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Climate New Zealand's Greenhouse Gas Inventory 1990-2007: An overview Online version
Agriculture sector
The agriculture sector includes emissions from enteric fermentation, agricultural soils, the management of manure and the burning of savanna and agricultural residues. Emissions of methane or nitrous oxide are produced when biomass (organic matter) is consumed, decays or is burned. Figure 8 provides an indication of the emission profile from the agriculture sector in 2007.
Enteric fermentation
Methane is a by-product of digestion by ruminant livestock. Enteric fermentation is New Zealand’s largest single emissions category, contributing 31 per cent (23.3 Mt CO2-e) of total emissions in 2007 and 64 per cent of all emissions from agriculture. Emissions from enteric fermentation had increased by 7 per cent (1.5 Mt CO2-e) from the 1990 level of 21.8 Mt CO2-e.
Ruminant livestock are animals 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 (enteric fermentation) and is mostly released when the animal exhales.
Agricultural soils
Emissions of nitrous oxide are associated with the application of nitrogenous fertilisers, burning of crop residues, animal wastes (dung and urine), cultivation of peat soils and the use of nitrogen fixing crops. Emissions can come directly from the soil, and indirectly through atmospheric deposition, leaching and run-off. In 2007, agricultural soils contributed 16 per cent of New Zealand’s total emissions and 34 per cent (12.3 Mt CO2-e) of all agricultural emissions. Emissions from agricultural soils had increased 22 per cent (2.3 Mt CO2-e) from the 1990 level of 10.0 Mt CO2-e.
Manure management
The manure management category estimates emissions from the decomposition of animal waste held in manure management systems before being applied to the soil eg, dairy effluent temporarily stored in lagoons or ponds. In 2007, emissions from manure management were 2 per cent (0.8 Mt CO2-e) of total agriculture emissions. The estimated emissions from manure management had increased by 28 per cent (0.2 Mt CO2-e) from the 1990 level of 0.6
Mt CO2-e.
Savanna burning
Emissions in the savanna burning category are from the controlled burning of tussock in the high country areas of Canterbury, Otago and Southland. The amount of tussock burned has been steadily decreasing over the past 50 years. In 2007, emissions were 0.001 Mt CO2-e, a decrease of 68 per cent (0.002 Mt CO2-e) from the 1990 level of 0.003 Mt CO2-e.
Burning of agricultural residues
Emissions are produced from field-burning crop residues, including those from barley, wheat and oats. In 2007, emissions were 0.02 Mt CO2-e, a decrease of 39 per cent (0.01 Mt CO2-e) from the 1990 level of 0.03 Mt CO2-e.
