The Crisis Beneath Our Feet:
On the Destruction of Soil
Isabella Tree on Rewilding the Land
Science is only just beginning to get to grips with the universe of soil organisms, the services they perform and how they interact with each other and affect the plant life above them. For decades, research into soil biology—”one of the most neglected components of the global system,” according to environmentalist Tony Juniper—has been woefully underfunded, sidelined by other, less complex fields of natural science, sexy projects like space technology, and the agro-industry’s funding of research into artificial systems. Only now are scientific techniques coming into play that allow the observation of soil microbes—microbial “dark matter”—in their natural environment rather than within the limiting scope of the laboratory. 99 percent of microbes will not grow in laboratory conditions. In 2015 the journal Nature reported the first discovery for thirty years of a new antibiotic in the soil—teixobactin—capable of killing Mycobacterium tuberculosis, Clostridium difficile and methicillin-resistant Staphylococcus aureus. Most antibiotics are derived from soil microbes and the great hope is that now many other antibiotics new to science can be uncovered in the soil in this way.
At last, things seem to be changing. Several of the United Nations’ Sustainable Development Goals for 2016 to 2030 relate to soils, and the UN’s Intergovernmental Technical Panel on Soils’ report documents how soils are changing globally and the consequences of this for humanity. According to a report published by the Economics of Land Degradation Initiative in September 2015, if sustainable land management was rolled out around the world, as much as $75.6 trillion could be added to the global economy every year through jobs and increased agricultural output. In the UK, major funding programs—like the Natural Environment Research Council’s Soil Security Programme, and the Biotechnology and Biological Sciences Research Council’s SARISA (Soil and Rhizosphere Interactions for Sustainable Agriecosystems) program—focus on the biology of soil and how to integrate this understanding into agriculture.
For Ted Green, the most exciting evidence of recovering soils at Knepp is the eruption of fruiting bodies of fungi. Walking with him along the edge of Hammer Pond in the Southern Block we discovered the rare Boletus mendax, a mycorrhizal mushroom associated with old oaks that, he suggested, could have waited as mycelia amongst the trees’ roots for decades until the right conditions above and below ground enabled it to grow. In a stand of 10-year-old sallow we were surprised by a semi-circle of milk-caps and a cluster of red fly agaric—the lurid red hallucinogenic mushroom of fairy stories. These are Ted’s “recyclers,” the agents of decay. They release enzymes that can break down some of the most durable substances in nature—the fibrous lignin and cellulose of plants, the hard shells of insects, animal bones and even broken rock in the soil.
Encouraging, too, is the presence of orchids—southern marsh, early purple and common spotted orchids, and the much rarer bird’s nest and greater butterfly. These are plants that depend on an exclusive, symbiotic relationship with mycorrhizae. Orchid seeds do not contain nutrition to support germination. This gives them the advantage of having minuscule seeds—weighing only a few millionths of a gram—which they can spread far and wide on the wind. Germination depends entirely on mycorrhizae which colonize the seeds and supply them with food. The appearance of orchids is visible evidence that creeping underground mycorrhizae, Ted’s “food-gatherers,” are spreading their web beneath our fields. Like soil bacteria, the mycorrhizae are freeing up essential elements in the soil, phosphorus, copper, calcium, magnesium, zinc and iron, making them available in a form that plants can absorb.
But mycorrhizae also contribute a final compelling argument to the value of rewilding the soil—that of carbon sequestration. One of the secrets, as Graham Harvey explains in his book Carbon Fields (2008), is an extraordinary substance called “glomalin.” For such a revolutionary substance glomalin is still, amazingly, little discussed. It was discovered in 1996 by soil scientist Sara Wright at the US Agricultural Research Service. A sticky glycoprotein, it is produced by mycorrhizal fungi from carbon extracted from the roots of plants. Its gluey proteins coat the hair-like filaments or hyphae of the mycorrhizae, protecting them from decomposition and microbial attack. Acting as microscopic underground conduits, the hyphae extend the reach of a plant’s roots to areas in the soil that the roots are unable to exploit on their own. Glomalin reinforces the hyphae, sealing the conduits to prevent leakage and ensuring the efficient transport of distant water and nutrients back to the plant.The great concerns of our time all boil down to the condition of the soil.
Glomalin has profound effects on soil as well. As plants grow, the fungal hyphae creep down the plant’s roots establishing new networks near the extending tips. Higher up the root, the defunct hyphae slough off their protective glomalin, which falls back into the soil and attaches to particles of sand, silt, clay and organic matter, forming lumps of soil, or “aggregates,” allowing water, air and nutrients to infiltrate the spaces between. Protected by their tough, waxy coating of glomalin these aggregates are what give soil its structure—the kind of friable tilth a farmer or gardener crumbles appreciatively between their fingers.
Glomalin is extraordinarily durable. Tests have shown it can survive intact in the soil for more than forty years. Its very toughness seems to be the reason it has gone undetected by science for so long. Back in her laboratory in Beltsville, Maryland, Wright found she could only separate glomalin from the soil by immersing it in citrate solution and subjecting it to intense heat for over an hour.
Glomalin is made up of protein and carbohydrate sub-units, both containing carbon, the total of which comprises 20–40 percent of the molecule – a considerable proportion compared to the 8 percent in humic acid, the element once thought of as the main storage material for soil carbon. Aided by glomalin, the “superglue of the soil,” aggregates protect organic carbon from decay by soil microbes. More mycorrhizae in the soil produce more stable aggregates, and more aggregates result in higher soil carbon storage. Amazingly, the world’s soils hold more carbon as organic matter than all the vegetation on the planet, including rainforest. 82 percent of carbon in the terrestrial biosphere—that is, the part of the earth’s land surface including the adjacent atmosphere where life exists—is in the soil.
One of the remarkable features of mycorrhizae is their ability to respond to rising carbon-dioxide levels in the atmosphere by increasing their production of glomalin. In a three-year experiment, scientists at the University of California used outdoor chambers to control carbon-dioxide levels on small areas of natural grassland. They found that when the gas reached a concentration of 670 parts per million—the level it is predicted to reach by the end of this century—the fungal hyphae grew three times as long and produced five times more glomalin than those exposed to today’s levels of carbon dioxide.
Improving the structure of our soils and returning unproductive agricultural land to permanent pasture could be a crucial weapon in the battle against rising levels of CO2. According to the Royal Society, carbon capture by the world’s farmlands, if they were better managed, could total as much as 10 billion tonnes of carbon dioxide a year—more than the annual carbon-dioxide accumulation in the atmosphere. Carbon Farmers of America, a company selling “Carbon Sinks” to clients interested in helping reverse climate change, endorse this. They estimate that if organic matter in the world’s farmed soils was increased by as little as 1.6 percent, the problem of climate change would be solved. Alan Savory, Zimbabwean ecologist, proponent of holistic land management and, in particular, a rotational, natural grazing system with the power to return areas of desert, or “brittle zones,” to productive grassland (a system that has come to be known as “mob grazing”), goes one step further. He estimates that restoring the world’s 5 billion hectares (19 million square miles) of degraded grasslands to functioning ecosystems could return ten or more gigatonnes of excess atmospheric carbon to the terrestrial sink annually. This, he claims, would lower greenhouse-gas concentrations to pre-industrial levels in a matter of decades.
Recently, after the Paris Climate Change talks in 2015, the French launched the “4 per 1000” initiative. Its aim is less ambitious but the reasoning is the same: the quantity of carbon contained in the atmosphere increases by 4.3 billion tonnes every year. The world’s soils contain 1,500 billion tonnes of carbon in the form of organic material. Increasing the quantity of carbon contained in soils by just 0.4 percent a year—through restoring and improving degraded agricultural lands—would halt the annual increase of CO2 in the atmosphere. This would go a considerable way to achieving the Climate Change objective of limiting the global temperature increase to 1.5/2 °C, while at the same time increasing global food security by improving soil fertility and stability.
The potential for rewilding projects like Knepp to provide carbon sequestration is of increasing interest to our own government, under pressure to meet its ambitious target of reducing carbon emissions by 57 percent of 1990 levels by 2030. In 2012, researchers from Bournemouth University and the Centre for Ecology and Hydrology prepared a report for DEFRA looking at large-scale restoration projects such as Ennerdale, the Great Fen, the Frome catchment, Pumlumon in Wales and Knepp. They quantified eight key “ecosystems services”—carbon sequestration, recreation, aesthetics, flood protection, provision of food, energy/fuel, raw materials/fibre and fresh water—provided by these projects. Scores were awarded from 0 (not relevant) to 5 (very high importance).
Under the previous intensive farming system Knepp scored 1 for carbon sequestration, 3 for recreation, 5 for aesthetics, 1 for flood protection, 5 for provision of food, 2 for energy/fuel, 3 for raw materials and 2 for fresh water. Under rewilding, most of these scores have risen significantly, up to 5 for carbon sequestration, 5 for recreation (and this was before we began our eco-tourism business), 4 for flood protection, 5 for energy/ fuel and 4 for raw materials. Provision of food remained the same with a top score of 5, and so—interestingly—did aesthetics. The fresh water score—concerned with water reserves for human consumption—remains the same at 2, as we don’t have reservoirs. But we are able to show that rewilding Knepp has improved water quality, something that is of huge ecological importance. Much of the water entering Knepp comes from adjacent farms and built-up areas and is significantly polluted. Testing in 2016 gave all standing water on the Estate the highest reading for water purity, indicating that our land is now providing an effective system of filtration and purification.
The greatest leap in the DEFRA assessment is in carbon storage—an estimated 51 percent rise resulting from the “increased carbon storage capacity of neutral grassland and broadleaved woodland under rewilding.” Over a period of fifty years, the report estimated, Knepp Wildland will have stored an additional £14 million worth of carbon.
The great concerns of our time—climate change, natural resources, food production, water control and conservation, and human health—all boil down to the condition of the soil. It seems we are, at last, beginning to reappraise the essential medium of earth’s biology, that thin, living skin. We are starting to appreciate its potential for doing many of the things we thought, arrogantly, we could do on our own. By returning to the soil we are beginning, after centuries of exploitation and technological hubris, to seek an understanding of how our species can survive in the world not just for the next few decades but for the thousands of years to come, how we can combine our creative intelligence and expertise with systems that have benefitted, unlike us, from millions of years of R and D. It is perhaps unsurprising that the Latin word for soil—”humus”—gives us “human” and “humility.” The soil is, quite literally, what grounds us.
From Wilding: Returning Nature to Our Farm by Isabella Tree. Used with the permission of NYRB. Copyright © 2019 by Isabella Tree.