滇池双龙流域不同土地利用方式下土壤侵蚀与土壤养分分异

在滇池双龙流域选取耕地、撂荒地、草地和林地4种土地利用方式,分别取0～40 cm土壤样品,测定样品中的137Cs比活度及w(TN)、w(TP)、w(TOC),同时根据土壤有机质中δ13C(稳定性碳同位素丰度)的剖面分布特征,分析不同土地利用方式对该流域土壤侵蚀程度、土壤养分分异及有机质来源和变化的影响. 结果表明:①耕地、撂荒地、草地和林地土壤的137Cs比活度分别为0.65、0.21、3.92和0.61 Bq/kg,土壤侵蚀模数大小表现为耕地>撂荒地>林地>草地. ②不同土地利用方式下,土壤剖面w(TOC)、w(TN)和w(TP)的平均值差异显著(P<0.001)；w(TOC)表现为草地＞林地＞耕地＞撂荒地,w(TN)表现为草地＞耕地＞林地＞撂荒地,w(TP)表现为耕地＞草地＞林地＞撂荒地；各种土地利用方式土壤剖面养分质量分数均随土壤深度增加呈降低趋势. ③耕地、撂荒地、草地和林地土壤的δ13C平均值分别为-22.28‰±1.49‰、-23.29‰±0.24‰、-26.32‰±0.25‰和-25.94‰±0.22‰,推断该区域土壤有机质主要来源于陆生C₃植物. 土壤剖面δ13C的变幅差异反映了土壤有机质分解程度的强弱,δ13C变化规律表现为耕地＞林地＞草地＞撂荒地. ④土壤侵蚀模数越大,w(TOC)和w(TN)越低,草地和林地土壤侵蚀程度较低,土壤养分流失量较小,更有利于土壤质量的改善和流域水环境的保护. 

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. The 137Cs activities were determined by a high-resolution HPGe γ-spectrometry system (GWL-120-15, USA). The carbon stable isotopes (δ13C) 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) The 137Cs 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<0.001). The comparison of TOC contents was grassland > 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 δ13C 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 C₃ plants. The variation ranges of δ13C 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.