Characteristics of spatio-temporal changes of soil organic matter in typical fringe in Beijing for 25 years

Temporal and spatial variability characteristics of soil organic matter（SOM）content in fringe of the big city for 25-year interval （1981-2006） were evaluated using geostatistics and geographic information system（GIS）. Results show that there is remarkable correlation between the land use types and SOM. From1981 to 2000, the content of SOM increased in the whole area mainly because of the transformation from virgin grass land to cultivated land and increase of irrigable land. The average content of SOM increased by 28% and increased from 9.64 g/kg to 12.35 g/kg. Then the household changed their land use way by driven of interest and do not increase additional input anymore. So the content of SOM decreased from 12.35 g/kg to 11.46 g/kg in the period of 2000-2006. The content of SOM decreased from north to south in the district in 1981. Compared with 1981, the content of SOM increased one grade generally and most in the middle of the district and in this area the land use changed most significantly in 2000. Compared with 2000, the content of SOM increased only in three districts and the increasing extent was not significant, less than 1 g/kg.