Greenhouse gas abatement strategies for animal husbandry

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Abstract

Agriculture contributes significantly to the anthropogenic emissions of non-CO2 greenhouse gases methane and nitrous oxide. In this paper, a review is presented of the agriculture related sources of methane and nitrous oxide, and of the main strategies for mitigation. The rumen is the most important source of methane production, especially in cattle husbandry. Less, but still substantial, amounts of methane are produced from cattle manures. In pig and poultry husbandry, most methane originates from manures. The main sources of nitrous oxide are: nitrogen fertilisers, land applied animal manure, and urine deposited by grazing animals. Most effective mitigation strategies for methane comprise a source approach, i.e. changing animals’ diets towards greater efficiencies. Methane emissions, however, can also be effectively reduced by optimal use of the gas produced from manures, e.g. for energy production. Frequent and complete manure removal from animal housing, combined with on-farm biogas production is an example of an integrated on-farm solution. Reduced fertiliser nitrogen input, optimal fertiliser form, adding nitrification inhibitors, land drainage management, and reduced land compaction by restricted grazing are the best ways to mitigate nitrous oxide emissions from farm land, whereas, management of bedding material and solid manure reduce nitrous oxide emissions from housing and storage. Other than for methane, mitigation measures for nitrous oxide interact with other important environmental issues, like reduction of nitrate leaching and ammonia emission. Mitigation strategies for reduction of the greenhouse gases should also minimize pollution swapping.

Introduction

Global atmospheric concentrations of the most important greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have increased significantly within the last 150 years. Stabilisation at today's levels and even reduced concentrations, necessary to reduce climate change and corresponding effects, would require significant reductions in emissions of those gases (IPCC, 2001). These reductions are to be brought about through adoption of mitigation measures from all sectors, e.g. industry, agriculture, energy and households. Agriculture contributes significantly to total greenhouse gas (GHG) emissions. Approximately 20 and 35% of the global GHG emissions originate from agriculture. These figures are 40 and >50% of the anthropogenic emissions of CH4 and N2O, respectively (IPCC, 2001). Most important agriculture related CH4 sources are animals and their excreta (manure), whereas, most of the N2O is produced in the field (manure excreted during grazing, chemical fertilisers), and from animal houses where straw or litter is used (Freibauer and Kaltschmitt, 2001). The Kyoto protocol specifies that each complying country should provide adequate methods and instruments to quantify, monitor and verify GHG emissions and their reductions. In this paper, we present a summarised overview of the range of approaches for reducing emissions of CH4 and N2O from the various sources in the agricultural sector, particularly from livestock systems, with a focus on European farming practices.

Section snippets

Sources and processes

Methane and N2O originate from different cycles. Methane is usually produced following the degradation of carbon (C) components during digestion of feed and manure, whereas, N2O is related to the nitrogen (N) cycle with chemical fertilisers and manures as the most important sources.

Methane

Methane emission per unit of animal product will be reduced by any process that increases the ratio of livestock ‘production’ to ‘maintenance’. Thus faster growth, higher milk yields and shorter dry periods in lactating cows will lower CH4 emissions. Likewise, an increase in the average longevity of dairy cows (i.e. a greater number of lactations per lifetime) relative to the period from birth to first calving (usually 3 years) will reduce CH4 loss per unit of milk yield. Additionally, measures

Interactions with other policies

There are important interactions between mitigation measures for gaseous emissions and nitrate leaching (risk of pollution swapping), so mitigation practices need to be evaluated at the system level (i.e. holistically). Brink et al. (2001) indicated that NH3 abatement will result in a 15% lower emission of N2O, mainly due to adaptations in animal houses and low emission manure application techniques. Also reversed interactions are observed. A move from straw based cattle housing systems to

Conclusions

Agriculture in general, and livestock production in particular, contribute to global warming through emissions of the non-CO2 GHGes CH4 and N2O. Most CH4 is emitted from ruminants (animal + manure), whereas, N2O is mainly emitted from fertilized land.

Methane mitigation options from ruminants focus on increasing production per animal, modifying diet, decreasing numbers of methanogens and methanogen activity and by reducing livestock numbers. Manure related CH4 can be reduced by minimizing

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