Opportunities for reducing environmental emissions from forage-based dairy farms

Abstract

Modern dairy production is inevitably associated with impacts to the environment and the challenge for the industry today is to increase production to meet growing global demand while minimising emissions to the environment. Negative environmental impacts include gaseous emissions to the atmosphere, of ammonia from livestock manure and fertiliser use, of methane from enteric fermentation and manure management, and of nitrous oxide from nitrogen applications to soils and from manure management. Emissions to water include nitrate, ammonium, phosphorus, sediment, pathogens and organic matter, deriving from nutrient applications to forage crops and/or the management of grazing livestock. This paper reviews the sources and impacts of such emissions in the context of a forage-based dairy farm and considers a number of potential mitigation strategies, giving some examples using the farm-scale model SIMS DAIRY . Most of the mitigation measures discussed are associated with systemic improvements in the efficiency of production in dairy systems. Important examples of mitigations include: improvements to dairy herd fertility, that can reduce methane and ammonia emissions by up to 24 and 17%, respectively; diet modification such as the use of high sugar grasses for grazing, which are associated with reductions in cattle N excretion of up to 20% (and therefore lower N losses to the environment) and potentially lower methane emissions, or reducing the crude protein content of the dairy cow diet through use of maize silage to reduce N excretion and methane emissions; the use of nitrification inhibitors with fertiliser and slurry applications to reduce nitrous oxide emissions and nitrate leaching by up to 50%. Much can also be achieved through attention to the quantity, timing and method of application of nutrients to forage crops and utilising advances made through genetic improvements.Key words: ammonia, diffuse water pollution, farm-scale model, greenhouse gas, mitigation IntroductionThe dairy sector, in common with other agricultural sectors, currently faces a great challenge to meet rising global food demands, particularly for livestock-derived food products, in a sustainable way (Godfray et al. 2010). There are important interactions between food production and other ecosystem services, including climate regulation, air and water quality, nutrient cycling, soil erosion, biodiversity and landscape quality, as discussed by Pilgrim et al. (2010) for temperate grassland systems, and the sustainable intensification of production relies on a good understanding of these interactions and our ability to identify potential 'win-win' strategies.The assessment of such interactions for given management or mitigation scenarios on forage-based dairy farms was the primary aim of the development of the farm-scale SIMS DAIRY model (del Prado et al. 2011). SIMS DAIRY integrates all of the major components of a dairy farm into a modelling framework using a system-based approach. It consists of modules dealing with overall farm management, he...

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