Soil nutrient and microbial biomass in the Loess hilly area of Ningxia under different plant rehabilitation patterns

Nutrient and microbial biomass carbon (Cmic), nitrogen (Nmic), phosphorus (Pmic) in soils of Guyuan Loess hills of Ningxia Province under natural grassland, cropland, abandoned cropland and varying ages of rehabilitated Caragana korshinskii shrub lands were determined. Base on the results, soil nutrients contents increase with increasing age of rehabilitation, and are generally low in cropland and newly abandoned cropland, with the exception of available P and total nitrogen. Soil microbial biomass is significantly different under different vegetations. Cmic occurs in the order of abandoned cropland < cropland < natural grassland < 3-year-old C. korshinskii shrub land < 13-year-old C. korshinskii shrub land < 23-year-old C. korshinskii shrub land. While natural grassland has the lowest Nmic, cropland, abandoned cropland and the different-aged C. korshinskii shrub lands have higher Nmic. Pmic is sig-nificantly different under different vegetations, especially in the soil depths of 5～20 cm and 20～40 cm. Soil Cmic, Nmic and Pmic are significantly related with vegetation type and rehabilitation age. C. korshinskii shrub shows obvious enhancing ability on soil microbial biomass, which is improved by increased rehabilitation age.