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31 August 2022

Technologies for Today and Tomorrow to Reduce Greenhouse Gas and Ammonia Emissions

Technologies for Today and Tomorrow to Reduce Greenhouse Gas and Ammonia Emissions

On Stand No 2 at the Farming for a Better Future Open Day in Teagasc Johnstown Castle, Karl Richards and Gary Lanigan, Teagasc discuss the steps that farmers can take to reduce on-farm emissions. View the live boards and presentations here on Teagasc Daily

View the board and detailed information on Stand No 2 live from 'Farming for a Better Future Open Day' at Johnstown Castle

Introduction

Agriculture has been set a challenging sectoral target of reducing greenhouse gas (GHG) emissions by 25% or 5.75 Mt CO2e by 2030. Abatement measures that reduce GHG emissions associated with agriculture, land-use and bioenergy were previously assessed in Teagasc’s 2018 Marginal Abatement Cost Curve (MACC). In light of the new targets, this analysis is being revisited and extended to include extra measures currently under research. The ammonia targets also pose considerable challenges, with reductions in emissions from the current 120 kT NH3 to 112 kT NH3 needed by 2030, and further reductions to 107.5 kT NH3 required post 2030. Many of the technologies will reduce both greenhouse gas and ammonia emissions.

In order to reduce on-farm emissions, there are four steps that can be taken.

Step 1: Reduce Nitrogen (fertiliser and manure) emissions

Nitrous oxide emissions (N2O) have increased by 6% since 1990 but are relatively static compared to 2018. Mineral fertiliser application is the principal source (37%) of N2O emissions as well as being a key input cost for farmers. In addition urea fertiliser accounts for 12% of ammonia (NH3) emissions that can be readily reduced. Reducing fertiliser use can both reduce GHG and NH3 emissions and improve margins. The main fertiliser reduction strategies are:

  1. Get soil fertility correct. Moving from pH 5.5 to 6.3 can release between 50 – 70 kg N ha-1 per year as well as reducing N2O) emissions per kg N applied.
  2. Use legumes (clover) or multi-species swards. Clover can fix between 80 – 120 kg N ha-1 per year depending on underlying soil fertility and sward management. Multi-species swards also offer extra benefits in terms of drought resistance and cow health. However, care must be taken to ensure adequate dietary roughage (hay or straw) in order to avoid bloat.
  3. Apply slurry using LESS. Slurry nitrogen fertiliser replacement value can be increased (and ammonia emissions reduced) by between 25% - 50% by using trailing hose (dribble bar) or trailing shoe technology. However, for these measures to work, N fertiliser application must be decreased by the amount of N that each measure saves, otherwise there is little or no GHG saving. If mineral fertiliser must be applied, then switching from either CAN and straight urea to protected urea will directly reduce both GHG and NH3 emissions.  New research on low emission compound fertilisers has found that N2O emissions could be reduced around 40%.

Step 2: Reduce Enteric and Manure methane and NH3

 

Methane comprises the majority (70%) of agricultural GHG emissions, which is split between methane from enteric fermentation (87%) and manure methane (13%). While manure methane is the smaller source, it is the easier source to reduce emissions.

  1. Acidification with hydrochloric acid or ferric/aluminium chlorides to pH < 6 has been shown to reduce both methane and NH3 by 86% and 98%. Ongoing research is quantifying N2O), NH3 and CH4 emissions from landspreading of acidified manure to refine the national inventory. New research is investigating the efficacy of a range of manure additives and acidifying compounds on reducing emissions.
  2. Lower cost alternatives, such as dairy washings or grass silage effluent (at a 7% inclusion rate) has shown a 50-60% reduction in methane, although reductions in ammonia emissions were much lower (Kavanagh et al. 2021).
  3. Covering external stores. This measure reduces NH3 emissions by between 40% for floating covers, 60% for flexible covers and 80% for tight lid covers. It can also reduce methane if it is subsequently flared.
  4. Aeration can also reduce methane by up to 50%. However, NH3 emissions can be significantly increased depending on the aeration system being used.

In terms of reducing enteric methane, ongoing research for tomorrow’s technologies is showing that:

  1. Higher Economic Breeding Index (EBI). Increasing genetic merit via EBI reduces GHG emissions per unit of product by 2% for every 10 euro increase in EBI. There are also some indications that higher EBI cows may have lower associated methane yields.
  2. Feed additives can reduce methane. Several research trials are currently being conducted into the use of feed additives in bovine and sheep diets. Current data shows that bovines fed 3-NOP as part of a TMR diet exhibit a 30% reduction in methane emissions, while grazing dairy cows fed 3-NOP twice daily (during milking) are exhibiting an 8% reduction. The introduction of seaweed extracts and other products is also being investigated.
  3. Reducing finishing times. The inventory is being updated and linked to ICBF data to allow a more dynamic counting of animal numbers than relying on June and December numbers. This will allow the benefits of early slaughter in the last decade to be accounted for. As animals are slaughtered earlier, the total amount of methane produced on an annual basis is reduced and could account for up to 0.8 MtCO2e yr-1.
  4. Increasing time at pasture (i.e. reducing the housing period) can also reduce enteric methane as results are showing that the methane emission factor during grazing is reduced from 6.5% to 5.75% of gross energy intake. 

Step 3: Enhance Carbon sequestration and reduce peat emissions

Land–use is currently a source of GHG emissions, but has been excluded from the sectoral targets for 18 months pending a land-use strategy review. However, several measures can assist farmers to lower their total on-farm emissions by enhancing C sequestration or reducing emissions from any peaty soils on their farms. 

  1. Afforestation and forestry management. One hectare of forest sequesters about 7 tCO2e yr-1. Increased afforestation, decreased deforestation and forest management (such as continuous cover) can all contribute to larger carbon removals. While afforestation will contribute little to 2030 targets, (with a linear increase in afforestation to 8,000 ha or 16,000 ha by contributing only 0.2 and 0.23 MtCO2e yr-1), increased rates are crucial for achieving Net Climate Neutrality by 2050. In the short term, forest management, such as reduced forest thinning or delaying clearfell until mean maximum annual increment has been achieved, will achieve larger sequestration rates. New research is beginning on the benefits of agro-forestry where forestry is coupled with grazed grassland strips.
  2. Cropland/Grassland management. Improved cropland and grassland management can also sequester additional carbon. In the case of croplands, which have low soil carbon levels, this is achieved by increasing inputs of organic matter (from straw, manure or winter green cover). In the case of grasslands, it is achieved by improved fertiliser, lime and grazing management. New research is underway to quantify C sequestration on mineral soils emissions from a range of land-uses and farm management practices.
  3. Hedgerows. Hedgerows can sequester C in both above/below ground biomass and via increased soil organic carbon. Current estimates have indicated that hawthorn-dominated hedgerows sequester between circa 3.7 t C ha-1 yr-1, while allowing hedgerows to grow out 1m either side and upward increases sequestration by 1 – 2 t C ha-1 yr-1 . Planting 20,000km of new hedgerows and increasing height and/or width of 50,000km by 1m could increase sequestration by circa 0.26 MtCO2e yr-1.
  4. Peat soil management. Altering the water level of organic (peat) soils that have been drained comprises a large emissions saving (0.8Mt CO2e yr-1 for 40,000ha). Unlike forestry, this reduces CO2 emissions that are currently occurring rather than sequestering more C (although this will also occur, but very slowly). Drained peatlands represent a strong CO2 source (circa 20 tCO2 per annum) and account for a national CO2 emission source of 9 million tonnes CO2. New research is refining emissions from peatlands and quantifying the benefits of changing water table height.
  5. New research is underway to develop a Teagasc carbon farming decision support tool to assist farmers with reducing emissions and potentially monetising emission reductions and increasing carbon sinks. 

Step 4: Improve energy efficiency and displace fossil fuel

Farms can also reduce emissions by improving on-farm energy efficiency, while they can also contribute to wider energy decarbonisation via the use of biomass for heat substitution or solar PV/biogas/biomethane for electricity or gas power substitution.

  1. Energy efficiency & Solar PV: These measures include plate coolers to pre-cool milk, variable speed drives (VSD) on vacuum pumps, solar photovoltaics (PV) and heat recovery systems (additional to pre-cooling). All measures either reduce energy consumption or in the case of solar PV, generate energy. Cumulative GHG emissions reductions during the whole lifetime of each measure were 76.3, 25.5, 17.05 and 57.2 tCO2e per unit for plate coolers, VSD, heat recovery and solar PV, respectively.
  2. Wood thinnings/woodchip. Wood biomass is made up of harvested fuel-wood and sawmill residues for electricity and heat generation and waste wood for heat production. Biomass energy value of 2.5 MWh per tonne assuming a moisture content of 30%. This can deliver a fossil fuel displacement of 0.7 – 0.8 MtCO2e from 2022- 2030.
  3. Biomass/biomethane. Anaerobic digestion of biomass produced from Irish agriculture (i.e. grass-fed biomass) would produce biogas (55% methane) that could be used directly for heat and electricity generation. In addition, the biogas can be processed to the same standard as natural gas (bio-methane), and injected into the natural gas grid and subsequently used for a range of commercial purposes. Gas Networks Ireland has a target of 1.6 TWh/yr of biomethane production by 2030 which would displace 0.4 Mt CO2e yr-1. Research is currently looking at further optimising the AD process for grass and alternative forage feedstocks to improve biogas yields. In addition research is refining the GHG and NH3 emission factors associated with the land-spreading of digestate on soil as a fertiliser replacement. 

Authors:

Gary J. Lanigan1, Trevor Donnellan2, Kevin Hanrahan2, Cathal Buckley2, Dominika Krol1, Laurence Shalloo3, Jonathan Herron3, Sinead Waters4, John Spink5, Karl G. Richards1

  • 1Teagasc, Johnstown Castle, Co. Wexford;
  • 2Teagasc, REDP, Athenry, Co. Galway;
  • 3Teagasc, Moorepark, Co. Cork;
  • 4Teagasc, Grange, Co. Meath;
  • 5Teagasc, Oak Park, Co. Carlow.

Other resources & online information

Email: gary.lanigan@teagasc.ie

Teagasc Website: An Analysis of Abatement Potential of Greenhouse Gas Emissions in Irish Agriculture 2021-2030 (PDF)

NH3 Ammonia MACC (PDF)

See Johnstown Castle Open Day - Technologies for farms of the future 

Check out the hashtag #GrassSoilsTechnology