Effects Of Tillage Practices On Soil Microbial Diversity

Due to the pressure of population, resources and food, human intervention in the soil environment are increasing. Different tillage practices have a profound effect on soil physical, chemical and biological properties. Soil microorganisms are important components of soil ecosystem. In recent years, more attention has been paid to the effects of soil management practice on soil microbial community structure. Due to the effect of environmental factors (such as soil type, farming systems, the amount of stubble, etc.), the responses of microbial community structure and diversity to different tillage practices on are different.In this dissertation, the variation of soil microbial C and N, as well as the diversity of bacteria community structure under different tillage practices is studied using PCR-DGGE method. The evolution characteristics of soil microbial community structure throughout maize growing period are observed at physio-biochemical and molecular levels.The main results are as follows:(1)Different DNA templates should select different PCR methods. PCR reaction system and response procedures must be adjusted according to the actual results. DGGE using 8% polyacrylamide gel concentration, denaturing gradient ranging from 40% to 60%, can get the best results.(2) The characteristics of soil microbial communities of whole growing period of maize were studied by using the PCR-DGGE technique. The results shows that at early growth period of maize (seedling,jointing and tasseling stage), the micro-organisms under conservation tillage (NT and RT) is more abundant compared with CT. However, at the late growth period of maize (silking and mature stage), population and structure of microbial are similar under different tillage practices. The total number of population at the late growth period is less than the early period for all treatments. Nitrogen application at our experimental level shows slight effect on the composition of microbial community structure; while tillage practices have a significant effect on it.(3) The characteristics of soil microbial community structure show big different between early growing period (seedling, jointing and tasseling stage) and late growing period (silking and mature stage). An obvious seasonal variation on composition of the community structure was observed. Temperature is the most dominant factor influencing the composition of maize soil bacteria community structure, followed by tillage measures and soil moisture content.(4) The contents of SMB-C and SMB-N under conservation tillage (RT and NT) are higher than these under CT, especially on the surface soil. Nitrogen application have a significant effect on SMB-C and SMB-N concentration has a significant influence, However, SMB-C and SMB-N concentration did not increase with the increasing nitrogen application rate.(5) Adopting of RT could increase maize yield in short term. Long term practice of NT could increase maize yield. Furthermore, it has a Stability effects in dry years; Maize yield does not show significant difference at different nitrogen levels indicating nitrogen application is excessive. alkali-hydrolyzable nitrogen, available K, organic matter, microbial biomass carbon are signigicant positive correlation with yield. conversation tillage has the high practical value and can extend widely.