July 16, 2008 7:32 pm

Soil under strain

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farmers planting maize lesotho

Civilisation sprang from dirt. The thin layer of topsoil, formed on parts of the earth’s surface over thousands or hundreds of thousands of years, enabled crops to be cultivated and gave early farmers a reliable food source. On average, that layer is only three feet deep.

But now that dirt is in danger. “The world’s cropland is losing topsoil through erosion faster than new soil is forming, thereby reducing the land’s inherent productivity,” warns Lester Brown, founder of the Earth Policy Institute, in his book Plan B. “Where losses are heavy, productive land turns into wasteland.”

Farmland across the world is affected, stretching from the wheat-covered prairies of the US to chemically contaminated tracts of eastern Europe and China. But the problem is most acute in Africa, where farmers tilling some of the world’s oldest soils are among the least able to take action to protect their most important resource.

These problems are not new. Some archaeologists assert that civilisations such as the Mayans, the Easter Islanders and the Norse settlers of Greenland collapsed because of the depletion of their soils, caused by over-use, deforestation or climate change. More recently, the “dust bowl” of 1930s America provided a stark warning of the dangers.

What has changed is population pressure: there are now more than 6.5bn people on the planet, a figure that is forecast to rise to 9bn by mid-century. Though scientists estimate that there is enough suitable uncultivated land to meet increased demand until at least 2020, feeding the world demands that existing fields remain productive.

The soil degradation problem has been worsening for decades but it has taken the food price rises of the past two years to spur policymakers to take the issue seriously. A report from the International Assessment of Agricultural Science and Technology, which found that the rate of yield increases was faltering, concluded that a large part of the reason was the declining quality of soils.

“Land degradation is certainly linked to the food crisis,” says Parviz Koohafkan, director of the land and water division at the United Nations Food and Agriculture Organisation in Rome. “It is not such a direct and immediate threat [as changing supply and demand pressures] but we will have more and more of a problem, as soils in many places are becoming less and less resilient.”

The reasons for soil degradation are as varied as the soils themselves. In the US, soils have been protected since the 1930s, when the federal government was forced to take action on conservation. Nevertheless, North American farmers are still losing topsoil at 1 per cent a year, according to David Montgomery, a geologist and author of Dirt: The Erosion of Civilisations. The losses often occur through erosion by water, as downpours or even irrigation wash topsoil into rivers and dams. A study published in Science in the 1990s found that soil erosion cost the US economy about $44bn (€28bn, £22bn) a year.

In Australia, one of the world’s most important wheat producers, increased salinity is a serious problem, as farmers pump more water from underground aquifers and as years of heavy fertiliser and pesticide use take their toll.

The European Union is consulting on a Soil Directive to address the issue. According to a “soil atlas” published in 2005 by the EU’s Joint Research Centre, in southern Europe nearly 75 per cent of soil had an organic matter content – a measure of fertility – low enough to be a cause for concern. “Soil is a non-renewable resource and we need to take action to protect it,” says Arwyn Jones, a research scientist at the centre one of the authors of the atlas.

In Spain and Italy, in particular, the erosion of soil by water and wind is a serious problem. An increasing tendency for farmland to fall out of cultivation exacerbates the problem: when the crops are taken away, the bare soil is vulnerable until wild vegetation re-establishes itself.

In the EU’s new member states to the east, more than one-third of land is affected by soil degradation, according to the soil atlas. In China, meanwhile, industrial pollution is one of the main culprits. Rivers running black with industrial effluent do not tend to bode well for farmland, while increasing demand for water is also taking its toll, allowing desert to swallow the drier areas of what was once fertile land.

It is Africa that is suffering the most. “Africa’s soils are among the poorest in the world, and poor soils produce poor crops,” said Kofi Annan, former secretary-general of the UN, at the launch last year of the Alliance for a Green Revolution in Africa (Agra), of which he is chairman. Cereal yields in sub-Saharan Africa are barely 1 tonne per hectare, compared with yields in Asia of well over 3 tonnes. While cereal yields in other developing regions rose by between 1.2 and 2.3 per cent a year from 1980 to 2000, those in Africa increased by just 0.7 per cent a year, according to the World Bank.

Africa’s soils suffer from several disadvantages. First, the continent is geologically old and has been home to people for a long time. Ancient soils are thin and often lack the structure necessary to hold water and nutrients. The deep red colour characteristic of the continent’s soils betrays another difficulty: such earth is heavily laden with iron, which “binds” phosphorus, rendering it unavailable to plants. African soil also often lacks the key nutrients of nitrogen and potassium, as well as less important substances such as zinc, says Otto Spaargaren, head of the World Data Centre for Soils at the International Soil Reference and Information Centre.

These problems are compounded by poor agricultural practices. Mr Koohafkan explains: “Farmers are driven by their immediate needs to provide food and income.” As a result, “they are ‘mining’ their own resources”, he says. “They are using up their capital and they can’t re­invest in those resources.”

Traditional farming practices that might have preserved the soils have fallen away under the pressure of feeding so many more mouths. “No longer can traditional systems answer the demand of [an] increasing population,” says Mr Koohafkan.

“The [practice of leaving ground] fallow has disappeared. The size of the plots is smaller, so they don’t provide a sufficient income for people to both feed themselves and invest in the future.” A lack of security of tenure in some areas exacerbates the problem, as people are unwilling to invest in the future of land they do not own or that they could be thrown off, he adds. “[Soil degradation] is a structural problem, not a temporary problem,” he concludes.

As a result, according to the International Centre for Soil Fertility and Agricultural Development, Africa loses about 8m tonnes of soil nutrients a year, while more than 95m hectares of land have been degraded to the point where productivity is greatly reduced.

As Agra notes, “such severe soil depletion results in a vicious cycle of declining yields, deepening poverty, and increased degradation of the natural resource base that farmers depend upon ... As soils decline and farm yields drop, impoverished farmers move on to clear forests and savannah, where the cycle begins again.”

African farmers are among the lowest users of artificial fertilisers in the world. Could shipping in millions of tonnes of the chemicals used to enhance soil in the US, Europe and Asia be the answer? It is not so simple, warns Mr Spaargaren.

“The soils themselves can’t hold much fertiliser, because their nutrient retention is so poor,” he says. “You can pour fertiliser on to land like that but most of it will be washed away.” Even if large quantities of fertiliser are applied to degraded soils, it would still take centuries to recover their health, he says. Overuse of fertiliser can also generate problems such as the acidification of the soil that has occurred in places such as Europe and Australia.

Yet the overuse of fertilisers is a problem that most African farmers can only dream of having. Many lack the income to buy even small amounts, and the infrastructure that developed-world farmers take for granted – banks that will give credit and wait until the crops are sold to be repaid, together with reliable networks of agricultural suppliers – is seldom in place.

What about natural fertilisers? Again, soils that are too poor to hold artificial nutrients cannot hold on to natural ones either and some of it is washed into water courses. Using animal manure also requires sufficient land to graze animals, which is not always possible – and some experts suggest that over-grazing on unsuitable lands is exacerbating soil erosion and desertification.

If soil degradation is to be halted, experts agree, the answer will be some combination of fertiliser use and improvements in farming methods. “We need a 21st-century green revolution designed for the special and diverse needs of Africa,” said Robert Zoellick, president of the World Bank, when announcing an initiative this year in which Agra was granted $164.5m from the Bill and Melinda Gates Foundation and $15m from the Rockefeller Foundation to establish a soil health programme for the continent. “It must be driven by greater investments in technological research and dissemination, sustainable land management, agricultural supply chains, irrigation, rural microcredit and policies that strengthen market opportunities while assisting with rural vulnerabilities and insecurities.”

The lessons are not unique to Africa, moreover. Improved farming methods are required around the world to ensure that erosion is minimised and the nutrient content is maintained. “Farmers can be taught better practices,” says Steve McGrath, a scientist at the Rothamsted Institute, a centre for agricultural research. One example is no-till farming, says Julian Little, chairman of the ABC. This requires a mixture of carefully managed crop rotation, the introduction of secondary “undercrops” to prevent the growth of weeds, as well as “the judicious use of herbicide”.

The US Soil Conservation Service, set up after the devastation of the dust bowl, has been teaching similar techniques for years, along with manuring and the use of artificial fertiliser. Other techniques are simple, such as ploughing along the contour of fields so that water does not run off and take topsoil with it, and maintaining hedgerows or ditches as field boundaries.

About three feet of topsoil represents the foundation of human civilisation. The pressure of feeding a population of 9bn people is likely to stretch that resource to the limit.

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