How monitoring soil carbon content can boost productivity

Measuring soil carbon content is providing growers with valuable insights for farm management – while helping to generate income from the government’s Sustainable Farming Incentive.

“There’s so much evidence of a direct and linear relationship between soil organic matter and soil function that carbon content is rapidly becoming one of the most important management KPIs in crop production,” says NRM agronomist Allison Arden.

“It is an essential indicator of a farming business’s overall viability and production potential, but there are wider implications of developing management practices that build soil carbon content too.

At farm level, improved soil carbon content is linked to a multitude of benefits, says Ms Arden. These include better soil structure, more efficient key nutrient use, improved moisture retention, healthier soil biology and greater overall resilience.

“Soil carbon content is a very good starting point in itself but there are many associated areas that give additional insight into what is really happening in the soil.”

Natural assets

Many people use NRM’s CarbonCheck system to evaluate the natural assets across their farm to get a handle on their existing carbon stocks and to start their own carbon capture journey, adds Ms Arden.

“Those joining the new SFI scheme also use the analysis to ensure they meet their soil action obligations and have supporting evidence for their claims.

“But the ones that benefit the most are definitely those that use the service beyond this and realise it’s an invaluable tool in helping them fine-tune their management, reduce input costs and improve crop production efficiency.

“Measuring a range of parameters associated with soil carbon content is a very effective way to monitor soil health and production potential.

“Benchmarking on-farm results to national and regional best practice then allows producers to make the most informed decisions about adopting and integrating more long term sustainable farming practices.

“CarbonCheck measures organic and active carbon as part of a comprehensive suite, as well as total carbon, inorganic carbon, carbonate classification and bulk density.”

This not only gives details on traditional information such as organic matter, but combines information from a number of different carbon measurements, total nitrogen and the C:N ratio, explains Ms Arden.

“Active carbon, for example, is a management tool that looks at the readily available portion of soil carbon that provides the immediate food source for soil microbes that is easily digested and turned over by the soil microflora.

“Importantly it’s also the precursor to building humus-type organic matter which is the type that can really lock away carbon in a more permanent state.”

Soil bulk density measurement is also an important consideration, says Ms Arden. “The denser and more compacted the soil the less effective the soil microflora are able to function and process organic inputs and residues.

“The better structured and more open the soil texture, the more efficiently the biology can work and the better it can turn over and recycle key nutrients.

“Carbon to nitrogen ratio is also an increasingly important area to look at with regard to crop nutrition particularly when aiming to get the most out of every kg of nitrogen from environmental, crop production and cost perspectives.

“The proportion of organic carbon relative to nitrogen gives an indication of the right balance for soil microbes to aid the release of nutrients with the optimum C:N ratio for nitrogen release being between 10 and 12.

“So again, it’s a great example of how managing and improving the carbon content of soils can have a significant effect on cost-effective use of inputs and overall productivity.”

Soil types

Whilst there is a lot producers can do to build carbon content from a management perspective, some areas are less flexible, says Ms Arden.

“One of the key drivers behind how easily you can build soil organic content is the type of soil and in particular the clay content.

“Clay content does drive organic matter and generally speaking we know grass-based production systems on more medium to heavier soil types have the most carbon and organic matter in them.

“In arable soils in areas like East Anglia, where much of the arable land is lighter textured, organic matter can be as low as 1 – 2%. Drier soils tend to be lower in organic matter too.

“According to AHDB, using green composts as your organic fertiliser source can lead to a 25% improvement in soil carbon levels in nine years; the same improvement can be achieved from FYM in 20 years and 20 years of using livestock slurry results in just a 7% change.”