Carbon and Nitrogen Footprints of Major Cereal Crop Production in China:A Study Based on Farm Management Surveys

Greenhouse gas(GHG)emissions and reactive nitrogen(Nr)releases are central environmental problems,which are closely linked to climate change,environmental ecology and crop production.Sustainable development of agriculture plays an important role in GHG emissions and Nr loss.The life cycle assessment(LCA)method was used to calculate the product and farm carbon footprints(CFs)and nitrogen footprints(NFs)in rice,wheat and maize production in China based on farm survey data.The results pinpointed that the CFs of rice,wheat and maize were 0.87,0.30 and 0.24 kg/kg.Meanwhile,the computed NFs were 17.11,14.26 and 6.83 g/kg,respectively.Synthetic nitrogen fertilizer applications and methane(CH4)emissions were dominant CF sources,while ammonia(NH3)volatilization was the main NF contributor.Moreover,significant decreases in CF and NF by 20%–54%and 33%–61%,respectively,were found in large-size farms(>20 hm^(2))when compared to small-size farms(<0.7 hm^(2)).Furthermore,the significantly positive relationships between CF and NF indicated the potential for simultaneous mitigation in the regions with high agricultural inputs,like amounts of fertilizer.Based on our results,some effective solutions would be favorable toward mitigating climate change and eutrophication of the major cereal crop production in China,especially optimizing fertilizer use and farm machinery operation efficiencies,as well as developing large-size farms with intensive farming.

Biochar and organic substitution improved net ecosystem economic benefit in intensive vegetable production

Biochar amendment and substituting chemical fertilizers with organic manure(organic substitution)have been widely reported to increase crop production and decrease reactive nitrogen(Nr)loss including nitrous oxide(N_(2)O),nitric oxide(NO),and ammonia(NH3)emissions,and N runoff and leaching.However,few comprehensive evalua-tions have been performed on the environmental and economic aspects of biochar amendment or organic sub-stitution.Here,we studied the comprehensive effects of biochar amendment,organic substitution,and biochar amendment combined with organic substitution on crop production,Nr loss,and net ecosystem economic benefit(NEEB)in intensive vegetable production by integrating life-cycle assessment for Nr footprints,empirical models for NH3 volatilization and N runoff and leaching derived from peer-reviewed publications and validated by the current measurements and direct field measurement for N_(2)O and NO emissions during 5 consecutive years of vegetable crop rotations.Five fertilization treatments were applied(SN:synthetic fertilizer application;SNB:SN plus 20 t ha^(−1)biochar amendment;SNM:substituting 50%of chemical N fertilizer with organic manure;SNMB:SNM plus 20 t ha^(−1)biochar amendment;and CK:no fertilizer or biochar addition).Compared with the SN,the SNB increased vegetable yield(28.4%,p<0.05;interannually varying from−10 to 74.9%)and nitrogen use efficiency(29.2%,interannually varying from−39.7 to 150.4%),and decreased field Nr loss(45.4%,p<0.01;interannually varying from−40.3 to 78.4%),and thus improved NEEB by 7.1%;meanwhile,the SNM increased vegetable yield(11.6%,interannually varying from−5.4 to 27.1%)and nitrogen use efficiency(45.7%,p<0.05;interannually varying from 2.3 to 154%),reduced field Nr loss(34.9%,p<0.01;interannually varying from 8.4-39.0%),and thus improved NEEB by 17.8%(p<0.05)compared to the SN,being 56.0×10^(3)Chinese Yuan(CNY)ha^(−1)crop^(−1).Due to the high foreground Nr loss during organic manure production and high input costs of biochar production,the SNMB decreased the NEEB by 8.0%as compared to the SN.Moreover,the SNB and SNM improved vegetable qualities by increasing protein,soluble sugar,and vitamin C contents while decreasing nitrate content(p<0.05).Therefore,single application of biochar amendment or organic substitution would achieve better NEEB and product quality in vegetable production.