Change of soil organic carbon reserve in northern Manasi county in last 30 years

The temporal and spatial variations of the soil organic carbon (SOC) were studied in order to provide a theoretical basis for the soil fertility management in the northern Manasi county. With the geostatistics and geographic information system (GIS) methods, the temporal and spatial variations of SOC content in the northern Manasi county in last 30 years were investigated. The results indicated that SOC density and reserve presented a rising tendency, which increased 1.81 kg/m2 and 7.7 ×106 kg compared with that of the Second General Survey of Soil in 1980s, respectively. The average values of SOC in 2011 year were 5.74、4.44 and 2.17 g/kg, respectively, for 0-20, >20-60 and >60-100 cm soil layers. Results show that SOC at the 0-20 and >20-60 cm soil layers were normally distributed after excluding the outliers. By experimental semivariograms analysis, SOC were best fitted to exponential and spherical models at 0-20 and >20-60 cm soil layers, respectively. SOC had a moderate spatial variability at 0-20 and >20-60 cm soil layers. The maps of SOC were interpolated using the method of ordinary Kriging. Due to the joint influence of the structural factors such as soil parent material, topography and random factors such as fertilization, crop system etc, the SOC contents at 0-20 and >20-60 cm soil layers had the spatial distributions with a high content in the south and northeast regions and a low content in the central region. The SOC content at 60-100 cm soil layer had a spatial distribution with a high content in the south region and a low content in the north region. The results of temporal and spatial variations of the SOC were of great significance for the soil fertilizer management of the North part of Manasi county.