This is a subscriber-only article
The challenge of reducing greenhouse gas (GHG) emissions at farm level was the focus of discussion during last week’s cereal monitor farm meeting in Ballykelly.
The monitor farm programme is run by the Agriculture and Horticulture Development Board (AHDB), with the Northern Ireland representative being Alistair Craig.
Alistair farms with his father Robert and uncle Thomas, running a mixed operation of 220 pedigree Holstein cows, and cereals on a 500-acre unit split evenly between grassland and cropping.
Cereals grown are used on farm as feed and bedding for the dairy herd. Slurry and farmyard manure are then returned to cropping land as a soil conditioner and fertiliser.
Alistair has served as the NI monitor farmer since July 2022 and relays his experiences in growing crops to other farmers during regular discussion group meetings.
Carbon audit
During last week’s meeting, the results of a carbon audit for the Craigs'' farm were detailed by environmental consultants working with ADAS in Britain using the Agrecalc calculator.
Figures produced gave a combined farm total (Table 1), as well as separate analysis for the dairy herd and cereals.
The results published were expressed as a CO2 equivalent (CO2E) for every litre of milk produced on farm and per kg of grain.
Over the four years of data analysed, there has been a 5% reduction in total farm emissions from 3,209t CO2E during the baseline year of 2020 to last year’s 3,040t CO2E.
The main driver for that reduction is a 30% drop in purchased feed from 705t to 494t CO2E/year.
However, that figure has to be put into context, as back in 2020, there was a trial to see how little fertiliser could be applied before yields were significantly reduced.
“We pushed it too far and as a result, homegrown feed was severely reduced, because not enough fertiliser was applied. That meant we ended up buying in additional forage and concentrate to make up the shortfall in feed for the cows.
“Purchased feed in 2022 and 2023 would be more reflective of what we use, so the overall drop in CO2E is not as big as it would initially appear,” Alistair outlined.
That said, emissions from fertiliser use are down 15%, as the farm switches to liquid and foliar products rather than granulated products.
Carbon dioxide equivalent or CO2e is a term used to describe the climate impact of different GHGs in a common unit.
For example, nitrous oxide added to the atmosphere has an impact that is 298 times more severe than CO2, so the emission of 1t of nitrous oxide is the equivalent of 298t of CO2.
Dairy unit
Breaking the audit down to enterprise level, the dairy herd has reduced CO2E levels from a base of 1.25t to 1.2t CO2E per litre of milk produced in 2023.
As shown in Table 2, that is lower than the average of all other dairy units measured through the carbon calculator.
Cow numbers have been relatively static during this period, with enteric fermentation (emissions from ruminants) accounting for close on 50% of total emissions.
Slurry and manure are the second largest contributor to emissions, followed by purchased feed. This is likely to fall in future, with protein crops like beans now in the rotation for homegrown feed.
Cereals
While CO2E per litre of milk is lower, the equivalent value has increased per kg of grain as outlined in Table 3, rising by 36% from the baseline to 2023 levels for winter barley.
Fertiliser and organic manure from the dairy unit makes up two thirds of this figure.
Limitations
While carbon auditing will play a major role within farming over the coming years, there are serious flaws and limitations to the figures produced during such exercises.
In the case of the Craigs’ farm, that is evident in the increase in emissions attributed to the cereal enterprise.
The wet summer and autumn of 2023 led to a disastrous harvest. Grain yields were significantly reduced as a result, due to in-field losses and delayed harvesting.
As grain yields were lower in 2023, this automatically increases CO2E per kg of grain as a paper exercise and was raised during group discussion.
Alistair has also started using minimum cultivation methods to plant cereals, rather than conventional ploughing.
While there have been financial savings with less diesel used to establish crops, in terms of carbon savings, the difference is negligible year on year.
Higher output
Alistair raised a similar concern with the auditing of the dairy enterprise. In recent months, there has been a move to ease back annual yields per cow.
So far, this is having a positive impact, as it has practically eliminated lameness within the herd.
Fertility has also improved, with more cows holding to first service and, if maintained, this should lower herd replacement rates and enteric emissions.
But with less milk being produced, physical herd benefits are slow to filter through to CO2E per litre.
The farm also has a wealth of mature hedgerows, is making use of cover crops and has wildlife habitats that are not being taken into account within carbon audits.
“From a purely carbon perspective, we would be better off increasing yields to reduce emissions on a per litre basis, but that is not profitable or sustainable.
“At the end of the day, we are focusing on farming as profitably and sustainability as we can.
“We are cutting fertiliser use, bought in feed and diesel use. These things will deliver an environmental benefit,” Alistair concluded.
SHARING OPTIONS: