Agriculture sector

The agriculture sector reports on 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 burnt. Naturally occurring emissions are modified by human activities such as cultivation, addition of nitrogenous fertilisers, farming of livestock, or burning of crop residues. Figure 8 shows agriculture emissions by category in 2006.

Figure 8: Emissions from the agriculture sector: 2006

See figure at its full size (including text description).

Enteric fermentation

Enteric fermentation is a by-product of digestion by ruminant livestock. This is New Zealand’s highest single emissions category, contributing 31 per cent (24.1 Mt CO₂-e) of total emissions in 2006 and 64 per cent of all emissions from agriculture. Emissions from enteric fermentation have increased 11 per cent (2.3 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 and is mostly released when the animal exhales (enteric fermentation).

Agricultural soils

Emissions of nitrous oxide 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 (12.7 Mt CO₂-e) of all agricultural emissions in 2006 and 16 per cent of New Zealand’s total emissions. Emissions from agricultural soils have increased 27 per cent (2.7 Mt CO₂-e) from the 1990 level of 10.0 Mt CO₂-e.

Manure management

The manure management category estimates emissions from decomposition of animal waste held in manure management systems, eg, dairy effluent temporally stored in lagoons or ponds. In 2006, emissions from manure management were 2 per cent (0.8 Mt CO₂-e) of total agriculture emissions. The estimated emissions from manure management have increased 31 per cent (0.2 Mt CO₂-e) from the 1990 level of 0.6 Mt CO₂-e.

Savanna burning

Emissions from 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. Emissions from this category comprised 0.003 per cent (0.001 Mt CO₂-e) of agricultural emissions in 2006, 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 of crop residues, including those from barley, wheat and oats. In 2006, emissions were 0.01 Mt CO₂-e, a decrease of 49 per cent (0.01 Mt CO₂-e) from the 1990 level of 0.03 Mt CO₂-e.

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