CONTRIBUTION OF FERTILIZERS TO YIELD INCREASE AND ITS EFFECT ON SOIL ORGANIC MATTER

This paper deals with the contribution of fertilizers to yield and the effect of different fertilization system on rice yield through a ten-year field experiment. Results indicated that fertilization system greatly affected rice yield. The general trend was MNPKNPKMNP, MNNP; M,NCK. Using chemical fertilizer was a major measure for higher output and its contribution accounted for 70% of all the output increased, and other 30% attributed to organic fertilizer. Yield increase from organic fertilizer was mostly attributed to K (80%) carried by organic material. About 44% of yield increase was attributed to N applied, mainly inorganic form. Potassium fertilization contributed to 50% of yield increase, with similar effect from organic and inorganic sources. So the use of organic fertilizer in combination with chemical one might fulfil 90% requirement for higher output. Effect of P fertilizer was rather poor, even it might cause a decrease in yield owing to the stress of some microelement which may be induced by overuse of P fertilizer. Long-term application of chemical fertilizer had little effect on soil organic matter content, but signiticantly increased output of grains. However when organic fertilizer was used with chemical one, not only a good output might be attained, but an increase in soil organic matter might become possible so as to establish a better foundation for further more output.