By Henrietta Appleton, GWCT Policy Officer (England)
Thursday 5th December is the FAO’s World Soils Day with a theme of caring for our soils through “measure, monitor, manage.”
The Importance of Good Data for Soil Management
The importance of good data to support informed decision-making is a key driver for GWCT advice and policy formulation and so this theme is very much “business as usual” for us. Our focus is always to try and present a balanced viewpoint and, in this regard, our recent research on GHG emissions from soils is poignant.
Balancing Carbon and Soil Health
As with many other policy areas, carbon emissions have been a driver of soil policy, perhaps at the detriment of wider soil health. A point we have made in previous blogs – most recently in June this year. Much is made of the value of reducing soil disturbance (ploughing mainly) in minimising carbon emissions and maximising carbon storage.
Diagram courtesy of Habitat Podcast
Beyond Carbon: Methane and Nitrous Oxide
But carbon (CO2) is only a third of the story. Consideration must also be given to methane and nitrous oxide emissions, which are both more powerful (although shorter-lived) greenhouse gases. We are currently focusing on trying to ‘manage’ legacy carbon emissions at the expense of considering the implications of this management for emissions that will have an impact on this decade’s climate.
Agriculture’s Contribution to Greenhouse Gas Emissions
Agriculture accounts for about 68% of nitrous oxide emissions, largely due to nitrogen fertiliser usage and manure management, and is the largest contributor to methane emissions (49.2% of total UK methane emissions in 2022), mostly from livestock farming. As a result, most attention has been focused on these contributors, and the role of soil management is largely overlooked.
The Impact of Extreme Weather on Soil Management
As our climate changes, the occurrence of extreme weather events, such as the significant rainfall we have seen in the last two autumns, will need to be considered in how we manage our soils. As previously reported, increasing soil organic matter can aid the ability of soil to retain water/moisture, but there are limits to a soil's capacity to do this – as there is a limit (saturation level) in the amount of carbon that can be stored. These limits will differ for different soil types and conditions (soil health).
GWCT Research on Soil Greenhouse Gas Emissions
We are one of only a few research institutions in the UK with the ability to measure the full range of GHG emissions from soil. Of particular note in our soil gaseous emissions data has been an increase in nitrous oxide emissions where soils are compacted and waterlogged – in this case in our long-term direct drill plots. Given that about a third of lowland soils in England are heavy land, akin to that at Allerton, these results are significant.
Climate Change and Under-Estimated Emissions
In addition, soils with higher carbon content in the warmer, wetter conditions we are experiencing under climate change mean that it is likely the nitrous oxide emissions from UK agriculture are being under-estimated. Furthermore, wet weather means farmers are driving on fields with big machinery, e.g., harvesting sugar beet and maize, which creates the ideal ‘anaerobic’ conditions for nitrous oxide losses (due to compaction and waterlogging).
Understanding the Science of Nitrous Oxide Emissions
Nitrous oxide is released through two complementary processes – nitrification following wet-to-dry transitions in the soil, whilst denitrification occurs when the soil is rewetted – which are influenced by complex environmental controls. It is commonly called a ‘belching gas’ as emissions are not released in a constant stream, varying spatially and temporally. This has made it more difficult to measure and monitor.
A Broader Approach to Soil Health
We hope that the World Soils Day message of “measure, monitor and manage” will result in more evidence of how we can sustainably manage our soils through the wider consideration of soil health and not the tunnel vision of carbon.