Greenhouse Gas Mitigation Strategies Research Articles

DEXi-Dairy: an ex post multicriteria tool to assess the sustainability of dairy production systems in various European regions

Growing awareness of global challenges and increasing pressures on the farming sector, including the urgent requirement to rapidly cut greenhouse gases (GHG) emissions, emphasize the need for sustainable production, which is particularly relevant for dairy production systems. Comparing dairy production systems across the three sustainability dimensions is a considerable challenge, notably due to the heterogeneity of production conditions in Europe. To overcome this, we developed an ex post multicriteria assessment tool that adopts a holistic approach across the three sustainability dimensions. This tool is based on the DEXi framework, which associates a hierarchical decision model with an expert perspective and follows a tree shaped structure; thus, we called it the DEXi-Dairy tool. For each dimension of sustainability, qualitative attributes were defined and organized in themes, sub-themes, and indicators. Their choice was guided by three objectives: (i) better describe main challenges faced by European dairy production systems, (ii) point out synergies and trade-offs across sustainability dimensions, and (iii) contribute to the identification of GHG mitigation strategies at the farm level. Qualitative scales for each theme, sub-theme, and indicator were defined together with weighting factors used to aggregate each level of the tree. Based on selected indicators, a list of farm data requirements was developed to populate the sustainability tree. The model was then tested on seven case study farms distributed across Europe. DEXi-Dairy presents a qualitative method that allows for the comparison of different inputs and the evaluation of the three sustainability dimensions in an integrated manner. By assessing synergies and trade-offs across sustainability dimensions, DEXi-Dairy is able to reflect the heterogeneity of dairy production systems. Results indicate that, while trade-offs occasionally exist among respective selected sub-themes, certain farming systems tend to achieve a higher sustainability score than others and hence could serve as benchmarks for further analyses.

Partitioning carbon dioxide emissions from soil organic matter and urea in warm and cold cropping seasons

Soil-based emissions of carbon dioxide (CO2) triggered by intensive nitrogen (N) fertilization originate from different sources including fertilizer application and soil organic matter. It is crucial to understand each contributing source of the total CO2 fluxes to develop effective greenhouse gas mitigation strategies and enhance the soil organic carbon (SOC) accumulation approaches. A 2-year field experiment was conducted in the warm and cold upland cropping systems by incorporating urea as a N source at 0, 50, 100, and 200 % of urea, following the Korean recommendation levels for the chosen crops, while 13Carbon-labelled urea was used to investigate the source-specific CO2 emissions under different climatic conditions. N fertilizer for red pepper during the warm season was applied at 90 kg N ha−1, whereas that for garlic during the cold season was applied at 250 kg N ha−1. CO2 fluxes were highly influenced by increases in N fertilization application levels in correlation with soil temperature during the warm season but were not significantly affected during the cold season. The total CO2 fluxes from soil organic matter were not influenced by an increase in N fertilization level; however, the percentage of CO2 coming from urea was greatly influenced by increasing the N fertilizer application level. Additionally, CO2 fluxes from urea during the warm season were considerably higher than those from the cold upland soil. The current research may provide a comprehensive understanding of CO2 partitioning sources and factors responsible for the SOC balance between warm and cold upland cropping systems.

A balancing act: the interplay of food supply chain resilience and environmental sustainability in American cities

Global food systems must be a part of strategies for greenhouse gas (GHG) mitigation, optimal water use, and nitrogen pollution reduction. Insights from research in these areas can inform policies to build sustainable food systems yet limited work has been done to build understanding around whether or not sustainability efforts compete with supply chain resilience. This study explores the interplay between food supply resilience and environmental impacts in US cities, within the context of global food systems’ contributions to GHG emissions, water use, and nitrogen pollution. Utilizing county-level agricultural data, we assess the water use, GHG emissions, and nitrogen losses of urban food systems across the US, and juxtapose these against food supply resilience, represented by supply chain diversity. Our results highlight that supply chain resilience and sustainability can simultaneously exist and are not necessarily in competition with each other. We also found a significant per capita footprint in the environmental domains across Southern cities, specifically those along the Gulf Coast and southern Great Plains. Food supply chain resilience scores ranged from 0.18 to 0.69, with lower scores in the southwest and Great Plains, while northeastern and Midwestern regions demonstrated higher resilience. We found several cities with high supply chain resilience and moderate or low environmental impacts as well as areas with high impacts and low resilience. This study provides insights into potential trade-offs and opportunities for creating sustainable urban food systems in the US, underscoring the need for strategies that consider both resilience and environmental implications.

Green House Gas Emissions and Mitigation Strategies for Sustainable Dairy Farming


 The global dairy industry is estimated to be worth billions of dollars, with India being the leading producer of dairy products. Milk is a vital source of nutrition, providing energy, protein, and essential micronutrients. It has been linked to various health benefits, such as improved bone health and reduced risk of cardiovascular disease and type-2 diabetes. However, the livestock industry also contributes to greenhouse gas emissions, which contribute to climate change. The carbon footprint of dairy products is measured by assessing the emissions of greenhouse gases throughout the production process. Methane emissions from enteric fermentation and manure management are the primary sources of emissions in the livestock sector. Strategies aimed at enhanced milk production, reducing animal mortality rates and enhancing reproductive performances can also help reduce emissions. To ensure long-term sustainability of the livestock production system, the Indian dairy cattle farming system must address key intervention areas such as feeding management, animal health and reproductive performance, and manure management to reduce its carbon footprint.

Meeting industrial decarbonization goals: a case study of and roadmap to a net-zero emissions cement industry in California

Recent decarbonization policies are expected to significantly impact high greenhouse gas (GHG) emitting industries, as they will be forced to find ways to operate with a lower environmental footprint. Due to the energy required for the kilns and the unavoidable chemical-derived emissions during manufacturing, in addition to its high global consumption levels, the cement industry is anticipated to be among the early industries affected. California State Bill (SB 596) is one of the first rigorous legislative measures that sets GHG emissions from cement production to net-zero by 2045. As such, a case study on California cement production is evaluated here. While several groups have developed cement technology roadmaps with GHG mitigation strategies, these roadmaps do not consider concomitant environmental impacts, such as those that can influence local populations, thus limiting potential implementation from a policy perspective. Here, we examine several GHG emissions mitigation strategies for cement production and show the greatest reduction from an individual measure is from implementing carbon capture storage for cement kiln flue gas (87%), use of alternative clinkers (78%), or use of alkali-activated materials (88%). Yet even if GHG emissions are reduced, use of high-polluting energy sources could increase risks to human health impacts. Further, the efficacy of these decarbonization measures is lowered if multiple measures are implemented simultaneously. Finally, we examine the potential to meet net-zero emissions, focusing on California production due to recent legislation, and find a pathway to 96% GHG emissions reduction. Notably, these reductions do not reach goals to hit zero emissions, suggesting direct air capture mechanisms will need to be implemented.

Higher Food Yields and Lower Greenhouse Gas Emissions from Aquaculture Ponds with High-Stalk Rice Planted.

Aquaculture ponds are an important artificial aquatic system for global food fish production but also are a hot spot of greenhouse gas (GHG) emissions. The GHG mitigation strategy and the underlying mechanism for aquaculture ponds are still poorly understood. In this study, we conducted a 2 year field experiment to determine the effects of planting high-stalk rice (an artificially bred emergent plant for ponds) on GHG emissions from aquaculture ponds. Our results showed that planting high-stalk rice reduced CH4 emission by 64.4% and N2O emission by 76.2% over 2 years. Planting high-stalk rice significantly increased the content of O2 and the abundance of pmoA in the sediment, thus prompting CH4 oxidation in the ponds. The reduction of N2O emission from ponds was attributed to the decreased inorganic nitrogen, amoA-B and nirS in the sediment induced by rice. Furthermore, high-stalk rice culture in the pond increased shrimp yields and gained rice yields, resulting in a significant reduction of yield-scaled global warming potential. Our findings suggest that breeding appropriate emergent aquatic plants is a potential pathway to mitigate GHG emission from aquaculture ponds with more food yields and economic benefits.

Reimagining the Role of Health Departments and Their Partners in Addressing Climate Change: Revising the Building Resilience against Climate Effects (BRACE) Framework.

Public health departments have important roles to play in addressing the local health impacts of climate change, yet are often not well prepared to do so. The Climate and Health Program (CHP) at the Centers for Disease Control and Prevention (CDC) created the Building Resilience Against Climate Effects (BRACE) framework in 2012 as a five-step planning framework to support public health departments and their partners to respond to the health impacts of climate change. CHP has initiated a process to revise the framework to address learnings from a decade of experience with BRACE and advances in the science and practice of addressing climate and health. The aim of this manuscript is to describe the methodology for revising the BRACE framework and the expected outputs of this process. Development of the revised framework and associated guidance and tools will be guided by a multi-sector expert panel, and finalization will be informed by usability testing. Planned revisions to BRACE will (1) be consistent with the vision of Public Health 3.0 and position health departments as "chief health strategists" in their communities, who are responsible for facilitating the establishment and maintenance of cross-sector collaborations with community organizations, other partners, and other government agencies to address local climate impacts and prevent further harm to historically underserved communities; (2) place health equity as a central, guiding tenet; (3) incorporate greenhouse gas mitigation strategies, in addition to its previous focus on climate adaptation; and (4) feature a new set of tools to support BRACE implementation among a diverse set of users. The revised BRACE framework and the associated tools will support public health departments and their partners as they strive to prevent and reduce the negative health impacts of climate change for everyone, while focusing on improving health equity.

Agricultural Greenhouse Gas Emissions and Mitigation Strategies for Promoting Sustainable Agroecosystems in Canada – A Review

Agricultural Greenhouse Gas Emissions and Mitigation Strategies for Promoting Sustainable Agroecosystems in Canada – A Review

The role of hydrogen for the defossilization of the German chemical industry

Within the European Green Deal, the European industry is summoned to transform towards a green and circular economy to reduce CO2-emissions and reach climate goals. Special focus is on the chemical industry to boost recycling processes for plastics, exploit resource efficiency potentials, and switch to a completely renewable feedstock (defossilization). Despite common understanding that drastic changes have to take place it is yet unknown how the industrial transformation should be accomplished. This work explains how a cost-optimal defossilization of the chemical industry in the context of national greenhouse gas (GHG) mitigation strategies look like. The central part of this investigation is based on a national energy system model to optimize the future energy system design of Germany, as a case study for a highly industrialized country. A replacement of fossil-based feedstocks by renewable feedstocks leads to a significant increase in hydrogen demand by +40% compared to a reference scenario. The resulting demand of hydrogen-based energy carriers, including the demand for renewable raw materials, must be produced domestically or imported. This leads to cumulative additional costs of the transformation that are 32% higher than those of a reference scenario without defossilization of the industry. Fischer-Tropsch synthesis and the methanol-to-olefins route can be identified as key technologies for the defossilization of the chemical industry.

Combined Effects of Biochar and Inhibitors on Greenhouse Gas Emissions, Global Warming Potential, and Nitrogen Use Efficiency in the Tobacco Field

Biochar (BC), nitrification inhibitors (methyl 3-(4-hydroxyphenyl) propionate, MHPP), and urease inhibitors (n-butyl phosphorothioate triamine, NBPT) have emerged as effective soil greenhouse gas (GHG) mitigation strategies in agroecosystems. However, the combined use of BC and inhibitors in karst areas has no available data. Therefore, the combined effects of BC, MHPP, and NBPT on GHG emissions, global warming potential (GWP) and nitrogen use efficiency (NUE) in roasted tobacco cropping systems were studied to improve the understanding in climate mitigation. CO2, CH4, and N2O emissions from soils were measured using static chamber-gas chromatography. Results showed that the combined use of BC and inhibitors significantly increased soil total nitrogen, available potassium, electric conductivity, pH, and soil organic matter compared to the control. The combined use of BC and MHPP or NBPT significantly increased cumulative soil CO2 emissions by 33.95% and 34.25%, respectively. The exponential–exponential function of soil CO2 fluxes with soil moisture and temperature demonstrated good fit (R2: 0.506–0.836). The combination of BC and NBPT increased the cumulative soil CH4 emissions by 14.28% but not significantly compared to the fertiliser treatment. However, the combination of BC and MHPP resulted in a significant reduction in cumulative soil CH4 emissions by 80.26%. In addition, the combined use of BC and MHPP or NBPT significantly reduced the cumulative soil N2O emissions by 26.55% and 40.67%, respectively. The inhibition effect of NBPT was better than MHPP. Overall, the combined use of BC and inhibitors significantly reduced the yield-scaled GWP, markedly increased crop yield and NUE, and mitigated climate change in the southwest karst region.

Greenhouse gas emissions embodied in electric vehicle charging infrastructure: a method and case study of Georgia, US 2021–2050

Electric vehicle (EV) charging infrastructure buildout is a major greenhouse gas (GHG) mitigation strategy among governments and municipalities. In the United States, where petroleum-based transportation is the largest single source of GHG emissions, the Infrastructure Investment and Jobs Act of 2021 will support building a national network of 500 000 EV charging units. While the climate benefits of driving electric are well established, the potential embodied climate impacts of building out the charging infrastructure are relatively unexplored. Furthermore, ‘charging infrastructure’ tends to be conceptualized in terms of plugs and stations, leaving out the electrical and communications systems that will be required to support decarbonized and efficient charging. In this study, we present an EV charging system (EVCS) model that describes the material and operational components required for charging and forecasts the scale-up of these components based on EV market share scenarios out to 2050. We develop a methodology for measuring GHG emissions embodied in the buildout of EVCS and incurred during operation of the EVCS, including vehicle recharging, and we demonstrate this model using a case study of Georgia (USA). We find that cumulative GHG emissions from EVCS buildout and use are negligible, at less than 1% of cumulative emissions from personal light duty vehicle travel (including EV recharging and conventional combustion vehicle driving). If an accelerated EVCS buildout were to stimulate a faster transition of the vehicle fleet, the emissions reduction of electrification will far outweigh emissions embodied in EVCS components, even assuming relatively high carbon inputs prior to decarbonization.

The Effect of Land Consolidation Projects on Carbon Footprint

In this study, transportation-induced carbon footprint values before and after the consolidation projects in two areas with similar agricultural characteristics were calculated. The IPCC Tier 1 method recommended by the IPCC (Intergovernmental Panel on Climate Change) was used to calculate the carbon footprint. Furthermore, the effects of changes in road lengths and routes in these areas after Land Consolidation (LC) on the fuel consumption of tractors and, accordingly, the carbon dioxide (CO2) emission values were also determined. As a result of the study, the carbon footprint value (GgCO2) decreased by 10% in the Fatih neighborhood and 33% in the Selimiye neighborhood after the land consolidation project. Carbon equivalent (CE) is used to measure the effects on greenhouse gas emissions and global warming and corresponds to the amount of carbon dioxide (CO2) emissions. In total, 490.21 kg CO2·ha−1 of greenhouse gas (GHG) emissions were mitigated. In light of these results, it can be concluded that LC can be considered a useful process in greenhouse gas mitigation strategy. Based on the values obtained from the study results, it was concluded that land consolidation contributed to reducing carbon footprint and increasing agricultural production and productivity in rural areas. The reduction in fuel consumption and carbon emissions in rural areas will contribute to reducing the adverse effects of air pollution and climate change.

Development of city-scale air pollutants and greenhouse gases emission inventory and mitigation strategies assessment: A case in Zhengzhou, Central China

The development of anthropogenic air pollutants and greenhouse gases (GHGs) emission inventory is important for air pollution and climate change. This study developed a high-resolution emission inventory of consistent sources of air pollutants and GHGs in Zhengzhou. Designed scenarios with 2030 as the target year to estimate future emissions from power plants and on-road mobile. The 2019-based total emissions of SO2, NOx, CO, PM10, PM2.5, VOCs, NH3, CO2, CH4, and N2O were 39.2, 174.6, 586.9, 134.1, 59.2, 176.8, 19.3, 83,014.8, 239.3, and 4.3 kt, respectively. Stationary combustion and mobile source were the top contributors to SO2, NOx, CO, and CO2 emissions. PM10 emissions were mainly from fugitive dust, while CH4 emissions were other sources. Most PM2.5 and VOCs emissions came from industrial process. Agriculture was the primary source of NH3 and N2O emissions. Most air pollutants and GHGs were mainly concentrated in the main urban area, which were closely related to population density, traffic flow, and industrial activities, while winter heating and higher electricity consumption in summer were the main reasons for higher emissions during these seasons. Air pollutants and GHGs from power plants and on-road mobile are reduced by 16.0%–84.7% in the best reduction scenario.

Greenhouse gas balances and yield-scaled emissions for storage and field application of organic fertilizers derived from cattle manure

Manure treatment such as anaerobic digestion and solid-liquid separation has shown a potential to abate greenhouse gas (GHG) emissions, but few studies have considered GHG emissions from both storage and field application regarding crop yield. In this study, four different organic fertilizers were studied: untreated cattle manure (CA); digestate of cattle manure anaerobically co-digested with grass-clover (DD); a liquid fraction from the separation of DD (LF); and a liquid fraction derived from a biogas desulfurization biofilter enriched with sulfur and ammonium (NS). The CH4, N2O and NH3 emissions during storage of CA, DD and LF between August and November 2020 (11 weeks) were quantified. Storage continued until April 2021 when these materials, as well as the NS fertilizer and a mineral NKS fertilizer, were applied at a rate of 100 kg total N ha−1 to spring barley. N2O emissions and soil mineral N content were monitored during the growing season. Overall, CH4 emissions during storage were the main source of GHG emissions independent of treatments, accounting for 85 %, 40 % and 11 % of total GHG emissions (based on field application of 100 kg ha−1 total N) from treatments CA, DD and LF, respectively. Anaerobic digestion and separation significantly reduced CH4 emissions during storage due to the diminished content of degradable organic matter available for methanogens. The N2O emissions from treatments CA, DD, and LF during storage were not significantly different. Treatments DD and LF emitted more NH3 than CA during storage, presumably because of higher pH and ammonium content. In the field experiment, the dilute solution of NS emitted the most N2O, while emissions from treatments CA, DD and LF were comparable. Yield-scaled GHG emissions for treatments CA, DD, LF and NS during both periods of storage and field were 44.4, 17.1, 8.5 and 24.3 kg CO2 eq hkg−1 grain yield, respectively. Anaerobic digestion with or without separation were thus effective strategies for the mitigation of GHG emissions from cattle manure in this study. Yields and nitrogen use efficiencies of the processed manure materials were not significantly different from those observed with the same N application rate as inorganic fertilizer, and hence anaerobic digestion with or without separation were promising GHG mitigation strategies.

3-Nitrooxypropanol supplementation of a forage diet decreased enteric methane emissions from beef cattle without affecting feed intake and apparent total-tract digestibility.

Supplementation of ruminant diets with the methane (CH4) inhibitor 3-nitrooxypropanol (3-NOP; DSM Nutritional Products, Switzerland) is a promising greenhouse gas mitigation strategy. However, most studies have used high grain or mixed forage-concentrate diets. The objective of this study was to evaluate the effects of supplementing a high-forage diet (90% forage DM basis) with 3-NOP on dry matter (DM) intake, rumen fermentation and microbial community, salivary secretion, enteric gas emissions, and apparent total-tract nutrient digestibility. Eight ruminally cannulated beef heifers (average initial body weight (BW) ± SD, 515 ± 40.5 kg) were randomly allocated to two treatments in a crossover design with 49-d periods. Dietary treatments were: 1) control (no 3-NOP supplementation); and 2) 3-NOP (control + 150 mg 3-NOP/kg DM). After a 16-d diet adaption, DM intake was recorded daily. Rumen contents were collected on days 17 and 28 for volatile fatty acid (VFA) analysis, whereas ruminal pH was continuously monitored from days 20 to 28. Eating and resting saliva production were measured on days 20 and 31, respectively. Diet digestibility was measured on days 38-42 by the total collection of feces, while enteric gas emissions were measured in chambers on days 46-49. Data were analyzed using the mixed procedure of SAS. Dry matter intake and apparent total-tract digestibility of nutrients (DM, neutral and acid detergent fiber, starch, and crude protein) were similar between treatments (P ≥ 0.15). No effect was observed on eating and resting saliva production. Relative abundance of the predominant bacterial taxa and rumen methanogen community was not affected by 3-NOP supplementation but rather by rumen digesta phase and sampling hour (P ≤ 0.01). Total VFA concentration was lower (P = 0.004) following 3-NOP supplementation. Furthermore, the reduction in acetate and increase in propionate molar proportions for 3-NOP lowered (P < 0.001) the acetate to propionate ratio by 18.9% as compared with control (4.1). Mean pH was 0.21 units lower (P < 0.001) for control than 3-NOP (6.43). Furthermore, CH4 emission (g/d) and yield (g/kg DMI) were 22.4 and 22.0% smaller (P < 0.001), respectively, for 3-NOP relative to control. Overall, the results indicate that enteric CH4 emissions were decreased by more than 20% with 3-NOP supplementation of a forage diet without affecting DM intake, predominant rumen microbial community, and apparent total-tract nutrients digestibility.

Greenhouse gas mitigation strategies and decision support for the utilization of agricultural waste systems: A case study of Jiangxi Province, China

Taking the agriculture waste system in Jiangxi Province as a case study, we strive to investigate how the resource flow and greenhouse gas mitigation can be considered as a basis for policy arrangements and sustainable use of agrowaste. In this case, we apply a combination of material flow analysis, life cycle assessment and objective optimization model, with a wide range of observed data in 2020. The salient results reveal that: 1) Co-distribution of straw and manure in bioenergy facilities contributes most to greenhouse gas mitigation. 2) The results of scenario analysis suggest that when the percentage of agrowaste goes from 4.41% to 8.61%, the current greenhouse gas mitigation potential increases by about 3.3 times subsequently. 3) Calculated by an objective optimization model, the maximum greenhouse gas mitigation capacity can be 16.44 × 108t CO2e in Jiangxi. Our proposed framework provides a comprehensive instrument to assess the environmental performance of improving waste utilization efficiency and greenhouse gas mitigation, with wide applicability and reference significance in countries and regions with major cropping and livestock industries. Great emphasis should be placed on synergistic disposal between multiple sectors to improve the sustainable supply of agricultural waste systems.

The potential of mitigating greenhouse gas emissions from urban domestic water systems in highly urbanized areas

In highly urbanized areas, domestic water consumption and wastewater discharge are affected by several dynamic factors, such as economy, population, and environment, which further influence the greenhouse gas (GHG) mitigation potential of urban domestic water systems (UDWSs). To analyze GHG emission features of the UDWSs and their interactions with urban economic development, a hybrid approach of correlation analysis and a programming model was incorporated in a life-cycle framework to provide decision-making support for GHG mitigation strategies in the UDWSs. To verify the applicability of the method, Shenzhen city in Guangdong Province was chosen to analyze the potential of the UDWS for mitigating GHG emissions. The GHG emissions from the UDWS in Shenzhen was 747.82 kt CO2 eq in 2020. Compared with 2020, domestic water consumption would increase by 11.35 % and 18.67 % in 2025 and 2030, and wastewater discharge would increase by 12.88 % and 19.73 % in 2025 and 2030, respectively. In the trend of socio-economic development, the amount of water demand and wastewater discharge of urban residents would increase by 11.49 % to 18.75 % and 12.88 % to 19.75 % from 2020 to 2030, respectively. Optimum strategies of technologies for wastewater treatment and energy mix for electricity generation were obtained, with consideration of GHG mitigation goals in the future. As energy consumption contributed more than 25 % of GHG emissions in the USDWs of Shenzhen, the contributions of new energy sources for electricity production (i.e., offshore wind, solar photovoltaic, biomass, and nuclear) would increase by 0.58–1.02 times and 0.68–1.20 times from 2020 to 2025 and 2025 to 2030, respectively. The capacity of wastewater treatment would increase by 53.33 % to 80.00 % and 27.44 % to 29.82 % of the SBR and AAO technologies, respectively. Thus, it is suggested that decision makers should pay close attention to optimizing energy mix of electricity production.

Climate justice and digitalization: A plea to consider broader socio-economic implications of digitalization and climate change

Digitalization can be a promising tool in the fight against climate change. Besides influencing greenhouse gas emissions and mitigation strategies, digitalization affects matters of climate justice, including the way the impacts of global warming and the co-benefits of climate protection are distributed. For example, to advance fair benefit sharing of digital climate technologies, the decentralization of technological development must be initiated, and rules for fair competition must be established. Political action and the shaping of digitalization are necessary to govern the societal implications of these urgent developments.

Drying and rewetting cycles increased soil carbon dioxide rather than nitrous oxide emissions: A meta-analysis

The increased frequency of extreme weather variations worldwide has resulted in dramatic changes in the soil water content via pronounced drying and rewetting cycles (DWCs). A comprehensive exploration of carbon dioxide (CO2) and nitrous oxide (N2O) emissions in response to DWCs can help summarize the existing results and better estimate terrestrial greenhouse gas emissions under the intensified drought and precipitation variations. This meta-analysis based on soil emissions of CO2 (868 observations, 29 studies) and N2O (52 observations, 19 studies) at the global scale investigated the direction and intensity of the changes in soil CO2 and N2O emissions in response to DWCs as controlled by experimental variables including land use type, soil texture, soil nutrients, and frequency and duration of DWCs. The results showed that, compared to the constant soil water content, DWCs led to the increase in CO2 emissions by 35.7% (95% confidence intervals ranging from 0.300 to 0.415), whereas it had no significant effect on N2O emissions (−0.2638 to 1.4751). The random-effects model indicated that soil water-filled pore space during wetting, soil clay content, days of drying and wetting, and frequency of DWCs significantly affected CO2 and N2O emissions in response to DWCs. Furthermore, potential biotic and abiotic factors affecting soil CO2 and N2O emissions under DWCs are also summarized, and it was proposed that mobility and availability of carbon substrate as well as enhanced microbial activity and abundance are the main drivers facilitating soil CO2 and N2O emissions in response to DWCs. However, soil gas diffusion or oxygen availability also dominated soil N2O emissions under DWCs. Overall, this study improves our understanding of soil CO2 and N2O emissions in response to various DWC scenarios and facilitates the development of better greenhouse gas mitigation strategies against the background of a rapidly changing climate.

Carbon footprint assessment of a whole dairy farming system with a biogas plant and the use of solid fraction of digestate as a recycled bedding material

Biogas generated from livestock manure is a renewable energy source and the digestate is used as a fertilizer. Moreover, dewatered biogas digestate can be used as a bedding material (recycled bedding material). The aims of the present study were to model a whole dairy system with a biogas plant using recycled bedding material and to assess the life cycle greenhouse gas (GHG) emissions. Emissions from the material flow of dairy cattle production, manure treatment and organic fertilizer application to on-farm crops were evaluated. In the emissions from organic fertilizer storage and recycled bedding material production, CH4 emission was decreased by 43.0%, and consequently the system with a biogas plant reduced total GHG emissions by 6.8% compared with conventional slurry storage and straw bedding. The use of recycled bedding material from a biogas plant has the potential to create a resource cycle and to be beneficial as a GHG mitigation strategy.