Conservation tillage can play an important role in minimizing soil erosion and improving soil quality. The function of soil ecology system is mainly controlled by soil microorganism which is one of the most sensitive indicators. But the main difficulty of the utilization of microbial indicators was the lack of knowledge about the relationships between soil management and characteristics of soil microorganism. Further, the baseline and threshold value for each indicator were still unclear. It is critical for soil management to study the effects of conservation tillage on soil microbial characters. This experiment was carried out at different time after tillage in order to elucidate the effects of conservation tillage on soil microorganism from the aspects of time and space.
Six treatments were exposed as conventional tillage with no straw returning(CN), conventional tillage with straw returning(CS), subsoiling tillage with straw returning(PS), harrow tillage with straw returning(HS), rotary tillage with straw returning(RS), no tillage with straw covered(NS). Soil microbial biomass C, active microbial biomass and soil respiration rate were studied with methods of substrate induced respiration, respiration curve mathematics analysis and CO₂ emission amount respectively.
The results showed that conservation tillage had higher soil microbial biomass C in 0-10 cm soil layer than in 10-20 cm soil layer, while soil microbial biomass C of conventional tillage in both soil layers were almost the same. Straw returning significantly increased soil microbial biomass C at seeding stage, over-wintering stage and erecting stage but reduced soil microbial biomass C at anthesis, harvesting stage. The microorganism in 10-20 cm soil layer of minimum tillage with straw returning could regulate the supply of soil nutrition. Conservation tillage enhanced active microbial biomass in 0-10 cm soil layer. Straw returning and conservation tillage increased soil respiration rate at over-wintering stage and erecting stage but reduced soil respiration rate at anthesis and harvesting stage. NS had higher respiratory quotient（qCO₂）in 10-20 cm soil layer and CN had higher qCO₂ in 0-10 cm soil layer. Microbial biomass C and soil respiration rate were important indicators of soil microbial characters. But further research is necessary in time effects of tillage treatments on soil respiration rate and microbial characters.