Eastern Africa: Barren Soils Threaten Future of Farming in the Great Lakes Region, Says Study
Dar es Salaam - Most of the soils in the Great Lakes region of Eastern Africa are poor with very little fertility left in them and what is there is mostly due to the organic matter in the topsoil. This is one of the main reasons behind the low yields in the area, which has one of the lowest rates of fertilizer use in the world and a rapidly increasing population to feed, according to a recent study.
The barren soils are a result of years of mining and insufficient replacement of nutrients by small-holder farmers mostly practicing low-input agriculture. They remain a threat to the future of small-holder farming and the food and income of millions of people in the region if appropriate action is not taken.
The study, which sought to identify and rank the constraints faced by small-holder banana growers in the region, also measured the actual nutrient content left in the soils―in both the organic and mineral part―across different agroecoregions in Rwanda and Uganda.
This was after establishing that poor soil fertility was one of the main causes of the current low banana yield of 5-30 tons/year against a potential yield of over 70 tons/year. It accounted for up to 50 per cent of the yield gap.
The study found that the amount of important minerals for plant growth in the soils in the study areas was low and the little fertility left was mostly due to the organic matter in the topsoil. Furthermore, while banana is a very important crop for the region, providing food and income for over 85 per cent of the population, the use of external inputs such as fertilizers was virtually non-existent. Soil fertility was mostly managed by recycling local organic residues which was not sufficient in quantity and quality.
Furthermore, the intensification of farming to meet the needs of a growing population and increased competition for crop residues for uses such as for animal feed, fuel and as building material is expected to lead to even more depletion of the soil nutrients. The study therefore urges for the usage of both organic and mineral fertilizers to improve the soils and for site-specific fertilizer recommendations that take into account the differences in nutrient deficiencies from one area to another and are therefore more sustainable and economical.
The study was conducted from 2007 to 2011 in four agro-ecological regions in Rwanda (Butare, Kibungo, and Ruhengeri) and South-West Uganda (Ntungamo) and looked at the banana plants, various crop management practices, pests and diseases, and the chemical properties of soils.
It was undertaken by Séverine Delstanche as a PhD student of the University of Louvain in Belgium and formed part of the Belgium (DGD)-funded project titled 'Sustainable and profitable banana-based systems for the African Great Lakes Region' led by the International Institute of Tropical Agriculture (IITA). It was also part of the Consortium for Improving Agriculture-based Livelihoods in Central Africa (CIALCA) project.
Delstanche says that despite the acknowledgment by farmers and researchers of the importance of soil fertility in agricultural production, little research has been carried out to understand the current state of soils and the impact of past and present farming practices.
Therefore, she says, farmers are unaware of the nutritional status of their soil and how best to make use of the little resources available to them to increase production and productivity.
Dr Piet van Asten, IITA systems agronomist, says the findings of this research are very significant. "We knew that our soils were poor but we did not know just how poor. But now, we've calculated the nutrient stocks and have learned that very little nutrients are left. Moreover, the soil fertility almost entirely depends on the organic matter in the soil."
"The study therefore stresses the importance of recycling crop residues to improve soil fertility. Over 80 per cent of the nutrients in the soil comes from the organic matter and not from the clay or sand itself."
A related study by Van Asten and his team estimated that the over 100 trucks of banana bunches that reach Kampala everyday deplete 1.5 million kg of potassium (K) and 0.5 million kg of magnesium (Mg) from the soils in the rural areas annually.
The study supports the Africa Union's Abuja declaration on fertilizers for an African green revolution which has stated that efforts to reduce hunger on the continent must begin by addressing its severely depleted soils and recommends countries to increase fertilizer use from the current 8 tons/ha to at least 50 tons/ha by 2015 to boost agricultural production.