Scottish Environment, Food and Agriculture Research Institutes (SEFARI) fellowship Blog - 22 June 2020

Scottish grasslands and soil carbon by Dr Gemma Miller, the Scottish Environment, Food and Agriculture Research Institutes (SEFARI) fellowship with NFU Scotland.

(Note Dr Miller's factsheet on Scottish grasslands and soil carbon is available to read at:

The UK Committee on Climate Change (2019)1 estimates that more than 50 per cent of agricultural greenhouse gas (GHG) emissions could be removed through the introduction of mitigation approaches that target methane and nitrous oxide emissions.

But what about the other 50 per cent? One common assertion is that carbon (C) is sequestered in soils, particularly in permanent pastures and is not taken account of in GHG inventories.

There is some incentive to maintain permanent pastures through the Greening element of the Common Agricultural Policy, but is it true that grasslands in Scotland can help bridge the gap between actual and net zero GHG emissions?

Soil C sequestration is the process whereby C, in the form of organic matter (e.g. from plant roots, manures and plant litter), is incorporated into the soil. The organic matter can be stabilised through binding to soil minerals, preventing it from being further decomposed by soil microbes and releasing CO2 back to the atmosphere, but this process is incredibly slow.

Soil C can be lost rapidly due to disturbances, including ploughing pasture to reseed. It can take many years for organic matter to become stabilised in soil and up to 100 years for soil to recover to an equilibrium C stock (the C stock is the total mass of C sequestered in the soil).

Sequestration rates are rapid to begin with but get progressively slower over time. Where permanent grasslands are observed to be sequestering C, it is highly likely that they are recovering from some previous land management practice.

So, the potential for soil C sequestration to mitigate GHG emissions in grassland is not insignificant, but it is limited and easily reversible.

It is currently assumed in the UK Inventory of GHG Emissions that grasslands that have not been recently associated with a land-use change maintain a constant C stock. The justification for this assumption is provided by national soil survey data and detailed analysis of C fluxes from individual sites.

Although this assumption will not allow for individual circumstances where management activities have been used to increase C stocks, it is likely to be broadly true of the C balance in most cases.

What is arguably more important is protecting current soil C stocks from being lost and to value them for more than just their ability to sequester C. Soils also provide vital ecosystem services such as flood prevention, maintaining fertility, encouraging biodiversity, water quality and nutrient cycling, which are often supported by higher levels of soil organic matter. These wider benefits will be covered in greater detail in the next blog.

  • I would like to thank Professor Bob Rees (SRUC), Professor Pete Smith (University of Aberdeen),  and Dr Alasdair Sykes (SRUC) for advice and comments they provided during the writing of this blog and the accompanying factsheet “What is the potential of managed grasslands in Scotland to sequester carbon?”.
  • 1 Committee on Climate Change (2019) Net Zero – The UK’s contribution to stopping global warming.

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