Decomposition And Their Effects On Soil Greenhouse Gas Emissions Of Changwu Soybean And Ryegrass As Green Manures

The decomposition and their carbon and nitrogen of releasing dynamics of Changwu soybean and ryegrass as green manures were studied by using in situ nylon mesh bags method as well as using the static transparent chamber and gas chromatography technique in a dry farming land of the Loess Plateau.The research focused on the decomposition and patterns of carbon and nitrogen release of two green manures.Two treatment factors were included as green manures(Changwu soybean,ryegrass and bare land)and nitrogen fertilization(0 and 90 kg N ha-1).Our result showed:(1)The cumulative decomposition rates of green manures showed a trend of “increasing rapidly-remaining stable–increasing slowly” and reached over 80% after 281 d of being incorporated into the soil.A positive correlation was found between the decomposition rate with air temperature.The carbon and nitrogen were also released rapidly with the decomposition of green manures and the accumulative releasing rates of biomass carbon and nitrogen were over 70% and 60% after the first 33 d of being incorporated into the soil,respectively.Across nitrogen fertilization,the releasing rates of carbon and nitrogen were greater with Changwu soybean than ryegrass.Nitrogen addition increased the biomass nitrogen releasing but had no effect on carbon releasing when average across green manures.(2)The cropping ecosystem in Loess Plateau was the source of CO2 and N2 O emission and the sink of CH4.The emission flux of CO2 and N2 O has obvious seasonal variation.Green manures could increase the emission fluxes of CO2 and N2 O.Under the same nitrogen application,the Changwu soybean CO2 fluxes was significantly higher than that of ryegrass,and increased by 16.37%-19.75%(except the 58-173 days and the 281 day).Meanwhile,the corresponding cumulative emissions increased by 16.28%-19.55%.N2 O fluxes of Changwu soybean were higher than that of ryegrass with the increment of about 16.25%-17.86% on the first 0-55 days and the days of 163-281,the corresponding cumulative emissions increased by 17.06%-17.93% at the same time(P <0.05).The CH4 absorption flux was greater with ryegrass than other treatments.Compared with no nitrogen,accumulated emission of CO2 and N2 O with the nitrogen treatments increased by 7.38%-12.35% and 5.49%-6.87%,respectively(P<0.05).Under nitrogen treatments,the soil CH4 absorption with Changwu soybean and control were decreased when compare with no nitrogen treatments,but ryegrass had no difference between different nitrogen levels.CO2?N2O and CH4 emissions were significantly correlated with soil temperature.(3)Compared to the bare land soil,Changwu soybean and ryegrass significantly increased soil global warming potential(GWP).GWP was greater with Changwu soybean than ryegrass,increased by 16.67%-19.88%.GWP was greater with nitrogen treatment than that without nitrogen.Compared with the bare land soil,the incorporation of green manures increased soil total nitrogen content which was greater with Changwu soybean than ryegrass.Nitrogen application increased soil nitrate nitrogen but had no significant influence on soil total nitrogen and ammonia nitrogen.