Land use Change is the results of interactions between physical factors and human activities.Land ues change may influence many natural phenomena and ecological processes,including
soil nutrient and soil water change,runoff and soil erosion,biodiversity and biogeochemical cycle.
Land use changes can results in land degradation,such as water and soil loss,land desertification.It also can control water and soil loss,land desertification,and improve soil quality.Since late 1970s,the new land policy “Household Responsibility System” was implemented in the Chinese countryside,which has advanced China's agriculture and led to great changes in land use structure.Land use change has resulted in some changes in
soil nutrients.This paper took Zunhua County,a typical agricultural area in northern China as a case study to analyze the relationship between land use changes and soil nutrient changes.The objectives are (1)to identify land use change within two typical periods of 1980 and 1999.(2)to examine soil nutrient changes between 1980 and 1999,and (3)to analyze the relationships between land use changes and soil nutrient changes. Land use change from 1980 to 1999 shows:(1)the area of farmland,
grassland and paddy field decreased by 40%～50%;(2)the areas of
forest,residential land,and water field increased by over 60%;(3)unutilized land had been
transformed to farmland,forest,and residential land.The results of a transition matrix reflected the area increase or decline of each land use type.Between 1980 and 1999,29%,10%,and 10% of cultivated farmland were converted to forest,residential land and grassland respectively.About 64% of grassland was transformed to forest.About 59% of unutilized land was transformed to grassland,and 31% was transformed to forest. The soil nutrient status of farmland in 1999 increased significantly( p <0.10%)compared to 1980.The increase in organic matter content was because of an increase in straw incorporation.The differences in organic matter content for forest between 1980 and 1999 were not statistically significant.Except for avaliable P, soil nutrient levels for grassland improved significantly between 1980 and 1999.Soil nutrient changes could be related to large changes from grassland to forest and from farmland to forest and grassland.The introduction of forest grassland may have reduced the loss of soil nutrients by erosion and leaching. Land use changes have resulted in soil nutrient changes in the study area.The soils under forest in 1999 transformed from farmland in 1980 increased in organic matter by 21%,total nitrogen by 18%,available nitrogen by 65%,avaliable phosphorus by 17% and available potassium by 17%.Similarly,in the area which was converted from farmland in 1980 to grassland in 1999,soil organic matter,total nitrogen,available nitrogen,available phosphorus,and available potassium increased by 38%,37%,71%,2%,28%,respectively.Changes from farmland to forest and grassland not only changed land cover but also improved soil fertility and probably reduced soil nutrient losses.
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