The effects of erosion on the microbial populations and enzyme activity in black soil of northeastern China

Soil erosion may deteriorate soil microbial ecosystems, and assessing the impacts of soil erosion on soil micro-biological properties is important for eroded-soil restoration. Based on the simulated erosion plots with treatments of eight erosion depths (0, 10, 20, 30, 40, 50, 60 and 70 cm) and two sub-treatments of no fertilizer and chemical fertilizer situated in black soil region, northeast China, soil samples of the 0–20 cm layer in each plots were collected and several key soil biological parameters were determined. The results indicated that the values of all the variables of soil micro-biological properties had a linearly decreasing trend with increasing erosion depths. From erosion depth of 0–70 cm, the soil microbial biomass C (MBC), microbical biomass N (MBN), numbers of bacteria, mold, actinomyces, azotobacter, phosphorus bacteria, potassium bacteria, and catalase, urease, β-glucosidase, cellulase activities decreased by 93.4%, 93.1%, 87.7%, 78.2%, 82.9%, 72.7%, 79.7%, 79.6%, 91.3%, 89.8%,91.7% and 69.5%, respectively for fertilized plots, and 94.8%, 78.2%, 89.7%,59.0%, 92.3%, 72.7%, 79.7%, 78.4%, 90.0%, 87.9%, 92.6% and 75.0%, respectively, for unfertilized plots. There were significant correlations between soil organic matter (SOM), total N (TN) and soil micro-biological properties. Chemical fertilization increased available P (AP) (P < 0.001) and SOM (P < 0.05) significantly, but had no significant effect on MBC, MBN, microbial quantities and enzyme activities. The results showed that local conventional chemical fertilization did not enhance soil biological status and was not able to counterbalance the fertility loss incurred by soil erosion, and also suggest that protective measures to improve soil biological properties should be taken immediately.