Livestock soils nearing maximum carbon, Scottish study suggests
© Joaquin Corbalan/Adobe Stock The soil carbon content of many fields on beef and sheep farms may already be at or near equilibrium.
This could mean scope to increase soil carbon in livestock systems could be limited, meaning payments scheme rewarding livestock farmers for increasing soil carbon levels may have limited returns.
This is one of several take-home messages from a recent Scottish project undertaken by Farm Stock and funded by the Scottish government to help meet national net-zero targets.
The project involved working with 20 livestock farmers to develop a soil health scorecard.
A healthy soil must have good chemistry (such as pH, phosphate and potash levels), be physically well structured (no compaction) and biologically full of life, farmers were told.
See also: Grassland survey: More farmers seeing gains from testing soils
What did the study find?
The project, co-ordinated by Jonny Williams of Farm Stock, involved expert input from Kev Bevan of KBevan Consulting, Bill Crooks of Wardell Armstrong, and precision farming specialists SoilEssentials.
Mr Bevan made the following conclusions about what the wider industry could learn about soil testing and carbon:
- Organic matter powers biological activity in the soil, so measuring soil organic matter percentage is an indicator of soil biology
- The loss on ignition test is a cheap measure of soil organic matter that can be completed from the normal pooled soil sample used to assess soil nutrients
- However, only a small proportion of organic matter binds to soil particles and associated aggregates to help form the crumbly texture of topsoil. This is sequestered soil carbon
- Measuring soil carbon directly is technically demanding and, therefore, expensive. So, while the projects tested the fields with the recognised bulk density test to 30cm, the limited number of cores taken meant the results were only indicative of soil carbon levels
- Still, the results were broadly consistent with the loss on ignition result and suggest that the opportunity to sequester and store more carbon in many fields on beef and sheep farms may be limited
- The management of these fields under long-term grass explains good carbon levels, though there will be variation between fields, with sandy, shallow soils inherently low
- Beware of “get-rich-quick” soil carbon schemes.
How the project worked
- Twenty livestock farmers, split into four groups across southern Scotland, were asked to nominate their best and worst in-bye fields for soil testing in December 2021. One (focus) farm in each group was tested at a more detailed level. Information covering land use, livestock numbers, production, fertiliser, manures and feed use was also collected.
- In January 2022, each group met at their focus farm for a demonstration of assessing soil structure and to discuss the soil test results in the context of how fields were managed.
- Two webinars were run in February to discuss the options available to farmers to manage their soils to improve both environmental footprint and profitability.
- All farmers were supported in compiling a soil health scorecard for each field, which included 28 assessments and measurements such as rainfall, topography, field use, nitrogen applications and carbon levels.