Mining of Nutrients in African Soils Due to Agricultural Intensification - Principles of Sustainable Soil Management in Agroecosystems - page 417

projects in 20 countries during the 1990s and 2000s. The lessons learned included
the need to scale up and spread science and farmer inputs into technologies and
practices that combine crops and animals with agroecological and agronomic man-
agement. Additionally, the private sector must be engaged; capacities and knowledge
of farmers should be enhanced. The microfinance and technology needs of women
should be a focus, and public sector support for agriculture should be ensured. An
indicator of progress with the last issue is the Abuja Declaration from the African
Union Ministers of Agriculture at the 2006 Africa Fertilizer Summit, which declared
fertilizer, from both inorganic and organic sources, to be a strategic commodity
without borders (African Development Bank 2012). The stated goal was to increase
the level of fertilizer use from the current average of 8 kg ha −1 to at least 50 kg ha −1 by
2015. Achieving such a goal would no doubt effectively resolve the nutrient mining
problem. As a directly related case study, the Malawi subsidy scheme was devised
to supply improved seed and heavily subsidized fertilizer to maize producers dur-
ing the period from 2005 and 2006 to 2008 and 2009 (Dorward and Chirwa 2011).
Maize productivity was increased as were food availability, real wages, and poverty
reduction. The economic impact of the program was clear, but high international
fertilizer prices and higher maize prices undermined the poverty reduction impacts.
Subsequent commodity price reductions from the 2008 spike provide a scope for
building on the original program achievements. An alternative or complementary
form of subsidy may arise from carbon pricing, which Marenya et al. (2012) estimate
may provide a means for farmers to break through the resource barriers constraining
their adoption of productivity-enhancing nutrient management technologies. This
approach, driven by global concern about the effects of GHGs from SOM decom-
position on climate change, may provide valuable support to African farmers, who
themselves face serious environmental, economic, and social impacts from global
warming (Fosu-Mensah et al. 2012).
15.5 CONCLUSIONS
With half the population of Africa now living in cities, it is unavoidable that large
quantities of nutrients mined from the farms are concentrating there and in need of
disposal. With many cities located along rivers or near the coastline, it should be no
surprise that many of these nutrients are finding their way into the oceans, which
makes them almost impossible to retrieve, and which causes untold environmental
damage. This review indicates that concerns about nutrient mining of SSA soils are
well justified. The evidence for this conclusion is founded on the following: farmers
intensify their crop cultivation and reduce fallow periods as population grows; sta-
tistics show the continuing low rates of average fertilizer use in most countries; and
research data show negative nutrient balances at a range of scales. There is spatial
and temporal variation in the rate and impact of nutrient mining, but the law of con-
servation of mass dictates that nutrients repeatedly removed in harvests must eventu-
ally be replaced, or else crop yields will suffer and farming will become uneconomic.
The social impacts of declining yields, then, are manifested in the migration of rural
populations to urban areas, driving additional demands for food and further nutrient
exports from the land.