What GHG reduction options are 2-5 years away?
New options for reducing total emissions may become available in the next few years, based on evidence from laboratory studies and small-scale animal trials. The critical challenge for those options is to commercialise them and ensure they are viable within New Zealand farming systems.
BREEDING LOW-EMITTING SHEEP AND CATTLE
Research has found that some animals emit less methane than others and that this trait is genetic and can be passed on to their offspring. This has been demonstrated clearly for sheep, and low-emission traits could be available in breeding indices by as early as 2017. Work on cattle began in 2015, and researchers hope that lessons learnt from the sheep programme will allow faster progress for cattle, so that the commercial availability of low-emitting cattle could be as little as five years away. Based on data obtained to date, naturally low-emitting animals appear to be as productive as average animals, so there would be no direct financial penalty from selecting these sheep. There is still an opportunity cost, however, since adding this additional breeding trait lowers the rate of gain in achieving other breeding objectives. Dollar estimates of this opportunity cost are being explored, but specific policies or market premiums for ‘climate-friendly’ animals may be necessary to encourage widespread adoption of low-emitting sheep. Further work is also continuing to conclusively demonstrate in a range of practical situations that there is no production penalty associated with the low emission trait or any trade off with nitrous oxide emissions.
LOW METHANE FEEDS AND FEED ADDITIVES
Brassicas have been tested extensively in sheep in New Zealand and forage rape has consistently reduced methane emissions by 20-30% when fed as full diet. Limited work has been done with cattle but the results are also very encouraging. However, it appears that in some circumstances nitrous oxide emissions can increase considerably when brassicas are grazed, and implications for animal health of any increased use also need further study. If these issues can be overcome, greater use of forage rape may yield overall emissions reductions. Preliminary studies with fodder beet have shown reduction in methane when fed at >75% of the diet. However the consequences of feeding fodder beet at such high levels need to be studied further.
Other feeds or feed additives have also been shown to reduce methane production in animals in some studies. However this does not necessarily mean they will work under New Zealand conditions:
- there is strong evidence that high cereal diets can reduce methane emissions per unit of product; but cereal must
make up at least 30-60% of the diet. This makes it unlikely to be cost-effective for New Zealand’s pastoral grazing
systems. It is also important to factor in the emissions generated to produce and transport the cereal feed
- lipid supplementation (fats such as tallow) appears to reduce emissions by up to 20% in some circumstances, but
results from New Zealand studies have shown no decreases. This may be because New Zealand’s pasture-based diets
differ from the mixed diets used in overseas testing
- limited testing of New Zealand’s largest imported feed, PKE (palm kernel expeller), has found no effect on methane
- diets containing maize silage, the most common non-pasture feed in the dairy industry, have also been found to have
no consistent effect on methane emissions and the effect could depend on the percentage of silage in the diet
- tannin-containing plants reduce emissions generally but have poor agronomic characteristics
- garlic and essential oils (e.g. from sandalwood) added to feed have been found to reduce methane emissions in some
trials but can taint milk and their very high costs rule currently them out as practical mitigation approaches
- some biochemical substances, including some antibiotics and growth promoters (e.g. monensin), have been shown
to reduce methane emissions in intensive feedlot systems but they seem to have limited effects in pasture-based
systems. There can also be strong market resistance to the use of such substances
METHANE INHIBITORS – FEEDLOT OPERATIONS
Researchers are looking for animal-safe compounds that would suppress the methane-producing microbes in the rumen and thus reduce overall methane emissions from animals, without side effects. An inhibitor suitable mainly for feedlot animals has been successfully tested in long-term trials overseas, where it has been shown to reduce methane emissions by 30%. This inhibitor is being developed by the Dutch company DSM, with commercial release planned by 2019. However, this inhibitor is unlikely to be effective in grazing systems as it relies on it being mixed in with cattle feed. Work is underway to develop inhibitors suitable for New Zealand grazing systems (see What options are more than 5 years away?).
LOW-NITROGEN FEEDS AND ENHANCED PLANT GROWTH AT LOWER NITROGEN LEVELS
Research to date has demonstrated that nitrification inhibitors are viable tools from an emissions and soil health perspective. While use of the commercial product DCD has been suspended, researchers are investigating whether some plants naturally produce nitrification inhibitors that could be promoted for more widespread use in New Zealand’s pastures. Some plants also influence the balance and composition of urine and dung and thus could influence the emissions of nitrous oxide from pastures; the use of such plants could be promoted more widely if they show no negative effects on productivity. Read more
Some substances promote plant growth without relying on high nitrogen inputs, such as the commercially-available natural plant hormone gibberellin. Currently available evidence, mainly from short-term trials, suggests that gibberellin could be used to maintain herbage production when nitrogen fertilizer use is reduced. Further work to confirm these initial findings and analyse the long-term effects of repeated gibberellin use is underway. Read more
There is good evidence that biochar (organic matter carbonised under controlled conditions) represents a very stable form of carbon, so it could be used to store more carbon in soils. Research has indicated that specific biochars could also help reduce nitrous oxide emissions although the specific mechanisms are not yet clear; other potential benefits for improving soil functions and reducing emissions from pastures are also being tested. However, the main challenge at present to any widespread use of biochar in a pastoral system remains its cost and the large area that would need to be covered, which makes this strategy not economically feasible for NZ farmers.
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