Effect of straw returning to field on rice productivity in different cropping systems

Effect of straw returning to field on productivity of rice has been studied in three cropping systems, rice-rice-green manure, rice-rice-rapeseed and rice-rice-fallow. The main results show that under the condition of winter crop straw returning to field, yield of early rice in rice-rice-green manure system is the highest, and that in rice-rice-rapeseed is next to it, both of them are higher than that in rice-rice-fallow system by 3.1% and 1.8% respectively. The winter crop and early rice straw returning to field have increased the yield of late rice significantly, the output of late rice in rice-rice-green manure system and the output in rice-rice-rapeseed system are higher than that in rice-rice-fallow system by 15.4% and 11% respectively. The main reasons of rice yield increase are the straw returning to the field helps to expand the leaf area, improve the dry matter accumulation, effective panicles, grain number per panicle and ratio of grain number to leaf area. The differences in yield increasement by straw returning have been observed between different winter crops' straw. Dry matter accumulation of rice has been improved by straw returning, while there exists clear difference in early rice dry matter increasing functional mechanism between two types of straw, green manure mainly helps to increase dry matter accumulation before booting stage, while rapeseed straw mainly operate after heading stage.