Effects Of Introduced Legume Species On Microbial Biomass And Nutrients Of Abandoned-fields

The impacts of sowing legumes (Medicago sativa, Melilotus suaveolens and Astragalus adsurgens) on soil microbial biomass, soil moisture, pH, soil bulk density, organic matter and total nitrogen were studied in abandoned-fields of the loess plateau northwest of China. The results showed as follows:1. 3 years after introduction of legume species, soil moisture in surface layer (0-20cm) fluctuated significantly, and soil moisture in deeper layer (20-100cm) fluctuated insignificantly. Soil moisture content in deeper layer (20-100cm) under legume species introduction was lower than that under controls. The soil moisture content 20-40cm,40-70cm showed similar trends as the soil moisture content 70-100cm, The difference of soil moisture content exhibited in the inner of treatments and among the treatments.2. 4 years following introduction of legume species, soil (0-20cm,20-40cm) under Medicago sativa-adding had the lowest pH. Adding legume species decreased the layer soil bulk density. Soil (0-10cm) under Medicago sativa-adding had the highest bulk density.3. There was a positive correlation between Corg and TN (p<0.05). These results suggest that introduced legume in abandoned-fields significantly improved the soil carbon and the soil TN (0-20cm), which may help in sustaining soil productivity. Soil (0-20cm) under Medicago sativa-adding had the highest Corg and TN. With increasing succession times, the content of soil Corg and TN increased, but TN did not change dramatically.4. Introduction of legumes species significantly increased microbial biomass, soil(0-20cm) under Medicago sativa-adding had the highest microbial biomass carbon and nitrogen. With the increasing of succession times, the content of soil(0-20cm) MBC increased, but the content of soil MBN were not dramatically. Along the soil depth, the content of soil (0-20cm) MBC was higher than the content of soil(20-40cm) MBC, but MBN did not change dramatically. These results demonstrated that introduction of legume species to abandoned-fields could accelerate the succession and increase soil fertility by improving levels of soil organic matter, total nitrogen and soil microbial biomass during the first few years in the central loess plateau, northwest china. Further long time research is necessary to determine the effect of introduced legume species on abandoned-fields succession.