Effects of different land uses on soil erosion and soil nutrient variability in the Shuanglong Catchment of Dianchi Watershed

In this study, four types of land uses including tillage, abandoned farmland, grassland and forestland in the Shuanglong Catchment of Dianchi Watershed were investigated to determine the effects of land use on soil erosion and nutrients. The137Cs activities were determined by a high-resolution HPGe γ-spectrometry system (GWL-120-15, USA). The carbon stable isotopes (δ13C) were analyzed using a thermo Delta plus XL mass spectrometer (UK). Contents of Total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) in the soil samples were measured as well. The results are as follows: 1) The137Cs activities in the soil samples from tillage, abandoned farmland, grassland and forestland were 0.65, 0.21, 3.92 and 0.61 Bq/kg, respectively. The decreasing order of soil erosion modulus was tillage > abandoned farmland > forestland > grassland. 2) The differences of TOC, TN and TP contents among the four land uses types were of great significance (P forestland > tillage > abandoned farmland. The TN contents were grassland > tillage > forestland > abandoned farmland. The TP contents were tillage > grassland > forestland > abandoned farmland. The soil nutrient concentrations in different land use types decreased with depth. 3) The average values of δ13C in the soil samples from tillage, abandoned farmland, grassland and forestland were -22.28‰±1.49‰, -23.29‰±0.24‰, -26.32‰±0.25‰ and -25.94‰±0.22‰, respectively. It was deduced that the organic matter in the Shuanglong catchment was mainly derived from terrigenous C3plants. The variation ranges of δ13C values in different soil profiles decreased in the following order: tillage > forestland > grassland > abandoned farmland. 4) The decline in soil quality was associated with soil erosion and decreased soil nutrients. Grassland and forestland would be beneficial for regional environmental protection, because of their low levels of nutrient loss.