Soil physico-chemical properties and microbial quantities in different pastures in arid area of saline-alkali soil

Soil of 0-20 cm and 20-40 cm soil layer were sampled from 6 different cultivated grassland in arid and saline-alkali area of Ningxia to analysis their physico-chemical properties, nutrient content and soil microbial quantity and screen the best grassland to improve soil quality. The results showed that soil moisture content, bulk density, pH in 0-20 cm layer were lower than that in 20-40 cm layer in the cultivated grassland. Soil nutrient and soil total salt content in 0-20 cm layer were higher than that in 20-40 cm. Leguminous pasture grassland performed better in increasing soil organic matter, total nitrogen, available nitrogen in both sampled layers and reducing soil salinity in 20-40 cm compared with other gramineae pastures. Gramineous pastures performed better in improving water conservation, reducing soil bulk density and increasing soil available phosphorus in 20-40 cm soil compared with other leguminous pastures. The ability of legume to improve the soil quality decreased in the following order: Medicago sativa＞Astragalus adsurgens＞Melilotus offcinalia. The ability of gramineae to improve soil quality decreased in the following order: Elymus cylindricus＞Agropyron cristatum＞A.cristatum×A.mongolicum. For all of the studied cultivated grassland, there were more soil bacteria, actinomycetes, fungi in 0-20 than in 20-40 cm. The numbers of these 3 tested microorganism also varied with cultivated pasture. For leguminosae, the number of microorganism decreased in the following order: M.sativa＞A.adsurgens＞M.offcinalia. For gramineae, the number of microorganism decreased in the following order E.cylindricus＞A.cristatum＞A.cristatum×A.mongolicum. Soil water content in 0-20 cm was significantly positive correlated with numbers of fungi (P0.05). Soil pH value and the number of actinomycetes and fungi in 20-40 cm were significant negative correlated (P0.05). Soil total salt contents in both layers were negatively correlated with the numbers of bacteria, actinomyces and fungi. Organic matter, total nitrogen, available nitrogen, phosphorus and potassium were significant positive correlated (P0.01) with the numbers of bacteria, actinomyces. Available phosphorus and available potassium were significantly positively correlated with the number of fungi (P0.01).