Effects of mixed species,mixed ratios of legume and grass on soil nutrients in surface soils of legume-grass mixture pasture

The legume-grass mixtures included three legumes (Onobrychis viciaefolia, Medicago sativa, Trifolium pretense) and three grasses (Dactylis glomerata, Bromus inermis, Phleum pretense). The mixed combinations were 6, 5, 4, 3 species mixture at three sowing ratios of legume∶grass with 5∶5, 4∶6, 3∶7, respectively. The experiment was conducted in Zhaosu Basin of Xinjiang with the randomized complete block design. The soil organic matter, total nitrogen(N), alkaline hydrolysis nitrogen, total phosphorus (P), available phosphorus, total potassium and available potassium were measured for analyzing the influence of mixed species and ratios of legume and grass on soil nutrients distribution and accumulation. The results showed that soils with the legume-grass mixtures had higher soil alkaline hydrolysis N content than soils with grass monoculture. And soils with the legume-grass mixtures had higher soil available P content than soils with grass and legume monoculture. The soil organic matter, alkaline hydrolysis N, total P and available P content decreased with the mixed ratios of legume and grass decreasing. The soil organic matter, total N, available P and total K content in soils with 3 and 4 species mixtures were higher than those in soils with 5 and 6 species mixtures whereas the soil alkaline hydrolysis N and available K content in soils with 3 and 4 species mixtures were lower than those in soils with 5 and 6 species mixtures. The two-way variance analysis indicated that the mixed species, interaction of mixed species and ratios of legume and grass were the main factors which influenced the variance of soil nutrients distribution and accumulation. The mixed ratios of legume and grass could significantly influence the variance of soil total P and K. Therefore, the legume-grass mixtures could improve the content of soil alkaline hydrolysis N and available P. The soil nutrients did not significantly increase with the increasing of legume ratios.