Reducing carbon emissions won’t be easy

Reducing carbon emissions won’t be easy

Friday, October 18, 2019

A case study of greenhouse gas emissions on deer farms has shown that only small reductions in emissions can be achieved by making management changes, short of reducing the number of livestock on the farm.  

Farms with land classes that are suitable for other uses, such as carbon and/or production forestry, or cash cropping, are likely to have the greatest ability to reduce their emissions when farming is included in the Emissions Trading Scheme.

Converting parts of a farm to forestry is one of the few ways farmers can significantly reduce emissions, but under proposed legislation carbon forests cannot be used to offset a farm’s methane emissions

The study by environmental agribusiness consultant Alesha Cooper, from AgFirst Manawatu-Whanganui, was of four farms selected by DINZ to represent typical deer farms, two on North Island hill country, one on South Island high country and one on South Island flat to rolling country. Two of the farms were breeder/finishers, one was velvet-focussed and the other was venison finisher. Carbon emissions were estimated using Overseer FM.

All four farms were running deer, cattle and sheep, with ratios ranging from 22% to 79% deer. In all cases, sheep had lower carbon emissions per stock unit than deer or cattle, which had similar emission levels.

The effectiveness of mitigation options depends on the farm. Options might include:

  • Increase per animal performance and lower stocking rate (opportunity to maintain or improve profitability while reducing dry matter intake and therefore methane emissions).
  • Reduce the rate at which breeding females are replaced (opportunity to maintain performance while reducing feed demand).
  • Improve breeding performance (increase lambing & fawning percentages).
  • Optimise N fertiliser use (reduce nitrous oxide emissions).
  • Reduce N intake by using low N feeds such as grains and fodder beet. However these feeds need to be a major part of the diet to have much effect.
  • Increase the ratio of lower-emitting stock classes, for example by going from 40% sheep to 60% sheep.
  • Reduce the number of breeding animals, for example by replacing breeding cows with finishing bulls (this increases feed efficiency, by channelling more feed to production rather than herd maintenance).

These and other options were assessed on the sample farms, but even if several mitigations were adopted and the resulting emissions reductions added together, the net benefit was unlikely to be more than 5%. The most significant single reduction modelled was 5.7%, achieved by increasing the lambing percentage on one of the farms by 20%, which would allow a reduction in ewe numbers.

Much is made about the inability, under the proposed Zero Carbon Bill, for farmers to offset methane emissions with carbon forests, including shelter belts. If this rule is changed and offsets are allowed in trees planted since 1989, the offsets earned by the four case study farms from existing plantings would range from nil to 46.5%.

Cooper emphasises, however, that forestry is not a permanent solution for offsetting GHG emissions, as an additional area of trees needs to be planted after every harvest.

“For example, if we assume 100 ha of radiata pine forestry is sufficient for offsetting emissions on a farm, after 28 years the forest would reach maturity and need to be harvested. At that time the initial 100 ha would need to be replanted to offset the carbon removed at harvesting, plus an additional 100 ha would need to be planted to offset continuing emissions. At the second harvest, the 200 ha would need to be replanted, as well as an additional 100 ha; and so on,” she says.

“If you are considering forestry for carbon sequestration/offsetting it is important to get good advice.”

Cooper says a number of mitigation options may become available in the future, including methane and nitrification inhibitors.

A methane inhibitor for deer would need to be delivered by way of a slow-release bolus, or another technology that did not require animals to be frequently handled. Nitrification inhibitors have been shown to reduce nitrous oxide emissions, but they can’t be used on NZ farms because there is no internationally accepted tolerance for their use on feeds eaten by food animals.

Methane emissions also vary from animal to animal, a difference that is thought to have a genetic basis, so selecting for low-emitters may one day be possible.

To read the study summary report and individual farm reports >>