林地开垦对黄土区坡面土壤养分空间分布的影响

研究黄土高原侵蚀环境下林地开垦后坡面土壤养分空间分布状况,确立林地开垦后侵蚀驱动的坡地土壤养分空间变异特征。以黄土高原丘陵区子午岭林地和开垦28年的侵蚀坡面为研究对象,分析土壤主要性质和养分含量的变化情况,运用经典统计学和地统计法分析坡面土壤基本性质和养分空间分布规律。林地开垦后坡面土壤pH增加了0.24个单位,有机质、全氮、全磷和铵态氮、硝态氮、速效磷和速效钾分别降低了13.77,1.14,0.10 g/kg和6.05,1.63,4.99,58.44 mg/kg。林地的土壤有机质、全氮和全磷的变异系数大于开垦地,而pH和各速效养分的变异系数小于开垦地。开垦后中坡位和下坡位养分含量减少幅度较大,上坡位减少幅度较小。林地和开垦地的土壤各指标都呈中等或强烈的空间自相关。林地开垦增强了有机质、全氮、全磷、铵态氮、速效磷和速效钾的空间异质性,但减小了pH的空间异质性,地形等结构性因子主导了土壤养分空间异质性的形成。林地开垦后,pH、有机质、全氮和全磷变程增大,铵态氮、硝态氮和速效钾变程减小,速效磷在2个坡面上的变化趋势不一致。研究结果表明林地开垦极大地减少了坡面土壤养分含量,但减少幅度与坡位和坡面形态有关。同时,开垦增大了坡面土壤有机质、全氮和全磷的空间依赖性,减小了速效养分的空间依赖性。

Effects of Forestland Reclamation on Soil Nutrients Spatial Distribution Along Slope in the Hilly Area of the Loess Plateau, China

This study was aimed to investigate the distribution of soil nutrients along slope on the Loess Plateau and establish the spatial variation of soil nutrients driven by erosion after forestland reclamation. In this study, soils were collected in the Ziwuling forestland and forestland reclaimed for 28 years which was eroded, in the hilly area of the Loess Plateau. The spatial distributions of soil nutrients were analyzed with the methods of classical statistics and geostatistics. We found that the soil pH value increased by 0.24 units in the slopes after reclamation, while the soil organic matter (OM), total nitrogen (TN), total phosphorus (TP), ammonium nitrogen (NH₄⁺), nitrate nitrogen (NO₃^-), available potassium (AP), available phosphorus (AK) decreased by 13.77, 1.14, 0.10 g/kg, and 6.05, 1.63, 4.99, 58.44 mg/kg, respectively. The variation coefficients of soil OM, TN and TP in the forest were greater than those in the forestland reclamation, while the opposite trend was found in the soil pH value. The changes of the nutrients in the middle slope and lower slope was larger, but was smaller in the upper slope after the forestland reclamation. The soil nutrients in the forest and the forestland reclamation had medium or strong spatial self-correlation. The spatial heterogeneity of OM, TN, TP, NH₄⁺, AP and AK in the forestland reclamation was increased, but the spatial heterogeneity of soil pH was decreased, mainly due to the structural factors, such as terrain, dominated the formation of soil nutrients space heterogeneity. After the reclamation of forestland, the effective range of pH, OM, TN and TP were increased, while NH₄⁺, NO₃^- and AK were decreased, and the variation of AP on the two slopes was inconsistent. Our results demonstrated that soil nutrients contents on the slope decreased in the forestland reclamation, but the changes in the nutrients were related to slope position and slope pattern. Moreover, the spatial dependence of OM, TN and TP increased, but decreased in the available nutrients after the forestland reclamation.