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[NAIROBI] Hundreds of thousands of smallholder farmers in southern Africa are adopting fast-growing trees and shrubs to fertilise their fields naturally, for improved yields and incomes, according to a study.

Scientists at the World Agroforestry Centre (ICRAF), a non-profit research organisation in Kenya, analysed two decades-worth of efforts to bring 'fertiliser trees' to African farms and announced their findings — which were published in the International Journal of Agricultural Sustainability — last month (14 October).

Fertiliser trees, such as the acacia tree, capture nitrogen from the air and transfer it to the soil in a process known as nitrogen-fixing. This restores nutrients and increases crop productivity, with the potential to double or even triple harvests. They also improve water efficiency on farms and help prevent soil erosion.

"Four hundred thousand farmers in southern Africa [Malawi, Mozambique, Tanzania, Zambia and Zimbabwe] are growing the trees to boost their farm yields, and there are still millions of resource-poor smallholders who could benefit from them," said Oluyede Ajayi, lead author of the study and a senior scientist at ICRAF.

The study found that maize yields and farmers' incomes are significantly higher in areas where the trees are used. In Zambia, for example, incomes for farmers using fertiliser trees averaged US$230–330 per hectare, while those who did not use the trees earned just US$130. This increase in income provided food for up to 114 extra days.

Ajayi told SciDev.Net that soil fertility plays a critical role in ensuring food security for smallholder farmers in many African countries. Efforts must be made to take advantage of all available options — including fertiliser trees — rather than engage in less useful academic debates on organic versus inorganic fertilisers, he argued.

"Given the wide range of fertiliser trees that have been developed, [support for farmers] is required to ensure the fertiliser trees [are used] in the right locations," said Ajayi.

He called for policy and institutional frameworks that would support their use and for more information dissemination on the need for fertiliser trees.

Jackson Mulatya, a senior scientist at the Kenya Forest Research Institute, said that the practice [of planting these trees] could increase productivity and be widely adopted in Africa. "Herbaceous plants have been used to boost soil fertility since time immemorial … scientists have modified the practice," he said.

But he cautioned that some challenges remain, such as the availability of planting material, social biases, farm size and species management.

Link to full paper in International Journal of Agricultural Sustainability [212kB]


International Journal of Agricultural Sustainability doi:10.3763/ijas.2010.0554 (2011)