The Synergetic Effect Of N-fertilizer Postponing Application And Maize-pea Intercropping On The Reduction Of Soil GHG Emissions

Cereal-legume intercropping has typical features like high yield,high efficiency,low carbon emission,and sustainability,etc.N management strategy is the basical and vital element to determine whether these features can function or not.In monoculture pratices,N-fertilizer postponing application was largely adopted as a means to optimize the relationship between N supply and crop N requirement.Nevertheless,integrating N-fertilizer postponing application to cereal-legume intercropping lack of the thireotical and practical basises,referring to improvement of interspcific facilitation between two crops,and achievement of N-saving,GHG emission reduction,and yield stability.In 2014-2016,a fied experiment was conducted at Wuwei experinmental station in Hexi irrigatioin region,consisted with four N management systems,i.e.zero N?N0?,postponing application?N1?,equal application?N₂?,and traditional application?N3?,and three cropping systems,i.e.sole pea?P?,sole maize?M?,and maize/pea intercropping?P/M?.The study was projected to investgate the effect of N-fertilizer postponing application on GHG emission charecteristics,interspecific relationship,and nitrogen use characristics of pea and maize under sole and intercropping systems.Therefore,the objective was to reveal a basic mechianism on regulatory effect of N management systems on nitrogen use and GHG emission characristics of cereal-legume intercropping.The ultimate aim was to provide a theoretical base for further optimization of N-fertilizer management of cereal-legume intercropping.The main results are as follows:?1?N-fertilizer postponing application and intercropping significantly reduced the in growing season GHG emissions of pea and maize,and the integration performed a greater reduction than the additive effect of single practice.During the entire growing season,soil carbon emission of maize-pea intercropping was reduced by 20.5% compared to sole maize,and that of N-fertilizer postponing application was reducted by 26.4% compared to conventional application.Besides,the synergistic effect derived from integration reduced soil carbon emission by 8.9%.The soil N₂O-N emission of maize-pea intercropping was reduced by 26.9% over the sole maize,and that of N-fertilizer postponing application was reduced by 29.1% over the conventional application.In addition,the synergistic effect decreased soil N₂O-N emission by 7.2%.The GWP of maize-pea intercropping was 20.6% lower than athat of the sole maize;and postponing application decreased the GWP by 26.6% compared to the conventional application;and the synergistic effect decreased GWP by 8.8%.?2?N-fertilizer postponing application and intercropping reduced the sensibility of N₂ O emission rate to the varion of soil mineral N,depressed the response extent of N₂ O emission to the varion of soil WFPS,and inhibited the sensibility of soil respiration to the varion of soil temperature,thereby controled the GHG emission effectively.The correlation between soil CO₂ emission and soil mineral N content under both pea and maize was mainly performed before the pea harvest,and the accumulated mineral N content was the direct cause of the increased CO₂ emission during that cause.There was a significant exponential relationship between N₂ O emission and soil mineral N content,and the sensitivity of soil N₂ O emission to the varion of soil mineral N was decreased by intercropping and N-fertilizer postponing application.The response of soil respiration to WFPS was observed in the whole growing season of pea,while that of maize was mainly occurred in post-harvest of pea.Overall,soil N₂ O emission and WFPS accorded with the two regression curve,and the extent of N₂ O emission response to the varion of 0-30 cm WFPS was reduced by intercropping and N postponing aplication.The soil respiration and soil temperature accorded with the exponential regression,and the sensitivity of soil respiration to the varion of soil temperature was also reduced by intercropping and N postponing aplication.There was a negative correlation between the soil temperature and the N₂ O emission of pea and maize,indicating low temperature could promote the soil N₂ O emission,while high temperature would inhibit it.?3?The improvement of N accumulation rate in maize-pea intercropping by postponing application significantly increased the soil respiration,but decreased the soil N₂ O emission rate of the components crops.Postponing apply of N fertilizer delayed the emergence of maximum accumulation rate of maize,whereas,it increased?13.4%?the maximum value of accumulation rate.In addition,postponing of N fertilizer also extended?4.4 D?the days with high rate of N accumulation.At the early growth stage,N accumulation rate of pea and soil respiration accorded with the liner curve,while at the late growth stage,their relation accorded with the parabola curve.The soil respiration of maize was increased as N accumulation rate increases during the entire growing season,and was influenced much heavy under low rate conditions.There was a negative correlation between N accumulation rate of pea and the soil N₂ O emission,indicating increae of N accumulation in pea plants could reduce the N₂ O emission.However,a positive correlation between N accumulation rate of maize and the soil N₂ O emission rate was revealed.This was mainly attributed to the N top-dressing caused synchronization,where high N application,high N accumulation and high N₂ O emission were emerged in the same period.This may mark the real relationship between maize N accumulation and N₂ O emission.?4?In maize-pea intercropping systems,the interspecific competition of pea relative maize increased soil respiration,wihle decreased N₂ O emission rate of pea strips,whereas decreased soil respiration but increased N₂ O emission rate of maize strips.During the co-growth period,the competitive ratio of pea relative to maize was greater than 1,indicating the competitiveness of pea was greater than maize.Postponing apply of N-fertilizer intensified the competition by 6.9% over traditional N application.Meanwhile,the promoted accumulation rate of dry matter and nitrogen in pea plants by intensified competition greatly enhanced the soil respiration but decreased N₂ O emission rate.The relationship between dry matter and nitrogen accumulation rate in maize plants with interspecific competition accorded with a parabola curve,implied that interspecific competition restrained N accumulation of maize,and thereby decreased soil respiration but increased N₂ O emission rate.?5?The integration of postponing application to maize-pea intercropping significantly improved grain yield and N-fertilizer use efficiency,while greatly decreased the GHGi.Besides,an obvious synergetic effect was also revealed.For grain yield,intercropping improved it by 31.0% compared to the weighted mean value of two sole crops,and N-fertilizer postponing application increased it by 26.6% over the traditional application.The collaborative analysis showed that intercropping effect was the main reason for yield improvement of maize/pea intercropping,and the synergistic effect increased grain yield by 10.1%.For N-fertilizer use efficiency,intercropping improved it by 12.8% compared to the weighted mean value of two sole crops,and N-fertilizer postponing application increased it by 89.1% over the traditional application.Differed from grain yield,postponing effect was the main reason for the improvement of N-fertilizer use efficiency,and the synergistic effect increased it by 24.5%.Although intercropping increased two species' GHG emissions intensity?GHGi?,but at a system level,the GHGi of maize/pea intercropping was significantly lowered?by 26.8%?over the monoculture maize.In addition,N-fertilizer postponing application significantly reduced GHGi by 34.4% compared to traditional N application,and the synergistic effect decreased GHGi by 6.5%.