Review of greenhouse gas emissions from crop production systems and fertilizer management effects

Decreasing enteric methane (CH4) emissions from ruminants without altering animal production is desirable both as a strategy to reduce global greenhouse gas (GHG) emissions and as a means of improving feed conversion efficiency. The aim of this paper is to provide an update on a selection of proved and potential strategies to mitigate enteric CH4 production by ruminants. Various biotechnologies are currently being explored with mixed results. Approaches to control methanogens through vaccination or the use of bacteriocins highlight the difficulty to modulate the rumen microbial ecosystem durably. The use of probiotics, i.e. acetogens and live yeasts, remains a potentially interesting approach, but results have been either unsatisfactory, not conclusive, or have yet to be confirmed in vivo. Elimination of the rumen protozoa to mitigate methanogenesis is promising, but this option should be carefully evaluated in terms of livestock performances. In addition, on-farm defaunation techniques are not available up to now. Several feed additives such as ionophores, organic acids and plant extracts have also been assayed. The potential use of plant extracts to reduce CH4 is receiving a renewed interest as they are seen as a natural alternative to chemical additives and are well perceived by consumers. The response to tannin- and saponin-containing plant extracts is highly variable and more research is needed to assess the effectiveness and eventual presence of undesirable residues in animal products. Nutritional strategies to mitigate CH4 emissions from ruminants are, without doubt, the most developed and ready to be applied in the field. Approaches presented in this paper involve interventions on the nature and amount of energy-based concentrates and forages, which constitute the main component of diets as well as the use of lipid supplements. The possible selection of animals based on low CH4 production and more likely on their high efficiency of digestive processes is also addressed. Whatever the approach proposed, however, before practical solutions are applied in the field, the sustainability of CH4 suppressing strategies is an important issue that has to be considered. The evaluation of different strategies, in terms of total GHG emissions for a given production system, is discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/EA3281B79CF2653DF2D1CD946D698D1A/S1751731109990620a.pdf/div-class-title-methane-mitigation-in-ruminants-from-microbe-to-the-farm-scale-div.pdf

Methane mitigation in ruminants: from microbe to the farm scale

The price of protein: Review of land use and carbon footprints from life cycle assessments of animal food products and their substitutes

Can enteric methane emissions from ruminants be lowered without lowering their production

Electricity and heat generation are key contributors to global emissions of greenhouse gases (GHG). In this paper, specific attention is paid to renewable energy technologies (RETs) for electricity and heat generation and reviews current understanding and estimates of life cycle GHG emissions from a range of renewable electricity and heat generation technologies. Comprehensive literature reviews for each RET were carried out. The 79 studies reviewed involved the life cycle assessment (LCA) of renewable electricity and heat generation based on onshore and offshore winds, hydropower, marine technologies (wave power and tidal energy), geothermal, photovoltaic (PV), solar thermal, biomass, waste, and heat pumps. The study demonstrates the variability of existing LCA studies (results) in tracking GHG emissions for electricity and heat generation from RETs. This review has shown that the lowest GHG emissions were associated with offshore wind technologies (mean life cycle GHG emissions could be 5.3–13 g CO2 eq/kWh). Results compared with GHG estimates by fossil fuel heat and electricity indicated that life cycle GHG emissions are comparatively higher in conventional sources as compared to renewable sources with the exception of nuclear-based power electricity generation. In this present study, considering renewable energy sources, waste treatment and dedicated biomass technologies (DBTs) were found to potentially have high GHG emissions based on the feedstock, selected boundary and the inputs required for their production. The study identifies additional impacts associated with renewable electricity and heat technologies, points out the effectiveness of life cycle analysis (LCA) as a tool for assessing environmental impacts of renewable energy sources and concludes with opportunities for improvement in the future.

R. Friedrich

Papers

Mitigation of greenhouse gas emissions in European conventional and organic dairy farming