Mitigations And Emissions Of Greenhouse Gases Of Typical Farmland In Arid Oasis Irrigated Regions,Northwest China

In view of the high water and fertilizer input status for obtaining high yield of typical farmland in arid oasis irrigated areas,northwest China,it is urgent to explore the sustainable agricultural development system that can achieve high yield of crops,efficient utilization of resources and low environmental cost.From 2011 to 2015,long-term observation study on greenhouse gas emissions of typical farmland was carried out in an irrigated spring wheat and maize system.The year round and high frequency measurements of soil nitrous oxide?N₂O?,methane?CH₄?and carbon dioxide?CO₂?fluxes were taken using the closed static chamber-gas chromatography method across six treatments:no N fertilizer as a control?CK?,conventional N fertilization and irrigation?Con?,optimum N fertilization and irrigation?Opt?,optimum N and irrigation with nitrification inhibitor?Opt+NI?,and optimum N as slow-controlled release fertilizer?Opt-SRF?,or Opt-ZT,optimum N with zero tillage?ZT?.The objectives of this study were to examine annual N₂O,CH₄ and CO₂ fluxes and their key regulating factors,and elucidate the effects of the different management practices on the characteristics of GHG emissions and agronomic performances,and evaluate the net globle warming potential?Net-GWP?and greenhouse gas intensity?GHGI?using the the full loop method of carbon flux of farmland ecosystem under the different mitigation practices.Based on the done work,we put forward a effective way to high grain yield,efficient utilization of resources and low GHG effects.The main conclusions are follows:?1?High nitrogen fertilizer input combined with flood irrigation was the main source of soil N₂O emission from the farmland of spring wheat and corn.Optimized water and fertilizer+nitrification inhibitor or slow-controlled release fertilizer can significantly reduce soil N₂O emission.The direct N₂O emission coefficients of spring wheat were 0.18% and 0.27% and maize were 0.29% and 0.42%,respectively,all of which were significantly lower than the recommended values?1%?of IPCC?2013?.?2?The farmland soil of spring wheat and maize showed a weak sink of atmospheric CH₄.There were no significant differences in the cumulative CH₄emission under different management practices,but there were high inter-annual temporal variation.The cumulative CH₄ emission for spring wheat was 0.16-0.25 kg CH₄-C ha^-1 and 0.88-1.14 kg CH₄-C ha^-1 for maize.The cumulative absorption of CH₄ of spring wheat growth season explained 47-93%of the annual absorption,and that of maize in growing and fallow season was similar.?3?Soil CO₂ emissions from the farmland of spring wheat and maize varied with the seasonal change of soil temperature.There were no significant differences in the cumulative CO₂ emission under the different management practices.The annual cumulative CO₂ emission for spring wheat was 2.3-2.9×10³ kg CO₂-C ha^-1,and 5.1-6.1×10³ kg CO₂-C ha-1 for maize.For the spring wheat,CO₂ fluxes had a negative value during the 1/3 days of the whole year,while that of maize with plastic mulching basically had a little negative value,which can effectively reduce the CO₂ emission from soil.?4?Soil N₂O and CO₂ emission during the whole growing season of spring wheat were controlled by soil moisture and temperature,while soil CH₄ absorption and soil respiration were determined by soil inorganic nitrogen content.Soil temperature,water and inorganic nitrogen content jointly determined the N₂O emission from maize field.Soil temperature was the main factor to control soil respiration and CH₄absorption during the non-flourishing period of maize,while root respiration was the main factor to control soil respiration during the joining-trumpet stages of maize.?5?Compared with traditional water and fertilizer treatment,the grain yields of spring wheat under the optimized+nitrification inhibitors or slow-controlled release fertilizer treatment which reduced 35.7% nitrogen fertilizer and 25.9% water rate maintained the high yield level of 6.4t ha^-1,and the water and nitrogen use efficiency were increased by 29% and 50% on average,respectively.Yield-scale N₂O emissions of the optimized+nitrification inhibitors or slow-controlled release fertilizer treatment were 0.12 and 0.14 g N₂O-N kg^-1 grain,respectively,and Net-GWP and GHGI of them were reduced by 43% and 42% on average,respectively,and only released 0.34 and 0.33 kg CO₂ into the atmosphere while were produced of every 1kg grain,respectively.On the basis of optimized 33.3% nitrogen fertilizer and 25.0%irrigation water,the high yields of 12.7 t ha^-1 for maize were maintained by adding nitrification inhibitors,applying slow-controlled release fertilizer or no-till with straw returning to the field.The water and nitrogen use efficiency were increased by 12% and 66% on average,respectively.Yield-scale N₂O emissions of Opt+NI,Opt-SRF and Opt+ZT treatments were 0.10,0.13 and 0.16 g N₂O-N kg^-1 grain,respectively,and Net-GWP and GHGI of them were reduced by 219% and 209% on average,respectively,and realized that the production of each 1kg grain could fix 0.12,0.14 and 0.33kg CO₂ from the atmosphere.?6?To sum up,the integrated soil-crop water and nutrient management system which included water and fertilizer optimization,nitrification inhibitor/slow-controlled release fertilizer application and no-till with straw returning to the field,should be established for mitigating climate change to ensure yield benefits,improve resources use efficiency and reduce GHG emissions effect in an irrigated spring wheat and maize system of the arid oasis areas,northwest China.