Effects Of Soil Carbon And Nitrogen And Methane Emissions From Rice Fields Under Rice And Wheat Straws Return During The Tillering Stage

Straw returning changed the soil carbon and nitrogen content in rice paddies, and it has a large impact on the methane emissions in rice paddies.Further, not only do it impact the soil organic carbon and total nitrogen, but also influenced active carbon pool, plant direct utilization of nitrogen. In addition, straw returninginfluenced the microbial activity and enzyme activity of soils.A field experiment based on three-year rice-wheat rotation rice paddies including three straw returning treatments(WR:rice straw+wheat straw to field full amount; W:wheat straw to field full amount; R:rice straw to field full amount) and one control treatment(CK: without returning to the field) was conducted in the danyang experimental station to measured methane emissions, water-soluble organic carbon, microbial biomass carbon and nitrogen, ammonium nitrate, urea activity and cellulase activity from transplanting to field drying during rice growing season, analyzed the straw’s influence on soil carbon and nitrogen and methane emissions, and explored the relationship between these. The main results are as follows:1. The changes of soil carbon under different treatments of straw returningWheat straw significantly increased the content of water-soluble organic carbon and microbial biomass carbon, and there is no significant difference between the rice straw and the control. From transplanting to paddy drying, water-soluble organic carbon graduallyincreased with the rice growing, and decreased after paddy drying. In comparison, microbial biomass carbon remained higher levels at early tillering reviving, then gradually reduced, and rebounded after paddy drying.2.The changes of soil nitrogen under different treatments ofstraw returningUnder four treatments, ammonium nitrogen content soon reached maximumafter applying tillering fertilizer, then gradually reduced to a lower level afterfield drying (32 days after transplanting). The ammonium nitrogen content before field drying under WR and R are higer than other two treatments besides it in 14 after transplanting, but it showed on difference among four treatments.There was no significant difference in nitrate content under four treatments in addition to it in 29 days after transplanting. Nitrate content was lower at early tillering stage, and quickly increased to a higher level on 32 days after transplanting. After applying N in tillering stage, microbial biomass nitrogen gradually increasing to the maximum on 14 days after transplanting, then gradually decressed to lower amount and rebounded on field drying. Wheat straw raised microbial biomass nitrogen content during transplanting and field drying, and reached significant or highly significant level on 7,14,29,32 days after transplanting.3.The changes of soil enzyme activity under different treatments of straw returningCellulase activity was higher at the beginning of tillering, after the tiller fertilizer being applied, it decreased to a lower level,then gradually increasedandbegan to flatten on 16 days after transplanting. Finally, it reached to a lower levelon 32 days after transplanting.Among four treatments, cellulose activity showed thatWR> R> W> CK, but the difference was not significant.The urease activity variation law was not obvious during the tillering to field drying,compared with each treatment, treatmentWR and R were greater than treatment W and CK.4.The changes of methane emission under different treatments of straw returningWheat straw significantly increased methane emissions from rice fields during transplanting to field drying.Rice straw reduced methane emissions from rice paddies, but it did not reach a significant level.Undertreatment WR and W, Methane emission rates peaked within 15 days after transplanting,then gradually decreased to a lower level on field drying. Treatment R and CKremained lowin the whole process.5.The relationship of soil carbon and nitrogen to methane emissionThe relationship of Water-soluble organic carbon, microbial biomass carbon and nitrogen to seasonal average total methane emissions and methane emission rates reached significantly positive correlation.It also reached significantly positive correlation between cellulase activity and methane emissions. There were not significant correlation among the other parameters.