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13 Sep 2022

Laying the net zero egg

As featured in Arable Farming Magazine

Laying the net zero egg

by Arable Farming Magazine August 2022 issue

How does a high-production, integrated farm reduce its carbon footprint without compromising its ability to produce arable crops?

A dogged pursuit of yield drives A.J. Duncan Farms arable enterprise across the 2,430 hectares it crops over 24 farms near Turriff, Aberdeenshire.

The land varies from sandy loams to sandy clay loams.

There is 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 across 10 sites, making the farm one of Scotlands leading producers.

Now there is a new goal for the business: the net zero egg.

Alistair McBain, the farms rearing and production development manager, has been tasked with tracing the carbon emissions across the farming enterprises and identifying where reductions can be made.

About 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.

Arable manager Sandy Norrie explains that it is an unashamedly high-input system, refined to achieve the results theyre looking for.

He says: We tailor variety choice and inputs to the situation and task in hand, but dont skimp and believe in using the latest technology in getting the crops to perform.

Wheat varieties are ‘handpicked for high yielding, low protein performance.

Weve worked hard to adapt the rotation and bring in more wheat to replace bought-in feed, says Mr Norrie.

Were getting on really well with soft Group 4 wheat KWS Colosseum that yielded over 11 tonnes/ha last year, while our five-year average yield is 9.8t/ha.

SY Insitor is another wheat that suits us well.

Analyses The feed cereals benefit from 5t/ha of chicken litter applied just before ploughing, with the sample analysis showing each tonne delivers 9.5kg of nitrogen, 8.5kg phosphorus, 8.5kg potassium and 4kg SO3.

Where restrictions prevent us spreading, well always apply 30kg/ha of P down the spout at drilling to get the crop going.

Traditionally weve used 0:24:24 to maintain indices, but recent soil analyses indicate a switch to 0:20:32 would suit us better, Mr Norrie adds.

Two Agrifac 36-metre sprayers with 5,000-litre tanks are kept busy through 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 180kg N/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.

The OSR management follows the same high input strategy as the cereals, with variety carefully tailored around clubroot risk and hybrids favoured for their advanced traits.

This season the farm is also growing a 26ha crop of spring beans, which may present a new opportunity to increase the home-grown feed and reduce carbon emissions.

Its not a crop many people grow in this part of Scotland and Im reserving judgement on its potential for us.

What we cannot afford to do in reducing our carbon footprint is to reduce overall production, says Mr Norrie.

Potential 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 powerharrow combination drill and Horsch Pronto give the farm the drilling flexibility it needs.

Monitoring reports show 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 were 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, theres no cost benefit from switching out of it but there could be a lot to lose, he says.

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 Im hoping the roots may act as a green drainage system, as well as offer carbon savings, says Mr Norrie.

Reducing emissions isnt all down to the arable side, however, with around 30 wind turbines framing the landscape.

Mr McBain says: 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.

And the business has one other natural capital asset with carbon sequestration potential.

Garty Estate, Caithness, is an upland holding of 1,400ha, uncropped but home to around 900 North Country Cheviot breeding ewes.

Restoration Within the estate theres 80ha of peat and were currently discussing a peatland restoration scheme and looking at planting trees on less productive areas across our farms, says Mr McBain.

Despite all were doing on the renewable energy side it will still be a challenge for us to achieve the net zero egg.

But were confident we can and want to reduce emissions on the production side before we look to offset them elsewhere.

Productivity priority shapes the carbon savings

While there are several carbon tools available, Duncan Farms has decided to use Sandy by Trinity AgTech to determine its balance of emissions.

Sandy is a software tool that brings in the farms data from Gatekeeper records.

Its claimed to accurately assess emissions across enterprises, including the poultry side and brings in the woodland sequestration, too.

Trinity AgTech managing director for science Prof Jonathan Hillier says there are essentially two routes to reducing agricultures carbon footprint.

One is to reduce emissions, while the other is to raise productivity, he says.

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 and 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 must firstly maintain the level of productivity in the laying hens.

But the change on the arable side must also be considered.

Crops vary significantly in their carbon footprint because the 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.

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 agrochemicals have an important impact on the carbon footprint but in reality the contribution is fairly small around 2-4% of the total.

Efficiency savings 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.

Whats more, by not moving the soil you retain its carbon, and if soil organic matter 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.

Mr Norrie agrees, saying: Ours is a business that feeds a lot of people and we cant risk making changes that compromise that ability.

I think there may be potential to raise nitrogen use efficiency, though, and Id 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.

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