Spatial variability of soil organic carbon and available phosphorus in a typical Karst depression,northwest of Guangxi
Spatial variability of soil organic carbon and available phosphorus in a typical Karst depression,northwest of Guangxi
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作者：
Chen Hong
土壤养分的空间变异性为农业生产和生态管理提供了重要的信息。峰丛洼地是典型的喀斯特地貌景观，农业以洼地为主，如在中国西南喀斯特地区。以广西喀斯特地区典型景观单元洼地为研究对象，研究了土壤有机碳的空间变异特征。和表层土壤（015 cm）有效磷（AP）。网格采样法（20 m×20 m）和地质统计学方法分析了土壤有机碳和速效磷含量的空间分布特征，土壤有机碳和速效磷的样本变异函数分别用球形和指数模型拟合，由于随机误差或采样间隔距离（20 m）内的变异性造成的金块效应占SOC总体变异的37.9%，土壤有机碳的空间变异主要受地形条件和土地利用类型等结构性因素的控制，而土壤有效磷的空间变异主要受随机性因素的控制，其主要原因是施肥水平的差异性较大，土壤有机碳的相关长度约为135.5m，方向半变异函数分析表明，该凹陷土壤有机碳的空间分布呈带状各向异性，在长轴方向上具有低基台和长变幅的特征，土壤有效磷也具有各向异性，但其空间分布格局与土壤有机碳有很大不同，因为AP具有更长的相关长度（413.4 m），并显示出明显的漂移趋势，增加了长轴方向的变异性，这可能是由于磷肥的随机施用造成的，如果扣除漂移趋势的影响，AP的相关长度减小到167.4m，说明喀斯特洼地土壤有机碳的空间分布格局主要受控制受地形条件和土地利用类型等结构因素影响，而受施肥等随机因素影响较大。
Spatial variability of soil nutrients provides useful information for improving agricultural practices and ecological management.Peak-cluster depression forms a typical Karst landscape with agriculture mainly based in depressions,such as in the Karst region in south-west China.In this study,the depression area in a typical landscape unit selected from the Karst region of Guangxi province was investigated for the spatial variability of soil organic carbon(SOC)and available phosphorus(AP)in the surface soil(015 cm).Grid sampling method(20 m×20 m)and geological statistics were applied to analyze the spatial distribution of SOC and AP contents.Sample variograms of SOC and AP were fitted well by spherical and exponential models,respectively.Nugget effects due to random errors or variability within the distance of the sampling interval(20 m)contributed to 37.9% of the overall variation for SOC,and 49.8% for AP.This suggests that the spatial variation in SOC was mainly controlled by structural factors,which mainly depended on topographic conditions and land use types in the study area,but AP rather more controlled by random factors mainly due to the variability of fertilizer application which differed widely in the depression.Correlation length of SOC was about 135.5 m,which had similar scope to the average range of difference in land use types.Based on directional semi-variogram analysis,zonal anisotropy,and lower sill and longer range in the long axis direction were found in the spatial distribution of SOC in the depression.AP also had anisotropy,but the pattern in its spatial distribution was quite different from that of SOC,as AP had much longer correlation length(413.4 m)and showed clearly a drift trend which enhanced variability in the long axis direction,presumably due to the random application of P-fertilizers.If the effects of drift trend were subtracted,the correlation length of AP decreased to 167.4 m.This study suggests that the pattern in the spatial distribution of SOC in the depression area in Karst regions was mainly controlled by structure factors(topographic conditions and land use types),but for AP rather more by random factors such as fertilizer application.