Greenhouse gas abatement strategies for animal husbandryIntroductionSources and processesMethaneEnteric fermentationFactor 1Factor 2Factor 3Animal manureNitrous oxideMitigation optionsMethaneDietary measuresHousing and storageNitrous oxideChoice of fertiliser formAddition of a nitrification inhibitorLand drainageSolid manure storesN2O:N2 ratioHousing system and managementInteractions with other policiesConclusionsReferencesGreenhouse gas abatement strategies for animal husbandryGert-Jan Montenya,*, Andre Banninkb, David ChadwickcaWageningen University and Research Centre, Agrotechnology and Food Innovations,Livestock Environment, P.O. Box 17, 6700 AA Wageningen, The NetherlandsbWageningen University and Research Centre, Department of Nutrition and Food,Animal Science Group, Lelystad, The NetherlandscInstitute of Grassland and Environmental Research, North Wyke Research Station, Okehampton, Devon, UKAvailable online 26 October 2005AbstractAgriculture contributes significantly to the anthropogenic emissions of non-CO2greenhouse gases methane and nitrous oxide. In thispaper, a review is presented of the agriculture related sources of methane and nitrous oxide, and of the main strategies for mitigation. Therumen is the most important source of methane production, especially in cattle husbandry. Less, but still substantial, amounts of methane areproduced 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 methanecomprise a source approach, i.e. changing animals’ diets towards greater efficiencies. Methane emissions, however, can also be effectivelyreduced by optimal use of the gas produced from manures, e.g. for energy production. Frequent and complete manure removal from animalhousing, combined with on-farm biogas production is an example of an integrated on-farm solution. Reduced fertiliser nitrogen input, optimalfertiliser form, adding nitrification inhibitors, land drainage management, and reduced land compaction by restricted grazing are the best waysto mitigate nitrous oxide emissions from farm land, whereas, management of bedding material and solid manure reduce nitrous oxideemissions from housing and storage. Other than for methane, mitigation measures for nitrous oxide interact with other importantenvironmental issues, like reduction of nitrate leaching and ammonia emission. Mitigation strategies for reduction of the greenhouse gasesshould also minimize pollution swapping.# 2005 Elsevier B.V. All rights reserved.Keywords: Agriculture; Livestock production; Environment; Mitigation; Climate change; Manure; Fertiliser; Animal husbandry1. IntroductionGlobal atmospheric concentrations of the most importantgreenhouse gases carbon dioxide (CO2), methane (CH4) andnitrous oxide (N2O) have increased significantly within thelast 150 years. Stabilisation at today’s levels and evenreduced concentrations, necessary to reduce climate changeand corresponding effects, would require significant reduc-tions in emissions of those gases (IPCC, 2001). Thesereductions are to be brought about through adoption ofmitigation measures from all sectors, e.g. industry,agriculture, energy and households. Agriculture contributessignificantly to total greenhouse gas (GHG) emissions.Approximately 20 and 35% of the global GHG emissionsoriginate from agriculture. These figures are 40 and >50%of the anthropogenic emissions of CH4and N2O,respectively (IPCC, 2001). Most important agriculturerelated CH4sources are animals and their excreta (manure),whereas, most of the N2O is produced in the field (manureexcreted during grazing, chemical fertilisers), and fromanimal houses where straw or litter is used (Freibauer andKaltschmitt, 2001). The Kyoto protocol specifies that eachcomplying country should provide adequa te methods andinstruments to quantify, monitor and verify GHG emissionsand their reductions. In this paper, we present a summarisedoverview of the range of approaches for reducing emissionsof CH4and N2O from the various sources in the agriculturalwww.elsevier.com/locate/ageeAgriculture, Ecosystems and Environment 112 (2006) 163–170* Corresponding author.E-mail address: [email protected] (G.-J. Monteny).0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved.doi:10.1016/j.agee.2005.08.015sector, particularly from livestock systems, with a focus onEuropean farming practices.2. Sources and processesMethane and N2O originate from different cycles.Methane is usually produced fol lowing the degradation ofcarbon (C) components during digestion of feed and manure,whereas, N2O is related to the nitrogen (N) cycle withchemical fertilisers and manures as the most importantsources.2.1. MethaneThe rumen is the most important site of CH4productionin ruminants (breath), whereas, in monogastric animals, likepigs, CH4is mainly produced in the large intestine (flatus).Animal manures, stored indoors in sub-floor pits oroutdoors, are also relevant CH4sources, since conditionsusually favor methanogenesis in both slurry and solidmanure heaps (Husted, 1994). Monteny et al. (2001) foundthe following data for CH4produced from entericfermentation and from manure, respectively, for variousanimal species (Table 1).Enteric fermentation is the most important source(approximately 80%) of CH4in dairy husbandry, whe reas,most (70%) of the CH4on pig and poultry farms originatesfrom manures. The wide range in the total CH4emissionfrom dairy cows is caused by differences in diets andhousing systems (lower values for tying stalls; g reateremissions from cubicle houses; Groot Koerkamp and Uenk,1997).2.1.1. Enteric fermentationThe rate of CH4produced from enteric fermentation indairy cows depends greatly on the level of feed intake, thequantity of energy consumed (see IPCC, 1997), and feedcomposition. The three most important factors are: (1) rateof organic matter (OM) fermentation; (2) type of volatilefatty acids (VFA) produced, which strongly determines theexcess of hydrogen [H] produced in the gastrointestinal tractand the need for CH4production as a sink of excesshydrogen, and (3) efficiency of microbial biosynthesis.2.1.1.1. Factor 1. The rate of OM f ermentation is stronglyinfluence d by level of feed intake and the degradationcharacteristics of the carbohydrate fraction. For example,Mills et al. (2001)