We are losing soil at a rate of 30 soccer fields a minute. If we don’t slow the decline, all farmable soil could be gone in 60 years. Soil grows 95 per cent of our food and sustains human life in other more surprising ways, so this is a huge problem. “Many would argue soil degradation is the most critical environmental threat to humans,” says Peter Groffman, who studies soil microbes at the Cary Institute of Ecosystem Studies in Millbrook, New York.

Soils don’t just grow our food, but have been the source of nearly all of our existing antibiotics, and could be our best hope in the fight against antibiotic resistant bacteria. A single gram might contain 100 million bacteria, 10 million viruses, 1000 fungi, and other populations living amid decomposing plants and various rocks and minerals.

Soil is also a surprising ally against climate change: as nematodes and microorganisms within soil digest dead animals and plants, they lock in their carbon content. Even in their degraded state, it is estimated the world’s soils hold three times the amount of carbon as does the entire atmosphere.  Water is also lost when soils degrade. A UK government report published in 2012 suggested soil degradation costs the country £233 million in flood damage each year.

Small wonder endangered soil is making ecologists so nervous. Soil extinction transforms a fecund soil into a dusty, micro-biologically flat shadow of its former self. Once that diversity is gone, it’s gone for a long time. Soil takes thousands of years at a minimum to be productive. Worn out soil tends to form a dense, compacted layer that repels both roots and water. Farmers try to get rid of it.  “Everything we do causes soil to erode,” says Groffman.  In the past farmers left fields fallow or rotated crops that needed different nutrients. Or they grew peas or beans that added nitrogen to the soil via the nodules in their roots that host rhizobia bacteria .  This kept the soil in balance.  But so industrial has farming become, and so mono-cultural, that these good practices have been abandoned .  Instead they cover the ground with ammonium nitrate.   But chemical fertilisers can release polluting nitrous oxide into the atmosphere and excess is often washed away with the next rain. This leaches nitrogen into rivers, damaging algal blooms. More recently, we have found that indiscriminate fertiliser use hurts the soil itself, turning it acidic and salty, and suppressing the symbiotic relationships between fungi and plant roots, sometimes turning beneficial bacteria against each other.

Tomorrow: what is being done about it.