Studies On Soil CO₂ Emission And Carbon Release From Retuning Straw Decomposition

Soil CO₂ emission is an important part of the global carbon cycle, and it is the key proces s of global climate change. Straw returning has an important effect on reducing the environment pollution from straw burning and the nutrient elements from the straw decomposition have great help for the fertility. In order to study the law of soil CO₂ emissions in soil of different organic matter contents and the effect of straw decomposition on soil organic matter. According to the climate conditions in the central Song-nen Plain, 6 organic matter treatments were established. Using the static chamber method to measure the soil CO₂ emissions during the growing seasons from 2013 to 2014 to study the law of soil CO₂ emission’s seasonal variation and diurnal variation and to analyse the effect of soil temperature and soil moisture on soil CO₂ emission. Established 4 straw decomposition treatments to study the law of straw current year decomposition and years decomposition, to analyse the effect of straw decomposition on soil carbon and organic matter content, The result showed that:Different organic matter soil CO₂ emission fluxes showed obviously seasonal variation. It increased in spring and summer, maintained a high level in summer and decreased in autumn and winter. The order of max CO₂ emission flux among different treatments in two years was S5>S4>S6>S2>S3>S1. The order of average CO₂ emission flux among different treatments in two years was S5>S3>S4>S6>S2>S1. The CO₂ emission flux of high organic matter treatment was significantly higher than that of low organic matter treatment.The CO₂ emission flux of diurnal variation in different organic matter soil showed a similar trend with a single peak curve. The peak of S1 and S6 appeared at 10 a.m.,and the other treatments’ peak appeared at 12 a.m.. After 12 a.m. soil CO₂ emission flux began to decrease and soil CO₂ flux increased after 0 a.m..There was a significant correlation between soil CO₂ emission flux of different organic matter soil and soil temperature, and the trend of soil temperature in different soil layers was basically consistent with that of soil CO₂ emission flux. The relationship between soil CO₂ emission flux and soil temperature can be fitted through linear equation, quadratic equation and exponential equation, and the coefficient of determination（R2）of exponential equation was significantly higher than that of linear and quadratic equations, indicating that the exponential equation can be better to described the relationship. The correlation of soil CO₂ emission flux and different layers soil temperature was highest in 20 cm soil layer, and lowest in 5cm soil layer. The respiratory temperature sensitivity coefficient（Q10）among different soil layers was between 1.70 and 3.39.The Q10 of different soil layers was 20 cm layer>15cm layer>10cm layer>5cm layer.There was no significant correlation between CO₂ emission flux and soil volumetric water content. linear equations, quadratic equation and exponential equation can not explain the relationship between soil CO₂ emission flux and soil moisture.With the increase of soil organic matter content, the CO₂ emission max flux,CO₂ emission average flux and total CO₂ emissions showed a single peak curve, and it can be well fitted with quadratic equation. In 2013,the fitting equation of soil organic matter content and max CO₂ emission flux was y=-0.064x2+8.197x+241.464, the fitting equation of soil organic matter content and average CO₂ emission flux was y=-0.026x2+3.212x+93.823. In 2014,the fitting equation of soil organic matter content and max CO₂ emission flux was y=-0.039x2+5.219x+242.980, the fitting equation of soil organic matter content and average CO₂ emission flux was y=-0.023x2+2.773x+100.958.The peak of soil CO₂ emission max flux appeared in the range of 64.04-66.91 soil organic matter content. The peak of soil CO₂ emission average flux appeared in the range of 60.28-61.77 soil organic matter content. The fitting equation of soil organic matter content and total CO₂ emissions was y=-1.348x2+161.192x+5089.924. When the soil organic matter content was 59.79, the total CO₂ emissions reached the maximum.In the current year of straw decomposition, at the beginning of straw decomposition the carbon release rate was relatively fast. Several months later, the rate began to slow down. The release rate of inserted ridge treatment was faster than that of surface mulch treatment. After 1 year, the carbon release rate of inserted ridge and surface mulch of soybean straw returning was in range of 62.02%-66.43% and 51.10%-58.31% respectively., the carbon release rate of inserted ridge and surface mulch of maize straw returning was in range of 57.57%-63.9% and 36.87%-45.3% respectively. Carbon releasing for years, the carbon release rate was fastest in the first year and then the rate tended to be gentle. The release rate of inserted ridge treatment was significantly higher than surface mulch treatment. The law of years’ carbon release was fitted well with the logarithm equation.Soil carbon simulation showed that straw returning can significan tly increase the soil organic matter. Maize straw returning can supply more carbon than soybean straw returning and increase the content of soil organic matter.