岩溶区土壤肥力的时空变异及影响因素--以云南小江流域为例

Temporal-spatial varibility of soil fertility and its affecting factors of varability in Karst region:a case study of Xiaojiang watershed,Yunnan Province

运用地统计学,结合GIS研究了云南小江典型岩溶流域1982到2005年表层(0～20cm)土壤肥力包括pH、有机质、全氮、全磷、全钾5个指标的时空变异规律及影响因素。20a来,流域土壤肥力发生显著变化,pH值、全钾含量升高,而有机质、全氮、全磷含量降低;同时土壤肥力的空间变异显著:各指标的块金方差与基台值的比值、自相关阈值明显增大;pH值在流域东部和东南部升高,而在中部降低;有机质含量在流域东部和东南部降低,而东北部、中部含量增加;全氮含量在东部降低,中部增加;全磷含量普遍降低,东部地区下降幅度最大;全钾含量在东部、西南地区升高。土壤肥力的时、空变化与地质、地貌以及土地利用密切相关。

Through application of Geostatistics combined with GIS, the temporal-spatial variability of the pH, organic matter, total nitrogen, total phosphorus and total potassium in soil in Xiaojiang watershed from 1982 to 2005 were analyzed. The data of soil fertility for 174 points in the Second National Soil Survey in 1982 was collected, then 177 soil samples in surface layer （0-20cm） was collected and analyzed in 2005. Results showed that： （1） The average content of pH, organic matter, total nitrogen, total phosphorus and total potassium in soil in 1982 was 6.64, 33.3, 1, 7, 1.7, 10.56 g kg^-1 , respectively; and that in 2005 was 6.74, 29, 1.6, 0.97, 11.05g kg^-1, respectively, Independent samples t test indicated that those indices have changed significantly in the past 20 years. （2） The ordinary Kriging analysis indicated the spatial pattern of the soil fertility changed significantly in the past 20 years in Xiaojiang watershed. The soil pH increased in the east and southeast part of the watershed, but decreased in the middle part of the watershed. The content of the soil organic matter decreased in the east, southeast and southwest part of the watershed, but increased in the northeast and middle part of the watershed. The content of the soil total nitrogen decreased in the east part of watershed, but increased in the middle part of watershed. The content of the soil total phosphorus decreased in the whole watershed. The content of the soil total potassium increased in the southwest and southeast part of the watershed, but decreased in the middle part of the watershed. （3） Soil properties modified significantly in different geology and physiognomy types. The variability of soil properties is larger in the carbonate stratum than that in sandstone stratum, which indicates that the soil developed from carbonate stratum is fragile. Soil erosion was easily triggered because limestone soils are typically shallow and because the open joint systems facilitate the washing underground of soil material. The variability of soil properties is larger in karst depression and mountain and hill than that in karst basin and karst trough valley, because there are the higher elevation and slope in karst depression and mountain and hill, which soil erosion was easily triggered. Also, modifying land-cover and management measures of soil caused significant modifications in soil properties. The increase of soil pH was mainly contributed to the transformation of the forestland and unused land into the cultivated land. The decrease of the content of the organic matter, total nitrogen and total phosphorus in soil was mainly contributed to the transformation of the forestland and unused land into the cultivated land, which induced water and soil erosion.