Effects Of Straw Incorporation In Combination With N Fertilizer In Winter On Microbial Properties And Carbon Pools Of Paddy Soil

Straw incorporation, as an important way of straw utilization, not only avoids the waste of resources and environmental pollution, but also improves soil fertility, improves soil structure, physical and chemical properties, optimizes the ecological environment, and increases crop yield. Straw incorporation in wintry fallow period reasonably, making full use of natural resources in winter and spring, not only reduced environmental harm of straw buning, but also may replaced green manure, realizing the fixation of carbon and nitrogen under low temperature and unflooded conditions. When straw got incorporated, different decomposition stages decided different organic carbon fractions. Straw returning should be done with N fertilizer at the same time, for straw C/N is high. In this paper, we studied the effects of straw incorporation timing and amount of N fertilizer on microbial properties and carbon pools of paddy soil under long-term straw returning with N fertilizer in winter for carbon fixation, so as to provide theory basis for cultivating paddy soil fertility and stabilizing paddy ecosystem function, regulating the comprehensive ecological benefit of full straw incorporation. The main research results were as follows:1、The dynamic analysis results of six enzymes(β-Glucosidase, β-Cellobiosidase, β-Xylosidase, Phenol oxidase, Peroxidase and Invertase)activities related to carbon cycle showed: straw incorporation in winter, making full use of accumulated temperature and extending straw decay time, could increase enzyme activities related to carbon cycle. The ratio of N fertilizer had no significance to soil enzyme activities. In addition, despite Phenol oxidase, other 5 enzyme activities all had significantly positive correlation with organic carbon inputs. This showed that to a certain extent, the processing of straw incorporation with N fertilizer eased the N competition between straw decomposing and seedlings growth, but the ratio of N fertilizer didn’t affect enzyme activities significantly due to the later fertilizer supply. The analysis results of soil microbial biomass showed: straw incorporation in winter could increase the soil microbial biomass C and N with wintry fallow period, while not during the early-rice growth stages. Straw incorporation with N fertilizer significantly increased soil microbial biomass C in wintry fallow period, and soil microbial biomass C、N in growth stages. But soil microbial biomass of different ratio of N fertilizer had no significant differences. Correlation between microbial biomass and enzymes further illustrated that farmland management measures of N fertilizing when returning straw in winter could promote soil microbial breeding and regulate enzyme activities related to soil carbon cycle.2、The analysis results of long-term straw incorporation with N fertilizer measures showed: long-term straw incorporation with N fertilizer measures could significantly increase soil total organic carbon, soil physical organic fractions(except particulate organic carbon)and chemical organic fractions(except dissolved organic carbon)content. Content of total organic carbon, light fration organic carbon, particulate organic carbon, acid dissolved organic carbon and recalcitrant organic carbon was higher than that of spring incorporation, indicating that compared to spring incorporation, the carbon fixation effect of winter incorporation was more obvious. Compared tomanagement of straw returning and no N fertilizer all the course, straw incorporation with N fertilizer measures contributed more to the accumulation of organic carbon fractions.Straw incorporation in winter with low temperarture and unflooded conditions, increased inputs of organic matter, reinforced soil microbial activities, enhanced enzyme activities related to carbon cycle, promoted organic carbon accumulation, and the application of N fertilizer contributed to the straw fixation in soil. Thus, from the perspective of soil carbon fixation, rice straw should be encouraged to be incorporated in winter with joint 54 kg/ha N application instead of incorporation.