| The North China is the main grain-producing area where the wheat-maize rotation is the dominating cropping pattern.However,several problems exist in the agricultural production system,such as nitrogen?N?over-fertilization,low fertilizer utilization rate and crop yield,as well as serious environmental pollution.In the present study,taking wheat-maize rotation system as the research object,field experiments and indoor analysis method were adopted.Seven N regulation treatments were designed consisting of no N fertilization?CK?,farmers'N fertilization rate?FN?,N reduction treatment?RN?,RN with dicyandiamide application?RN+DCD?,RN with nitrapyrin application?RN+CP?,RN using coated controlled-release fertilizer?RN+CR?,RN with nano-carbon application?RN+NC?.The characteristics of greenhouse gas emission,N balance,temporal-spatial change dynamic and transformation behavior of soil N,crop physiological characteristics,assimilates distribution,yield and economic benefits were analyzed.Moreover,comprehensive index method was used to evaluate the effects of different N regulation modes on greenhouse gases,soil environmental condition,crop biological parameters and economic benefit.The main conclusions were summarized as follows:1.The emission characteristics as well as the greenhouse gases global warming potential?GWP?of CO2,N2O and CH4 in the rotation system under N regulation modes were illustrated.The emission flux of N2O and CO2 in the rotation system showed obvious seasonal variation,and the emission flux during maize growing season was higher than that of wheat growing season.However,the absorption flux of CH4 varied between experimental years and different crops.The GWP of CO2 accounted for 98%of total GWP,while N2O and CH4 made very low contribution to the GWP.The total GWP and net GWP of the rotation system decreased significantly when the amount of N fertilizer was reduced.Compared with FN,the total GWPs and the net GWPs of N reduction treatments in the two rotation cycles.were decreased by 10.530.1%and 23.9%64.4%.Compared with RN,the total GWPs of RN+CP and RN+NC in the two rotation system were decreased by 5.1%and 15.5%,respectively,while the results of RN+DCD changed little.Compared with RN,the average net GWPs of RN+DCD,RN+CP and RN+NC in the two rotation cycles were decreased by 22.8%,42.5%and 6.8%,respectively.The total GWP and net GWP of RN+CR were increased by 8.2%and 22.8%.These results indicated that N regulators such as DCD,CP and NC have great potential in reducing emissions.2.The effects of different nitrogen regulation modes on greenhouse gas emissions from wheat maize rotation system were verified.The application of N enhanced the emission of N2O and CO2 from soil.The soil was the source of CO2 and N2O emission and reducing N application rate could significantly reduce the emissions of N2O and CO2 from soil.Compared with FN,the average emission fluxes,the total N2O emission and emission intensity from N reduction treatments in the two rotation cycles.were reduced by more than50%.Besides,the average emission fluxes and total CO2 emission from the two rotation cycles.were reduced by more than 17%as well.Nitrogen regulator application could significantly reduce the N2O emission.Compared with RN,the emission fluxes and the total N2O emission from RN+DCD and RN+CP in the two rotation cycles.were reduced by more than 40%and 42%,respectively.Compared with RN,the total CO2 emissions from RN+DCD and RN+CP treatments were increased by 18.4%and 9.9%during maize growing season,respectively,while those during wheat growing season were decreased by8.1%and 12.9%,respectively;and the total CO2 emissions from RN+DCD were increased by 1.9%,while that of the RN+CP were decreased by 4.2%in the two rotation cycles.The soil was the weak absorption of CH4 under the experimental conditions.Compared with FN,the average absorption flux and the total absorption of CH4 from N reduction treatments in the two rotation cycles.were increased by 11%253%and 13.9%184.0%,respectively.Compared with RN,the absorption fluxes and the total absorptions of CH4were increased by 7.6%111.4%and 4.8%67.1%,respectively.This indicated that reducing N application rate increased CH4 absorption,and N regulator application could promote CH4 absorption.3.The rational N regulation measures could improve the crop physiological index and enhance N use efficiency.Compared with FN,the physiological index,photosynthetic capacity and N accumulation of crops were not significantly reduced under the condition of reducing 20%N fertilizer.N fertilizer production efficiency,agronomy efficiency and accumulated N utilization rate were increased by 41.4%,87.4%and 12.7 percentage points,respectively.N production efficiency,agronomic efficiency and accumulated N utilization rate of N regulator treatments increased by 3.2%,6.5%and 7.7 percentage points compared with RN,respectively.4.The temporal-spatial dynamic changes of NO3--N and NH4+-N,transformation behavior in soil profile and characteristics of soil nitrogen balance under N regulation modes were revealed.With the extension of crop growth,soil NO3--N in different soil layers showed a decreasing trend.Meanwhile,the NO3--N content decreased with the depth of soil profile.The NO3--N contents of FN were the highest in each soil layers?030,3060 and 6090 cm?compared with other treatments.Compared with RN,the treatments with N regulators DCD,CP and coated controlled-release fertilizer could significantly reduce soil NO3--N content and reduce NO3--N leaching risks.The temporal-spatial dynamics of soil NO3--N showed that RN+CP in maize growing season reduced NO3--N leaching to the highest extent,followed by RN+DCD treatment.While in wheat growing season,RN+CR showed the highest potential in reducing NO3--N leaching,followed by RN+CP.At the same growth period of the same crop,the NH4+-N content in soil profile was higher at the upper layers than that of the middle and lower layers.Besides,the NH4+-N contents of RN+DCD and RN+CP in each soil layer were all higher than that of the RN,indicating that the applications of these two regulators could effectively inhibit the transformation of soil NH4+-N to NO3--N,which improved the utilization efficiency of N fertilizer.Compared with FN,the N apparent loss under the condition of reducing 20%N fertilizer was reduced by 32.9%,and compared with RN,the N the apparent loss of N regulator treatments was decreased by 9%.5.The rational N regulation measures could improve crop yield and economic efficiency.N fertilization significantly increased single grain weight,grain number per spike and the yield of crops.Furthermore,compared with FN,the maize and wheat yields of N reduction treatments were increased by 7.9%and 10.9%,respectively.Compared with RN,the maize and wheat yields of N regulator treatments were increased by 4.2%and2.2%,respectively.The rational application of nitrogen fertilizer could significantly improve the economic benefit.Compared with FN,the average net income of the N reduction treatments was increased by 17%in the two rotation cycles.The net incomes of RN+DCD and RN+CP were about 10%higher than that of RN.The total net income of RN+CP was the highest in the two rotation cycles,reaching 35860 yuan?hm-2,followed by RN+DCD(34779 yuan?hm-2),while RN+CR treatment achieved the lowest net income.6.The comprehensive index method was used to evaluate the effect of N regulation model.The results showed that the RN+DCD comprehensive evaluation index was the highest in maize season,followed by RN+CP treatment,and the RN+CP comprehensive evaluation index of wheat season was the highest,followed by RN+DCD.In conclusion,compared with FN,under the condition of reducing 20%N fertilizer,the total N2Oemission,CO2 emission and the apparent N loss of N regulator treatments in the two rotation cycles were reduced,yet the total CH4 absorption,the N utilization rate,the average crop yield and average net income were increased.The comprehensive index method was used to evaluate the performance of N regulation modes,RN+CP and RN+DCD showed more obvious effects in reducing greenhouse gas emissions,increasing soil N storage capacity,increasing N use efficiency,reducing N loss,as well as increasing crop yield and economic benefits,and RN+DCD(N 300 kg·hm-2+DCD15 kg·hm-2)is the most suitable treatment for maize season,while RN+CP(N 225 kg·hm-2+CP 0.54 kg·hm-2)is the best in the wheat season.Therefore,considering environmental,economic and biological benefits,RN+CP and RN+DCD are suitable for the wheat-maize rotation system in North China. |
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