Effect of intensification of pastoral farming on greenhouse gas emissions in New Zealand

2007, greenhouse gas (GHG) emissions in New Zealand were 16% higher than in  1990.    Agriculture  accounts for 48% of GHG emissions in New Zealand, and 10–12% of emissions in  most other ‘developed’ countries.Methane  (CH4) accounts for 35% of GHG emissions in New Zealand, mostly from ruminal  fermentation. Nitrous oxide (N2O) accounts for 17% of GHG emissions in New Zealand,   mostly from urinary N, exacerbated by excessive application of nitrogenous  fertiliser.   GHG  are often expressed as carbon dioxide equivalents (CO2-e), and 1  kg CH4 has a similar global-warming potential as 21 kg CO2,  whilst 1 kg N2O has the same warming potential as 310 kg CO2.  Methane  is derived from H2 produced during ruminal fermentation, and  losses account for 6–7% of gross energy in feeds. This is about 9–10% of  metabolisable energy intake.  Methane  production tends to be lower when legumes, rather than grasses, are fed, and  emissions are greater (per kg dry matter intake; DMI) when mature grasses and  silages are fed. There are small differences between individual animals in their  CH4 production (g/kg DMI) but there are few profitable options  available for reducing CH4 production in ruminants.  Emissions  of N2O can be reduced by more strategic application of nitrogenous  fertiliser, avoidance of waterlogged areas, and use of dicyandiamide in some  cooler regions.  GHG  mitigation should be based on life-cycle analyses to ensure a reduction in one  GHG does not increase another. Current and future strategies are unlikely to  reduce GHG emissions by >20%.  Food  production is central to human survival, and should not be compromised to  mitigate GHG emissions. Efforts should be directed toward increasing animal  efficiency and reducing GHG emissions/unit edible food. 

KEY WORDS: Greenhouse gas  emissions, dairy farming, methane, nitrous oxide, mitigation, abatement, farm  management, ruminants