Temporal and spatial variability of soil organic matter in a county scale agricultural ecosystem

In agricultural ecosystems, soil organic matter (SOM) is a major determinant and indicator of soil fertility and quality, and is closely related to crop productivity. This paper examines the ternporal and spatial variation of SOM in Pinggu district at a county scale using data for 1980 and 2005 and traditional statistics, geostatistics, and geographic information system (GIS) analyses. Pinggu district, Beijing, China is an area characterised by changing farming practices and land uses. A lognormal distribution feature was observed for both datasets, and the difference between them was significant (1-test). The geostatistical characteristics were analysed using a GIS platform. The distributions of SOM content in 1980 and 2005 both exhibited a linear trend and anisotropy. Spherical sernivariogram models and relative parameters were developed. The spatial distribution maps for 1980 and 2005 were generally similar, with the SOM content increasing gradually from south-west to north-east. The difference between the two maps was determined using map algebraic functions and was found to show considerable spatial change. Changes in farming practices and land use are thought to be the main reason for the temporal change. Therefore, a combination of geostatistics and GIS map algebra provides a useful toot for examining spatiotemporal changes in the environmental sciences and may detect features that are not discernible when only conventional statistics are used.