Origins of soil organic carbon with the method of natural~(13)C abundance in maize fields

Following the conversion of forest ecosysterm to agricultural ecosysterm, the introduction of C4 plant to a soil,previously developed under C3 vegetation,brings to a different origin of soil organic carbon.In consequently it leads to the isotopical change in the composition of organic carbon. The results showed that the proportion of soil organic carbon derived from the forest still predominates after several decades of cultivation in maiz fields in Guizhou Maolan Karst Forest. The soil organic carbon originated from initial C3 vegetation amounts to 66.7 % of the total. The contents of easily mineralizable organic carbon which can efficiently supply nutrients to plant are very small. Therefore, it is necessary to optimize the management of plant residues incorporated into the soils.