Inspired by an amazing book by Matthew Evans on Soil[i] I wrote two blogs last year trying to summarise parts of what he wrote.[ii]  [iii]This is my third.

I have previously described the harm that humans have done to soil by mining and eroding it particularly with the use of the plough, but we can also build it and indeed in some parts of the world humans have been doing this for thousands of years. Most of the land in the Amazon valley is not  actually as fertile as many people think. In fact as a rule it's a pretty poor place to grow crops, thanks to nutrient leaching from high rainfall and the fast rate of organic carbon decomposition due to the warm temperatures. Amazon soils are generally not very suitable for agriculture. However, certain parts of the Amazon basin have far richer soil than the relatively impoverished soils nearby and these patches have been made highly fertile by the deliberate actions of people. They used charcoal. They added it deliberately to the soil in relatively small quantities which have an extensive impact. It seems that carbon, in the form of charcoal, can store minerals in a manner that plants can take up, but water can't flush out. Its porous, so it holds air to provide a safe home for microbes, and the hyphae from fungi can wheedle their way through it. Different cultures in South America, New Zealand, Europe and Asia have worked out ways to either conserve soil or make more of it.

Most of us think that weeds in our garden should just be weeded out. However, the weed can tell you a lot of things about the soil underneath. The weed is just an opportunistic plant, after all. Dock thrives where the soil is dense, where it's a bit airless and compacted. Bracken likes well-drained soil. Clover can indicate low nitrogen. A weed is simply a plant in the wrong place. They're not bad in or of themselves but rather can be a useful tell-tale symptom of soil. Some weeds are soil conditioners helping to break up the earth and allowing more air while drawing up minerals from deeper down. They exist because they are eating soil. They are colonising your garden because there's a vacancy in the ecosystem for them.

A gardener or a farmer should use such evidence and indeed other visual signs to manage and improve the health of their piece of land. It's important to look for diversity. Nature hates monocultures and our tendency to forget that farmers used to know about rotation of crops. They would never have thought that a  healthy forest consisted of just one species of commercially desirable tree. We might not be able to see very much below the ground but we can infer a great deal from what we can see near the top.

Those of us (and this does not include me) who are lucky enough to know how to grow their own food, also know that it tastes better than the commercial stuff. Growing food on an industrial scale has become overly complicated commercially. It is not just the result of 1000 industrially made chemicals, but also vast distances. In the United States the average food stuff on a supermarket shelf has travelled an average of 1500 miles. In a fossil fuel truck. At least in some parts of the world including the USA some people know this and, for example, in Detroit over 23,000 residents are involved in urban gardening and the city boasts more than 1500 individual urban gardens. People might live in apartments but they still garden.

The incidence of this in the UK has varied greatly depending on external events. The number of allotments sky rocketed at the outbreak of the First World War increasing from about 440,000 to over 1.5 million three years later. These numbers then gradually halved to about 700,000 just prior to World War Two. But the fresh outbreak of war in 1939 led to a new more concerted urban garden scheme. By 1942 food imports had halved but allotment numbers had doubled again. Public parks, school playgrounds and factory courtyards were all transformed into allotments. By 1943 there were 3.5 million allotments in Britain producing over 1,000,000 tonnes of vegetables. Even the lawns outside the Tower of London were used to grow food.

Soil also has some impact on our physical health as an urban existence removes us from soil, and from the genesis of much of our inner community that is in the human gut. We simply don't get the bugs in and on us that we used to. This removal from soil has mirrored the upward trajectory in the incidence of simple autoimmune diseases, non-communicable diseases, and mental health disorders.

When expert gardeners are asked how to improve your soil and your garden they might often say in the manner of Tony Blair ‘these three things will make your garden more productive, more pleasurable, the soil more alive. Just remember them in this order: compost, compost and compost.’ Compost is decayed organic matter but it's also a living system, with trillions of microbes. It contains the building blocks that soil life loves. Whole ecosystems are built on decay, and its ability to reuse what's been living. Compost, when it's finished, comes from the same kind of composite materials that nature mixes in forests, when leaves, animal matter, branches and all once living things fall to the forest floor and are consumed by worms as well as microbial and arthropod life. We don't fully understand how it works but we know that it does and we do know how to make it.

The organic soil movement began in the United Kingdom. Lady Eve Balfour used her not inconsiderable inherited wealth to explore the role of soil in plant health. In 1919 she bought a property, Haughley, that later became the first testing ground of organic agriculture alongside modern chemical based farming which became known as the Haughley Experiment. In 1943 her book The Living Soil introduced many to the idea that soil was indeed alive and she followed that success in May 1946 by founding The Soil Association, widely regarded as one of the first soil health focused groups in the world. Today the Soil Association is still active and still tries to focus on the biological, the living part of soil which is often neglected in the mainstream world where soil has been seen as just physical and chemical.

Dead things including people are terrifically good for soil. There have even been research experiments where volunteers after death have simply been laid out to decompose. Blood and bone - a common soil amendment - are great for fertility in the garden or on crops. We know that animals must die in nature and be returned to the earth first by scavengers, maybe carrion eaters and insects and then by bacteria and other microbes. These experiments have confirmed that soil does become much more fertile when a human body is laid on the ground and decomposes. Perhaps this concept might seem somewhat gruesome, but it does show how soil fertility and microbial life can vary a lot within a very small distance.

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