Distribution of soil organic C, N and P in three adjacent land use patterns in the northern Loess Plateau, China

The northern Loess Plateau is an important cropping-pastoral ecotone and wind-water erosion crisscross region in China, but the distribution of soil organic carbon (C), nitrogen (N) and phosphorus (P) in different land uses across this vulnerable ecoregion is not well understood. This study was carried out to determine the distribution patterns of soil organic C, N and P in native grassland and in two woody lands (Chinese Pine land and Korshinsk Peashrub land) that were established on the native grassland 28 years ago. In the north part of the Loess Plateau, the concentrations of soil organic C, N and P were lower than in the southern Loess Plateau either across or within the land use patterns. The concentrations and stocks of organic C and total N were significantly decreased in Chinese Pine and Korshinsk Peashrub lands compared with those in native grassland in the surface 0-40 cm soil layer, where more than 70% of the roots were distributed. The decreases in organic C in 0-40 cm soil layers were 2.6 and 3.0 Mg C ha(-1) (26.3 and 27.7%) by Chinese Pine and Korshrinsk Peashrub, while those of total N were 0.6 and 0.4 Mg N ha(-1) (31.5 and 17.2%), respectively, compared with native grassland. Both concentration and stock of total P varied only slightly with land use. The findings suggested that the conversion of natural grass into Chinese Pine and Korshinsk Peashrub resulted in decreased soil organic C and total N in the surface 0 to 40 cm soil layer of the northern Loess Plateau. Our results further indicated that a combination of low temperatures, little precipitation and large soil degradation impede increasing C and N stocks by afforestation, and the afforestation on grassland should be viewed very critically in such areas.