Research On The Soil CO₂ Emission Effects And Its Mechanism Of Summer Maize-Winter Wheat Rotation System In The North China Plain

In recent years, the Global Climate Warming has become one of the most attracting extensive world wild hot topics with increasing greenhouse gas concentration in the atmosphere and aggravation of Global Climate Change, especially the extreme weather often appear all over the world. While CO2 takes one kind of most significant atmosphere greenhouse gas, its greenhouse effect approximately composes 50%~70% of the greenhouse effect. Soil, as one of the main sources of atmospheric CO2, plays an influential role to the atmospheric CO2 density increasing. Due to the field ecosystem has been the place which strongly influenced by artificial active and where the carbon cycling is the most frequent, the research on the mechanism of soil respiration releases CO2 has also become the most essential link of farmland carbon cycling. For this reason, to research the CO2 release effect and its mechanism under soil respiration function would have important significance to investigate the influencing factors of land ecosystem carbon cycling and its feedback mechanism and the greenhouse gas mitigation.The method which the big field fixed point localization and the micro area simulation combined with the laboratory analysis was used in this article .Firstly, the characteristic of soil organic carbon, soil enzyme activities and soil respiration intensity of chestnut soil under different utilization types in Hebei northwest had been carried on the preliminary discussion, and analyzed their relationships. On this basis, the soil CO2 emission effect and its mechanism of summer maize—winter wheat rotation system under different tillage control measures and applied fertilizer ways and levels in meadow cinnamon soil of Hebei Province had been deeply researched from soil physics and biochemistry angle. Regression analysis was used to investigate the relationships between soil respiration intensity and its influencing factors, and initially determined the main factors which influence soil respiration intensity by principal component analysis. The main results were as follows:(1)The soil respiration intensity, total organic carbon, easily oxidized organic carbon and soil enzyme activities of chestnut soil where stand different vegetation types were studied, and the results showed that: the correlations between soil respiration intensity and the total organic carbon, easily oxidized organic carbon and soil enzyme activities were not significant. There were significantly positive correlation (p<0.05) or very significantly positive correlation (p<0.01) between soil organic carbon (TOC and EOC) and soil catalase and soil invertase; and a significantly positive correlation(p<0.01)was found between soil catalase and invertase activities. Thus it can be seen that the soil catalase and invertase activities could commendably response the soil organic carbon (organic matter) levels of chestnut soil, and they should be used as better indexes to evaluate its fertility.(2) Soil CO2 release effect of summer maize under different fertilizer treatments in meadow cinnamon soil region was also studied, the results indicated that: nitrogen application could enhance the soil respiration intensity and increase the amount of CO2 released through soil respiration; single application of P did not enhance the soil respiration intensity, but the release peak delayed for approximately 20 days, and the average amount of CO2 released in the whole growth period was lowly approximately 15% compared to that of nitrogen fertilizer. The average total amount of CO2 released through soil respiration was about 568.3 g/m2 when nitrogen mixed with phosphorus at different levels.After summer maize harvest, the soil total organic carbon content reduced 1.14g/kg equally, and difficultly oxidized organic carbon reduced 1.51 g/kg equally, while the easily oxidized organic carbon increased 0.07g/kg equally. The result indicated that the meadow cinnamon soil manifested as a carbon source during the period of summer maize.(3) Through to analyze the soil respiration intensity and its influencing factors in the whole period of the winter wheat under different cultivates and fertilizer treatments, the soil respiration intensity, taking the temperature as the leading factor, roughly changed as"V"glyph, and achieved the peak in the filling stage. The total amount of CO2 released through soil respiration manifested as: fertilizer with wheat > fertilizer with bare land > no fertilizer with no crop; the quantity of soil CO2 emission increased along with the increasing amount of organic fertilizer applied. And the wheat root respiration approximately composes 32.8% of the soil total respiration which in the winter wheat entire period.(4) Carried on the regression analysis to analyze the relationships between soil respiration intensity and different soil depth temperature and moisture of summer maize, the results showed that quadratic curve model: y=β0+β1x+β2x2(β2<0)could be used to simulate the correlation between soil respiration intensity and different soil depth temperature and moisture,respectively. When the soil temperature was lower than 25℃, the soil respiration intensity will enhance along with the temperature increase, while it will be inhibited when the soil temperature surpasses 25℃. The topsoil moisture changing(0~20cm)has obvious influence on soil respiration intensity compared to that of lower level (20~40cm).And the soil moisture content threshold which could influence the soil respiration intensity was about 17%, which was when the soil moisture was lower than 17%, the soil respiration intensity will enhance along with the moisture increase, while it will be inhibited and decrease when the soil moisture surpasses 17%. Univariate regression analysis of winter wheat showed that. significant positive correlation existed between the soil respiration intensity and soil enzyme activities (p<0.05),and it could be expressed by linear equation; the correlations with soil organic carbon(p<0.05)and soil moisture(p<0.01)could be expressed by quadratic polynomial;and there were significant positive exponent correlations between soil respiration intensity and soil microbial biomass carbon (SMBC) and soil temperature(p<0.05).Multiple regression analysis showed that we could use soil invertase, soil catalase activities and soil moisture (depth of 20~40cm) to construct a multiple regression model to estimate the soil respiration intensity: y=5.253+0.930x1+4.366x2-0.889x3(x1—invertase;x2—catalase;x3—soil moisture of the depth 20~40cm ). Principal Component Analysis showed that soil total organic carbon, soil microbial biomass carbon (SMBC) and topsoil moisture (depth of 0~20cm) were dominant influencing factors which affect the soil respiration intensity at a certain region.