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• Executive Summary
• National Inventory
• Nitrous Oxide
• Methane
• Whole Farm Systems
• A Framework for Developing a Research Strategy

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Part Two - An Assessment of the Needs for Research on the Abatement of Non-Carbon Dioxide Greenhouse Gas Emissions from Agriculture: A Review of Current and Published Research

Executive Summary

This report is a review of current and published research on agricultural methane and nitrous oxide emissions, with particular emphasis on research into the abatement of these emissions.

The New Zealand government's policy is to exempt the agricultural sector from any emission charges related to methane and nitrous oxide emissions, at least in the first commitment period (2008 to 2012), in exchange for a commitment from the sector to fund research that will lead to a permanent reduction in emissions.

In the period 1999 to 2002, approximately $23,500,000 per year was invested in all aspects of climate change research. Ninety percent of this came from government sources. Indicative figures of current investment in agricultural greenhouse gas emissions, based on a survey of the principal research providers, shows the following levels:

1999/00	$582,000
2000/01	$510,000
2001/02	$2,649,000

Expenditure by the Foundation for Research, Science and Technology (FRST) and the Ministry of Agriculture and Forestry (MAF) in 2002/03 is $3,263,000 and will be $4,715,000 in 2003/04.

Improving the National Inventory, and the re-ordering of production systems research to examine abatement options, were the main areas of investment over the period 1999 to 2002. A strong emphasis on measurement and inventory related research is maintained in the period 2002/2004, and research on abatement technologies has been boosted 3.5 to 5 times over the 1999/00 level.

The establishment of the Pastoral Greenhouse Gas Research Consortium represents a significant new area of investment in methane research, and is an important step in the establishment of a partnership between government and the agricultural industry in finding ways to manage agricultural greenhouse gas emissions.

National Inventory

In 2000, the official estimates of New Zealand's greenhouse gas emissions showed that methane and nitrous oxide represented 59.6% of total emissions in CO₂ equivalent terms, and emissions from agriculture were 55% of total emissions. Compared to 1990, methane emissions were 6.17% less, a fall largely attributable to the fall in sheep numbers, and nitrous oxide was 6.35% more.

The most important source of agricultural methane is ruminant enteric fermentation (98.7%). The most important sources of nitrous oxide are faeces and urine deposited by grazing animals on pasture, animal waste and fertiliser nitrogen in soils, and indirect emissions from these sources through atmospheric deposition and leaching.

Revised models for estimating methane and nitrous oxide emissions that take into account animal numbers, animal productivity and New Zealand specific emission rates that are based on empirical data show that the official estimates understate the trends in emission rates and that there is a rising linear trend. Extrapolation of the curves to 2010 indicates that methane emissions will exceed 1990 levels by 15.7% in gross terms, and nitrous oxide emissions will exceed 1990 levels by 20-30%. In the decade 1990 to 2000, productivity gains have been significant, particularly in the dairy and sheep industries. For example, the production of sheep meat in 2000 exceeds that of 1990, in spite of a one third decline in sheep numbers. The use of nitrogen fertiliser is increasing at an exponential rate.

Emission rates are most sensitive to changes in total animal numbers and to productivity. An emerging policy question is how the trade-off will be made between that national objective of maintaining emissions at 1990 levels and individual farmer's objectives for the performance of their livestock. A number of abatement strategy options may confer productivity advantages as well as reduced emissions.

Current and planned research is directed at:

• Extending the range of methane emission measurements from animals
• Improving the measurements of nitrous oxide release from excreta under a variety of soil and seasonal conditions
• Improving the assessment of indirect emissions
• Improving (or selecting) the models that can be used to estimate emissions in the future leading to robust estimates that conform with IPCC good practice
• Developing methodologies that allow broad scale assessments of herbage quality and paddock/farm/locality emissions.

Measurement and estimation that can verify that any abatement strategies adopted in the future are delivering the expected effects will be crucial. Methods of measuring and estimating methane and nitrous oxide emissions are discussed in Chapter 6.

Nitrous Oxide

Addition of nitrogen to soil in any form (animal excreta, synthetic fertiliser, crop residues or biological fixation) results in increased nitrous oxide emissions. In New Zealand, agriculture is based largely on animals grazing grass-legume pastures, but the animals do not utilise the nitrogen they ingest efficiently. On average only 10.5% of the nitrogen in grass, silage or other feedstuff is converted into milk, meat, eggs or wool (Table 7.5) and the remainder is excreted in dung and urine. Thus the bulk of the nitrogen added to New Zealand soils comes from the excreta of animals (1 282 Gg N/y) and addition of fertiliser (213 Gg N/y) (Table 7.1).

Additional nitrous oxide is emitted directly from soil as a result of these inputs. It is also generated indirectly when nitrate lost by leaching or run-off is converted to nitrous oxide in water bodies, and when nitrogen from excreta and fertiliser is lost as ammonia to the atmosphere and subsequently deposited on land. During 2000, nitrous oxide emissions from these sources amounted to 25.2 Gg N, compared with the 1990 base value of 24.4 Gg N.

• Of the direct emissions, 53% came from excreta and 10% resulted from the application of fertiliser.
• Indirectly leaching and run-off of nitrogen from animal excreta or fertiliser application contributed 23%, and deposition of ammonia which had been volatilised contributed a further 11%.
• Because of their larger numbers, sheep were responsible for the bulk of the direct nitrous oxide emissions from animal excreta (5.5 Gg N/y or 45.5% of the total), and dairy cattle (3.3 Gg N/y or 27.3%) generated more nitrous oxide than non-dairy cattle (3.0 Gg N/y or 24.8%).

It is apparent from this discussion of sources that mitigation options need to focus on limiting the direct loss of nitrogen from animal excreta and synthetic fertilisers and the indirect loss caused by leaching, run-off and ammonia volatilisation. Options are available that could result in considerable reductions in nitrous oxide emission from grazing animals and fertiliser application. These include:

• Manipulating the diet of animals. Feeding dairy cattle low degradable protein and high starch diets should result in 24% less nitrogen being excreted in the urine, reduced ammonia volatilisation and less nitrous oxide emission.
• Breeding cultivars that improve nitrogen efficiency. Dairy cows fed grasses high in water soluble carbohydrate excreted 24% less nitrogen than those fed normal diets.
• Keeping cattle on feed-pads during the wet autumn/winter period, so that excreta can be collected and utilised as fertiliser later in the year. Nitrous oxide emission from dairy excreta could be reduced by 25% and nitrate leaching by 40%.
• Improving drainage and preventing soil compaction can reduce nitrous oxide emission by 3% each.
• If these options were adopted by farmers, and the effects were additive, there is the potential for nitrous oxide emission to be reduced from the sheep, dairy cattle, and beef cattle sectors by 16% (0.9 Gg N), 28% (0.9 Gg N) and 25% (0.8 Gg N) respectively (Table 7.8).
• Matching nitrogen supply with crop demand, tightening nitrogen flow cycles, and optimising tillage, irrigation and drainage could reduce nitrous oxide emissions from fertiliser use by 19% (0.6 Gg N).
• Nitrate leaching can be reduced by lowering fertiliser application rates, synchronising nitrogen supply to plant nitrogen demand, growing cover crops and using buffer zones.
• If the total reduction of 3.2 Gg N was achieved, it would reduce the emissions calculated for the year 2000 to 22 Gg N (i.e. 2.43 Gg below the 1990 base value).

However, even if nitrous oxide emissions were reduced below the 1990 level by implementing these options, it will only be maintained at that level if nitrogen inputs remain static. This means that fertiliser nitrogen use and animal numbers can not increase. Production could only increase by increasing the efficiency of nitrogen use by sheep and cattle.

• If the options proposed for reducing emissions from fertiliser use were implemented they would increase rather than decrease farmer's income. If fertiliser nitrogen is used more efficiently less money will be spent on fertiliser.
• The options proposed for reducing nitrous oxide emission from animals could only be implemented at a cost to the farmer, and thus may not be accepted.

However, making more efficient use of animal manures and slurries will have numerous indirect benefits.

Methane

The predominant source of methane in New Zealand is the fermentation of pasture plants in the rumen of farm animals. Methane is synthesised from H₂ and CO₂ at the end of the microbial digestion chain by the methanogenic archaea, a group of microorganisms that are widely distributed in nature and are also responsible for methane synthesis in manure, effluent ponds and the soil. If H₂ is allowed to accumulate in the rumen it depresses digestion, so the archaea remove it as methane. Management of H₂ in the rumen is the key to controlling ruminant methane emissions.

There is limited data available in the world literature on methane emission from animals grazing pasture. The best set is from New Zealand, where measurements have been made over a range of pasture types and management scenarios using the SF₆ tracer technique. There is good agreement that mature dairy cows and sheep grazing high quality pastures (>75% DM digestibility) produce about 26 g methane per kg DM digested (DDMI). On poorer quality diets, dairy cows and sheep produce about 35 g methane per kg DDMI. Other sources of methane such as manure, dairy effluent ponds and the soil appear to be trivial compared to enteric digestion. The soil in fact is a major sink for methane through oxidation by methanotrophic bacteria.

Several major nutritional factors are known to have an influence on methane emission which increases with feed intake, although the relationship is not strong because of the high degree of variation between individual animals. However, there is a stronger negative relationship between methane emitted per unit of feed intake and feed intake. So there is an advantage, in terms of methane emission, to feed animals on as high an intake as possible. It is generally accepted that digestion of cell wall carbohydrates produces more methane than the digestion of soluble carbohydrates. Protein and lipids appear to have a negative effect on methane production, but the effects are variable, and in the case of lipids toxicity to the rumen microbes can be a problem.

Many technologies have been proposed for mitigating ruminant methane emission. Livestock numbers are the major determinant of emission at the national scale. While it might be considered politically naive to advocate reducing livestock numbers, sheep farmers over the last 15 years have reduced numbers by 33% without compromising total production. This shows that farming has the inherent flexibility to respond to a meaningful economic incentive.

There are possibilities for reducing methane via improvements in animal efficiency. All animals have an obligatory maintenance requirement that results in no production, yet has an associated methane emission. The strategy must be to dilute the effects of maintenance by various measures such as increasing feed intake, manipulation of dietary composition to increase feed quality (e.g. decrease cell wall carbohydrate), increasing metabolic efficiency and genetic improvement. Dairy cows that have been selected for feed conversion efficiency produce less methane on the same diet. These efficiency improvements should form the basis for on-farm strategies to reduce methane in the short-term.

A wide range of feed additives have been proposed to reduce methane. These include alternative hydrogen acceptors (e.g. malate, fumarate), halogenated methane analogues (e.g. chloroform, bromoethanesulphonic acid), antibiotics (e.g. monensin, mevastatin), defaunating agents (e.g. manoxol, teric), probiotics, bacteriocins and naturally occurring plant compounds (e.g. condensed tannins). There are problems with these compounds such as toxicity to the microbes and the animal, short-lived effects due to microbial adaptation, volatility, expense and failure to meet consumer acceptance. With grazing animals, other than dairy cows, a delivery system would be required to ensure regular delivery into the rumen. Delivery by breeding into pasture plants is possible, but the time needed to get a viable plant established in the national pasture should not be underestimated.

Immunisation of animals against methanogens has been suggested by Australian scientists. This is a good concept, but we are still a long way from the delivery of an efficacious vaccine.

There are many possibilities available for manipulating the rumen microbial ecosystem to achieve methane reduction. These include targeting methanogens with microbial antibiotics, bacteriocins or phage, removing protozoa, and developing alternative sinks for H₂ such as acetogenic bacteria. The development of mitigation technologies from this type of research are well in the future because of the need to first understand the complexities of the rumen microbial ecosystem.

Investment on research into methane mitigation should cover a suite of technologies that range in their potential delivery time from short-term (on-farm systems research) to long-term (rumen microbial manipulation). A successful technology will deliver a win/win result with respect to methane reduction and increased animal production.

Whole Farm Systems

There have been only a limited number of studies of whole farm management systems and strategies that aim to reduce greenhouse gas emissions. However, the available evidence points to this approach in providing medium-term gains in emission management, and in the more efficient use of the energy intake (carbon) converted to methane by rumen microbes (6% of gross energy intake) or nitrogen that is cycled in the farm production system. More efficient capture of methane-carbon or nitrogen as animal tissue or product offers a win/win situation in terms of reduced emissions and increased productivity. Further, it appears that measures to reduce losses of methane-carbon and nitrogen may be complementary or even synergistic.

The continuing development of farm-scale modeling, resource accounting techniques and complementary on-farm testing protocols to support technology-based developments of abatement strategies is seen as a high priority. Core skills and expertise to do this already exist.

A Framework for Developing a Research Strategy

It is suggested that all future research that is related to agricultural production should have specific regard to greenhouse gas emissions.

However, to be considered as research on abatement, the research objectives should have some aspect of greenhouse gas abatement as its primary purpose. This research could include basic studies to understand the processes by which the gases are produced or abated, measurement and inventory development (particularly that which enables the impact of any abatement strategies to be measured), and research to develop specific abatement strategies based on technologies, products or farm practices. Research to integrate such strategies into whole farm management systems would also qualify.

A framework that is based on deriving a national research strategy from an identification of national objectives for agricultural greenhouse gas emissions is set out in Chapter 9.

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