Soil(III) 移花接木2022-05-28 01:57:51
We might barely detect the loss of a soil’s resilience until, when drought strikes, fertile lands turn to dustbowls
Some crop scientists believe we can counter these trends by raising yields in places that remain productive. But their hopes rely on unrealistic assumptions. The most important of these is sufficient water. The anticipated growth in crop yields would require 146% more fresh water than is used today. Just one problem: that water doesn’t exist.
Over the past 100 years, our use of water has increased six-fold. Irrigating crops consumes 70% of the water we withdraw from rivers, lakes and aquifers. Already, 4 billion people suffer from water scarcity for at least one month a year and 33 major cities, including São Paulo, Cape Town, Los Angeles and Chennai, are threatened by extreme water stress. As groundwater is depleted, farmers have begun to rely more heavily on meltwater from glaciers and snowpacks. But these, too, are shrinking.
A likely flashpoint is the valley of the Indus, whose water is used by three nuclear powers (India, Pakistan and China) and several unstable regions. Already, 95% of the river’s flow is extracted. As the economy and the population grow, by 2025 demand for water in the catchment is expected to be 44% greater than supply. But one of the reasons why farming there has been able to intensify and cities to grow is that, as a result of global heating, glaciers in the Hindu Kush and the Himalayas have been melting faster than they’ve been accumulating, so more water has been flowing down the rivers. This can’t last. By the end of the century, between one- and two-thirds of the ice mass is likely to have disappeared. It is hard to see this ending well.
And all this is before we come to the soil, the thin cushion between rock and air on which human life depends, which we treat like dirt. While there are international treaties on telecommunication, civil aviation, investment guarantees, intellectual property, psychotropic substances and doping in sport, there is no global treaty on soil. The notion that this complex and scarcely understood system can withstand all we throw at it and continue to support us could be the most dangerous of all our beliefs.
Soil degradation is bad enough in rich nations, where the ground is often left bare and exposed to winter rain, compacted and wrecked by overfertilisation and pesticides that rip through its foodwebs. But it tends to be even worse in poorer nations, partly because extreme rainfall, cyclones and hurricanes can tear bare earth from the land, and partly because hungry people are often driven to cultivate steep slopes. In some countries, mostly in Central America, tropical Africa and south-east Asia, more than 70% of the arable land is now suffering severe erosion, gravely threatening future production.
Climate breakdown, which will cause more intense droughts and storms, exacerbates the threat. The loss of a soil’s resilience can happen incrementally and subtly. We might scarcely detect it until a shock pushes the complex underground system past its tipping point. When severe drought strikes, the erosion rate of degraded soil can rise 6,000-fold. In other words, the soil collapses. Fertile lands turn to dustbowls.
Some people have responded to these threats by calling for the relocalisation and de-intensification of farming. I understand their concerns. But their vision is mathematically impossible.
A study in the journal Nature Food found the average minimum distance at which the world’s people can be fed is 2,200km. In other words, this is the shortest possible average journey that our food must travel if we are not to starve. For those who depend on wheat and similar cereals, it’s 3,800km. A quarter of the global population that consumes these crops needs food grown at least 5,200km away.
Why? Because most of the world’s people live in big cities or populous valleys, whose hinterland is too small (and often too dry, hot or cold) to feed them. Much of the world’s food has to be grown in vast, lightly habited lands – the Canadian prairies, the US plains, wide tracts in Russia and Ukraine, the Brazilian interior – and shipped to tight, densely populated places.
As for reducing the intensity of farming, what this means is using more land to produce the same amount of food. Land use is arguably the most important of all environmental issues. The more land farming occupies, the less is available for forests and wetlands, savannahs and wild grasslands, and the greater is the loss of wildlife and the rate of extinction. All farming, however kind and careful, involves a radical simplification of natural ecosystems.
A new understanding of soil could be the answer to safer, more productive growth of cereals, roots, fruit and vegetables.
Environmental campaigners rail against urban sprawl: the profligate use of land for housing and infrastructure. But agricultural sprawl – using large amounts of land to produce small amounts of food – has transformed much greater areas. While 1% of the world’s land is used for buildings and infrastructure, crops occupy 12% and grazing, the most extensive kind of farming, uses 28%. Only 15% of land, by contrast, is protected for nature. Yet the meat and milk from animals that rely solely on grazing provide just 1% of the world’s protein.
One paper looked at what would happen if everyone in the US followed the advice of celebrity chefs and switched from grain-fed to pasture-fed beef. It found that, because they grow more slowly on grass, the number of cattle would have to rise by 30%, while the land area used to feed them would rise by 270%. Even if the US felled all its forests, drained its wetlands, watered its deserts and annulled its national parks, it would still need to import most of its beef.
Already, much of the beef the US buys comes from Brazil, which in 2018 became the world’s largest exporter. This meat is often promoted as “pasture-fed”. Many of the pastures were created by illegally clearing the rainforest. Worldwide, meat production could destroy 3m sq km of highly biodiverse places in 35 years. That’s almost the size of India.
Only when livestock are extremely sparse is animal farming compatible with rich, functional ecosystems. For example, the Knepp Wildland project in West Sussex, where small herds of cattle and pigs roam freely across a large estate, is often cited as a way to reconcile meat and wildlife. But while it’s an excellent example of rewilding, it’s a terrible example of food production.
If this system were to be rolled out across 10% of the UK’s farmland and if, as its champions propose, we obtained our meat this way, it would furnish each person here with 420 grams of meat a year, enough for around three meals. We could eat a prime steak roughly once every three years. If all the farmland in the UK were to be managed this way, it would provide us with 75kcal a day (one 30th of our requirement) in meat, and nothing else.
Of course, this is not how it would be distributed. The very rich would eat meat every week, other people not at all. Those who say we should buy only meat like this, who often use the slogan “less and better”, present an exclusive product as if it were available to everyone.
Campaigners, chefs and food writers rail against intensive farming and the harm it does to us and the world. But the problem is not the adjective: it’s the noun. The destruction of Earth systems is caused not by intensive farming or extensive farming, but a disastrous combination of the two.
So what can we do? to be continued ...
