Distribution of Soil Organic Carbon and Total Nitrogen of Grassland in Yunwu Mountain of Loess Plateau

Distribution of organic carbon(C) and total nitrogen(N) in different natural grassland,artificial Medicago stativa L.grassland with different growth years,Hippophae rhamnoides Linn.shrubland and farmland in Yunwu Mountain of the Loess Plateau were studied.Results show that the ranking of organic carbon and total nitrogen contents in four studied samples are: natural grasslandartificial grasslandshrublandfarmland.As soil depth increased,except in the 10～20 cm of nine-year artificial alfalfa grassland,the contents of soil organic carbon and total nitrogen generally decreased in every 10 cm of 0～40 cm soil depth.The soil organic carbon and total nitrogen contents show significant differences among 10～20 cm,20～30 cm and 30～40 cm soil depth in all natural grassland types,and every 10 cm of 0～40 cm soil depth among 5,7,and 9 growth years for artificial alfalfa grassland.There is a significant linear correlation(P0.01) between soil organic carbon and total nitrogen in natural grassland and artificial grassland.In artificial grassland,the contents of organic carbon and total nitrogen increased with the growth years increased,and the increment of total nitrogen is higher than that of soil organic carbon.Therefore,natural grassland plays a more essential role for the accumulation of the soil organic carbon and total nitrogen contents.