research also indicated that soil organic matter (SOM) and WSAC has more effect than mechanical aggregate. SOM has significant positive correlation with MWD and GMD, and significant negative correlation with PAD0.25 and FD. Lack of SOM and exposed led to soil structure stability deterioration. These can be the reason why soil erosion seriously and can’t grow vegetation in red bare soil area.