Abstract: The study on the soil nutrients accumulation and their loss risk under effects of biological soil crust (BSC) in a typical basin of Loess Plateau in northern Shaanxi Province showed that with the development of BSC, the nutrient contents in BSC and in 0-2 cm soil layer increased rapidly, but those in deeper layers had less change. Within the 20 years of rehabilitation, the relationship between the nutrient contents in BSC and the rehabilitation age could be described by the exponential equation (y=a［b-exp(-cx)］). The increasing rates of organic matter (OM), total nitrogen (TN), and available nitrogen (AN) in the 20 years changed less, but the contents of total phosphorus (TP), available phosphorus (AP), and available potassium (AK) increased very fast at first 5 years. The yearly average contribution of naturally developed BSC to soil nutrients was 50.15 g·m^-2 of OM, 1.95 g·m^-2 of TN, 0.44 g·m^-2 of TP, 164.33 mg·m^-2 of AN, 9.64 mg·m^-2 of AP, and 126.21 mg·m^-2 of AK. Compared with naturally developed BSC, cultivated BSC had a faster growth rate, and its contribution to soil nutrients, especially to soil available nutrients, was greater. However, the increase of soil nutrients under effects of BSC could intensify the loss risk of soil nutrients with sediments. In this study, 39.06% of increased soil nutrients by BSC were lost with sediments, and 69.04% of them were conserved. Therefore, even though the loss risk of soil nutrients was increased, their net accumulation was still significant, indicating that BSC had better effects on soil nutrients accumulation.

Key words: species diversity, soil microbe, soil enzyme activity, vegetation restoration, purple soil.