Measuring soil health
The Microbiology Society is undertaking a project entitled A Sustainable Future as part of our 75th Anniversary, which aims to highlight the Sustainable Development Goals (SDGs) to our members and empower them to use their research to evidence and impact the goals. Earlier this year, we put a call out to our members to submit case studies in the following three areas: antimicrobial resistance, soil health and the circular economy.
This case study is written by Professor Bridget Emmett, who is the Head of Soils and Land Use Science Area for the UK Centre for Ecology and Hydrology. It focuses on Soil Health; maintaining the health of our soils has gained increasing prominence in recent years. Soils are essential for the global food system and regulate water, carbon and nitrogen cycles but are put under pressure from population growth and climate change.
Can we measure soil health?
The first response to that question of course is what is soil health? There are various definitions but in general soil health is understood to go beyond its agricultural potential (often referred to as soil quality) to cover the continued capacity to deliver a much wider set of functions and benefits such as a habitat for biota, provide clean water and carbon storage (EC 2020).
Can we measure it? Coming from the perspective of someone who has managed large integrated monitoring programmes at a national scale, our understanding of soil health and indicators is as good as those for other natural resources we routinely monitor. We want good chemical, physical and ecological status, and we have tried and tested soil indicators for each of these three characteristics.
Some say isn’t soil too diverse, spatially variable and too slow to respond to monitor efficiently? In fact, in comparison to other natural resources, soil is rather ‘well-behaved’. Whilst soils are very diverse, to suggest this is more so than for our fauna and flora or classic ‘biodiversity’ seems odd? And yes, soil varies across a field but monitoring does not require full spatial description of every field. Most monitoring programmes select representative, permanent, point locations and then track those using a population approach across multiple sites. As to the issue of soils being slow to respond? Well they can be slow although they can be frighteningly fast as well (e.g. erosion), but is this not just the other end of a temporal scale which is equally challenging to track. Soils don’t annually migrate to other countries (e.g. birds) only come out when the sun shines (pollinators), have peak and low flows (rivers) or change with the direction of the wind (e.g. air quality). In my experience, the real problem for soil monitoring is just inadequate funding to go to depth, take sufficient samples and capture a similar range of indicators routinely collected for e.g. waters.
Are we starting from scratch with soil monitoring? Absolutely not. Just in the UK, there is the National Soil Inventory (NSI) for England and Wales; NSI Scotland, the GB Countryside Survey and others. Furthermore, soil health trends reported since the 1970s to late 2000s have effectively answered policy questions such as: Is soil organic carbon being lost and if so in which habitats?; Are heavy metals levels increasing?; Is recovery from acidification continuing (e.g. Countryside Survey, Emmett et al. 2010).
What next? To help policy makers and land managers we need to define standards for soil health for our mix of soil types, land uses and climate zone combinations. This may seem overwhelming but this has already been tackled for the EU Water Framework Directive for surface waters. It is just a question of sufficient funding to provide a structured and consistent approach to quantifying those standards covering the range of variability we have. Meanwhile, there is no reason not to collect soil health data. Most soil scientists agree that we can recognise when a soil is becoming more unhealthy if regular data is available e.g. a loss of soil organic carbon, increased compaction; more bare soil and soil sealing; rising levels of contaminants. There really is no reason not to start robust monitoring programmes now to track these trends and respond to them. New technologies such as EO will help but we need to be honest that it currently cannot detect the level of change we need for most soil indicators.
We also need a policy ‘pull’ at government level to ensure soil health and monitoring is on an equal standing as that for our other natural resources. Some countries have already responded e.g. Wales has soil carbon as one of its 46 National Indicators to track progress to achieving the UNSDGs and tracks progress with ongoing soil monitoring. The EU has raised soil health as one its top 5 priorities. We need to start monitoring and taking action now as we are already behind the curve with 60-70% soil across the EU estimated as unhealthy using the incomplete data we have available (EC 2020).
EC (2020). European Commission, Independent Expert report (2020): Caring for soil is caring for life. Ensure 75% of soils are healthy by 2030 for healthy food, people, nature and climate. Luxembourg: Office for Official Publications of the European Communities.
Emmett, B.A., Reynolds, B., Chamberlain, P.M., Rowe, E., Spurgeon, D., Brittain, S.A., Frogbrook, Z., Hughes, S., Lawlor, A.J., Poskitt, J., Potter, E., Robinson, D.A., Scott, A., Wood, C., Woods, C. (2010) Countryside Survey: Soils Report from 2007. Technical Report No. 9/07 NERC/Centre for Ecology & Hydrology 192pp. (CEH Project Number: C03259).
About the author
Professor Bridget Emmett is Head of Soils and Land Use Science Area and Head of Bangor station for the UK Centre for Ecology and Hydrology. Find out more about her research here.