Today is World Soil Day, a United Nations initiative aimed at highlighting the huge importance of soil in providing the world with healthy food and the need for sustainable soil management across the globe. Soil is a hugely rich resource - amazingly, one tablespoon of soil contains more living organisms than there are people on earth!
According to the UN, 95% of our food globally comes from soil. But over the last 70 years, the level of vitamins and nutrients in food has drastically decreased. Like us, soils need a balanced and varied supply of nutrients to be healthy. Agriculture loses nutrients with each harvest, and if soils are not managed sustainably, fertility is progressively lost, and soils will produce nutrient-deficient plants.
Looking more locally, into our own gardens, the undoubted hero of the soil is the humble earthworm. Nearly 30 species of earthworm can be found in the UK, of which around 16 are found in our gardens. These different species vary in size and colour, but all do a huge amount for the structure and fertility of our soil. Looking first at the structural element of their work, earthworms can make both horizontal and vertical burrows in soil, some of which can be very deep. These burrows are vital for allowing oxygen and water to enter the soil and carbon dioxide to leave. Earthworm casts (their faeces) are also very important in soils and contribute to some of the fine crumb structure of soils.
Earthworm Lumbricus terrestris Photo: Ben Andrew (rspb-images.com)
Earthworms also play an important role in decomposing dead organic matter, releasing nutrients locked up in dead plants and animals and making them available for use by the plants we’re growing in our gardens. Earthworms do this by eating organic matter and breaking it down into smaller pieces, allowing bacteria and fungi to feed on it and release the nutrients.
Earthworms' final main job in our gardens is as 'nature's ploughs' (as Charles Darwin referred to them), mixing soil layers and incorporating organic matter into the soil. This improves the fertility of the soil by allowing the organic matter to be dispersed through the soil and the nutrients held in it to become available to bacteria, fungi and plants.
And of course earthworms play a big role in the food chains of our gardens, providing a vital food source for some of our favourite garden birds. Song thrushes, robins and blackbirds feed on the ground, and for them an earthworm is an absolute favourite. These birds have strong bills that enable them to pull struggling earthworms from the soil, and large eyes that help them to see in the early morning light, when earthworms are most active near the surface.
Turdus merula, adult female picks up a piece of an earthworm
Photo: Rob Carmier (rspb-images.com)
According to the UN, up to half of our household waste could be composted to nurture our soil. This can be done in a variety of ways and improves the fertility of our garden soil, as well as reducing the waste that goes to landfill. The RSPB has lots of great advice on how to get started with home composting, including a Wild Challenge for children.