Variability and determinants of soil organic matter under different land uses and soil types in eastern China

Assessing the spatial and temporal variability of soil organic matter (SOM) and identifying determinants of its stability are crucial to measure carbon (C) sequestration and emissions and to understand the evolution of soil functionality. In this study, a spatially dense dataset (5207 topsoil samples (0 - 20 cm) based on a 1 x 1 km grid) was used to produce SOM maps using geostatistical interpolation by kriging methods and to identify the determinants of SOM distribution in an intensive agricultural region of eastern China. The SOM contents were relatively low and ranged from 10 to 20 g kg(-1) for 96.6 % of the total study area, indicating low-fertility soil conditions in the study area. Compared with historical soil data, the SOM content differed among different counties, and increased in most parts of Changfeng and Feidong County from 1981 to 2003. The SOM content was significantly impacted by altitude, aspect, pH, soil texture, as well as soil type and land use, but not by slope gradient, topographic wetness index (TWI) or normalized difference vegetation index (NDVI). The increased application of chemical fertilizer and organic manure in paddy and vegetable-based systems likely contributed to SOM accrual during the 22-year period. Agricultural land uses of paddy rice (Oryza saliva) and vegetable production are conductive to soil C sequestration in agricultural soils in eastern China.