Greenhouse Gas Emission From Growing Season Of Sown Pastures In Inland Arid Area

Northwest inland arid area is production base of cultivated grass and alfalfa area is the largest in China. The research use static box- gas chromatography to measure GHG emissions of perennial mowing pasture, annual mowing pasture, perennial grazing pasture, annual grazing pasture in growing season.（1） Perennial mowing pasture is the CH₄ sink, source of CO₂ and N₂ O, CH₄ absorption fluxes present the trend of rising after reduced in the growing season, total CH₄ absorption（y） in the growing season and the planting fixed number of year（x） exist available equation y = 0.0471 x2-0.503 + 0.6322 x（R2= 0.9038, P = 0.9038） The relationship between CH₄ absorption and the aboveground（R=-0.633,P=0.019） and underground biomass（R=-0.889,P=0.000） is significant negative correlation; The relationship between CO₂ emissions present a tendency of reduce after rising, total CO₂ emissions（y） and the planting fixed number of year（x） exist available equation y=-6.3729x2 + 59.337 x + 96.495（R2 = 0.6011, P = 0.6011）, CO₂ emission and the aboveground（R=0.753,P=0.005）and underground biomass（R=0.656,P=0.021）is significantly positive correlation; NO₂ emission flux presents a trend of reducing after rising, total emissions（y） and the planting fixed number of year（x） exist available equation y = 0.013x2 + 0.129 x 0.129（R 2 = 0.7297, P = 0.7297）, The relationship between N₂ O emission and the aboveground（R=0.647,P=0.023） and underground biomass（R=0.766,P=0.004） significantly positive correlation.CO₂, CH₄, N₂ O emission flux and 0-20 cm layer soil TP content is significantly negative correlation（R=-0.442,P=0.008; R=-0.400,P=0.013; R=-0.358,P=0.036）, and SOM content is significantly positive correlation（R=0.716,P=0.002; R=0.39,P=0.019; R=0.705,P=0.004）, CO₂ emission flux and 0-20 cm layer soil TN content is significantly negative correlation（R=-0.337,P=0.042）.（2） In the growing season, annual mowing pasture CH₄ absorption, CO₂ and N₂ O emission flux showed a trend of reducing after rising, the CH₄ absorption of Gaodan grass is significantly higher than the common vetch（P=0.038）and Yu grass（P=0.040）, the CO₂ emission flux of common vetch is significantly higher than Gaodan grass（P=023） and Yu grass（P=0.011）, CH₄ absorption flux（y） and soil temperature（x） exist available equation y= 0.0878x2 + 4.8615 x+ 4.8615（R 2 = 0.8445, P= 0.00）, CO₂ / NO₂ emission flux and soil temperature is significantly positive correlation（R2 = 0.748,P=0.002; R2 = 0.0519,P=0.008）.（3） In the growing season, CH₄ absorption flux and NO₂ emission flux of annual pasture（wheat, barley and rye） all showed a trend of decline, CO₂ flux are showing a rising trend. Grazing did not change sink or source function of CO₂, CH₄, N₂ O, it significantly reduce CH₄ absorption flux of barley（P=0.041）, wheat（P=0.006）, significantly reduce the CO₂ emission flux of barley, wheat, rye（P=0.009; P=0.018; P=0.023）, in different extent inhibited the three annual grass of N₂ O emission.（4） Sheep rotational grazing alfalfa and tall fescue mix sowing grass, in the growing season, CH₄ absorption fluxe shows a rising trend after down, CO₂ and N₂ O emission flux showed decline after increase. Grazing significantly reduced the CH₄ absorption fluxe of perennial grazing grassland（P = 0.018） and CO₂ emission flux（P = 0.011）.（5）The research measure GHG of several kinds of legume forages,5yr alfalfa has the strongest absorption ability of CH₄, N₂ O emission of alfalfa×tall fescue pasture is the highest; The CH₄ absorption ability of wheat and Gaodan grass is the strongest, C3 grass of CO₂ emission flux is significantly higher than C4 grasses（P=0.025）, total N₂ O emission flux of C4 grass is significantly higher than C3 grass（P=0.022）.（6） The GHG emission of barley, wheat, rye produce unit quality hay is significantly higher than Yu grass, Gaodan grass, common vetch pea and alfalfa grassland（P<0.05）;In the grazing pasture, greenhouse gas emission of contrast（zero grazing） grassland produce unit quality CP is significantly higher than grazing grassland（P<0.05）, GHG emission of barley, wheat produce unit quality CP is significantly higher than rye, alfalfa/tall fescue pasture（P< 0.05）.