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Prospects for mitigation
It appears unlikely that actual on-farm methane emissions can be reduced more than fractionally by 2012 relative to business-as-usual. It is, however, possible that some mitigation tools may have reached a stage of “developed, tested and available in principle” by 2012. Continued research may reduce methane emission relative to business-as-usual by 2020. Sector growth strategies to increase productivity by 50% over the next 10 years (Dairy Insight 2004) imply that even substantial emissions reductions relative to business-as-usual may not lead to a reduction in gross methane emissions from agriculture out to 2020.
One of the key messages from research to date is that no single solution will be able to significantly reduce total agricultural greenhouse gas emissions, but may apply to only one or a few livestock types and related farming systems, and processes that lead to nitrous oxide and methane emissions. The overall effectiveness of any mitigation tool will also be limited if it is applied only on a fraction of farms, or is effective only during some seasons (Clark et al, 2001; PGGRC, 2005).
There are realistic prospects based on currently identified solutions to reduce nitrous oxide emissions by a few percent relative to business-as-usual by 2012, and more significantly by 2020. Widespread use of nitrification inhibitors, if combined with reduced use of nitrogen fertilisers and increased use of stand-off pads, may reduce nitrous oxide emissions relative to business-as-usual for the period from 2010 to 2020. However, the practicality of such emissions reductions depends on the results of further research and testing of the long-term effectiveness and environmental sustainability of nitrification inhibitors and possible similar future technologies, and the integration of specific mitigation management practices into normal farm operations.
Options for mitigation
Options to reduce non-CO2 emissions from agriculture include:
- new technologies and forages that reduce methane production in the rumen
- new technologies that reduce the production of nitrous oxide in the soil from nitrogen deposited in urine and excreta and in nitrogen fertilisers
- farm management practices that reduce total nitrogen loading of soils through reduced fertiliser application or changes in stock management that minimise greenhouse gas emissions.
The potential for each of these mitigation options will be discussed in turn.
Most of the research to date has focused on increasing fundamental understanding of the processes that lead to methane production in the rumen. Several leads have been identified, but no cost-effective methane-mitigation technology for free-ranging animals has been proven either in New Zealand or elsewhere in the world (PGGRC, 2005).
The use of some alternative forages has the potential to reduce methane emissions by 10% to 20%. Their overall cost and sustainability, and consistency with New Zealand’s climate and soils, is yet to be evaluated, but it is unlikely that alternative forages tested to date could simply replace existing standard pastures on a large scale. However, their further evaluation may offer clues to selectively breeding new pasture species that meet farm management and (current and future) climate conditions but also retain their methane-reducing properties. The time horizon for developing and introducing new pasture species is in the order of a decade or more, and the rate of adoption would be limited by the pasture renewal rates that farmers use and any associated changes in costs and farm productivity.
Apart from alternative forages, the feed additive sodium monensin has been shown to reduce methane emissions as a co-benefit to its main purpose of reducing bloat in lactating dairy cows. It achieves this by both reducing the feed intake of cows without reducing their milk production, and by reducing the amount of hydrogen produced in the rumen. Since monensin is normally fed only to lactating dairy cows for a limited period, it could be expected to deliver only a small reduction in overall methane emissions of, at most, 1% below business-as–usual (Sauer et al, 1998; McGinn et al, 2004).
The most significant single impact on nitrous oxide emissions could come from the use of nitrification inhibitors, which desktop studies estimate could reduce total on-farm nitrous oxide emissions by up to 50%, while also reducing nitrate leaching by up to 20% (de Klein and Monaghan, 2005). Given their recent introduction into the market two years ago, data and knowledge about any long-term environmental effects are limited, and there are no systematic experimental studies of emission changes at the farm or catchment scale for a range of climates, soils and animal systems.
If nitrification inhibitors were applied on 50% of all dairy farms and were to sustainably reduce nitrous oxide emissions on those farms by 50% between 2010 and 2020, total non-CO2 greenhouse gas emissions from agriculture would reduce by up to 3% relative to business-as-usual. The use of nitrification inhibitors appears marginally cost-effective to dairy farmers even when no price of greenhouse gas emissions is taken into account. Cost-effectiveness would decline for more extensive farming systems. The estimated emissions reductions do not take into account the possible increase in pasture productivity, which could offset reductions in nitrous oxide emissions through higher methane emissions from higher stocking rates.
Changes in farm management to reduce greenhouse gas emissions
Some emissions reductions could be achieved by better nutrient management and optimised fertiliser application. Fertiliser nitrogen was responsible for about 18% of total nitrous oxide emissions in 2003, growing to over 20% in 2010 and beyond. Better management of fertiliser use could also have co-benefits through reduced nitrate leaching and improved water quality.
Limiting the growth in nitrogen fertiliser use to below business-as-usual projections by 2010 and 2020 could further reduce nitrous oxide emissions. If fertiliser use were held constant at 2003 levels, total agricultural non-CO2 emissions would reduce by 1.5% and 2.5% relative to business-as-usual by 2010 and 2020, respectively. However, there is insufficient information to estimate the extent to which fertiliser use could be reduced through improved management and nutrient budgeting tools without also reducing overall farm productivity. Cost-effective opportunities will differ between farms and depend on individual management practices and expertise, including the timing, forms and quantities of nitrogen fertiliser. Biosecurity risks such as clover root weevil may require replacement of the nitrogen previously fixed by clovers by fertiliser nitrogen to maintain previous productivity levels.
Other farm management practices with the potential to reduce greenhouse gas emissions, mainly for nitrous oxide, include the use of stand-off or feed pads for wintering systems, and possible adjustments to seasonal timing of farm operations such as milking and slaughtering.
The total gains that are possible by such farm management changes are uncertain. Desktop studies have shown that reductions in nitrous oxide emissions, which could be up to 30% on a seasonal basis for some farms, could be offset by increases in methane and carbon dioxide emissions resulting from a more intensive management regime including greater reliance on supplementary feed. Recent research does indicate, however, that stand-off pads could achieve some nitrous oxide emissions reductions for relatively little extra costs and effort. These farm management changes would also have significant co-benefits in terms of reduced nitrate leaching into water ways (de Klein and Monaghan, 2005; de Klein and Ledgard, 2005).
Very little work has been undertaken to optimise total on-farm greenhouse gas emissions relative to overall production through adjustment of milking and slaughtering times, and variations in stocking rates. Consequently, the scope and cost of such management changes to reduce emissions is currently not clear.
Trade-offs and co-benefits of mitigation options
Reducing non-CO2 emissions is likely to offer co-benefits in increasing productivity and reducing other environmental impacts. These co-benefits offer both positive and negative prospects for overall emission trends from agriculture:
- the presence of co-benefits in the form of improved farm productivity can lead to more rapid adoption of new technologies and practices
- the increased productivity associated with some mitigation options means that agriculture could become more intensified, with higher stock numbers and more intensive feeding regimes, so that overall sectoral growth offsets emissions reductions.
Desktop studies have shown that the use of nitrification inhibitors could reduce nitrous oxide by up to 50%, but some of these gains could be offset by an increase in methane emissions arising from increased pasture production and resulting higher stocking densities. The resulting possible intensification of farms means that while emissions per unit of product would decline, absolute emissions of greenhouse gases per animal and at the farm level could increase (de Klein and Ledgard, 2005).
This demonstrates that partial mitigation options can have positive outcomes in terms of emissions intensity (ie, emissions per unit of product, or emissions per value of total farm production), but may have perverse outcomes in terms of absolute emissions (de Klein and Monaghan, 2005).
Since the amount of arable land in New Zealand is limited, land prices and alternative land uses also provide an important mitigation incentive for the agriculture sector. Economic returns and mitigation policies, in particular for the forestry sector, will affect land-use and emission trends from agriculture. The effect of such policies is not covered here. Other land-use decisions such as subdivision of semi-rural areas for small “lifestyle farms” and urban sprawl can also affect emission trends.
Protection of landscapes of national significance and retirement of government-owned land for the purpose of biodiversity protection provide further indirect mitigation results. An example is the current high-country tenure review, which will probably retire large blocks of land currently under extensive sheep farming to native tussock vegetation.
Projected emission trends
As outlined in Section 3.1.2, agriculture contributes the single largest share of any sector to New Zealand’s total greenhouse gas emissions, and emissions of both methane and nitrous oxide have been increasing since 1990. This emissions growth is expected to continue into the future. Best estimates for projected emission trends for the sector as a whole to 2010 and 2020 are provided in Table 11.
Table 11 - Projected Non-CO2 Emissions from Agriculture
|1990 kt CO2e||2003 kt CO2e||2010 estimated kt CO2e||2020 estimated kt CO2e|
|Projected Emissions||32,194||37,203||40,476 (38.5Mt – 42Mt)||43,801|
|Excess above 1990||0||5,009 (15.6%)||8,179 (25.4 ± 5%)||11,607 (36.1%)|
Source: Draft New Zealand fourth national communication under the UNFCCC (2005)
The projections in Table 11 assume that no significant new mitigation technology is developed and implemented by 2012 or 2020, and that sector growth continues along historical lines. The projections therefore form a business-as-usual baseline. This baseline assumption needs to be assessed against two additional strategic goals stated by animal sector industries (Dairy Insight, 2004):
- increase total productivity by 50% by 2014, including increasing the amount of metabolisable energy per hectare and the amount of milk produced per cow
- reduce the net production of methane and nitrous oxide from New Zealand dairy farms by 20% by 2012 relative to business-as-usual.
Figure 35 provides more detail on the historical and projected changes in emissions for specific subsectors. The largest growth occurs in dairying, while emissions from sheep have declined up to now due to significant reductions in total sheep numbers. This latter trend is expected to be reversed over the coming years, despite relatively constant sheep numbers, due to the increasing productivity and emissions per head of sheep.
Figure 35 - Historical and Projected Non-CO2 Emissions from Agriculture Sub-sectors
Source: Draft New Zealand fourth national communication under the UNFCCC (2005) and New Zealand, Ministry for the Environment (2005b)