Improving production efficiency as a strategy to mitigate greenhouse gas emissions on pastoral dairy farms in New Zealand P.C. Beukes *, P. Gregorini, A.J. Romera, G. Levy, G.C. Waghorn DairyNZ Ltd., Private Bag 3221, Hamilton 3240, New Zealand 1. Introduction In New Zealand, methane (CH 4 ) contributes 38% and nitrous oxide (N 2 O) 17% (CO 2 equivalents; CO 2 -e) of the annual emissions (NZ Climate Change Office, 2003). Agriculture contributes about half of New Zealand GHG emissions, most of them coming from grazed pasture-based livestock production systems. In these systems, enteric fermentation and urinary-nitrogen (urinary-N) are the most important sources of CH 4 and N 2 O(Waghorn, 2008). Previous studies have summarized the current and future strategies available to pasture-based farmers for reducing GHG emissions by animal, feed-based, soil and management interven- tions (Beauchemin et al., 2008; de Klein and Eckard, 2008). There is a need to evaluate the impacts of these strategies when incorporated into the farm system and also the cumulative effects when some of these strategies are combined. Furthermore, variability, as influenced by climate and animal-feed dynamics, needs to be considered (Beauchemin et al., 2008). Farm-scale models are cost effective ways of exploring the cost/benefits of practical and multiple mitigation options over several years. Dairy farming in New Zealand is responsible for about 36% of agricultural GHG emissions (Ministry for the Environment, 2008). Seasonal calving dairy cows are fed ryegrass-dominant pastures. Typically, all cows calve at the end of winter (July–September) and are milked for 8–9 months so feed requirements are largely met Agriculture, Ecosystems and Environment 136 (2010) 358–365 ARTICLE INFO Article history: Received 29 April 2009 Received in revised form 13 August 2009 Accepted 19 August 2009 Available online 6 September 2009 Keywords: Feed conversion efficiency Nitrogen fertilizer Stocking rate Nitrous oxide Methane Kyoto Protocol ABSTRACT New Zealand’s commitment to the Kyoto Protocol requires agriculture, including dairy farming, to reduce current greenhouse gas (GHG) emissions by about 20% by 2012. A modeling exercise to explore the cumulative impact of dairy management decisions on GHG emissions and profitability is reported. The objective was to maintain production, but reduce GHG emissions per unit of land and product by improving production efficiency. A farm-scale computer model that includes a mechanistic cow model was used to model an average, pasture-based New Zealand farm over different climate years. A mitigation strategy based on reduced replacement rates was first added to this baseline farm and modeled over the same years. Three more strategies were added, improved cow efficiency (higher genetic merit), improved pasture management (better pasture quality), and home-grown maize silage [increased total metabolizable energy (ME) yield and reduced nitrogen intake], and modeled to predict milk production, intakes, methane, urinary-nitrogen, and operational profit. Profit was calculated from 2006/2007 economic data, where milksolids (fat + protein) payout was NZ$ 4.09 kg 1 . 1 A nutrient budget model was used with these scenarios and two more strategies added: cows standing on a loafing pad during wet conditions and application of a nitrification inhibitor to pasture (DCD). The nutrient budget model predicted total GHG emissions in CO 2 equivalents and included some life cycle analysis of emissions from fertilizer manufacturing, fuel and electricity generation. The simulations suggest that implementation of a combination of these strategies could decrease GHG emissions by 27–32% while showing potential to increase profitability on a pasture-based New Zealand dairy farm. Increasing the efficiency of milk production from forage may be achieved by a combination of high (but realistic) reproductive performance leading to low involuntary culling, using crossbred cows with high genetic merit producing 430 kg milksolids yr 1 , and pasture management to increase average pasture and silage quality by 1 MJ ME kg dry matter 1 . These efficiency gains could enable stocking rate to be reduced from 3 to 2.3 cows ha 1 . Nitrogen from fertilizers would be reduced to less than 50 kg ha 1 yr 1 and include ‘‘best practice’’ application of nitrification inhibitors. Considerable GHG mitigation may be achieved by applying optimal animal management to maximize efficiency, minimize wastage and target N fertilizer use. ß 2009 Published by Elsevier B.V. * Corresponding author. Tel.: +64 7 858 2761; fax: +64 7 858 3751. E-mail address: pierre.beukes@dairynz.co.nz (P.C. Beukes). 1 At time of publication 1 NZ$ = 0.65 US$. Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee 0167-8809/$ – see front matter ß 2009 Published by Elsevier B.V. doi:10.1016/j.agee.2009.08.008