Global use of nitrogen fertiliser is forecast to grow by 1.4 per cent each year to above 119 million tonnes in 2018, according to a report published last week (16 February) by the UN’s Food and Agriculture Organization (FAO).
But less than five per cent of that growth will come from Sub-Saharan Africa, largely because fertiliser is often too expensive for subsistence farmers, it says.
The lack of nitrogen in Africa’s soils is the “most limiting factor” holding back agriculture on the continent, says Rob Horsch, who leads the agricultural research and development team at philanthropic organisation the Bill & Melinda Gates Foundation.
As an alternative to fertiliser, Africa’s meagre crop yields are getting a boost from an edible and more environmentally friendly source instead: beans.
When growing legumes such as beans and peas, nitrogen fertiliser is not required because the plants grab all the nitrogen they need from the air with the help of bacteria living in their roots. Some of the captured nitrogen also enters the soil through fallen leaves and from decomposing roots. This helps to fertilise crops that are later farmed on the land.
Ken Giller, an agronomist at Wageningen University in the Netherlands, is leading a project called N2Africa that is teaching subsistence farmers in 13 African countries, including Rwanda and Uganda, to grow legumes. The project aims to use legumes to boost harvests of staple crops, such as maize, that have stagnated at around one tonne per hectare since the 1960s. The legumes also provide poor farmers with additional food and income.
“Legumes could be very important for improving the soil and providing extra nutrition.”
Bashir Jama, Alliance for a Green Revolution in Africa
“We want to feed the people and feed the soil,” says Giller.
The legumes are proving popular with farmers. Beatrice Sukuku is growing climbing beans for N2Africa field trials on a small, rocky plot around 1,800 metres up Mount Elgon in eastern Uganda. She prefers these beans to the variety she used to grow because they are quicker to cook, saving on firewood.
N2Africa began in 2009 and now involves more than 250,000 farmers. Data published last May shows that average legume harvests have increased by 12 per cent to nearly 400 kilograms per farm. On average, the legumes added 28 kilograms of nitrogen to the soil per farm, a rise of 169 per cent from previous levels.
The legumes have helped to boost average maize yields by at least 40 per cent, says Giller.
N2Africa was honoured for its contribution to nutrition and food security at a World Bank event on 19 February showcasing the winners of the 2013 Harvesting Nutrition Contest.
“Legumes could be very important for improving the soil and providing extra nutrition,” says Bashir Jama, who directs the Soil Health Program at the Alliance for a Green Revolution in Africa, an NGO working to improve food security. To ensure their long-term success, it is essential to help develop a market so farmers can get a good price, he says.
But beans are not just for subsistence farmers in Africa, says Jama. They are also becoming more popular among some of their richer counterparts in Brazil and the United States, where they are planted to cut down on nitrogen fertiliser use, which saves money and spares the environment.
The reporting in Uganda was funded by an Innovation in Development Reporting grant from the European Journalism Centre.
> Link to the FAO’s report World fertilizer trends and outlook to 2018