By James Morgan
Science reporter, BBC News
Maize farmers in Malawi will benefit from accurate soil assessments
The first detailed digital soil map of sub-Saharan Africa is to be created.
The £12.3m ($18m) project will offer farmers in 42 countries a "soil health diagnosis" and advice on crop yields.
Scientists from the International Center for Tropical Agriculture (CIAT) will take soil samples from across the continent and analyse nutrient levels.
These will be combined with satellite data to build a high-resolution map, to be disseminated freely to poor farmers by local extension workers.
The interactive online map, known as the African Soil Information Service (AfSIS), will be accompanied by advice on how to tackle soil deficient in nutrients.
If we are to feed growing populations and cope with climate change, we need accurate information on the state of Africa's soils
It is the first stage of project to build a global digital map - called GlobalSoilMap.net - covering 80% of the world's soils.
The initial four-year programme is being funded by a grant from the Bill & Melinda Gates Foundation and the Alliance for a Green Revolution in Africa (Agra).
"From the farmer in the field, right up to to the secretary general of the UN, we need precision soil information," said Pedro Sanchez, of Columbia University's Earth Institute, a partner in the project.
Soils are heavily degraded across large swathes of Africa
"But we do not have this in sufficient detail.
"For example, in the whole of Malawi there is only one fertiliser recommendation for maize - but there are many different soil types.
"We have to get into the 21st century," he told BBC News.
"While other disciplines, such as climate science, have created detailed digital maps, we are still catching up."
African soils are among the poorest in the world, and many farmers suffer from chronically low-yielding crops.
More than 50% of land in Africa is unsuitable for any kind of cultivated agriculture except nomadic grazing.
Of the remaining agricultural land, a large proportion is either moderately or severely degraded.
Soil quality is under pressure from growing populations and food demand. This is exacerbated by the extremely low input of nutrients.
Scientists will take thousands of soil samples across Africa
On average, African farmers are able to apply only 10% of the nutrients that farmers in the rest of the world return to the soil.
Agra is leading a drive to help them harness higher yielding practices, by widening access to improved seed varieties, irrigation and fertilisers.
These include organic inputs - such as manure, grain legumes and agroforestry.
But efforts so far have been hampered by a lack of up-to-date, comprehensive knowledge about current soil conditions.
AfSIS aims to pinpoint areas where soils are at risk, and identify the types of mineral and organic nutrient sources needed to increase crop yields.
Soils are considered "healthy" when they are able to produce crops, store carbon from the atmosphere and regulate water flows.
They will begin by making ground observations at 60 so-called "sentinel" sites (areas of 100 square kilometres) proposed for 21 African countries.
Climate change will increase pressure on soils and reduce staple crop yields
These will be combined with satellite imagery and "legacy" data found in archives and other repositories worldwide.
The resulting high resolution maps will display soil capacities and constraints such as aluminium toxicity, a common debilitating feature of tropical acid soils.
From this core data, scientists will then be able to predict soil data at locations across Africa where no direct observations have been made, using computer models to extrapolate.
The soil information will be made available via the internet in a "user-friendly manner" on a website - Africasoils.net.
The aim is to build an interactive online tool, which will give extension workers and policymakers the information they need to determine how best to restore their "sleeping soils".
Meanwhile, an "aggressive" program of dissemination will ensure that AfSIS is readily available to African farmer associations and extension services, said a spokesman.
From the farmer in the field, right up to to the secretary general of the UN, we need precision soil information
The plan is to continually monitor and update the map, with an ongoing soil surveillance service.
"If we are to reduce poverty, feed growing populations and cope with the impact of climate change on agriculture, we require accurate, up-to-date information on the state of Africa's soils," said Nteranya Sanginga, director of CIAT's Tropical Soil Biology and Fertility Institute.
"With accurate soil maps, we find farmers can increase their yields by around 60%, and sometimes double.
"But currently, our best African soil map has a resolution of 10km, squared.
An example of severe soil degradation in Kenya
"With this new project, we can improve that resolution to a level of one hectare (100 metres, squared)."
Scientists are expected to begin posting their data online by the end of the year, with the first full map completed in four years time.
Thereafter, AfSIS experts will offer training to people "on the ground" - including agricultural extension agents - on how to interpret and translate the soil map information for use in the field.
The project is being led by the Tropical Soil Biology and Fertility (TSBF) Institute, at CIAT, which is one of 15 centres supported by the Consultative Group on International Agricultural Research (CGIAR).
They will collaborate with national agricultural research programs across Africa, including the establishment of regional soil health laboratories in Tanzania, Kenya, Mali, Nigeria, and Malawi.
Other partners include the World Soil Information (ISRIC) at Wageningen University in The Netherlands and the Nairobi-based World Agroforestry Centre.