The distribution of soil nutrients on sloping land in the gully region watershed of the Loess Plateau

The deterioration of soil quality and the decline in productivity on sloping land are the main factors that limit the revegetation of the Loess Plateau.However,these two factors largely depend on soil nutrient status.The purpose of this study was to investigate the distribution of soil nutrients on sloping land located in the gully region of the Loess Plateau.The results showed that the soil nutrient content generally decreased with soil depth.Among the soil nutrients,soil organic carbon and total nitrogen decreased most compared with nitrate nitrogen,ammonium nitrogen,and total phosphorus.In addition,the variation of soil organic carbon and total nitrogen was greater compared to the variation of ammonium nitrogen and total phosphorus among different soil layers.The amount of 0.005-0.05 mm soil particles increased with soil depth,but the amount of 0.05-1 mm soil particles decreased with depth.There was little change in the content of 0.05-1 mm and 0.005-0.05 mm particles in 0-60 cm layer soils,but there was a large change in the 0.005 mm particles in the 0-40 cm layer soils.Soil organic carbon,total nitrogen,total phosphorus,and 0.005 mm soil particles all increased as the distance from the top of the slope increased.Furthermore,soil properties were closely related with the length and gradient of the slope.Specifically,variation in the soil nutrient content of sloping land increased as the length and gradient of the slope increased.For long and gentle slopes,the middle and lower positions of the slope tended to be enriched in nutrients and 0.005 mm soil particles;however,for short and steep slopes the nutrients and 0.005 mm soil particles tended to be transported away from the slope.As the gradient of the slope increased,soil erosion and sediment deposition became the predominant factors controlling nutrient distribution in the soil profile at different points along the slope.Slope gradient also affected the depth of carbon and nitrogen loss from the upper positions on the slope.In contrast,the distribution of total soil phosphorus in the soil profile was only slightly related with slope gradient.The results in this study recommed that the length and gradient of the slope should be considered in the soil nutrients management on sloping land.