| Global warming is a major environmental problem that mankind have to face, CO2concentration in the atmosphere has the most important influence on greenhouse effect. Terrestrial ecosystem making carbon in the form of CO2will be returned to the atmosphere from soil, Due to intensive human disturbance,farmland soil has become the most active part of Terrestrial ecosystem, it’s an important emission CO2source of atmosphere. Controlling CO2emissions of farmland soil will mitigate the atmospheric CO2concentration increasing and the greenhouse effect effectively. Song-Nen Plain is one of the most important commodity grain production areas of China, it is mainly concerned with maize and soybean planting. At present, soil CO2emission in the Maize-Soybean Rotation System in Song-nen Plain of northeast Chinese was lack of systematic study. This experiment was carried out from2011to2013, farmland soil of the Maize-Soybean Rotation System in Song-nen Plain was chosen as research object, using closed static chamber method, setting up the experiment that CO2emission of farmland soil under different tillages; CO2emission of farmland soil under different soil organic matter; distinguishing sources of CO2emission of soil, Through continuous observation that CO2emission of farmland soil of the Maize-Soybean Rotation System、Soil temperature and moisture. Analysing time change regulation of CO2emission of farmland soil in Song-nen Plain and its relationship with soil temperature, moisture, organic matter.Distinguishing the source of CO2emission of farmland soils, Establishing regression equation of CO2emission flux changed with time, estimating carbon balance of farmland soil of Maize-Soybean-Maize Rotation.The results showed that:CO2flux of farmland soil had obvious seasonal, Peak appeared at higher temperatures and abundant rainfall in late July to early August. You can use the quadratic equation to fit CO2flux of soil changes with time during the trial period, Test results of equation was significant, degree of fitting was well, Regression equation of CO2flux of farmland soil and sampling the number of days,Covered by minimum tillage:y=-0.0084x2+1.7010x+6.0147; Minimum tillage:y=-0.0057x2+1.2275x-7.7377; no tillage with mulch:y=-0.0098x2+2.0260x-1.3656; no tillage:y=-0.0054x2+1.1467x-6.9755;plowing:y=-0.0056x2+1.1798x-3.9688.Soil temperature had a significant effect on CO2flux of soil, Variation of Farmland soil temperature at different levels and CO2flux of soil remained Consistency, simulating the relationship of CO2flux of soil and soil temperature through Linear equation, quadratic and exponential equations well.The coefficient of R2of Exponential equation was significantly higher than the linear and quadratic equations. It showed that exponential equation would better express the relationship between them; Comparing soil temperature at different levels with CO2emission flux of soil, the result showed that20cm soil temperature was the highest correlation and5cm soil temperature was the lowest correlation. Sensitivity coefficient of farmland soil respiration temperature; Qio:between1.72and3.71. Soil moisture has a certain effect on CO2emission fluxes of soil, soil volumetric water content of10cm layer and CO2emission fluxes of soil weren’t fit with equation by regression equation analysis, soil volumetric water content of30cm.60cm,90cm layer and CO2emission fluxes of soil were fit with quadratic equation, Most of the equation would through test, but fitting equation coefficient of determination(R2)was smaller.The total of CO2flux of farmland soil were significantly affected by tillage practices during the trial period (April11-November11),showed that NTS>MTS>CT>MT>NT, Treatment of straw returning(NTS、MTS) was significantly higher than non-straw returning(CT、NT、MT), differences between the NTS and MTS was not significant, the differences was also not significant between CT, NT and MT. Treatment of CO2emission flux of straw returning soil compared to non-straw returning cumulative increase of65%to97%in sampling period.CO2emissions of Rhizosphere had a significantly effect on CO2flux of soil, contribution rate of the growing season of maize roots to CO2of soil fluctuated between7%to49%,average25.97%; contribution rate of the growing season of soybean roots to CO2of soil fluctuated between5%to62%, average33.25%.soil organic matter had a significantly effect on CO2emission of soil, You can use the quadratic equation y=-1.3542x2+153.66x+4226.6to fit the total of CO2flux of soil and the content of soil organic matter in the test. Derivation of this equation determined that the total of CO2emission of soil was maximum when the content of soil organic matter was56.73g-kg"’Tillage practices had a significantly effect on carbon balance of farmland soil. Three-year cumulative increase in the amount of carbon of covered by minimum tillage(MTS)and no tillage with mulch(NTS)farmland soil was6460kg C·hm-2and5521kg C·hm-2respectively in a rotation cycle (Maize-Soybean-Maize), the average annual increase in the amount of carbon was2153kg C·hm-2and1840kg C·hm-2respectively. Three-year cumulative reduce in the amount of carbon of Minimum tillage(MT). plowing(CT)and no tillage(NT)farmland soil was1764kg C·hm-2、1651kg C·hm-2and1482kg C·hm-2respectively, the average annual reduce in the amount of carbon was588kg C·hm-2.550kg C·hm-2and494kg C·hm-2respectively. |
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