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% 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% 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% 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.
# # #