Laying the net-zero egg
This article was originally produced for Arable Farming magazine’s August 2022 issue. It is based around a case study of AJ Duncan Farms, a large Scottish farm with arable and poultry enterpries; they use Sandy, by Trinity Agtech. It was written by Tom Allen-Stevens, a freelance journalist and Trinity Agtech contractor.
How does a high-production, integrated farm reduce its carbon footprint without compromising the ability to produce food?
As the rainclouds roll back after the morning’s downpour, a flash of sunlight glances across the winter barley crop – part of 800ha grown by AJ Duncan Farms near Turriff in Aberdeenshire.
By any account, it’s a stunning crop, and although only March, the tillers have filled out to occupy every pocket of bare soil to present an even spread of biomass that glints its potential in the spring sunshine.
“I’ve high hopes for this crop,” comments arable manager Sandy Norrie as he looks on. “Last year’s winter barley did 9t/ha, bringing our five-year average up to 8.9t/ha. This year, we might just push that even further.”
A dogged pursuit of yield drives the business’ arable enterprise across the 2430ha it crops over 24 farms. The land varies from sandy loams to sandy clay loams. There’s also winter wheat, oilseed rape and smaller areas of winter oats and spring barley in the rotation, with all the wheat and feed barley channelled towards the egg-production side of the business. There are 450,000 free-range laying hens spread across 10 sites, making the farm one of Scotland’s leading producers.
Now there’s a new goal for the business: the net-zero egg. Joining Sandy for the tour around the farm is Alistair McBain, the farm’s rearing and production development manager, who’s been tasked with tracing the carbon emissions across the farming enterprises and identifying where reductions can be made.
“80% of the carbon footprint on the poultry side comes from feed, and 80% of that is down to the soya in the diet,” says Mr McBain. “We can look to more sustainable sources of soya, but that only makes up 21% of the diet. It may also deflect from what we can do to reduce emissions for our home-grown feed, and perhaps reduce dependence on bought-in soya.”
So this brings the focus back to the arable side of the business. Mr Norrie explains that it’s an unashamedly high-input system refined to achieve the results they’re looking for.
The net-zero egg
80% of the carbon footprint of AJ Duncan Farm’s poultry comes from feed and 80% of that is down to soya. More sustainable soya is important, but it shouldn’t deflect from reducing home-grown emissions too.
“We tailor variety choice and inputs to the situation and task in hand, but don’t skimp and believe in using the latest technology in getting the crops to perform. This crop is SY Kingston hybrid barley, for example, but we’re also now looking at the BYDV-tolerant six-row conventionals. We’ll use SDHI and strobilurin chemistry at both the T1 and T2 spray timings, and apply a T0 of Helix (prothioconazole+ spiroxamine) where mildew is a problem.”
With the wheat he “hand picks” varieties for high-yielding, low protein performance.
“We’ve worked hard to adapt the rotation and bring in more wheat to replace bought-in feed,” says Mr Norrie. “We’re getting on really well with soft group 4 wheat KWS Colosseum that yielded over 11t/ha last year, while our five-year average yield is 9.8t/ha. SY Insitor is another wheat that suits us well.
“These will get a four-spray fungicide programme, with an SDHI at T1, followed by Univoq (fenpicoxamid+ prothioconazole) or Revystar (fluxapyroxad+ mefentrifluconazole) at T2 and a strob at T3.”
The feed cereals benefit from 5t/ha of chicken litter made just before ploughing, with the sample analysis showing each tonne delivers 9.5kg of N, 8.5kg P, 8.5kg K and 4kg SO₃. “
Where restrictions prevent us spreading, we’ll always apply 30kg/ha of P down the spout at drilling to get the crop going.
“Traditionally we’ve used 0:24:24 to maintain indices, but recent soil analyses indicate a switch to 0:20:32 would suit us better,” he adds.
Two Agrifac 36m sprayers with 5000-litre tanks are kept busy through the spring with a “little and often” liquid fertiliser policy, along with applying agrochemicals. An NKS dressing of 19.8:0:9.8 + 5 SO₃ is followed by usually two splits of N35 to bring total applied to the wheat of 180kgN/ha.
OSR forms the prime break crop with a “hard and fast” rule not to grow the crop closer than one year in five to limit clubroot. Mr Norrie moves to the field next door of the variety Aurelia and takes a trowel to a couple of plants to inspect the root and the soil below. This reveals a strong tap root while unearthed worms indicate a thriving soil biota.
“Our five-year average yield is 5t/ha, but this could yield closer to 6t/ha,” he says. The OSR management follows the same high-input strategy as the cereals, with variety carefully tailored around clubroot risk and favouring hybrids for their advanced traits.
While the OSR is sold off the farm, Mr Norrie drives next to a freshly drilled and rolled field that may present a new opportunity to both increase the home-grown feed and reduce carbon emissions. “This is 26ha of Raptor spring beans,” he says.
“It’s not a crop many people grow in this part of Scotland, and I’m reserving judgement on its potential for us. What we cannae afford to do in reducing our carbon footprint is to reduce overall production.”
Reducing tillage not always straight forward
Mr Norrie agrees that reduced tillage is a powerful tool for reducing carbon emissions; however, this isn’t their current priority. The focus in on food production.
And this is the balance that matters the most for the business. Mr Norrie explains the cultivations system is very much plough-based and he feels this is the best way to manage the high-production potential of the soils. A 6m Lemken power-harrow combination drill and Horsch Pronto give the farm the drilling flexibility it needs. Monitoring reports show that average soil organic matter (SOM) levels are rising, however, and currently stand at around 5%.
“We used to min-till much of the OSR with a He-Va five-leg subsoiler and Opico seeder box, but found the plough still brought the best results. This year we’re planning a min-till trial of 200ha of wheat. But sterile brome can be a problem for us, that min till could make worse. With the plough-based system costing us £70/ha, there’s no cost benefit from switching out of it but there could be a lot to lose,” he notes.
The farm also has an experimental 40ha of summer cover crops and is exploring their potential. “These are on land with old tile drains and I’m hoping the roots may act as a green drainage system, as well as offer carbon savings,” notes Mr Norrie.
Reducing the emissions isn’t all down to the arable side, however. On the way back to the office, Mr McBain points out one of around 30 wind turbines that frame the landscape.
“The farm has a sister company, Muirden Energy, with around 40% of our energy now coming from renewable sources. This includes 50kW solar arrays at each of the poultry sites and six biomass boilers, with a smaller one heating the farm office,” he explains.
The scale of the operation is revealed in the buildings just behind the farm office. Home-sourced timber is chipped, dried from 45% to 15% moisture and then fed into the large boilers.
And the business has one other natural capital asset with carbon sequestration potential. Garty Estate in Caithness is an upland holding of 1400ha, uncropped but home to a flock of around 900 north country cheviot breeding ewes.
“Within the estate there’s 80ha of peat and we’re currently discussing a peatland restoration scheme, and we’re looking at planting trees on less productive areas across our farms,” says Mr McBain.
“Despite all we’re doing on the renewable energy side it will still be a challenge for us to achieve the net-zero egg. But we’re confident we can and want to reduce emissions on the production side before we look to offset them elsewhere.”
Peatland potential
The estate is home to 80ha of upland peat, which is being considered for a peatland restoration scheme.
Peatland is a highly effective carbon sink so restoring or managing even small areas can have a disproportionately significant effect on carbon mitigation strategies.
Productivity priority shapes the carbon savings
While there are a number of carbon tools available, Duncan Farms has taken the decision to use Sandy by Trinity AgTech to determine its balance of emissions. Sandy is a software tool that brings in the farm’s data from Gatekeeper records. It accurately assesses emissions across enterprises, including the poultry side and brings in the woodland sequestration, too.
Sometime after the visit, Sandy Norrie and Alistair McBain join Trinity AgTech managing director for science Jonathan Hillier for a Zoom call to discuss opportunities to reduce the carbon footprint.
“Fundamentally, there are two routes – one is to reduce emissions while the other is to raise productivity,” explains Prof Hillier.
“Switching to home-grown feed from bought-in soya does present an opportunity on both fronts. The standard figures for soya are that every tonne used may carry with it up to 4-5t of CO₂ emissions. 60-80% of this footprint is the land-use change associated with imported soya, so the first step is to assure that the imported soya is not associated with deforestation.”
A different protein source in the diet firstly has to maintain the level of productivity in the laying hens. But the change on the arable side must also be taken into account.
“Crops vary significantly in their carbon footprint because both yield and the nature of inputs differ. Switching protein source from soya to beans can offer a big reduction in emissions for the poultry. But it could be counterproductive for the arable rotation.”
Prof Hillier explains that conventional cereals and oilseed rape have a relatively high carbon footprint – 70% of this in cereals is the use of synthetic fertiliser. Every tonne of home-grown beans that displaces soya reduces the poultry emissions, while growing the leguminous crop in place of cereals or OSR will also reduce fertiliser requirement.
“But the area required to grow beans could disproportionately displace from the rotation a large tonnage of cereals or oilseeds. That may not only be a financial hit, but could result in having to buy in more wheat grown with a higher carbon footprint than home-grown.”
Carbon footprinting the whole farm
In recent years, AJ Duncan Farms have planted 68,000 trees and over 20km of hedgerows. Sandy’s ability to footprint woodland alongside arable and poultry enterprises was a significant benefit.
So could the crops be grown more efficiently?
“The level of production is already high, so relatively efficient on a per-tonne basis. The biggest source of emissions will be synthetic fertiliser, but some of this has already been displaced by chicken litter, so I suspect nitrogen use efficiency for the business is already quite high. Many people assume that agrochemicals have an important impact on the carbon footprint but in reality the contribution is fairly small – around 2-4% of the total.”
One area of potential efficiency savings could be gaseous ammonia emissions and leaching.
“Gaseous losses here can reach around 15% of the available nitrogen, and leaching can be more than this, so urease and nitrification inhibitors are worth considering. Incorporating straw can also aid carbon sequestration. Every tonne of straw added to the soil equates to nearly two tonnes of CO₂e sequestered. Although much of this is released as it breaks down in the years following incorporation, the sequestration can still be substantial.”
Reducing cultivations can have a big effect – firstly, fuel use generally accounts for 10-12% of arable emissions, he notes.
“What’s more, by not moving the soil you retain its carbon, and if SOM increases, that can dwarf everything else – it can make a difference of 1-2t/ha of CO₂e. However, if farm monitoring records show the SOM is already building, the relative benefit would be lower.”
With the poultry units already making good use of renewable energy, Prof Hillier notes that Duncan Farms has correctly identified feed and specifically imported soya as the key opportunity for big reductions in carbon emissions without big losses in productivity.
“There is potential to produce a zero-emissions egg and the farm is already on that path by reducing dependence on imported soya. The advantage of Sandy is that, once you have your baseline calculation, you can run optimisation plans that give you a realistic outcome for your business in both financial and carbon terms.”
Mr Norrie agrees.
“Ours is a business that feeds a lot of people, and we can’t risk making changes that compromise that ability. I think there may be potential to raise nitrogen use efficiency, though, and I’d be interested to look at the difference reducing cultivations or chopping and incorporating straw makes. Understanding the benefits a bean crop may bring will also be key. But we must look at the changes over the entire business – productivity remains the priority,” he concludes.