All our food comes from soil, either directly or indirectly. And there’s a lot more to it than meets the eye!  Did you know …

Soil animals.

Almost a quarter of all described living species are soil animals. From data in a 2006 study.

  • Soil traps carbon dioxide from the atmosphere, potentially alleviating the effects of climate change. Of the increases in atmospheric carbon dioxide caused by human activities, two thirds is because of fossil fuel-burning, but the remaining third is from carbon previously trapped in soil but lost through changes in land use.
  • Soil stores a huge amount of water, serving an important role in absorbing rainfall and preventing flooding.
  • Speaking of water, soil acts as a filter too, removing pollutants and giving us clean rivers, lakes and groundwater.
  • The makeup of soil varies a lot from place to place: soil scientists have identified more than 10,000 different types of soil in Europe alone!

It’s organic carbon that gives soil most of its amazing properties. This carbon is released from dead plant and animal material when it’s broken down by microorganisms and bugs in the soil. It contains all the nutrients plants need for growth, and it binds all the inorganic sand, clay and silt particles together.

This organic matter needs to be protected to maintain healthy soils. But current agricultural practices can be extremely damaging to soil, leading to its erosion and exhaustion of its valuable nutrients. Good quality soil doesn’t come about overnight either; it can take a thousand years to create two square-centimetres of topsoil.

At first glance there hardly seems to be an issue. You don’t have to go very far to find soil. I can pop to my local garden centre and buy bags of lovely high quality soil for my plant pots. And at this time of year, a short cycle ride leaves me seemingly covered head to foot in it (I really need to get some mudguards …). Yet the Food and Agriculture Organisation of the United Nations (FAO) is concerned enough that it has declared 2015 the International Year of Soils. It estimates that a third of the world’s topsoil has already been degraded, and that if practices aren’t improved we may only have 60 years of healthy usable soil left.

US Fish and Wildlife Service

Damage caused by soil erosion. Photo: US Fish and Wildlife Service.

The impacts of soil erosion, the main driver of soil loss, are already being felt around the world. In dry climates, over-farming can lead to desertification, where once-fertile land is turned to desert and its organic material lost. When soil is eroded from fields, it ends up in streams and rivers nearby and is carried out to sea. Any pesticides or fertilisers that have been applied to the fields are carried along with it, polluting freshwater and causing algal blooms to form. And without the water-retention of soil, flooding becomes more common – and all the more dangerous.

But while modern practices are causing soil loss, relatively simple changes can have huge benefits. The end product of crop farming is usually just a small part of the plant – the head of a corn or wheat plant, for instance; the rest of the plant often goes to waste. Leaving this unwanted material  in the field to be broken down biologically helps replenish the soil’s carbon content, while intact root systems help bind the soil together to resist erosion.

By reducing the use of ploughing and cultivation (cutting up the soil to kill weeds), which break soil structure, soil erosion is reduced. Crops can also benefit from such changes: roots that penetrate better have greater access to nutrients, and more porous soils retain water better.

USDA NRCS South Dakota/Flickr

A farmer applying fertiliser to a no-till field, in which the soil isn’t ploughed or cultivated to avoid damage to the soil. Careful timing of fertiliser application can minimise run-off into rivers. Photo: USDA NRCS South Dakota/Flickr.

We can also increase the amount of organic carbon in soil by adding decaying plant material – applying compost, manure or crop residues. Reforestation or the creation of wetlands on exhausted land are highly effective at restoring soil carbon. Careful management techniques can even increase the amount of carbon beyond levels that would occur naturally. However, such approaches need to be balanced with the needs of farmers.

The FAO’s objective in 2015 is to raise awareness among the public and policymakers, and to use its position to encourage the use of sustainable soil management activities. Meanwhile, research into new approaches of land management will continue to find better ways of caring for the soil we rely on for so much.

Follow International Year of Soils activities on Twitter using #IYS2015.

FAO IYS 2015 infographic

Click the image for the full infographic.

Matt is a PhD student at the John Innes Centre. He tweets as @Mattjevans42.

Featured image background photo: Al Jazeera English/Flickr.

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