Mitigating the impact of Irish grass-based systems on climate change

Why is this research important?

Agriculture accounted for 37% of Irish national greenhouse gases (GHG) in 2022. The main GHG associated with agriculture are nitrous oxide (N₂O; sourced from synthetic fertiliser application, grazing, and manure management) and methane (CH₄; produced by ruminants and from manure management). Methane produced by ruminants is called enteric methane and is produced during digestion of feed by ruminants. Enteric CH₄ accounts for 65% of agricultural GHG emissions in Ireland. An emissions reductions target of 25% by the year 2030, relative to 2018 levels, has been set. Therefore, developing strategies of mitigating both CH₄ and N₂O will be crucial to meeting our climate targets. There is currently a large programme of work underway in Teagasc to learn more about enteric CH₄ emissions with a view to developing strategies to mitigate it by breeding for more efficient and low CH₄ emitting cows, and using animal nutrition to reduce CH₄ output. 

What the research tells us

Enteric methane

Research has investigated the impact of selecting dairy cows using the Economic Breeding Index (EBI) on CH₄ production. Results showed no difference in CH₄ production per cow between high EBI (€233) and average EBI (€133) cows, however, the increased milk solids output of the high EBI cows results in lower CH₄ being produced per kg of milk solids. This study also highlighted the variation in CH₄ output between individual cows at pasture, indicating that it may be possible to select cows for lower CH₄ production in the future. However, the generation of breeding values for traits such as CH₄ requires large quantities of records, therefore, research is continuing to identify proxies for CH₄ output.

Several experiments have also been conducted evaluating nutritional strategies to reduce CH₄ output in pasture-based systems. Incorporating clover into the grazing sward was found to increase total CH₄ output as a result of greater feed intake, however, when expressed per unit of dry matter intake, no differences were apparent between swards. Similarly, cows grazing mixed species swards containing grass, clover, plantain and chicory have been evaluated for their CH₄ output. This research found no impact on CH₄ output in comparison to standard grass-only swards.

Novel trials have also been undertaken to evaluate the efficacy of anti-methanogenic feed additives such as Bovaer in pasture-based systems. Bovaer was shown to last for short periods when fed to pasture-based dairy cows after morning and evening milking, with overall daily reductions amounting to 5%. Further work showed that reductions of 22-25% are possible when Bovaer is mixed continuously through forage and offered to animals indoors, while a buffer feeding study demonstrated reductions of 12% are possible when animals are fed silage with Bovaer mixed through it by night and grazed pasture by day.

A calcium peroxide-based feed additive, that could withstand the heat and pressure of the pelleting process, was also tested for its CH₄ abatement potential in grazing dairy cows. Cows supplemented with the additive produced, on average, 13.5 % less CH₄, however, this varied from 8.6% to 19.9%. Calcium peroxide supplementation also had a negative impact on milk solids output and dry matter intake. The variation in efficacy of the additive from week to week warrants future research on the correct dose rate of calcium peroxide as an anti-methanogenic feed additive for grazing dairy cows.  

Nitrous oxide

Agriculture produced 91% of total N₂O emissions in Ireland in 2022. The key emission sources include synthetic fertiliser application, deposition of excreta during grazing, and manure management. Some relatively easy steps can be taken on farm to reduce N₂O emissions. Protected urea is urea which has been treated with a urease inhibitor (NBPT) that prevents the conversion of urea to ammonia. The utilisation of protected urea instead of calcium ammonium nitrate (CAN) can reduce N₂O emissions by 70% relative to CAN, while growing the same quantity of pasture.

Similarly, the adoption of low emission slurry spreading equipment (LESS) to apply slurry in the spring will reduce N₂O emissions while tripling nitrogen availability in the slurry compared to spreading it later in the year using a splash plate. This will have a direct effect on GHG emissions and will also indirectly reduce chemical fertiliser usage through the increase in fertiliser value of slurry. An additional way to reduce chemical fertiliser is by incorporating clover into swards as it can fix between 90-120 kg N per ha per year depending on underlying soil fertility and sward management.

Climate change

Research is starting to investigate the future impact of climate change on pasture-based farming and identifying possible adaptation strategies. Preliminary findings show that while on average annual pasture yield should be increasing on farm, pasture growth pattern will change and the variability between years will increase. Due to milder weather, more pasture will grow during the winter but the utilisation of the extra pasture will be more challenging due to increased rainfall during winter. The variability of weather during summer months will also increase, and is likely to include more severe drought conditions, increasing the need for higher fodder reserves.

Outputs

Methane

• Teagasc Research on methane emissions in grazing dairy systems
• Enteric methane - facts and solutions
• Methane mitigation strategies within pasture-based dairy systems
• Evaluating enteric methane emissions within a herd of genetically divergent grazing dairy cows

Nitrous oxide

• First Steps to Reducing Emissions from All Farms - Reducing Our Reliance on Chemical Nitrogen
• Read more about Nitrous Oxide

Contacts

Methane: Hazel Costigan (Hazel.costigan@teagasc.ie)
Methane: Ben Lahart (Ben.lahart@teagasc.ie)
Climate adaptation: Elodie Ruelle (Elodie.ruelle@teagasc.ie)