桂西北喀斯特地区石灰土养分空间变异特征

从区域尺度出发,将整个桂西北喀斯特地区作为研究区域,以大面积野外调查采样和室内分析数据为基础,采用经典统计学和地统计学方法,探索喀斯特区域内石灰土养分的空间异质性和分布格局。结果表明:桂西北喀斯特地区石灰土pH为弱变异,其他养分变异系数为30%—75%,变异程度中等。石灰土各养分的空间变异特征不同,土壤有机质(SOM)、速效磷(AP)和速效钾(AK)的最佳拟合模型依次为球状模型、高斯模型和线性模型,pH、碱解氮(AN)、全氮(TN)、全磷(TP)和全钾(TK)的最佳拟合模型均为指数模型。SOM、AP、TN和TP表现为中等空间相关性,空间差异是由随机因素和结构性因素共同作用引起的;pH、AN、AK和TK呈弱空间相关性,空间变异主要受随机因素的控制;SOM和TN的空间变异尺度较大,pH、AN和TK的空间变异尺度最小。SOM、TN、TP和AP养分含量呈自西向东逐渐减少的趋势,pH、AN、AK和TK在区域尺度上的分布没有呈现一定的规律性。相关分析结果表明,在区域大尺度下,地形因子(如海拔、坡度和岩石裸露率等)和植被类型是影响桂西北喀斯特石灰土空间变异特征的重要因素。

Spatial variability of limestone soil nutrients in a Karst area of Northwestern Guangxi

Large-scale spatial heterogeneity and distribution patterns of limestone soil nutrients in the karst areas of northwestern Guangxi were evaluated in this study, based on regional field survey and laboratory analysis combing with classical statistics and geostatistics. The results showed that pH value of limestone soil had little variation in the karst areas of Northwestern Guangxi, while the variation coefficients of soil nutrients ranged from 30% to 75%, which can be considered as moderate variation. The characteristics of spatial variability differed among soil nutrients. Spherical model, Gaussian model, and linear model were the best-fit model for soil organic matter (SOM), available phosphorus (AP), and available potassium (AK), respectively. However, pH, available nitrogen (AN), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) could be best fitted by exponential model. In addition, SOM, AP, TN, and TP showed moderate spatial autocorrelation, and spatial variability was caused by both random and structural factors. On the other hand, pH, AN, AK, and TK showed weak spatial autocorrelation, and spatial variability was mainly controlled by random factors. The variation range for SOM and TN were large while that for pH, AN, and TK were small. The contents of SOM, TN, TP, and AP exhibited a decreasing trend from west to east but the distribution of pH, AN, AK, and TK did not show any regularity on a regional scale. The correlation analysis demonstrated that, on a large scale, topographic factors (i.e., altitude, slope and rock exposure rate) and vegetation type were important factors affecting the spatial variability of limestone soil nutrients in the karst areas of northwestern Guangxi.