By Ochieng’ Ogodo

For a continent where millions of people depend on agriculture as a source of livelihood and economic gains, the prospect of depleted soil fertility is not something one wants to hear.

But African soils are fast becoming nutrient deficient with low yields spelling a bleak future for many. Keith Shepherd, soil scientist with the Nairobi-based World Agroforesty Centre or ICRAF, said many factors account for the worrying scenario. “The organic matter in the soil has been mined intensely but supply has been suppressed. There has been low level of nutrient input,” he said. Because of this there isn’t enough nutrient supply for crops.

The decline in organic matter has led to soils becoming physically degraded and has accelerated water run-off, which erodes the richer part of soils into water bodies. “This has led to progressive decline in water quality and increased siltation, especially in lakes and dams.”

Another important soil capital, phosphorous, is inherently low and this basic problem has not been addressed in Africa as opposed to other regions such as Australia, the US and Europe. Many soils in Africa are also sensitive, including old lake deposits, and if you do not apply good farming methods the soils will be swept away leaving large portions less productive.
“Agricultural development,” he said, “was critical for poverty alleviation in Africa but despite this, there has been a decline in investment in agriculture in the last 30 years.

Not all is lost

“Both policy makers and scientists are now waking up to this,” said Shepherd. The realization is that without reviving the agricultural sector, the majority of people in Africa will remain stuck in a whirlpool of poverty and with ever diminishing ability to adapt to modern technologies.

“A lot can be done by improving support for farmers, like making inputs widely available, creating credit and supplying higher value crops,” Shepherd pointed out.
One of the ways of addressing the problem, according to Shepherd, is through agroforestry where farmers grow trees on farms along with other crops, and can use or sell products from their trees such as timber or fruits.

There are also trees that fix nitrogen in the soil and act as natural fertilizers. Another example is leguminous fodder trees which are grown by farmers in many places, including around Mount Kenya, to feed to dairy cows and goats.
Trees, Shepherd explained, can also be important for stabilizing ecological systems, and farmers can benefit from woodlots and planting trees on boundaries.
The World Agroforestry Centre is now involved in many projects aimed at replenishing the diminishing African soil capital for better yields and improved livelihoods.
“One of our main projects is to contribute to the African Soil Information Service (AfSIS) to enable stakeholders to get better information on problems and opportunities relating to soils in Africa,” he said. Taking advantage of georeferencing, the scientists are now sampling and analysing soils from all over sub-Saharan Africa.

Through infra-red spectroscopy - whereby light is shone on the soil sample and the reflected light collected back as a spectral signature - together with new similar x-ray techniques, it is possible to get information on the amounts and types of minerals and chemical elements in the soil. From this, the type and quantities of nutrients in a particular area can be determined and the amount of water it can hold. Thus helping to advise on optimal soil management.
Through AfSIS, the Centre and its partners are currently involved in soil survey across sub-Saharan Africa using randomly located sampling sites. Regional field crews in Tanzania, Mali, and Malawi study landforms, vegetation, and measure trees for biomass and water infiltration rates.

“This program started a year ago and is funded by Bill and Melinda Gates Foundation and the Alliance for a Green Revolution in Africa (AGRA), and is hosted by the Centre’s sister institute, the Tropical Soil Biology and Fertility Institute of the International Centre for Tropical Agriculture (CIAT-TSBF)” he explained. The project is also conducting crop testing trials to see how soils respond to fertilizers. “When we work in a particular country we train national teams from national programmes to contribute to the African Soil Information Service to help improve national services”

Advice to different stakeholders

A key goal of the World Agroforestry Centre says Shepherd, is to give advice to different stakeholders ranging from farmers to policy makers and development banks on constraints faced and appropriate land management interventions, like the right agroforestry and soil management techniques for different types of soils and locations. A key need in getting information to farmers, he said, is the building of national and private extension services for advising farmers on appropriate crops and trees, for example for acidic soils. There is also increasing opportunity, he pointed out, to get information to farmers through local internet services and mobile phone services.

At a national level, the Centre provides advice to governments in planning agricultural development programmes for different areas, in developing policies for protection of the environment, and on the role of agroforestry in these developments.

The Centre’s information is made available to the donor community and development banks to provide guidance on funding and support that they could be directed at agriculture. “Agriculture is vital for economic development, poverty alleviation and basic food security, and there will be a lot of spin-offs like processing of food and tree products for internal and external markets,” said Shepherd.