Strategies to mitigate nitrous oxide emissions from herbivore production systems

309

218

Although livestock production accounts for a sizeable share of global greenhouse gas emissions, numerous technical options have been identified to mitigate these emissions. In this review, a subset of these options, which have proven to be effective, are discussed. These include measures to reduce CH 4 emissions from enteric fermentation by ruminants, the largest single emission source from the global livestock sector, and for reducing CH 4 and N 2 O emissions from manure. A unique feature of this review is the high level of attention given to interactions between mitigation options and productivity. Among the feed supplement options for lowering enteric emissions, dietary lipids, nitrates and ionophores are identified as the most effective. Forage quality, feed processing and precision feeding have the best prospects among the various available feed and feed management measures. With regard to manure, dietary measures that reduce the amount of N excreted (e.g. better matching of dietary protein to animal needs), shift N excretion from urine to faeces (e.g. tannin inclusion at low levels) and reduce the amount of fermentable organic matter excreted are recommended. Among the many 'end-of-pipe' measures available for manure management, approaches that capture and/or process CH 4 emissions during storage (e.g. anaerobic digestion, biofiltration, composting), as well as subsurface injection of manure, are among the most encouraging options flagged in this section of the review. The importance of a multiple gas perspective is critical when assessing mitigation potentials, because most of the options reviewed show strong interactions among sources of greenhouse gas (GHG) emissions. The paper reviews current knowledge on potential pollution swapping, whereby the reduction of one GHG or emission source leads to unintended increases in another.

Section: Manure Applicationmentioning

confidence: 99%

Technical options for the mitigation of direct methane and nitrous oxide emissions from livestock: a review

Gerber

Hristov

Henderson

et al. 2013

309

218

“…Some of the impacts are from the animals and from animal feeds and associated upstream processes (Steinfeld et al, 2006). Major compounds derived from animal production that have a negative environmental impact are methane (CH 4 ), produced by rumen fermentation (Martin et al, 2010) and by faecal organic matter (OM) fermentation, and nitrous oxide and ammonia, produced from faecal and urinary N by different microbial mechanisms in soils (Schils et al, 2013). Strategies have been proposed for mitigating emission of these pollutants, among which changes in animal feeding may be promising, but such changes will find practical use only if they do not impair animal performance or other characteristics, such as product quality.…”

Section: Introductionmentioning

confidence: 99%

Effects of dehydrated lucerne and soya bean meal on milk production and composition, nutrient digestion, and methane and nitrogen losses in dairy cows receiving two different forages

Doreau

Ferlay

Rochette

et al. 2014

Dehydrated lucerne is used as a protein source in dairy cow rations, but little is known about the effects of lucerne on greenhouse gas production by animals. Eight Holstein dairy cows (average weight: 582 kg) were used in a replicated 4 × 4 Latin square design. They received diets based on either maize silage (M) or grass silage (G) (45% of diet on dry matter (DM) basis), with either soya bean meal (15% of diet DM) completed with beet pulp (15% of diet DM) (SP) or dehydrated lucerne (L) (30% of diet DM) as protein sources; MSP, ML, GSP and GL diets were calculated to meet energy requirements for milk production by dairy cows and degradable protein for rumen microbes. Dry matter intake (DMI) did not differ among diets (18.0 kg/day DMI); milk production was higher with SP diets than with L diets (26.0 v. 24.1 kg/day), but milk production did not vary with forage type. Milk fatty-acid (FA) composition was modified by both forage and protein sources: L and G diets resulted in less saturated FA, less linoleic acid, more trans-monounsaturated FA, and more linolenic acid than SP and M diets, respectively. Enteric methane (CH 4 ) production, measured by the SF 6 tracer method, was higher for G diets than for M diets, but did not differ with protein source. The same effects were observed when CH 4 was expressed per kg milk. Minor effects of diets on rumen fermentation pattern were observed. Manure CH 4 emissions estimated from faecal organic matter were negatively related to diet digestibility and were thus higher for L than SP diets, and higher for M than G diets; the resulting difference in total CH 4 production was small. Owing to diet formulation constraints, N intake was higher for SP than for L diets; interaction between forage type and protein source was significant for N intake. The same statistical effects were found for N in milk. Faecal and urinary N losses were determined from total faeces and urine collection. Faecal N output was lower for M than for G diets but did not differ between protein sources. Urinary N output did not differ between forage types, but was lower for cows fed L diets than for cows fed SP diets, potentially resulting in lower ammonia emissions with L diets. Replacing soya bean meal plus beet pulp with dehydrated lucerne did not change CH 4 production, but resulted in more N in faeces and less N in urine.

“…Anthropogenic emissions (6.7 Tg/year) represent 40% of the total annual (17.7 Tg/year) global emissions of N 2 O (Forster et al, 2007). The main anthropogenically derived substrates for N 2 O production include synthetic and organic fertilisers and excreta; thus, agricultural production of N 2 O (2.8 Tg/year) dominates anthropogenic emission sources (Denman et al, 2007;Schils et al, 2013). Davidson (2009) showed that the observed increase in tropospheric N 2 O between 1860 and 2005 could be explained by 2.0% of manure nitrogen (N) and 2.5% of fertiliser N being emitted as N 2 O over this period.…”

Section: Discussionmentioning

confidence: 99%

Using stable isotopes to follow excreta N dynamics and N2O emissions in animal production systems

Clough

Müller

Laughlin

2013

Nitrous oxide (N 2 O) is a potent greenhouse gas and the dominant anthropogenic stratospheric ozone-depleting emission. The tropospheric concentration of N 2 O continues to increase, with animal production systems constituting the largest anthropogenic source. Stable isotopes of nitrogen (N) provide tools for constraining emission sources and, following the temporal dynamics of N 2 O, providing additional insight and unequivocal proof of N 2 O source, production pathways and consumption. The potential for using stable isotopes of N is underutilised. The intent of this article is to provide an overview of what these tools are and demonstrate where and how these tools could be applied to advance the mitigation of N 2 O emissions from animal production systems. Nitrogen inputs and outputs are dominated by fertiliser and excreta, respectively, both of which are substrates for N 2 O production. These substrates can be labelled with 15 N to enable the substrate-N to be traced and linked to N 2 O emissions. Thus, the effects of changes to animal production systems to reduce feed-N wastage by animals and fertiliser wastage, aimed at N 2 O mitigation and/or improved animal or economic performance, can be traced. Further 15 N-tracer studies are required to fully understand the dynamics and N 2 O fluxes associated with excreta, and the biological contribution to these fluxes. These data are also essential for the new generation of 15 N models. Recent technique developments in isotopomer science along with stable isotope probing using multiple isotopes also offer exciting capability for addressing the N 2 O mitigation quest.