Objective Effects of different fertilizer applications on organic carbon fraction and carbon pool management index in soil were investigated under maize/soybean intercropping condition.

Method Taking no fertilization (CK) as the control, five different fertilizing treatments, which were chemical nitrogen+ phosphorus+ potassium fertilizers (NPK), 70%NPK+30% straw (J1), 70%NPK+30% cow dung (N1), 40%NPK+60% straw (J2) and 40%NPK+60% cow dung (N2) according to the same rates of N, P and K, were designed in a long-term field experiment. The contents of organic carbon, soluble organic carbon, readily organic carbon and microbial biomass carbon were measured, and soil carbon pool management index was calculated.

Result Compared to CK, soil organic carbon contents of N1, J2 and N2 treatments significantly increased in 2013, and the soil organic carbon contents of all fertilizing treatments significantly increased in 2014. Except for NPK treatment in 2013, the soil dissolved organic carbon contents in 2013 and 2014 were significantly higher than that of CK. The dissolved organic carbon content of J2 treatment was the highest, which was significantly higher than that of NPK in 2013. The readily organic carbon contents of N1, J2 and N2 treatments were significantly higher than that of CK in 2013 and 2014, and the highest value appeared in N2 treatment. The microbial biomass carbon contents of all fertilizing treatments were significantly higher than that of CK, and the highest value appeared in N2 treatment. Compared with CK in the same year, the carbon pool management indexes of fertilizing treatments significantly increased, and the carbon pool management index of N2 treatment was the highest.

Conclusion The combined application of 40%NPK fertilizer and 60% cow dung is the optimal treatment for improving soil organic carbon fraction and carbon pool management index under maize/soybean intercropping condition in Karst area of northwest Guangxi.