The researchers analyzed soil fertility changes in Xiaojiang watershed from 1982 to 2005 using Geostatistics and GIS. They found that soil pH, organic matter, nitrogen, phosphorus, and potassium levels varied significantly over the 20-year period. Soil pH increased in some areas but decreased in others, while organic matter decreased in some parts but increased in others. Different soil properties were affected by geology, physiognomy, and land management practices. Soils from carbonate strata were more fragile and prone to erosion, while higher elevations and slopes were more susceptible to soil erosion. Overall, the study showed that soil fertility in the karst region of Yunnan Province changed significantly over time and was influenced by various factors.