What options are available to limit emissions growth?
Options to further enhance production efficiency
New Zealand already operates a highly efficient and productive pastoral system. Over the past 20 years, farmers have steadily improved feed and nutrition, animal genetics, pasture management, and animal health. These provide permanent, cumulative gains: globally, for instance, genetic improvement is estimated to account for an average 0.5-1% efficiency increase per animal per year. The best way to keep reducing New Zealand’s greenhouse gas intensity is for farmers to continue to increase the production efficiency of their operations as much as possible, and as fast as possible.
By continuing to push production efficiencies, farmers could further reduce emissions intensity and constrain the expected growth in agricultural greenhouse gas emissions as overall animal production continues to increase.
Options to reduce growth in absolute emissions
Most of the additional currently available options to reduce the growth in absolute emissions are related to the dairy sector, which employs a greater diversity of management strategies and feed inputs than the almost entirely grazing-based sheep and beef sectors. The economic efficiency of those options will vary greatly between farms and farm systems and has not been assessed yet for New Zealand as a whole.
USE MORE LOW-NITROGEN FEED
New Zealand pasture-based diets provide more nitrogen to animals than necessary for their optimal growth and productivity. Livestock
excrete this surplus nitrogen in their dung and urine, where it contributes to nitrate leaching and nitrous oxide emissions.
Dairy production in New Zealand is increasingly making use of supplementary feed to improve animal performance and balance
year-to-year and seasonal variations in grass growth. Many of the supplementary feeds contain less nitrogen than normal pastures and
thus could help reduce nitrous oxide emissions on farms. Feeds include domestically-grown supplementary feed, commonly maize silage, hay
and silage, and imported supplements, such as palm kernel expeller (PKE). Whether increased use of supplementary feeds is viable depends
on international milk prices and domestic environmental regulations. If feeds are imported from overseas, care also needs to be taken
to avoid ‘pollution swapping’ – where New Zealand could achieve emissions reductions and higher production by driving up emissions
offshore – and to keep an eye on any biosecurity issues.
REDUCE NITROGEN FERTILISER USE
Another option is to use less nitrogen fertiliser per hectare or per animal. This requires careful management of nutrient flows, for
example by using more purchased feed and/or growing forages with a higher yield per hectare, and optimising the use of animal manures.
Fertiliser use per animal increased throughout the 1990s and peaked around 2004, but has declined since while productivity per animal has
continued to increase. There is reason to believe this can be pushed further without compromising production, although it may increase
risk to farmers and require higher farm management skills. Reducing overall nitrogen fertiliser use would also help improve water quality.
MANAGE MANURE FROM HOUSED ANIMALS
Dairy production in New Zealand is intensifying; temporary housing is becoming more common to avoid pasture damage in wet weather, or to
control nitrate leaching to waterways. Confinement of animals means that a greater proportion of dung and urine can be captured and treated
before being spread back onto land. Farmers can avoid spreading manure when soils are wet and nitrous oxide emissions and nitrate
leaching losses are high.
But there are two key challenges:
- more research is needed to determine the potential nitrous oxide reduction from spreading manure at different times, compared to
urine and dung being deposited directly
- storing manure generates methane from anaerobic ponds which may offset any reductions in nitrous oxide emissions. To make manure
storage a mitigation option, the methane has to be captured and either flared or used to generate biogas. This can be costly; options
and economic viability depend on the volume of manure treated.
The optimal balance between grazing and housing, and tools for minimizing emissions from housed animals, will continue to evolve over
the coming years and will also reflect other environmental goals such as reducing nitrate leaching.
MAINTAINING CARBON INPUTS TO SOILS
It has been difficult to demonstrate practices for New Zealand soils that reliably increase soil carbon, as the effectiveness of any management practice is highly dependent on climate and existing soil carbon stocks and management history.
Globally, one of the most robust good practices is to avoid overgrazing to ensure constant grass cover and production to continue carbon inputs
to soil and to reduce erosion risk. Farmers can also reduce the risk of soil carbon losses by avoiding too intense disturbance of the plant/soil
system such as frequent cultivation.
Overall in New Zealand, there is no consistent trend in soil carbon stocks in flat land. There is some evidence of increasing soil carbon
stocks in hill country, but the reasons for this are not clear yet (it could simply reflect a slow recovery of top soils following the initial clearing of
forests, or it could reflect improved management practices). Read more
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