Soil — The forgotten resource
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Soil is a crucial link between global environmental problems such as climate change, water management and biodiversity loss
José Luis Rubio, President of the European Society for Soil Conservation
Why should I care about soil?
Dirt, mud, clay, earth, soil: we have many words for it but few do it justice. In today's virtual world many of us have, literally, lost our connection with the soil. But soil is the earth's living skin, overlying the bedrock below and making life on earth possible. Like air and water, soil is part of our life support system.
Our ancestors had a much closer relationship with soil. Many of them would have worked with it every day. Then, as now, soil played a crucial role in supplying food. What was not understood in the past is the crucial role soil plays in climate change, serving as a huge, natural store of carbon.
Soil and carbon
Soil holds twice as much organic carbon as vegetation. Soils in the EU contain more than 70 billion tonnes of organic carbon or around 7 % of the total global carbon budget (8). More than half of the ground‑stored carbon in the EU is held in the peat bogs of Finland, Ireland, Sweden and the United Kingdom.
This figure is put in context when you think that EU Member States emit 2 billion tonnes of carbon every year from all sources. So, soils play a decisive role in climate change. Even a tiny loss of 0.1 % of carbon from European soils emitted into the atmosphere is equivalent to the carbon emission of 100 million extra cars on the road. That is an increase of about half the existing EU car fleet.
Soil is a limited resource
Pretend that this apple is the planet Earth. Cut the apple in quarters and throw three of them away. The quarter apple left represents dry land.
Fifty per cent of that dry land is desert, polar or mountains * — where it is too hot, too cold or too high to grow food. Cut the dry land quarter in half. Forty per cent of what remains is too rocky, steep, shallow, poor or wet to support food production. Cut this away and you are left with a very small piece of apple.
Notice its skin, hugging and protecting the surface. This thin layer represents the shallow cover of soil on earth. Peel it and you have some idea of how little fertile soil we depend on to feed our entire population. It must compete with buildings, roads and landfills. It is also vulnerable to the pollution and the impacts of climate change. Soil often loses out.(7)
*As you will read, much of the land that is not suitable for food production is important in terms of soaking up CO2.
Soil organic matter (SOM)
The key substance in the relationship between soil and carbon storage is 'soil organic matter' (SOM). This is the sum of living and dead matter in soil and includes plant residues and microorganisms. It is an extremely precious resource that performs essential functions for the environment and for the economy, and it can do so because it is a whole ecosystem at a microscopic scale.
SOM is a major contributor to soil fertility. It is the elixir of life, particularly plant life. It binds nutrients to the soil, storing them and making them available to plants. It is the home for soil organisms, from bacteria to worms and insects, and allows them to transform plant residues, and hold on to nutrients that can be taken up by plants and crops. It also maintains soil structure, thereby improving water infiltration, decreasing evaporation, increasing water-holding capacity and avoiding soil compaction. In addition, soil organic matter accelerates the breakdown of pollutants and can bind them to its particles, so reducing the risk of run-off.
Did you know?
Soil, plants, carbon
By photosynthesis, all growing plants absorb CO2 from the atmosphere to build up their own biomass. However, just as we see the plant grow above the ground, a hidden growth of similar magnitude takes place beneath the surface. Roots release various organic compounds continuously into the soil, feeding the microbial life.
This increases the biological activity in the soil and stimulates breakdown of SOM, so that mineral nutrients are released, which the plant need to grow. It also works in the opposite direction: some carbon is transferred into stable organic compounds that lock the carbon and keep it out of the atmosphere for hundreds of years.
Depending on a farmer's management practice, the type of soil and the climate conditions, the net result of the biological activity can be either positive or negative for SOM. Increasing SOM creates a long-term sink for carbon from the atmosphere (on top of other positive effects). Reducing organic matter means that CO2 is emitted and our management practices have added to total man-made emissions.
So, how we use land has a huge impact on how soil deals with carbon. Crucially, soil releases carbon when grasslands, managed forest lands or native ecosystems are converted
Deserts move to Europe
The process of 'desertification' — whereby viable, healthy soil is drained of nutrition to the extent that it cannot support life and may even blow away — is a very dramatic illustration of one of the issues facing soil across Europe.
'The natural conditions: aridity, variability and torrential nature of rainfall, vulnerable soils, together with the long record of past and present human pressure, mean that large parts of southern Europe is being affected by desertification,' says José Luis Rubio, President of the European Society of Soil Conservation and head of a soil research unit run by the University of Valencia and Valencia city.
In southern, central and eastern Europe 8 % of the territory, about 14 million hectares, currently show high sensitivity to desertification. This increases to more than 40 million hectares if moderate sensitivities are also taken into account. The countries in Europe most affected are Spain, Portugal, southern France, Greece and southern Italy (10).
'The gradual degradation of soil by erosion, loss of organic matter, salinisation or destruction of its structure is transmitted to the other ecosystem components — water resources, vegetation cover, fauna and soil microorganisms — in a spiral mechanism, which eventually creates a desolate and barren landscape'.
'It is often hard for people to understand or even see the consequences of desertification because, in general, these occur hidden and unnoticed. However their environmental impact on agricultural production, increased economic costs by floods and landslides, their impact on the biological quality of the landscape, and the overall impact on the stability of the terrestrial ecosystem, means that desertification is one of the most serious environment problems in Europe,' Rubio says.
Protecting Europe's soil
Soil is a key and very complex natural resource yet we are increasingly ignoring its value. EU law does not address all the threats in a comprehensive way and some Member States lack specific legislation on soil protection.
The European Commission has been developing proposals for soil policy for many years. Several Member States regard them as controversial, however, and the policy development has stalled. As a result, soil is not protected in the same way as other crucial elements such as water and air.
Focus: for peat's sake
Peatland ecosystems are the most efficient carbon store of all terrestrial ecosystems. Peatlands cover only 3 % of the world's land area but contain 30 % of all global soil carbon. That makes peatlands the most efficient long-term carbon store on earth.
However, human interventions can easily disturb the natural balance of production and decay, turning peatlands into carbon emitters. Current CO2 emissions from peatland drainage, fires and exploitation are estimated to be at least 3 000 million tonnes a year — equivalent to more than 10 % of global fossil fuel emissions. The current management of peatlands is generally unsustainable and has major negative impacts on biodiversity and the climate (11).
8. European Commission: European Commission, 2008, ‘Review of existing information on the interrelations between soil and climate change’