Methanogenic archaea reside primarily in the rumen and the lower segments of the intestines of ruminants, where they utilize the reducing equivalents derived from rumen fermentation to reduce carbon dioxide, formic acid, or methylamines to methane (CH4). Research on methanogens in the rumen has attracted great interest in the last decade because CH4 emission from ruminants contributes to global greenhouse gas emission and represents a loss of feed energy. Some DNA-based phylogenetic studies have depicted a diverse and dynamic community of methanogens in the rumen. In the past decade, researchers have focused on elucidating the underpinning that determines and affects the diversity, composition, structure, and dynamics of methanogen community of the rumen. Concurrently, many researchers have attempted to develop and evaluate interventions to mitigate enteric CH4 emission. Although much work has been done using plant secondary metabolites, other approaches such as using nitrate and 3-nitrooxy propanol have also yielded promising results. Most of these antimethanogenic compounds or substances often show inconsistent results among studies and also lead to adverse effects on feed intake and digestion and other aspects of rumen fermentation when fed at doses high enough to achieve effective mitigation. This review provides a brief overview of the rumen methanogens and then an appraisal of most of the antimethanogenic compounds and substances that have been evaluated both in vitro and in vivo. Knowledge gaps and future research needs are also discussed with a focus on methanogens and methane mitigation.

/pdf/rumen-methanogens-and-mitigation-of-methane-emission-by-anti-4r6c11m3qp.pdf

Rumen methanogens and mitigation of methane emission by anti-methanogenic compounds and substances

This review examines research aimed at reducing enteric methane emissions from the Australian dairy industry. Calorimeter measurements of 220 forage-fed cows indicate an average methane yield of 21.1 g methane (CH4)/kg dry matter intake. Adoption of this empirical methane yield, rather than the equation currently used in the Australian greenhouse gas inventory, would reduce the methane emissions attributed to the Australian dairy industry by ∼10%. Research also indicates that dietary lipid supplements and feeding high amounts of wheat substantially reduce methane emissions. It is estimated that, in 1980, the Australian dairy industry produced ∼185000 t of enteric methane and total enteric methane intensity was ∼33.6 g CH4/kg milk. In 2010, the estimated production of enteric methane was 182000 t, but total enteric methane intensity had declined ∼40% to 19.9 g CH4/kg milk. This remarkable decline in methane intensity and the resultant improvement in the carbon footprint of Australian milk production was mainly achieved by increased per-cow milk yield, brought about by the on-farm adoption of research findings related to the feeding and breeding of dairy cows. Options currently available to further reduce the carbon footprint of Australian milk production include the feeding of lipid-rich supplements such as cottonseed, brewers grains, cold-pressed canola, hominy meal and grape marc, as well as feeding of higher rates of wheat. Future technologies for further reducing methane emissions include genetic selection of cows for improved feed conversion to milk or low methane intensity, vaccines to reduce ruminal methanogens and chemical inhibitors of methanogenesis.

/pdf/reducing-the-carbon-footprint-of-australian-milk-production-1ddm0e7owj.pdf

Reducing the carbon footprint of Australian milk production by mitigation of enteric methane emissions

Grape marc consists of the skins, seeds and stems remaining after grapes have been pressed to make wine. Interest in grape marc for use as a dietary feed additive for ruminants has grown after recent research showed that inclusion of grape marc in the diet of dairy cows reduced their enteric methane (CH4) emissions. In the present research, in vitro fermentations were conducted on 20 diverse grape marcs to evaluate their potential as ruminant feed supplements and, in particular, mitigants of enteric CH4 emissions. The grape marcs, which were sourced from vineyards in south-eastern Australia, contained a range of red and white grape varieties with different proportions of skins, seeds and stalks, and had diverse chemical compositions. For each grape marc, four replicate samples, each of 1 g DM, were incubated in vitro with ruminal fluid. The volumes of total gas and CH4 produced after 48 h of incubation were determined. Total gas production ranged from 21.8 to 146.9 mL and CH4 production from 6.8 to 30.3 mL. White grape marcs produced more (P < 0.05) total gas (81.8 mL) than did red grape marcs (61.0 mL), but had a lower (P < 0.05) percentage of CH4 (25.3% and 30.3% of total gas). Grape marcs with a higher proportion of seeds produced less (P < 0.05) total gas than did the types composed of either skin or stalks; however, the seed types produced the greatest (P < 0.05) percentage of CH4 (49.8% of total gas). It is concluded that grape marcs differ greatly in their potential as mitigants of enteric CH4 emissions for ruminal production systems.

In vitro evaluation of the methane mitigation potential of a range of grape marc products

The objective of this study was to examine the process of aqueous extraction of organics and phenolics from winery wastes (grape marc and wine lees) and the anaerobic digestion of the extracts using a pilot-scale anaerobic digester. Samples of grape marc and wine lees were extracted with tap water under controlled laboratory conditions at different solid/liquid ratios 1:3, 1:5 and 1:10 (w/w). The extracts were characterized in terms of organic matter composition, and phenolic content. Following this, a 3 m3 stirred tank digester, inoculated with anaerobic granular sludge, was installed and operated at the premises of a winery using original grape marc and wine lees extracts. The recovered extracts were characterized by a high chemical oxygen demand (COD = 20–30 kg m3) and low concentration of phenolics (<100 mg L−1). They displayed high anaerobic degradability with a biogas yield of 0.50 m3 kg−1 COD, a methane content of 72 % and an effluent COD concentration between 0.6 and 1.6 g L−1. Based on a preliminary design and cost analysis it was demonstrated that for a medium sized winery (1000 tn grapes per season) a 40 m3 compact anaerobic digester suffices, while the payback period is around 6–7 years. Aqueous extraction of organics from winery wastes enables the recovery of readily degradable COD with low phenolic content. Generation of biogas from the recovered extracts was highly efficient using a compact anaerobic digester.

Energy Recovery and Treatment of Winery Wastes by a Compact Anaerobic Digester

Agriculture is currently facing major challenges related to ensuring the food security of a rising population and climate change with extreme weather patterns. At the same time, agriculture is a cause of environmental degradation, pollution and biodiversity loss. Climate-smart agriculture (CSA) is proposed as an approach that provides a roadmap to sustainable agricultural development. Despite this, farmer adoption rates of CSA practices and technologies in Europe remain low. This paper seeks to systematically review and synthesize the factors that facilitate or hinder farmers’ uptake of CSA in Europe. Out of the 2827 articles identified in the Web of Science and Scopus databases, a total of 137 research articles were included for analysis following the PRISMA methodology. The factors are categorized into seven categories, namely socio-demographics, psychological, farm characteristics, practice/technology-related attributes, biotic/abiotic, systemic and policy factors, with the majority of the studies focusing on the first four categories, while systemic and policy factors are relatively understudied. The results highlight for the first time that the adoption of CSA does not depend solely on farmer characteristics but also on the food systems and structures in which farmers operate, as well as the interactions with other value chain actors. To promote the adoption of CSA practices, extension and advisory services along with access to timely and reliable information, play a vital role in increasing awareness and in the provision of training and the encouragement of farmers’ behavioral shifts towards sustainable practices. From a technological point of view, adapting technologies to be easy to use, compatible with current farming objectives and cost-efficient will render them less risky investments for farmers and will foster adoption rates. Finally, support from the government in terms of financial support, subsidies and reduced bureaucratic procedures is crucial for motivating CSA adoption.

Farmers’ Transition to Climate-Smart Agriculture: A Systematic Review of the Decision-Making Factors Affecting Adoption

Drawing transformation pathways for making use of joint effects of food and energy production with biodiversity agriphotovoltaics and electrified agricultural machinery.

This study aimed to evaluate the effect of organic acids on in vitro fermentation characteristics. Four organic acids (tartaric, malic, fumaric and citric) and their enantiomers (L-tartaric, D-tartaric, DL-tartaric, L-malic and DL-malic) were analysed using in vitro batch culture incubations, at four concentrations (0, 5, 10 and 15 mM). Cumulative total gas and methane (CH4) production (mL/g DM) were measured at 6, 12 and 24 h; ammonia, pH, volatile fatty acids (VFA) and in vitro dry matter digestibility (IVDMD) were determined after 24 h of fermentation. Overall, addition of acids at 5 to 15 mM increased (P 0.10) of enantiomers, individual acid or interaction acid × concentration was detected at 12 and 24 h for cumulative gas or CH4 production. Addition of DL-malic, L-malic and fumaric acids increased (P < 0.0001) the percentage of propionic acid in the ruminal fluid total VFA compared with all concentrations of the other organic acids or their enantiomers. Ammonia concentration was not affected (P ≥ 0.28) by the addition of organic acids, concentrations or interactions. These findings are evidence that ruminal microorganisms can metabolise both D- and L-enantiomers of organic acids. None of the organic acids and their enantiomers at four different concentrations demonstrated potential as CH4 mitigation agents.

Comparison of enantiomers of organic acids for their effects on methane production in vitro

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Drawing transformation pathways for making use of joint effects of food and energy production with biodiversity agriphotovoltaics and electrified agricultural machinery.

Comparison of enantiomers of organic acids for their effects on methane production in vitro