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A digital map of the state of Africa's soils is to be put together in an initiative launched today (13 January).

The African Soil Information Service, launched in Nairobi, Kenya, will produce a digital map of 42 African countries revealing soil type and its component nutrients.

This information will guide farmers and policymakers on efforts to improve the fertility of Africa's soils, some of which are the most depleted in the world. The project will be coordinated by the International Center for Tropical Agriculture.

The coverage and detail of existing soil maps are poor, particularly in large, scarcely populated countries in Africa, says Alfred Hartemink, soil scientist at ISRIC – World Soil Information, part of Wageningen University in the Netherlands.

"The maps that do exist are 10–30 years old. That poses a problem, because the soil properties of interest — like pH, carbon or phosphorus content — change over time."

The project, funded with a US$18 million grant from the Bill & Melinda Gates Foundation and the Alliance for a Green Revolution in Africa, will gather existing local soil maps and combine them with new measurements to produce the digital map, which will be freely accessible on the web in a user-friendly format.

The new measurements will include those derived from remote sensing, which involves analysing the features of satellite images — such as colour and radiation — to infer the characteristics of the soil. These calculations are then calibrated against actual soil samples from the particular region.

The African map is the first stage of an initiative,, to map all the globe's soils to help informed decisions not only about agriculture, but also to monitor the effects of climate change, environmental pollution and deforestation.

Hartemink says the plan is to have 70 per cent of the world mapped within five years, with a full map completed within 10–15 years.

"The first step, the collection of existing soil and map data and the calibration of our satellite images, will be hard. After that, updating the maps will be easy," he says.

The project will be coordinated by Hartemink and his colleagues from ISRIC – World Soil Information in the Netherlands, who will ensure the same techniques and standards are used by the coordinating centre in each continent.

Over 50 soil scientists will be involved in the mapping effort.