SOM #3: managing carbon – a case study

Optimal soil organic carbon (SOC) levels has been proven to lead to increased microbial activity and enhanced nutrient supply. This helps growers sustainably maintain and raise yields — and, in light-textured soils, SOC is also essential in helping improve water and nutrient retention.

Additionally, if you want to benefit from environmental schemes or emerging carbon markets, benchmarking and raising soil carbon levels will help you transition towards more sustainable practices and take advantage of new income streams.

If you haven’t read my first blog on managing SOM and carbon, click here, or for my second blog on SOM and carbon data, click here.

Otherwise, read on for a deep dive into NRM’s soil organic carbon data from the last few years, as well as how Grosvenor Estate Farm utilised their carbon analysis results to target their management practices.

Total Carbon Stocks (TCS)

NRM has been diving into the data banks to look at carbon stocks in different systems. We have found that the amount of carbon measured in the soil is significantly influenced by the enterprise and how the enterprise is managed. The data in the chart below describes the distribution of total carbon stocks (t/ha) categorised by arable, livestock or mixed systems.

It is clear to see that soil originating from livestock systems has a higher TCS. Most livestock soils measured were between 91 and 140t/ha, but some were as low as 34t/ha or as high as 161t/ha (TCS). The median value was 113t/ha, which was 31% higher than soil measured from arable systems and 20% higher than soil measured from mixed systems.

Soils analysed from mixed systems also had a very wide range, which is probably due to the type of mixed system—that is, the intensity, how many animals the enterprise has, the type of animal, and so on.

However, the data does suggest that running a livestock enterprise alongside arable crops is, on the whole, better than just growing crops. The arable system had the lowest median TCS value, but the range was large, between 28t/ha and 178t/ha, so some arable producers are doing a good job of preserving soil carbon content.

Case study: how the Grosvenor Estate boosted productivity on farm with soil carbon analysis

The Grosvenor estate near Chester in Cheshire has been looking at how they can maintain and increase the organic matter and carbon content of their soils. Charlie Steer is the farm manager of the 2,350-hectare arable and dairy enterprise, and asserts that monitoring soil carbon content has helped boost the business’ productivity and fine-tune sustainable farming practices for the future.

The Grosvenor Estate believes that soil carbon is an essential indicator of the farming business’ overall viability and production potential. However, there are wider implications of developing management practices that build soil carbon content, too. At farm level, for example, improved soil carbon content is linked to a multitude of benefits, such as better soil structure, improved key nutrient use, better nitrogen utilisation efficiency, improved moisture retention, and healthier soil biology.

At a recent visit, Charlie stated that one of Grosvenor Farm’s key business objectives is to build soil carbon content year-on-year. This is in line with its journey towards being fully carbon-neutral by 2030. He commented that the farm has always been carbon-aware producers, but just hasn’t fully recognised it as such until recently.

‘Like all things: it’s not until you start measuring different aspects of your management that you can get a handle on what matters,’ Charlie said.

Charlie has found that tangible improvements on the arable side of the business have largely been down to using manures to build organic matter.

‘The farm applies separated solid and liquid manures from the dairy herd, plus a bit of farmyard manure,’ Charlie continued. ‘All of these are tested regularly by NRM before being spread so that we know exactly how much N is being applied and to ensure that P and K remain on target. Our business is definitely trying to reduce dependence on bought-in nitrogen, and doing so is of increasing priority.’

In last year’s ADAS YEN Zero initiative for combinable crops, the farm ended up within the top 10% of farms, with the lowest kg of CO2 equivalents per tonne of output—all without applying any manufactured nitrogen.

At the moment, just 33% of the combinable crop’s nutrition comes from non-organic sources. Charlie believes that this is a major reason behind the improvement in soil health and the increase in organic matter. A few years ago, the farm averaged 5% SOM, which has since increased to 5.5%. As typical values for cultivated land are around 3%, improvements are clearly being made.

Another significant factor in building SOM has been changes in the rotation, which have allowed fewer cultivations to be used. The farm ploughs very little land and they have a six-year arable rotation with three winter wheat crops interspersed with barley, a wholecrop cereal, or oats, oilseed rape, or forage rye. Cover crops and stubble turnips are also grown. With land also going into rotational grass and clover, it’s an approach that is starting to improve the health and carbon content of the soils.

The Grosvenor Estate is hosting the 2024 RABDF Down to Earth event, on Wednesday the 3rd of July. Click here to find out more and get tickets.

NRM: here to help

Measuring soil organic matter and soil carbon couldn’t be easier. NRM’s CarbonCheck services include soil organic matter analysis to help you qualify for the SFI, improve soil health, and get a head start on your carbon capture journey.

Click here to contact us directly or speak to your adviser for further information.