| Cropping systems,especially maize-soybean intercropping agroecosystem played an important role to influence greenhouse gas(GHG)emission in the feild.While few research has been done on the dynamics of GHG emission and mechanisms of emission reduction in maize-soybean intercropping system.We carried out a 3-year field experiment and a 1-year pot experiment to investigate the greenhouse gase fluxes and the relevant abiotic and biotic factors variation in maize-soybean intercropping system.We also investigated the mitigation potential when reducing nitrogen fertilizer input in maize-soybean intercropping.The main results were as following:(1)Maize-soybean intercropping system showed a lower GWP(CO2+N2O+CH4)than that of maize monoculture with a reduced rate of 6.6%averaged from the three growing season(2012-2014)in the field experiment:Maize(117468 kg CO2-cq ha-1)>intercrop(16311 kg CO2-eq ha-1)>Soybean(15738 kg CO2-eq ha-1).And C02 and N2O were reduced by 2.2%and 26.0%,respectively.While the pot experiment showed a similar trend with a 4.9%reduction from CO2 and a 13.5%reduction from N20 emission.N20 played an important role in reducing greenhouse gas emission in intercrop.And the further research showed that the mitigation mostly happened from maize side in the intercropping system with 655 CO2-eq ha-1 of C02 and 19.5%of N2O reduced(2)The mechanism of GHG mitigation from intercropping system was due to the combination effect of the abiotic and biotic.Firstly,the environmental conditon in maize-soybean intercropping was altered compared with monoculture maize.Soil water content(P<0.05),soil temperature(P<0.05)and soil nitrate nitrogen content(P<0.05)was significantly lower in intercrop than that of monoculture maize.And then soil water content and temperature was the two main factors to influence soil C02 flux in our experiment conditon(R2=0.631,P<0.001).Moreover,soil water content,soil ammonium nitrogen and nitrate nitrogen content were the main factors to determine soil N2O emission(R2=0.690,P<0.001).Therefore,GHG in intercropping system was reduced compared with monoculture maize.Secondly,intercrop reduced soil water conternt(P<0.01)and soil nitrate nirogen content(P<0.01)from maize side.Meanwhile,AOB abundence was remarkably decreased from maize side of intercrop as well as nisK(P<0.05)and nirS(P<0.01).Therefor the N20 production related process was decreased,leading to lower N2O emisison from maize side.(3)Maize-soybean intercrop with reduced nitrogen application showed a lower GWP than monoculture maize while withount a significant decrease in grian yield.The LER were ranged from 0.96 to 1.03 among the intercrop,indicating that reducing nitrogen application in maize-soybean intercrop has a relatively stable grain production.The LER based GWP showed the following trend:Monoculture maize(12039 kg CO2-eq ha-1)>Monoculture soybean(10856 kg CO2-eq ha-1)>MS-240(10767kgCO2-eq ha-1)>MS-120(9655 kg CO2-eq ha-1)>MS-180(9439 kg CO2-eq ha-1.Additionaly,the decreased global warming potential from MS-180 and MS-120 treatments was attributed to the decreased G WPsoil(with a reduction of 23.3%,and 22.7%,respectively)and GWPindirect(with a reduction of 13.3%,26.6%).It is concluded that maize-soybean intercropping system showed a remarkable lower greenhouse gase emission compared with monoculuture maize.It was due to the combined effect of the abiotic and biotic conditons in intercrop system.And maize-soybean intercrop with reduced nitrogen application showed a significant GHG mitigation without a reamarkeable decrease in garin yield. |
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