Our disappearing soil

 

Our disappearing soil

The earth beneath our feet is the source of a great deal of the life on this planet – but it’s under threat

How was the Earth’s soil formed? Although our planet is 4.54 billion years old, what we think of as soil today didn’t form until about 450 million years ago, thanks to the combined action of percolating water and living organisms. Essentially, soil consists of a mix of materials that have been broken up from rocks and minerals, combined with more or less decomposed organic matter and water. It’s also filled with living things: tiny micro-organisms such as bacteria, archaea and fungi; larger fauna such as insects and earthworms; and the mammals and reptiles that make their homes in it. One gram of soil is estimated to hold anything between 4,000 and 50,000 species of micro-organisms, while the ground beneath our feet is home to a quarter of all animal species on Earth.

Why is it so important? The complex food webs in soil recycle nutrients from the organic material in it, and fix nitrogen from the air. Soil is central to life on Earth: obviously, all human life depends on it – soil contains the nutrients for crops and vegetation to grow, and provides the foothold for their roots. But soil does plenty more besides. It is home to bacteria and fungi which are used in the production of foods ranging from cheese to wine and even soy sauce, and which are crucial to the development of drugs and vaccines, from wellknown antibiotics like penicillin to bleomycin (used for treating cancer) to amphotericin for fungal infections. Soil also imparts huge environmental benefits. It filters rainwater and stores it, regulating the discharge of moisture to prevent flooding. And it acts as a vast and crucially important store of carbon.

How does it store carbon? The world’s soils contain an estimated 2,500 gigatons of carbon – more than three times the amount in the atmosphere and four times what is stored in all living plants and animals. Scientists estimate that soil removes some 25% of fossil fuel emissions from the Earth’s atmosphere each year, making it an essential component in the fight against global warming. In fact, it’s such an effective carbon sink that if we could increase the amount it can store by just 0.4%, we could halt the buildup of CO2 in the air. But the ability of soil to effectively store carbon depends on it both remaining intact and in a healthy state. And, unfortunately, that hasn’t been happening for a long time.

How fast is soil disappearing? Very fast: the world is losing about 30 football pitches of fertile soil every minute, according to the Soil Association. Since the industrial revolution, about 135 billion tonnes of soil is estimated to have been lost from farmland, according to soil scientist Professor Rattan Lal. In Iowa’s fertile farmland, for instance, the average topsoil depth decreased from 14-18 inches at the start of the 20th century to 6-8 inches by its end. And it’s not just the speed at which soil is disappearing that’s the problem; it’s the quality of the soil that remains. “Many types of soil degradation are invisible,” says Ronald Vargas, of the UN Food and Agricultural Organisation. “You just don’t see the loss of organic carbon from soils or pollution building up in it until you try to plant crops there.” The ability of soil to support plant life is being reduced by erosion, compaction, nutrient imbalances, acidification and water-logging around the world.

Why is that happening? Several of the most significant causes are climate-related. Some 29 million acres of land are lost every year to desertification, the loss of vegetation often brought about by shifts in climate and by over-grazing. Rising temperatures also increase the frequency of droughts and wildfires, which degrade the quality of soil. Other causes are still more directly linked with human behaviour. One is urbanisation, as the growth of towns, cities and road networks seals soil beneath layers of asphalt and concrete. And another is deforestation: vegetation is being removed on a mass scale around the world, exposing soil to erosion from wind and rain and meaning that it cannot be replenished by organic matter. But perhaps the most immediate threat to the world’s soil comes from agriculture.

How does farming harm soil? It isn’t farming per se that’s the problem; it’s the way in which agriculture has evolved in recent history. Farms have increasingly come to rely on heavy tilling, multiple harvests and large-scale use of agrochemicals in order to increase yields and maximise profits. In the past 20 years, the world’s agricultural production has increased threefold and the amount of irrigated land has doubled, according to the European Commission’s Joint Research Centre. But that has come at a cost: the JRC has warned that productivity has decreased on 20% of the world’s cropland, 16% of forest land, 19% of grassland, and 27% of rangeland. Heavy ploughing not only disrupts soil ecosystems; it also releases carbon into the atmosphere, hindering the fight against climate change.

What can be done about this? There is a growing awareness of the need to start looking after the Earth’s soil. In 2017, then-Environment Secretary Michael Gove warned that intensive farming had left the UK 30 to 40 years away from the “fundamental eradication of soil fertility” in parts of the country. “Countries can withstand coups d’état, wars and conflict, even leaving the EU,” he said, “but no country can withstand the loss of its soil and fertility.” It’s clear that drastic changes in land use will be required, but the question is how to reduce pressure on the soil while feeding a growing world population (see box). On present trends, the future looks “bleak”, warned a lead author of a UN Food and Agriculture Organisation report in December – but they added that “it’s not too late to introduce measures now”.

Comments