Effects of long-term organic manure and inorganic fertilizer combined application on rice yield and soil organic carbon content in reddish paddy fields

An investigation was made in a double-rice paddy field in the Red Soil Field Experimental Station, Chinese Academy of Agricultural Sciences to study yield potential of double cropping rice and change of soil organic carbon after 31- year combined application of organic manure( M) and chemical fertilizer( NPK) with the same application rates of nitrogen( N),phosphorus( P),and potassium( K) contained in organic manure and chemical fertilizer. The fertilization can promote yields and shoot biomasses of rice,and the combined application of organic manure and balanced fertilization of N,P,and K( NPKM) has the largest effect on them. Compared to the NPM, NKM,PKM,M and NPK treatments,the annual average rice yield of the NPKM treatment is increased by 5. 8%, 10. 9%,16. 2%,15. 9% and 20. 4% respectively. The fertilization can increase soil organic carbon content,the combined application of organic manure and balanced fertilization of N,P,and K( NPKM) can make the effect most obvious,and compared to the NPM,NKM,PKM,M and NPK treatments,the average soil organic carboncontent of the NPKM treatment in the determination years is increased by 2. 5%,3. 5%,2. 0%,0. 6% and 32. 8% respectively. Compared to the only application of chemical fertilizer,the application of organic fertilizer has the stepwise effect of increasing rice yields and has the obvious effect of increasing soil organic carbon contents. The mode of combined application of organic manure and inorganic fertilizer should be recommended in double-rice red soil paddy fields with balanced applications of inorganic NPK fertilizers.