Evaluation Of Carbon Footprints And Mitigation Strategies Under Wheat-Maize/Fallow Cropping Systems In Guanzhong Plain,China

Improving agriculture intensity implies desirable crop productivity at a noteworthy environmental cost.Agricultural crop production has been linked to greenhouse gas emissions（GHG）which is a significant environmental concern,and assessing the carbon footprint（CF）of crop production can serve as a valuable tool in identifying essential strategies for mitigating these emissions from agriculture.Therefore,it is necessary to explore cleaner agronomic practices to reduce the CF of crops when producing more food to meet requirement of growing human population.We have three different studies:in the first study,the life-cycle assessment（LCA）was performed to assess the differences in CF of wheat and maize crops within irrigated and rain-fed cropping systems.The two 25-year experiments included a winter wheat-summer maize cropping under irrigated conditions with five treatments:Control without fertilization（CK）,combination of nitrogen and phosphorus（NP）,NP plus potassium（NPK）,NPK plus crop straw（S）（SNPK）,and dairy manure（M）integrated with NPK（MNPK）;and a winter wheat-summer fallow system under rain-fed conditions with four treatments as stated above except SNPK.In second study,a 7 years field experiment was conducted to evaluate the effects of substituting synthetic fertilizer with manure on crop productivity,SOC sequestration,GHG emissions and crop CF under a winter wheat-summer maize cropping system.Six treatments were included:synthetic nitrogen（N）,phosphorus（P）and potassium（K）fertilizers（NPK）;25%,50%,75%and 100%of the synthetic N substituted by dairy manure（25%M,50%M,75%M,and 100%M）;and NPK plus straw return（SNPK）.In third study,using farm survey data from a typical wheat production area in Shaanxi province of China,the CFs of wheat production were assessed by quantifying the GHG emissions from farming inputs and operations with a full life cycle assessment methodology.Main results and conclusions of the performed studies are stated below;1)Results from first study showed that high N input increased total GHG emission and CF across cropping systems in question.Comparing treatment effects it was observed that NP,NPK and SNPK remained statistically non-significant in both crops under irrigated system,however MNPK had a significantly lower CF in wheat season.In rainfed wheat significantly higher CF were observed in NPK treatment and lowest in MNPK as compared to CK.The mean GHGs’emissions ranged from 2000.9 to 7586.7 kg ha^-1 for irrigated cropping system,and 192.5–1834.6 kg ha^-1 for rain-fed cropping system.Over the 25 years,without considering SOC gain,the mean CF values for irrigated and rainfed cropping systems ranged from 0.51 to0.62 and 0.16–0.50 kg CO₂ kg^-1 of grain,respectively.When SOC gains were involved in,the mean CF values for the two investigated cropping systems ranged from 0.22 to 0.42 and-0.26to 0.29 kg CO₂ kg^-1 of grain,respectively（in exclusion of SNPK）.SOC sequestration played an important part in reduction of CF.2)Results from second study shows that SNPK,25%M and 50%M treatments increased or maintained mean annual yield（winter wheat plus summer maize）and annual yield sustainability index（SYI）,75%M and 100%M treatments significantly decreased mean annual yield,and 100%treatment significantly reduced annual SYI relative to NPK treatment.After7 years,SOC storage in manure application and straw return treatments increased by 6.70–15.15 Mg ha^-1 relative to NPK treatment.The mean annual GHG emissions ranged from 2200to 6252 kg CO₂ eq ha^-1 for the cropping system.Compared with NPK treatment,manure applied treatments reduced annual GHG emissions by 14%–60%,but SNPK treatment increased annual GHG emissions by 14%.Over the 7 years,without considering SOC change rate,the mean CF value for the cropping system was 0.30–0.53 kg CO₂ eq kg^-1 grain.When SOC change rate was considered,the mean CF value for the cropping system was-0.27–0.49kg CO₂ eq kg^-1 grain.The CF of SNPK treatment was significantly increased by 6%,while the CF of manure applied treatments were significantly decreased by 18%–58%relative to NPK treatment.Considering both crop yield and CF,replacing 50%of synthetic fertilizer with manure was a viable option under tested cropping system in Northwest China.3)Results from third study showed that the mean farm carbon footprint（FCF）and product carbon footprint（PCF）for wheat production were 3.29 t CO₂-eq ha^-1 and 0.57 t CO₂-eq t^-1grain,which were higher than the wheat production in other countries around the globe.Use of chemical nitrogen（N）fertilizer was the major contributor（～62.8%）and was significantly correlated with CF.Moreover,the relationship between N fertilizer rate and crop yields indicated that the high crop yields(～6 t ha^-1)can be achieved with the application rate of 150-200 kg N ha^-1in the studied area.Furthermore,the small sized farms had higher CFs as compared to medium and large sized farms.This dissertation is an attempt to summarize key options to mitigate GHGs emissions and corresponding CFs while ensuring the higher crop yields under current management practices in an agricultural intensive region（Guanzhong plain）of Shaanxi province China.This research may provide valuable information to promote the optimization of agricultural practices and guide the design/choice of future farming systems in the region and where with similar environmental conditions.Thus,based on findings it was concluded that the major contributors of CFs in winter-wheat-summer maize cropping systems of Northwest China were N fertilizer rate,irrigation（especially in case of irrigated system）and mechanical operations.Replacing 50%of synthetic fertilizer with manure can be a viable option to mitigate CF in tested cropping systems of the region.Moreover,CF in wheat production could be affected by farm size and crop management practices.Overall,this research underscores the significance of enhancing N management and straw return in crop production through improved agricultural practices and scaling up farm sizes.These measures can lead to increased yields while simultaneously reducing GHGs emissions,thereby averting the trade-offs between productivity and carbon-costs.