| Since the industrial revolution, with the rapid economic development, accelerate the destruction of human activities on the ecological environment, the atmosphere gradually deteriorated, resulting in rising global temperatures. In the carbon cycle, the terrestrial ecosystems plays an important role on the global carbon balance, in the terrestrial ecosystem, in addition to industrial emissions as oil, coal and other fuel combustion caused, the greatest impact of human activities are agricultural ecosystems. Therefore, It is important that in-depth study soil respiration CO2 emission reduction of carbon sequestration process on farmland to maintain the ecological balance of carbon and reduce greenhouse gas emissions. Songnen Plain arable 5.59 million hm2, fertile soil, is an important commodity grain base in Heilongjiang province and the country, mainly in corn, soybean based, but there are few systematic research and reports for CO2 and other greenhouse gas emissions and carbon footprint in Songnen Plain. This experiment using closed static chamber method to measured corn, soybean field soil CO2 emission flux in Songnen Plain, analysing time change regulation of CO2 emission of farmland soil in Songnen Plain and its relationship with soil temperature, moisture, and estimate the carbon footprint, the results showed that:CO2 emissions flux of field soil showed significant seasonal variations, peak appeared at higher temperatues and abundant rainfall in late July to early August, and maintained a low level emission flux in April and November, general showed single peak curve; the maximum flux, the average and annual total flux of soil CO2 emissions in straw-return treatment were higher than the straw-remove treatment.Soil CO2 flux and soil temperature farmland showed significant correlation, the relationship(P <0.01) can simulate well relations by linear equations, quadratic and exponential equations, the R2 value of three equations showed that, exponential equation> quadratic equation> linear equation, but they all did’t show a significant difference; R2 value of the three equations showed 25 cm> 20 cm> 15 cm> 10 cm> 5 cm, 5 cm and 20 cm soil, 25 cm soil layer reached a significant level in cornfield, 5 cm and 25 cm soil layer of soil was significant in soybean fields, indicating that the correlation of deep soil temperature and CO2 emission flux is higher than the shallow soil.7.6 cm and 12 cm soil volumetric water content did not show significant changes and the relationship did not reach a significant correlation, linear equations, quadratic and exponential equations can not simulate well relations, the performance was not significant.Estimated root respiration to soil respiration contribution rate by root exclusion method, the results show that, in the whole corn growing season, corn root respiration contribution rate varied from 3.0% ~ 54.3%, with an average of 35.1%; in the whole soybean growing season, soybean roots respiration contribution rate varied 5.1% ~ 71.3%, with an average of 24.3%.Estimated corn, soybean fields carbon footprint by two paths, the results show that, in the whole ring type, corn, soybean fields showed a carbon sink effect, the average carbon footprint in cornfield was 10609.4 kgCe ? hm-2 ? a-1, the average carbon footprint in soybean field was 1598.2 kgCe ? hm-2 ? a-1; in the semi ring type, corn, soybean fields showed a carbon source effect, the average carbon footprint in cornfield was-2045.4 kgCe ? hm-2 ? a-1, t the average carbon footprint in soybean field was-2028.4 kg Ce ? hm-2 ? a-1; indirect inputs in farmland carbon footprint, fertilizer and diesel contribution rate were higher than others, accounting for 85.7% ~ 96.1% in the cornfield, accounting for 70.5% ~ 87.4 % in soybean fields.Calculating the carbon cost of grain, the results showed that, the average carbon cost of corn was 0.17 kg(Ce) ? kg-1, the average carbon cost of soybeans was 0.69 kg(Ce) ? kg-1.The difference between the straw, stubble to field soil carbon and net soil CO2 emissions carbon as the characteristics of soil carbon balance, the results showed that, in straw-return treatment, the organic material return to field soil carbon is greater than the soil CO2 emissions carbon, the difference was positive, the average amount of carbon sequestration in STR-C treatment is 3465.5 kgC ·hm-2·a-1, the average of carbon sequestration in STR-S treatment is 3370.8 kgC ·hm-2·a-1; in straw-remove treatment, the organic material return to field soil carbon is less than the soil CO2 emissions carbon, the difference was negative, the average amout of carbon released in STM-C, RC and STM-S were 370.7 kg C ·hm-2·a-1, 290.7 kgC ·hm-2·a-1 and 645.3 kgC ·hm-2·a-1. |
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