All once-living matter returns to the soil that it grew from, to be dismantled and cycled again. Without the constant recycling work of tiny animals, fungi and bacteria we would be metres deep in the remains of the dead, all resources frozen, new life impossible.
Soil recycling is supported by a constant flow of carbon from air to soil as plants release sugars and other organic compounds made by photosynthesis in their leaves out from their roots. These chemicals support the teeming billions of micro-organisms, fungi and bacteria that the roots partner with. In return for this carbon the soil micro-organisms help the plant to gather water and nutrients and to resist diseases.
While all soils will support some plant growth, for maximum growth rates and productivity soils need to be very fertile, meaning they provide lots of inorganic nutrients (mainly nitrogen, phosphorus and potassium) and have good moisture retaining properties while avoiding becoming saturated. Natural undisturbed soils maintain adequate levels of fertility through natural processes, but fruit and vegetable growers will want to maintain high levels of fertility in the areas where they grow produce. For a wildlife garden however, high fertility, while not generally a problem, is certainly not necessary. Low fertility is very helpful when your desired plants are in competition with grasses as in a lawn or wildflower meadow patch.
Soils, erosion and climate change
Soils are massively important carbon sinks and the hidden subterranean world now known as the deep biosphere stores an estimated 15-23 billion tonnes of carbon, far more than is held in visible surface life.
Soils are easily degraded by human activities. Soil erosion occurs when soil hydrology is altered by drainage or removal of soil-binding trees and shrubs, causing soils to wash out or dry and blow away. Two posts at Holme Fen in Cambridgeshire record a drop in the peaty soil level of 4m
since 1848 caused by shrinkage and wind-blow after drainage works.
Erosion is not usually a problem within gardens, but they may be affected by erosion externally. More commonly, garden soils are damaged by repeated digging in the same way that ploughing has damaged agricultural soils. Both cause the humus content to oxidise, reducing soil fertility unless replaced by application of compost, and reducing the carbon trapping ability of the land. Digging also destroys the subtly different layers of soil which support different species of soil fauna, so digging damages biodiversity. Application of artificial fertilisers disrupts soil ecology, as will contamination by pesticides and especially fungicides. This damage is far less visible to the wildlife gardener than would be the effects of these chemicals above ground.
Avoiding soil erosion, loss of stored carbon or ecological damage is a major concern for climate change, since all will contribute to atmospheric CO2 release.
There are now several initiatives to make agricultural soil management more sustainable4. and the same principles apply to garden soil management
Managing your soil
1. Bickel, S., Or, D. (2020) Soil bacterial diversity mediated by microscale aqueous-phase processes across biomes. Nat. Commun. 11
:116 available here
2. European Commission (2010) The factory of life. Why soil biodiversity is so important. Luxembourg: Office for Official Publications of the European Communities. Available here
3. Pimentel, D. et al (1995). Environmental and economic costs of soil erosion and conservation benefits. Science. 267:
1117–23. Available here
4. Farmer’s Weekly (2020) Regenerative farming: The theory and the farmers doing it. Available here
Books and websites
Lowenfels, J. and Lewis, W. (2010) Teaming with Microbes: The Organic Gardener's Guide to the Soil Food Web. Timber Press
on soil types https://www.rhs.org.uk/soil-composts-mulches/soil-types
British society of Soil Science website
Page drafted by Tony Kendle, extended and compiled by Steve Head, reviewed by Ken Thompson