Soil degradation is one of the most pressing problems facing our planet. More than 80% of the world's farming land is 'moderately or severely eroded', with 75 billion tonnes of soil lost every year.
Over the past half-century, modern farming has failed to safeguard soil structure and organisms, reducing it to little more than 'dirt' - a sterile medium in which nothing can grow without artificial fertilisers. It is a self-perpetuating cycle of destruction and chemical dependence. Without soil organisms and soil structure to retain them, water and nutrients leach away, and the soil compacts and becomes prone to erosion.
Land degradation costs up to $10.6 trillion a year. In the UK, that cost is between £900 million and £1.4 billion a year - half of which is caused by loss of organic matter, over a third by compaction, and about 13% through erosion. The depletion of topsoil is so severe in the UK that in 2014 Farmer's Weekly magazine announced we have only a hundred harvests left.
Agronomists are increasingly advocating systems that produce food using 'min-till' (minimum tillage) or 'no-till' (no tillage at all), and concentrating efforts on restoring soil structure and soil organisms.
At Knepp we have seen life returning to the earth in a surprisingly short space of time, suggesting that rewilding could be a very effective, low-cost way of restoring depleted soils. This could be done on a cyclical basis, rather like the traditional fallow system, but using a much longer time frame. So you would take land out of intensive farming for a period of, say, 20, 40 or 50 years, allowing it to rewild and scrub up, giving the soil a chance to repair itself (with all the benefits to wildlife and other ecosystems services that entails), before returning it to a more sustainable form of agriculture.
We need to do proper analysis of our soils in order to understand the detail of what is happening here, but so far the signs are extremely encouraging.
Earthworms are a key indicator of soil health. Surveys of anecic, epigeic and endogeic earthworms at Knepp in 2013 recorded a total of 18 species. Using neighbouring farmland as a baseline, the comparison with Knepp showed an exponential rise in the populations of all three types of earthworm in all three areas of the rewilding project.
Dung beetles perform a vital function, pulling down organic matter into the soil. At Knepp we have found 23 species of dung beetle in a single cowpat. Ants, too, increase the fertility of the soil, creating micro-habitats for numerous other species with their ant-hills, some of which, at Knepp, are now over a half a metre high.
The eruption of fruiting bodies of fungi across the land is another exciting indicator, demonstrating the spread of mycorrhizae through the soil. Mycorrhizae are the fungal filaments that convey water and essential nutrients to the roots of plants. They can extend for miles in the soil, an invisible web transmitting chemical communications between plants. Mycorrhizae can even mine rock, extracting minerals and bringing them into the plant food cycle.
Encouraging, too, is the presence of Southern Marsh, Early Purple and Common Orchids, as well as the rare Bird's Nest and Greater Butterfly orchids - plants that depend on an exclusive, symbiotic relationship with mycorrhizae.
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