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Agriculture sector
New Zealand has a unique emissions profile with 49 per cent (37.4 Mt CO2-e) of emissions in 2005 produced by the agriculture sector. Typically emissions from agriculture for other developed countries make up around 12 per cent of totals. Agriculture emissions increased by 15 per cent between 1990 and 2005 (32.5 Mt CO2-e). The sector contributes 96 per cent of New Zealand’s total nitrous oxide emissions and 91 per cent of total methane emissions. Figure 6 shows agriculture emissions by category in 2005.
Emissions of methane or nitrous oxide are produced when biomass (organic matter) is consumed, decays or is burnt. Naturally occurring emissions are modified by human activities such as cultivation, addition of nitrogenous fertilisers, farming of livestock, or burning of crop residues.
Enteric fermentation
Enteric fermentation is a by-product of digestion by ruminant livestock. This is New Zealand’s highest single emissions category, contributing 23.9 Mt CO2-e, or 31 per cent to total national emissions in 2005, primarily as methane. Enteric fermentation represents 64 per cent of all emissions from agriculture. Emissions from enteric fermentation have increased by 10 per cent from 1990 levels (21.2 Mt CO2-e).
Ruminant animals are livestock with complex digestive systems consisting of a four-part stomach where microbes break down food. Methane is produced as a by-product of the microbial activity and is mostly released when the animal exhales (enteric fermentation).
Agricultural soils
Emissions of nitrous oxide in this category are associated with the application of nitrogenous fertilisers, crop residues, animal wastes (dung and urine), cultivation of peat soils and the use of nitrogen fixing crops. Emissions can be direct from the soil, and indirect through atmospheric deposition, leaching and run-off. Agricultural soils contributed 34 per cent of all agricultural emissions (12.7 Mt CO2-e) in 2005. Emissions were 27 per cent (2.7 Mt CO2-e) higher in 2005 than in 1990.
Manure management
This category produces emissions from decomposition of animal waste held in manure management systems. For example, emissions from animal waste stored in lagoons or ponds. Emissions were 0.8 Mt CO2-e in 2005, a growth of 28 per cent from 1990 (0.6 Mt CO2-e).
Savanna burning
Emissions are from the controlled burning of tussock grasslands. The amount of tussock burned has been steadily decreasing since 1959. Emissions from this category comprised 0.001 Mt CO2-e in 2005, a decrease of 71 per cent from 1990 (0.003 Mt CO2-e).
Burning of agricultural residues
Emissions are produced from field-burning of crop residues, including those from barley, wheat and oats. Emissions were 0.014 Mt CO2-e in 2005, a decrease of 44 per cent from 1990 (0.025 Mt CO2-e).
