| How to reduce the input of nitrogen fertilizer and other resources in agricultural production systems,meanwhile,improve crop yield continuously to ensure food security is a major challenge for agricultural green development in China.The North China Plain(NCP)is an important food production base,facing problems of low in soil organic carbon and total nitrogen(SOC and TN),excessive nitrogen fertilization,and unreasonable field management practices currently.The aims of this study were to address the above mentioned problems through establishing an integrated management strategy to realize green development of wheat-maize cropping system.That is,enhancing SOC and TN pools mainly through recycling of various organic resources in wheat season and no-tillage in maize season.Regulating and maintaining soil mineral nitrogen(Nmin)in the range of both ensuring the demand of high-yielding crop production and not causing great environmental loss via in-season root-zone nitrogen management on the basis of the double-high crop system.The study combined long-term field trials and LCA analysis methods,agronomic and environmental effects were evaluated.Main results were summarized as follows:1)Results of long-term field experiment showed that the integrated management strategy of recycling of different organic resources(biochar,maize straw,cow manure,compost and biogas-residue)combined with chemical fertilizer could increase SOC content in 0-15 cm significantly,from the initial(2008)of 8.19 g kg-1 to 14.71 g kg-1 in 2015.Among them,recycling of biochar was the most effective approach,followed by BgR,C,M>S>F.Although F treatment also increased SOC content in 0-15 cm,but the magnitude of the increase was less than that of either recycling of organic resources only,or application of different organic resources combined with chemical nitrogen.Meanwhile,the integrated management strategy could maintain soil Nmin concentration of root-zone in a reasonable range,the average concentration of wheat and maize season were 13.5(10.9-15.9)and 14.1(13.1-15.4)mg kg-1,respectively.2)Compared with treatment without application of both organic resources and chemical nitrogen(CK),recycling of organic resources only increased wheat yield by 66.5%(1.6-175.3%),in order of BgR>C,M>S>BC and CK;increased maize yield by 46.7%(3.1-74.2%),in order of BgR,C,M>S>BC and CK.Compared with treatment with chemical nitrogen only(F)(7.05 Mg ha-1),the integrated management strategy of recycling of organic resources combined with chemical nitrogen increased wheat yield by 11.2%(5.0-16.7%),but with no effect on maize yield.Meanwhile,maintain or even reduce nitrogen input rate compared with F treatment(186-264 vs.260 kg N ha-1).Recycling of compost and biogas-residue combined with chemical nitrogen declined the consumption of nitrogen fertilizer most obviously,with the reduction of 10.9%and 28.4%,respectively.3)High-yielding wheat was obtained depend on the enhancement of SOC content in 0-15 cm resulted from the integrated management strategy.The possible explanations were:the enhancement of SOC content could increase soil water-filled pore space and soil temperature at pre-winter stage,which was conducive to increase effective tillers.Also improve the deliverability of soil Nmin during flowering to harvest to prevent the premature aging of wheat.Additionally,the improvement of soil physical properties associate with SOC,including the decrease of soil bulk density and soil penetration resistance,the increase of soil field water content,available water content and soil physical quality index-S value etc.,are beneficial to support the growth of root systems,which may be another factor to support high-yielding wheat production.4)Influenced by exogenous nitrogen inputs,soil water-filled pore space and soil temperature,recycling of organic resources only increased cumulative emissions of N2O by 38.6%(10.5-78.9%)of wheat-maize rotation compared with CK(0.57 kg N2O-N ha-1),and in order of BgR>S>C,M,BC>CK.Compared with F(2.13 kg N2O-N ha-1),the integrated management strategy of recycling of organic resources combined with chemical nitrogen increased cumulative emissions of N20 by 12.2%(1.4-24.4%).However,the net global warming potential(Net-GWP)at field scale of all treatments(exclude CK)were negative due to the accumulation of SOC in 0-30 cm.The numeric data were-7.48 and-7.12 Mg CO2-eq ha-1 under no nitrogen and optimized nitrogen,respectively.And recycling of biochar was the most efficient treatment.But,the Net-GWP increased significantly,reached to 5.57 and 7.81 Mg CO2-eq ha-1,respectively,as the result of carbon emissions from processes of organic resources production,power consumption of irrigation,fertilizer production and direct soil N20 emissions.Among them,treatments with BC were the strongest carbon-sink,and treatments with BgR were the strongest carbon-source.In the further,the changes in power generation,the improvement of chemical fertilizers production processes,the transformation of organic resources management and application technologies may be effective ways to reduce the Net-GWP at system level.5)In conclusion,recycling of organic resources only normally with low crop yield,and failed to guarantee food security currently.Under the current production conditions,the integrated management strategy of recycling of compost,straw and manure combined with nitrogen input may be effective measures to increase crop yield,reduce nitrogen application rate and decline Net-GWP simultaneously.Treatment with BC and nitrogen was useful for reducing carbon emission,but had no benefit to increasing crop yield and reducing consumption rate of nitrogen.Treatment with BgR and nitrogen had capacity of saving fertilizers and increasing crop yield,but the Net-GWP at system level was the highest.And application of biogas-residue together with biogas-slurry in the future may make it an important fertilization pathway,but the production quantity of biogas manure and indirect greenhouse gas emissions from the production processes need to be considered. |
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