Digging top soil releases carbon dioxide and destroys habitat that invertebrates need. The worms, arachnids, and isopods that live in earth and leaf litter are the first level of many food chains. Wildlife such as; birds, bats, shrews, toads and newts rely on the soil in your garden to provide a varied diet all year round.
Fresh dug earth after the previous crop stubble has been turned into the top soil looks tidy and new but it gives little opportunity for bio diversity. A lower number of worms live in cultivated soil but one mollusk appears to thrive in it. The garden slug is every gardener's worst enemy. Slug numbers multiply. The natural predators; ground beetle and garden centipede are excluded from the surface of a vegetable garden once the soil is turned. Leaf litter provides habitat for spiders, ground beetles, ladybird larvae, centipedes and woodlice.
Woodlice are a garden work horse. They shred dead plant material that can then be distributed into the soil profile by worms. Here it is further processed by beneficial fungi and bacteria. Ground beetles, centipedes, ladybird larvae, and spiders predate; caterpillars, aphids and the eggs of the garden slug. Digging soil reduces the opportunity for habitat for mini beasts that live in leaf litter.
We introduce large amounts of air into the soil profile when we turn it over. Aerobic bacteria respond by multiplying into vast populations that permanent soil in its natural state could never sustain. These bacteria eat the carbon from the soil. Soil organic matter and humus is converted into carbon dioxide and water soluble substances in a short period of time. The result is carbon dioxide in the atmosphere and soil erosion. The organic matter is washed from between soil particles. The earth becomes a sterile aggregate that relies upon artificial fertilizer to feed subsequent cropping.
There are a few solutions to the problem of over cultivating top soil. We can consider permanent crops: top fruit, soft fruit, rhubarb and asparagus. The husbandry of these food crops doesn't require turning the soil and leaf litter yearly. Large root systems recycle nutrient from deep into the soil.
The majority of food crops need a seed bed or cultivation prior to planting. To enjoy a varied diet we rely on plants that produce a yield having grown from seed in a single season. We don't have to turn all the top soil. Minimal cultivation methods have been trialled by many gardeners not always successfully. Planting or sowing seed directly can be disappointing. Seedlings or young plants stand in saturated soil. Their roots don't develop and a stunted root equals a stunted plant.
Cultivating narrow drainage channels overcomes all the surface drainage issues minimal cultivation systems have suffered from previously. A channel 20 mm (3/4 inch) wide and 180 mm (7 inches) deep will usher excess surface water into deeper soil. Young plants and seedlings establish in the normal manner. Their roots grow looking for moisture lower down. When roots develop in a healthy way the rest of the plant grows normally as well.
Garden food crops that grow from seed and produce a yield every year can enjoy the benefits of permanent soil. At the same time healthy plants establish in free draining top soil. The permanent soil and extra leaf litter will provide opportunity for bio diversity. The soil will act as a giant sink and vast quantities of carbon dioxide will be locked into it. The effect of leaving large areas of soil undisturbed saves a lot of effort and sustains wildlife while slowing climate change.
Andrew Astle has grown food and ornamental crops for thirty years. He is a member of the Centre for Alternative Technology and the Permaculture Association.
He wrote the book "TINE" How to Garden Without Digging. This books explains a method of growing kitchen garden crops easily while sustaining wildlife and contributing to the removal of greenhouse gas from our atmosphere. There is more information at: http://www.soilisalive.com
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