| Emission fluxes of greenhouse gases from agricultural field soil has became a research focus recently. But there were a few achievements on the emission fluxes of greenhouse gases from agricultural field soil in Heilongjiang province, especially on the law of CO2 emissions. And this study was conducted using the soil from soybean field with five tillage methods including conventional tillage (CT), minimum tillage with stubble (MT), minimum tillage with straw mulch (MTS), no tillage with straw mulch (NTS), no-tillage (NT), to analyze the law of CO2 emissions by long-term continuous observation; to study the effects of various impact factors and tillage methods on the law of CO2 emissions; estimate the total CO2 emissions and establish the semi empirical model, in order to estimate the CO2 emissions from soybean field; to offer theoretical information and basis for the study on he CO2 emissions from farmland in Heilongjiang province. The results showed that:There was a lots of CO2 was exhausted from soybean field during the growth process, CO2 emissions showed a single peak curve with growth process; more in summer than in spring and autumn; CO2 emissions peak and minimum appeared at 12:00~ 14 : 00 and 0:00 ~ 4:00 respectively in a day, and differed with growth stage; CO2 flux was 84.68 ~354.35mg·m-2·h-1 for minimum tillage with stubble (MT), 55.86~613.51mg·m-2·h-1 for minimum tillage with straw mulch (MTS), 71.17~431.98mg·m-2·h-1 for conventional tillage (CT), 70.27 ~ 351.95 mg ? m -2 ? h-1 for no-tillage (NT), 103.15 ~ 590.09mg ? m -2 ? h-1 for no tillage with straw mulch (NTS), their mean value were 198.11 mg·m-2·h-1, 321.20 mg·m-2·h-1, 198.59 mg·m-2·h-1, 187.19 mg·m-2·h-1, and 333.68 mg·m-2·h-1 respectively.Temperature is an important factor which effect CO2 emissions from soybean field. The relationship between CO2 emissions and air temperature and soil temperature can be performed by the formula"y=Aebx", and the temperature of 10cm, 15 cm and 20 cm soil layer has a great influence on CO2 emissions. The range of Q10 value were 2.29~3.58 for minimum tillage with stubble (MT), 2.28~3.56 for conventional tillage (CT), 2.24~3.49 for no-tillage (NT), and 2.03~2.86 for no tillage with straw mulch (NTS). The sensitivity of CO2 emissions was more strong to temperature of soil layer than to air temperature Judging from Q10 value, and increased with the increment of soil depth.CO2 emissions was effected by soil water content and soil compaction. CO2 emissions increased with the increment of soil water content after raining, and there was a negative correlation between CO2 emissions and soil compaction.CO2 emissions was also increased by inertillage management, and CO2 emissions of minimum tillage with stubble (MT) and minimum tillage with straw mulch (MTS) were more than other treatments without straw covering, which indicated that tillage method has great influence on CO2 emissions; there were no significant difference among conventional tillage (CT),minimum tillage with stubble (MT) and no-tillage (NT), and CO2 emissions of no-tillage (NT) was minimum.The most important factors effect CO2 emissions was soil temperature, rainfall 10 days before sampling and days after emergence according principal factor analysis. Semi empirical model including the factors above was performed with five different tillage methods treatments.Total CO2 emissions during the soybean growth cycle could be estimated by the regression equation which was established between CO2 emissions and days after emergence were 6.64t·hm-2 for Minimum tillage with stubble (MT), 10.78t·hm-2 for no tillage with straw mulch (NTS), 6.46t·hm-2 for conventional tillage (CT), 6.06t·hm-2 for no-tillage (NT), and 10.85t·hm-2 for no tillage with straw mulch (NTS).
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