Soil crisis is holding back African recovery

The fertility of Africa's soil is being depleted at a rate that threatens to undermine the continent's attempts at eradicating hunger with sustainable agricultural development.

A study has found three-quarters of Africa's farmland is plagued by severe soil degradation caused by wind and soil erosion and the loss of vital mineral nutrients.

This degradation can partly explain why agricultural productivity in Africa has remained largely stagnant for 40 years while Asia's productivity has increased threefold, the authors claim. Julio Henao and Carlos Baanante of the non-profit International Centre for Soil Fertility and Agricultural Development in Muscle Shoals, Alabama, found bad farming practices have damaged soil health on the continent between 1980 and 2004.

Farmers in Africa have traditionally relied on clearing land to grow crops then leaving it fallow to regain some of its fertility. "But population pressure now forces farmers to grow crop after crop, 'mining' or depleting the soil of nutrients while giving nothing back," the report says.

"With little access to fertilisers, the farmers are forced to bring less fertile soils on marginal land into production, at the expense of Africa's wildlife and forests." Mr Henao and Mr Baanante found that during 2002 to 2004 about 85 per cent of African farmland was haemorrhaging mineral nutrients at an annual rate greater than 30kg per hectare, and 40 per cent of farmland was losing nutrients at the higher rate of 60kg per hectare a year.

"The very resources on which African farmers and their families depend for welfare and survival are being undermined by soil degradation caused by nutrient mining and associated factors, such as deforestation, use of marginal lands and poor agricultural practices," the report says.

The worst-affected countries in terms of soil depletion are Guinea Bissau, the Democratic Republic of Congo, Angola, Rwanda, Burundi and Uganda. With a population growth of 3 per cent per year, the number of malnourished people in sub-Saharan Africa has grown from about 88 million in 1970 to more than 200 million by the end of the last century, the report says.

"Fertiliser use in Africa is less than 10 per cent of that in Asia and that explains much of the contrasting trends," the report says. "Soil nutrient mining, the result of overexploitation of agricultural land, is in fact consumption of a key component of the soil's natural capital," it says.

"African countries face not only the challenge of increasing agricultural production with scarce overall resources, but must raise productivity in a way that conserves the natural resource base and prevents further degradation that has characterised African soils for generations."

Mr Henao and Mr Baanante say African farmers must have access to affordable mineral and organic fertilisers if they are to stand any chance of reversing the decline of soil fertility.

"The main factors contributing to nutrient depletion are loss of nitrogen and phosphorus through soil erosion by wind and water, and leaching of nitrogen and potassium," they say, adding: "Land is being degraded, and soil fertility is declining to levels unsuitable to sustain economic production."