Evolution and Influencing Factors of Soil Organic Carbon Under Long-term Fertilization in Subtropical Paddy Field of China

The evolution and influencing factors of soil organic carbon under long-term fertilization field experiment carried out from 1981 were studied based on the measurement of soil organic carbon(SOC), rice yield and soil nutrients in Poyang Lake Field Reddish Paddy Soil Pivotal Observational and Experimental Station of Agricultural Ministry. The treatments included CK(no fertilizer), N(nitrogen fertilizer), NPK(combined nitrogen, phosphorus and potassium fertilizers), NPK2(combination of high rate of nitrogen, phosphorus and potassium fertilizers) and NPKM(combination of nitrogen, phosphorus and potassium fertilizers and organic manure). The results showed that: SOC contents increased after 30 a by 18.95%, 17.72%,23.36%, 16.92% and 32.68% in CK, N, NPK, NPK2 and NPKM, respectively, and SOC contents of NPK, NPK2 and NPKM increased by 4.09%, 4.03% and 25.68% compared to CK, respectively. SOC content was significant correlated(P0.001) with grain yield, the correlation coefficient(r) was 0.410, it indicated that the grain yield could be improved by increasing soil SOC.SOC content was also significantly correlated(P0.001) with alkali solution nitrogen, total phosphorus, available phosphorus, r were 0.452, 0.559 and 0.487, respectively; but was not significant correlated with total potassium in this study. It indicated that it is wise way to combined use of nitrogen, phosphorus and potassium fertilizers and organic manure to improve soil organic carbon quickly and largely in paddy field and should increase the input of potassium fertilizers in combination use of nitrogen,phosphorus and potassium fertilizers and organic manure for maintaining soil fertility balance and ensure higher crop yields.