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Life, climate change and Scotland's soils

March 2010

48% of total UK carbon is in Scotland

Growing food begins with a healthy soil. Without a fertile, uncontaminated, and water retaining substrate, yields will never reach their full potential and can decline over time.

And it’s not all about yield; some nutrients and minerals that are essential for plant health and human wellbeing only come from the soil. And soils’ ability to retain and breakdown potentially harmful chemicals helps protect the food chain from contamination.

Soil is an integral part of life on Earth. Image: iStock

Soil is important, too, from an environmental perspective. Not only a source of raw materials, soil can usefully receive certain organic wastes and recover benefits from them. Soil and its biodiversity also help to transform and detoxify environmental pollutants which protect our air and water, and play a role in regulating the climate through the exchange of greenhouse gases. Soil also sustains particular and valued habitats and biodiversity, and is an archive of biological, geological and archaeological heritage.

Digging in the dirt

Soil quality is determined by a number of physical, chemical and biological functions and understanding the dynamic interplays between these factors is central to delivering food security.

‘Protecting the Nation’s Soils’ is funded by the Scottish Government and is one of the major research programmes managed at the Macaulay Land Use Research Institute (MLURI), Aberdeen and is a cross-institute programme that includes the Scottish Crop Research Institute (SCRI), BioSS, and the Scottish Agricultural College. The programme aims to record the status and quality of Scotland’s soil, improve understanding of the cycling of greenhouse gases, and develop new tools and methods to assess soil quality and biodiversity. It aims to provide knowledge that is crucial in both the context of the wider UK and global food security challenge, but also essential for local farmers and horticulturalists. Breeders and conservationists, too, can benefit.

All EU member states may, in the future, be obliged to monitor and map risks to soil under the EU Soil Framework Directive. The emerging legislation seeks to establish principles to protect the capacity of soil to perform environmental, economic, social and cultural functions.

Scotland’s soils differ from the rest of the UK. Only 25% are cultivated, 17% are under woodland, and the rest are largely under semi-natural vegetation. Although they have a lower pH and lower levels of many nutrients, they are richer in organic carbon (48% of total UK carbon is in Scotland). 75% of this carbon is in organic soils, and protecting the organic soils is therefore an important way to help combat climate change.

Scotland’s soils pose unique challenges and opportunities.
Image: Arran Frood

Data like these are compiled from the National Soils Inventory of Scotland (NSIS), which first ran from 1977-87 and is one of the best soil information databases and archives in Europe. It comprises 720 sites with over 3000 archived samples over 25 years, which have been analysed for their physical and chemical properties.

A partial re-sampling of the NSIS on a 20km grid started in 2007. The sampling allows scientists in Scotland to record what soil features are associated with certain land-use and soil-type combinations. The data can then be used to design and implement new land management programmes which can enhance future use of soils and prevent any further degradation.

A survey is also underway to sample how climate change is affecting the nation’s earthworm population. Earthworms are keystones of ecosystem structures because they influence soil structure through burrowing, add life-giving oxygen to the soil, recycle and make nutrients available, and provide drainage channels for water. Macaulay scientists are teaming up with compatriots at SCRI, Dundee, to carry out a second Scotland-wide earthworm survey.

SCRI scientists completed the first ever national earthworm survey in the early 1990s, and this new collaboration will revisit the same 100 farm sites so that data can be compared with the baseline 1990s measurements. It is the only scientific survey of its kind that has been conducted in the UK as no equivalent surveys have been carried out in England and Wales.

Life management

But soil contains much more than worms; it also contains many insect larvae and mites. A single gram of soil can contain 1Bn bacteria (made up of 10,000 to a million different species), and 10s of thousands of fungi, protozoa and nematodes.  

There is more life in the ground than above it.
Image: Felicity Crotty

The variety, diversity and abundance of life forms in soil – several orders of magnitude than above ground – lead some to describe it as a frontier because so much of it remains unexplored. Ultimately it is this biodiversity and the organisms’ activity that supports soil’s ecological functions.

This has been appreciated for some time. Indeed, American President F.D. Roosevelt remarked that “a nation that destroys its soil destroys itself.” Prescient words, but what Roosevelt didn’t know was how important soil science would later be to predicting and mitigating the effects of climate change.

Nitrous oxide (N2O) is a powerful greenhouse gas – 300 times more potent that carbon dioxide. Roughly half of N2O emissions stem from agriculture and primarily depend upon the amount of fertiliser applied to land. As well as fertiliser application rates, N2O emissions are influenced by grazing regimes, soil wetness and temperature, and how they vary with soil type and land management.

Geographic Information Systems (GIS) have already been combined with soil, climate and land use maps and weather data to calculate a national map of N2O emissions in Scotland (about 6M kg per year). This information can then be used to inform policies and management to reduce emissions in target areas, and to develop mitigation strategies to offset total emissions, by changing fertiliser application practises, for example.

Understanding how soils carry out its functions, from remote sensing by satellite to digging down deep, is critical to developing techniques to maintaining and improving the condition of soil for the current and future needs of society.