Vertical Profile Distribution of Soil Organic Matter and Humic Components in Tobacco-growing Soils in Baoshan

Plough-layer samples of 318 typical tobacco-growing fields and profile-horizon samples of 25 typical tobacco-growing fields were collected respectively from the 5 main tobacco-growing counties in Baoshan City of Yunnan Province in order to study the contents, spatial and profile distribution of organic matter, humus and its component carbon and their relationship with pH and soil parental materials. The results showed that the mean content of soil organic matter was 37.39 g/kg with a range from 6.20 to 150.09 g/kg, and the coefficient of variation was 52.32%. The contents of soil organic matter in soil derived from the parental materials the Quaternary red clays and weathered slope washes were significantly higher than that derived from the weathered residuals. The contents of soil organic matter, humus and its component carbon in all profiles decreased with the increase of soil depth. The content of soil organic matter had a significant negative correlation with soil pH (r=-0.238, p<0.05).