Study On The Mechanism In Improving The Sequestration Ability Of Soil Organic Carbon Under Straw Returning Conditions

Nowaday, with China vigorously promoting straw returning, straw returning has become an important way to increase soil organic matter, improve soil fertility, but a considerable portion of carbon will release into the atmosphere by CO2 in the process of straw decomposition. How to make more straw-carbon immobilize the soil has important significance for agricultural soil carbon sequestration and emission reduction. Therefore, firstly, a incubation experiment was conducted to investigate the mechanism of soil organic carbon loss; then, another incubation experiment was conducted to investigate the effects of maize straw decomposition with combined medium element and microelements application on arable soil organic carbon sequestration, and a field experiments was conducted to study the effect of nitrogen fertilizer reduction with biochar incorporation on increasing the organic carbon under straw returning. The main results are as follows:1. Under straw returning, with the increasing of the native soil organic carbon, the soil organic carbon cumulative emission, priming effect(PE) and soil microbial biomass carbon(SMBC) increased; straw addition accelerated mineralization of soil organic carbon, but reduced the loss of the original organic carbon, with the organic carbon content decreasing, the native soil organic carbon and straw residual carbon increased. Therefore, organic carbon sequestration was favored to returning straw at the high content of organic carbon.2. During the straw decomposition, soil microbial biomass carbon(SMBC) content and CO2-C mineralization rate increased with the addition of S, Fe or Zn. In addition, cumulative CO2-C evolution after 52-day laboratory incubation significantly increased in the treatments with S, Fe, or Zn addition, while there was no significant reduction of soil organic carbon content in those treatments. In addition, Fe or Zn application increased the inert C pools and their proportion, and apparent balance of soil organic carbon, indicating a promotion of Fe or Zn addition in soil organic carbon sequestration. In contrast, S application decreased the proportion of inert C pools and apparent balance of soil organic carbon, indicating an adverse effect of S addition on soil organic carbon sequestration. These results suggest that when nitrogen and phosphorus fertilizers were applied, inclusion of S, Fe, or Zn in straw incorporation can promote soil organic carbon mineralization process, while organic carbon sequestration was favored by Fe or Zn addition, but not by S addition.3. Under straw returning, reducing nitrogen application with biochar addition had no effect on grain and straw yield of wheat; nitrogen fertilizer reduction reduced the NO3--N, NH4+-N and TN content, and biochar application increased these three nutrients content; reducing nitrogen application had no significant effect on organic carbon and active organic carbon composition that were increased by biochar incorporation.In conclusion, it is not favored to organic carbon sequestration in soil organic carbon content with relatively high straw returned, the straw returned with adding trace elements(Fe or Zn) and biochar can improve soil organic carbon fixation.