Soil Organic Carbon and Nitrogen Stocks under Conservation Tillage in Upland Southern China

A 4-yr field experiment was conducted to investigate the effects of conservation tillage on soil organic carbon (SOC) and total nitrogen (TN) stocks in typical upland of Guizhou province. These plots were arranged by a randomized block design and soil samples were taken from each plot at 0~40 cm depth 3weeks after harvest. During the first three years of the experimentation, there was no significant difference in soil C or N stocks between the conventional tillage (CK) and conservation tillage (CT) treatments. However, after the 4-yr experimentation, soil C stocks for 0~20 cm and 20 cm~40 cm layers were significantly higher (7.1% and 8.5%, respectively) under the CT treatment than under the CK treatment. Compared with the CK treatment, surface soil (0~20 cm) N storage was significantly higher (7.7%) under the CT treatment after 4-yr experimentation. For 0~40 cm depth of soil body, soil C and N stocks under the CT treatment were significantly higher 7.7% and 6.5%, respectively, than under the CK treatment after 4-yr experimentation. The conservation tillage showed no effects on soil C:N ratio. The conservation tillage should be encouraged from the point view of increasing soil C and N levels in this region.