Soil erosion impacts on soil biological fertility in a purple hilly region

In order to better understand erosion-induced changes in soil quality, soil erosion impacts on soil microbial fertility of a purple soil with steep sloping farmland were explored in the Sichuan Basin of China by using 137Cs technique. Results showed that the contents of soil microbial carbon (MBC) and activities of soil alkaline phosphate and invertase significantly decreased by 41%, 44% and 17%, respectively, in these farmlands compared to a control slope, resulting in an obvious deterioration in soil microbial fertility with a 35% decrease in MFDI (soil microbial fertility degradation index). A significantly positive correlation was found between soil invertase activity and 137Cs inventory (r=0.643, p=0.024), suggesting soil invertase activity decreases with increasing soil erosion. Soil erosion by tillage resulted in the lowest soil MBC contents and enzyme activities in upslope positions, whereas soil accumulation by tillage created the highest soil MBC contents and enzyme activities in bottom positions. As a result of soil redistribution, the variations in soil MBC, alkaline phosphate, urease and invertase increased by 2.8, 0.8, 1.4 and 4.5 times, respectively, in these farmlands than those in the control slope. Land management strategies should involve combating the deterioration and increased spatial variation in soil microbial fertility in purple soil with steep sloping farmland.