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Peak soil

A Saskatchewan dust storm blows away the future.


Oil is what most of us think of as a strategic resource, yet in the long run it is soil which is the more important. Even so, people’s eyes tend to glaze over when talk turns to soil conservation, maybe because it’s so much easier to see the immediate relevance of rising gas prices and climate change in these days of peak oil. So while public attitudes on climate change have shifted dramatically over the past few years, a crisis in global agriculture remains hidden: we are, and have long been, using up the supply of topsoil we rely on to grow our food.

Those of us living in modern cities can easily forget that without fertile soil we could not survive. Yet modern agricultural techniques are eroding the very soil on which food production depends. This ongoing soil loss means we face the problem of feeding a growing population from a shrinking land base. This should be troubling because even a casual reading of history shows that, under the right circumstances, climatic extremes, political turmoil or resource abuse can bring down a society. And in the century ahead we face all three, as shifting climate patterns and depleted oil supplies coincide with progressive loss of farmland.

We have, in effect, been ‘mining’ soil for much of human history. Indeed, the decline in fertility and loss of agricultural lands through wind and water erosion is a problem as old as agriculture itself. Civilizations from Babylon to Easter Island have proven only as durable as the fertility of their land. The Roman Empire left Eastern Mediterranean agriculture in a state from which it has yet to recover. But the problem of soil loss is not just ancient history. Exacerbated by modern industrial farming, global agricultural soil loss of about a millimetre per year outpaces soil formation by at least tenfold.

Over the past century, the effects of long-term soil erosion were masked by bringing new land under cultivation and by developing fertilizers, pesticides and crop varieties to compensate for declining soil productivity. However, such ‘agrotech’ fixes become progressively more difficult to maintain because crop yields decline exponentially as soil thins. While fertilizers can temporarily offset the effects of soil erosion, the long-term productivity of the land cannot be maintained in the face of the reduced organic matter and thinning of soil that characterize industrial agriculture. Replacing soil fertility with chemical fertilizers and genetically engineered crops can boost productivity in the short run, but a world stripped of its soil cannot, in the end, feed itself. 

Feeding a doubled human population without further increasing crop yields would require doubling the area presently under cultivation. Such vast tracts of land could only be found in tropical forests and subtropical grasslands – like the Amazon and the Sahel. Experience shows that farming such marginal lands produces an initial return, but the land quickly becomes degraded and has to be abandoned – if the population has somewhere to go. With the land best suited for agriculture already under cultivation, expansion into marginal areas is not a long-term strategy.

Photo: Andrew Kokotka

Small and soil friendly

In contrast to the amount of arable land, which has varied widely through time and across civilizations, the amount of land needed to feed a person has systematically declined. Hunting and gathering societies used from 20 to 100 hectares per person; our current use of 1.5 billion hectares of cultivated land to feed roughly 6 billion people equates to about 0.25 hectares of cropland per person. And by 2050 the amount of available cropland is projected to drop to less than 0.1 hectare per person. So, simply keeping up will require major increases in crop yields.

Before 1950, increases in global food production came by either enlarging the area under cultivation or improved husbandry. Since 1950 most of the increase has come from mechanization and intensified use of chemical fertilizers. The ‘green revolution’ doubled food production and averted a food crisis through increased use of chemical fertilizers, massive investments in irrigation infrastructure in developing nations and the introduction of high-yield varieties of wheat and rice capable of producing two or three harvests a year. Subsequently, however, growth in crop yields has slowed and achieving further substantial increases through conventional means seems unlikely – since crops don’t take up half the nitrogen in the fertilizers farmers apply today, adding even more won’t help.

Perhaps genetic engineering could substantially increase crop yields – but only at the risk of releasing super-competitive species into agricultural and natural environments, with unknowable consequences. So far, the promise of greatly increased crop yields from genetic engineering remains unfulfilled. And it could prove catastrophic, should genetically modified genes that convey sterility cross to non-proprietary crops. Does it even make sense to design crops that can’t reproduce?

So how do we move to sustainable agriculture and still feed the world? The answer lies in better adapting what we do to where we do it. To do this we need to restructure agricultural subsidies to favour small-scale organic farms, encourage soil-friendly farming methods such as no-tilling (see below) for larger industrial farms, and develop urban agriculture.

Among soil scientists, concern over the world’s fast-depleting soil is almost universal

Public dialogue and media portrayals of organic farming tend to the simplistic, pitting those who consider modern industrial farming unsustainable against those who argue that organic methods are unethical when hunger plagues so many people. Representatives of agribusiness like to question the relevance of organic agriculture in feeding a 10-billion-person planet and instead promote agrochemicals and genetically modified crops as keys to food security. Yet many studies over the past decades have shown that crop yields under organic methods are comparable to those achieved through conventional methods. Indeed, some of the highest crop yields come from small-scale, labour-intensive organic farms.

Many currently profitable industrial farming methods would become uneconomic if their true costs were incorporated into market pricing. Direct financial subsidies and failure to include the costs of depleting soil fertility encourage practices that degrade the land. In the US, for example, the top 10 per cent of agricultural producers now receive 66 per cent of the more than $10 billion handed out in annual subsidies, and they use it to support large farms growing single crops, particularly wheat, corn and cotton. We need to curb the $300 billion in global agricultural subsidies – more than six times the world’s annual development assistance budget – that encourage unsustainable industrial farming. Shifting public support to make organic agriculture more competitive is part of the answer.

No-till alternative

No-till agriculture also warrants greater public support, as it can effectively maintain crop yields and slow down soil loss, even on large, mechanized farms. Instead of using a plough to turn the soil and open the ground, no-till farmers push seeds into the ground through the organic matter left over from prior crops, minimizing direct disturbance of the soil. Although adoption of no-till methods is often accompanied by increased herbicide use, crop residue left at the ground surface acts as mulch, helping to retain moisture and retard erosion by as much as 90 per cent. With no-till practices currently being used on less than 10 per cent of global cropland, there is tremendous potential to expand them, and to research how to couple them better with organic methods.

Industrial agriculture will never provide a way out of hunger for the third of humanity that lives on less than two dollars a day. More innovative thinking is necessary, and on a global scale. If we are to feed those too poor to buy food, the naïve idea that all we need to do is produce cheap food must go. While food was still cheap there were still far too many hungry people on the planet. A different approach – one that might actually work – would be to promote the prosperity of small farms in the Global South so that subsistence farmers can feed themselves, generate an income and become stewards of the land. To do this they need access to enough land to grow a marketable surplus, and an agricultural support system that builds on indigenous agricultural knowledge and provides appropriate tools.

Finally, as oil and the cost of shipping food around the world become more expensive, it will become increasingly attractive to take food production to the people – into the cities. With 800 million people already involved, urban farming is not restricted to developing countries; by the late 1990s two-thirds of Moscow’s families were engaged in urban agriculture. City agriculturalist Will Allen has been pioneering urban farming in Milwaukee, Wisconsin, as a way to provide healthy, affordable diets to low-income urban populations. He has come to realize that urban farms not only deliver fresh produce to city dwellers at a lower cost of transportation, but that they typically use far less water, fertilizer and oil, and can reduce urban waste disposal problems and costs.

Among soil scientists, concern over the world’s fast-depleting soil is almost universal. Unfortunately, saving dirt just isn’t a very sexy issue. However, time grows short and industrial agriculture is proving an expensive and increasingly risky dead end. We are left with a fundamental challenge: how do we merge traditional agricultural knowledge with modern understanding of soil ecology to promote and sustain intensive agriculture? Herein lies our real hope for feeding a hungry world.

David R Montgomery is the author of Dirt: The Erosion of Civilizations and professor of geomorphology at the University of Washington.