Studies On Effect Of Soil Tillage And Straw Returning To Field In Multi-Cropping Paddy Field

To prove up effects of minimum tillage and no-tillage and straw returning to field on diversity and activity of microorganism in paddy field and yield formation of rice, several experiments about effect of all-year straw returning to field under different rotation system, effect of different soil tillage measures and different amount of straw returning to field in early rice season on late rice, and effect of straw-decomposition accelerant on decomposition of straw were conducted under multi-cropping system in double cropping rice region of South China in 2004-2007. The main results were as follows:1) Leaf area, effective panicles, grain number per panicle and yield of rice were increased by straw returning to field (SRF), whlie yield components showed different trends between early rice and late rice. Contet of total N, active P and availabe K in soil were increased, and the effect of two-season SRF was better than one-season SRF, while content of available N was decreased by SRF. SRF affected quantity of soil microorgnism, that of fungi was decreased and that of bacterium was increased, while that of actinomycetes showed different trend in early rice and late rice. Because of SRF, activities of soil proteinase, urease and cellulase were improved, while that of catalase was decreased.2) Effect of yield increase in 1/3 and 2/3 straw returning treatments was better than that in total straw returning treatment. Activities of main enzyme and quantities of main microbes in soil were heightened by SRF, while the positive correlation between those and straw returning amount was not found. Improvement in quantity of bacterium and functional diversities of soil microbial communities in 2/3 and total straw returning treatments was clearer than that in 1/3 straw returning treatment. Synthetically consider effects of straw returning amount on yield of rice and biological characteristics in soil, 2/3 straw returning treatment was the best.3) Soil tillage mode affected crop yield and soil characteristics. In minimum and zero tillage treatments, effective panicle number of rice was decreased, while grain number per panicle, seed setting rate, 1000-grain weight and yield were increased.In zero tillage treatments, expansion of leaf area was quick in prophase of rice, and premature senility phenomena was not observed in anaphase of rice. Activities of soil enzyme were improved by tillage in short term, and amination intensity of soil was decreased by tillage. Activities of soil microbe in prophase and anaphase of late rice were improved by soil tillage, while those in metaphase were slightly decreased. Minimum and zero tillage could increase quantity of anaerobic bacterium, while tillage could promote the propagation of aerobic microbes.4) Effect of straw returning was evidently affected by soil tillage mode. As for improvement of soil nutrition content by straw returning, 1/3 straw returning should be adopted in minimum tillage trearments, while total straw returning should be adopted in tillage and zero tillage trearments. Effect of straw returning amount on activities of soil microbe and nitration intensity of soil showed different under different tillage modes.5) Clear differences in straw returning effects of straw from different crops was observed. The highest stem and tiller number per hill, effective panicle number per hill and yield of rice in green manure (Astragalus sinicus L.) treatments were higher than those in rapeseed straw treatments. There existed clear difference in dry matter increasing functional mechanisms of two types of straw in early rice season, green manure mainly increased dry matter accumulation before booting stage, while rapeseed straw mainly operated after heading stage. The effects of straw returning on nutrition content, activity of enzyme and quantity of microbe in soil between two types of straw were clear different. In general, effect of green manure was better than that of rapeseed straw.6) Leaf area, effective panicle and grain number per panicle were increased and yield was significantly increased in straw-decomposition accelerant (SDA) treatments. SDA affected chemical and biological characteristcs in soil, quantity of bacterium and contents of total N and available K were increased, while quantity of fungi was decreased. Quantity of actinomycete was increased in straw-decomposition microbe treatment, while it was decreased in Fuganling treatment. Compare to Fuganling, the effects of straw-decomposition microbe on improving activities of soil main enzyme, activities of microbes and soil nutrition content and promoting occurrence of tiller, expansion of leaf area, accumulation of dry matter and increase of rice yield were better.