Greenhouse Gases Emission From Paddy Field As Affected By Rice Straw Incorporation And Its Response To Water Regime

Global warming result from rising of atmospheric concentration of greenhouse gases is an environment issue of common concern among all people. Paddy field is a major source of greenhouse gases in the atmosphere, which are paid more attention by more agriculture environmental scientists. This study was carried out in paddy field ecosystems of subtropical regions. The characteristics of CH4emission, N2O emission, soil and rice system respiration and soil heterotrophic respiration under different rice straw incorporation rate and water regime were studied by using field plot experi-ment. We also carried out thermostatic incubation experiment and to research the effect of external source organic materials incorporation on greenhouse gases emission, and revealed the mechanism of the source of greenhouse gases after rice straw incorporation. The main results of this study are presented as follows:(1) CH4cumulative emission of high rice straw incorporation rate (6t·hm-2) and continuous flooding treatment is4.7times as much as that of no rice straw incorporation and continuous flooding treatment. CH4cumulative emission of high rice straw incorporation rate and intermittent flooding treatment, low rice straw incorporation rate (3t·hm-2) and intermittent flooding treatment is8.8and4.8times as much as that of no rice straw incorporation and intermittent flooding treatment, respectively. CH4cumulative emission of no rice straw incorporation and continuous flooding treatment is2.7times as much as that of no rice straw incorporation and intermittent flooding treatment. CH4cumulative emission of high rice straw incorpora-tion rate and continuous flooding treatment is1.2times as much as that of high rice straw incorporation rate and intermittent flooding treatment (average value of three rice season); Soil drying not only reduced CH4emission of soil drying period, but also reduced CH4emission of re-flooding period. Under no straw incorporation, compared with non-drying, soil drying reduced CH4emission by57.6%and86.3%, during soil drying and re-flooding period, respectively. Under high straw incorporation rate, compared with non-drying, soil drying reduced CH4emission by14.1%and81.7%, during soil drying and re-flooding period, respectively. CH4emission rate of no rice straw incorporation and continuous flooding treatment, no rice straw incorporation and intermittent flooding treatment, low rice straw incorporation rate and intermittent flooding treatment, high rice straw incorporation rate and intermittent flooding treatment and high rice straw incorporation rate and continuous flooding treatment at tillering stage was accounted for34.2%,56.9%,72.2%,73.6%and62.8%of the whole stages, respectively. CH4emission rate of each treatment in the rice planting region is3.1,2.4,1.4,2.2and1.9times as much as that of the corresponding treatment in the non-rice planting region, respectively. CH4emission was closely related to environmental factors (soil temperature and depth of the water), soil factors and biological factors.(2) In the rice planting region, N2O cumulative emission rate of high rice straw incorporation rate and continuous flooding treatment accounted for36.8%of no rice straw incorporation and continuous flooding treatment; N2O cumulative emission rate of high rice straw incorporation rate and intermittent flooding treatment and low rice straw incorporation rate and intermittent flooding treatment accounted for47.0%and70.5%of no rice straw incorporation and intermittent flooding treatment, respectively; N2O cumulative emission rate of no rice straw incorporation and continuous flooding treatment accounted for77.0%of no rice straw incorporation and intermittent flooding treatment, high rice straw incorporation rate and continuous flooding treatment accounted for60.8%of high rice straw incorporation rate and intermittent flooding treatment; In the non-rice planting region, N2O cumulative emission rate of high rice straw incorporation rate and continuous flooding treatment accounted for166.0%of no rice straw incorporation and continuous flooding treatment; N2O cumulative emission rate of high rice straw incorporation rate and intermittent flooding treatment and low rice straw incorporation rate and intermittent flooding treatment accounted for93.0%and74.9%of no rice straw incorporation and intermittent flooding treatment, respectively; N2O cumulative emission rate of no rice straw incorporation and continuous flooding treatment accounted for12.4%of no rice straw incorporation and intermittent flooding treatment, high rice straw incorporation rate and continuous flooding treatment accounted for26.3%of high rice straw incorporation rate and intermittent flooding treatment; Relative to non-drying, soil drying not only increased N2O emission of soil drying period, but also increased N2O emission of re-flooding period. N2O emission each season rice are mainly concentrated in tillering stage, jointing stage and mature stage; N2O emission rate of each treatment in the non-rice planting region is1.2,7.4,10.2,24.2and5.0times as much as that of the corresponding treatment in the rice planting region, respectively. N2O emission was closely related to environmental factors (soil temperature and depth of the water) and soil factors(3) Total respiration rate of soil and rice system of high rice straw incorporation rate and continuous flooding treatment is1.2times as much as that of no rice straw incorporation and continuous flooding treatment; Total respiration rate of soil and rice system of high rice straw incorporation rate and intermittent flooding treatment and low rice straw incorporation rate and intermittent flooding treatment is1.02and0.98times as much as that of no rice straw incorporation and intermittent flooding treatment, respectively; Total respiration rate of soil and rice system of no rice straw incorporation and continuous flooding treatment is0.91times as much as that of no rice straw incorporation and intermittent flooding treatment, high rice straw incorporation rate and continuous flooding treatment is1.05times as much as that of high rice straw incorporation rate and intermittent flooding treatment; Soil heterotrophic respiration rate of high rice straw incorporation rate and continuous flooding treatment is1.81times as much as that of no rice straw incorporation and continuous flooding treatment; Soil heterotrophic respiration rate of high rice straw incorporation rate and intermittent flooding treatment and low rice straw incorporation rate and intermittent flooding treatment is1.36and1.08times as much as that of no rice straw incorporation and intermittent flooding treatment, respectively; Soil heterotrophic respiration rate of no rice straw incorporation and continuous flooding treatment is0.65times as much as that of no rice straw incorporation and intermittent flooding treatment, high rice straw incorporation rate and continuous flooding treatment is0.83times as much as that of high rice straw incorporation rate and intermittent flooding treatment; In general,soil drying not only increased soil heterotrophic respiration of soil drying period, but also increased soil heterotrophic respiration of re-flooding period. Total respiration rate of soil and rice system of each treatment is6.5,4.5,4.2,3.5and4.3times as much as soil heterotrophic respiration rate of the corresponding treatment, respectively; Total respiration rate of soil and rice system and soil heterotrophic respiration rate were closely related to environmental factors, such as temperature, water depth; Total respiration rate of soil and rice system were extremely positive correlated to rice biomass above the ground and under the ground. Total respiration rate of soil and rice system and soil heterotrophic respiration rate were significantly or extremely positive correlated to soil DOC content.(4) Water regime and rice straw incorporation had no significant effect on the rice yield of each rice season; Water regime had effect on soil heterotrophic respiration and net primary production of rice, thus affected the net CO2exchange between paddy field ecosystem and atmosphere, which was the dominant factor of affecting the paddy NEE (Net Ecosystem CO2Exchange) value. Rice straw incorpora-tion had significantly or extremely effect on NGHGE (Net Greenhouse Gas Emission) and GHGI (Greenhouse Gas Intensity), which was the dominant factor affecting the NGHGE and GHGI. On annual time scale, the rice paddy fields did not increase net greenhouse gases emission.(5) CH4cumulative emission of adding original rice straw was the highest, and which had big priming effect on soil intrinsic organic carbon; CH4cumulative emissi-ons of adding decomposed straw, low molecular organic material and non-active ingre-dient straw were obviously higher that of non-adding organic materials treatment, which had priming effect on soil intrinsic organic carbon; CH4emission rate was closely related with soil texture. CO2cumulative emission of adding original rice straw was the highest, and which had big priming effect on soil intrinsic organic carbon; CO2cumulative emission of adding low molecular organic material treatment was higher that of non-adding organic materials treatment, and which had priming effect on soil intrinsic organic carbon decomposition; CO2cumulative emission of adding decomposed straw and non-active ingredient straw treatment was no significant differences as compared with non-adding organic materials treatment, and it’s priming effect on soil intrinsic organic carbon decomposition was not obvious; Priming effect of adding exogenous organic materials containing low molecular organic material was stronger than that of adding single material such as cellulose, and response of soil organic carbon decomposition to different exogenous material was different;CO2produced mainly at rapid decomposition stage of the easy decomposition material in rice straw;CH4produced at rapid decomposition stage of the easy decomposition material and slow decomposition stage of the difficult decomposition material in rice straw, but it produced mainly at rapid decomposition stage.N2O cumulative emission rate of S treatment is the highest, N2O cumulative emission rate was reduced due to adding the various organic materials, reduction degree of N2O cumulative emission rate was closely related with soil texture; CH4, N2O and CO2cumulative emission rate were closely associated with soil factors. The relationship between CH4, N2O and CO2cumulative emission rate and soil factors existed difference due to different soil.