The soil under your feet is a living ecosystem. Soil is made from eroded rocks and minerals together with decomposed organic material and many, many living organisms. The biomass of living creatures belowground can equal or exceed the biomass above ground, and soils host at least one quarter of all living organisms. Soils are like massive tropical rainforests or coral reefs, mostly invisible and under our feet.
Different kinds of soils have distinct structures with pores and holes of different sizes which are filled with gases, liquids, viruses, bacteria, fungi, worms, slugs, insects and arachnids. Even many “aboveground” organisms use the soil ecosystem. For example, several species of bees have nests in the ground, and many beetles have larvae which live and feed in the soil as grubs, sometimes for many years. Soils are critical to the functioning of aboveground ecosystems like grasslands, peatlands and forests, but are often ignored because it is difficult to see and appreciate what is going on in the subterranean darkness.
If you asked someone to name a creature that lives in soil they would probably mention earthworms; the giants of the soil ecosystem, enormous in comparison to most of the species they live with. There are 31 species of earthworm alone in Ireland and Britain. Earthworms do the heavy lifting, moving decomposing plant material from the surface and processing it until it becomes part of the soil.
The roots of plants and the web of fungal filaments hold the soil together, give it complex structure, move nutrients around and store carbon. However, the real biodiversity riches of soil are in the microscopic and microbial worlds. Many of these micro-organisms cannot be grown in a lab dish, they are only known from genetic material that can be extracted from soil samples.
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Much soil biodiversity is therefore nameless, it consists of strings of letters which are the building blocks of genetic codes – DNA and RNA. One gram of soil contains anything from ten thousand to ten million different kinds of organisms.
While this underground biodiversity is largely invisible, we rely on it for food security, to maintain our forests, regulate the climate, store water and recycle nutrients. The living biodiversity of soils is critical to its functions, and just like aboveground biodiversity, soil biodiversity is under threat from the intensification of agriculture, land-use change and pollution.
As we lose species from the soil the ability of soil ecosystems to resist and recover from damage is reduced. The loss of biodiversity is like removing blocks from a tower, the tower can still stand up as some blocks are removed, but once a critical piece, or too many blocks are removed, the tower becomes unstable and eventually collapses.
Soils can be brought into being through human ingenuity – a great example is the soil created from sand and seaweed on the west coast of Ireland. As the seaweed decays through the action of microbes, it combines with the sand and the limestone on which it is placed to produce a fertile, productive soil, used for growing pastures and small-scale crops such as potatoes on the Aran Islands.
We rely on good soil health for maintaining agricultural production. However monoculture cropping, fertilisation and the use of pesticides reduce soil biodiversity and make the functions of soils more vulnerable to further degradation. Ploughing disrupts the structure of the soil and exposes soil-stored carbon which is oxidised and emitted back into the atmosphere, intensifying climate change.
No-till methods of crop cultivation such as direct sowing into stubble, the use of perennial crops and pastures, and reducing fertiliser and pesticides all contribute to reducing greenhouse gases and maintaining soil biodiversity.
Sustainable farming practices must conserve soil biodiversity and soil health so that future food production is not sacrificed for short-term gain. We are increasingly seeing the erosion of that short-term gain. however, as energy costs climb and with them the costs of ploughing, fertiliser and pesticides.
Sustainable agricultural practices, including no-till methods, multi-species pastures and the use of cover crops, can provide some of the solutions to higher energy costs, as well as reducing the environmental costs of conventional production systems. Simply stated, we need to stop treating soil ecosystems like dirt.
Yvonne Buckley is an ecologist, Irish Research Council laureate and professor of zoology at Trinity College Dublin