Agriculture Reference
In-Depth Information
In its simplest terms, the problem of nutrient mining calls for minimizing the
export of nutrients by returning as much of the residues to the field as possible.
Local processing of foodstuffs would favor recycling as nutrients in residues can-
not be economically returned to the field when distances exceed tens of kilometers.
The remaining deficit will require the replacement/supplementation of soil nutri-
ent reserves by nutrient additions. In the case of N, this can be achieved by the
use of legumes that fix N from the atmosphere (BNF), and various models such
as intercropping and relay cropping with leguminous ground cover,
Azolla
culture,
and agroforestry systems have been proposed. Soil scientists and agronomists have
proposed many novel systems, but there is no magic bullet. The research base on the
various systems is extensive, but the rate of adoption has been disappointing. The
overarching lesson of the past is that development of such complex cropping systems
needs participation of farmers as a way of ensuring that innovations have a reason-
able chance of adoption.
Ultimately, SSA farmers will need to expand their use of fertilizers beyond the
current rate of 10 kg ha
−1
to guarantee food security over the long term. This will
require farmers to have liquidity for investment and to move away from purely subsis-
tence farming and introduce cash crops, preferably on the same farms. Government
policies and programs that facilitate or even subsidize fertilizer marketing and dis-
tribution are needed, as well as efforts to educate farmers on the use of fertilizers.
Governments will also have to take measures to avoid the market distortions due to
importation of heavily subsidized food grains from industrialized countries, against
which SSA farmers cannot compete. Progress may ultimately depend on whether
sufficient political will can be mobilized in Africa and the industrialized countries to
remedy an unsustainable agricultural sector in SSA. If as a consequence, the nutrient
balance on the farm in SSA has been brought into equilibrium, there remains only
the problem of disposing of nutrients accrued in cities in an environmentally accept-
able fashion. That problem may be resolved in part by the recycling of the waste
nutrients in peri-urban agriculture.
ABBREVIATIONS
AGDP:
agricultural gross domestic product
BNF:
biological nitrogen fixation
CA:
conservation agriculture
GHGs:
greenhouse gases
NT:
no-till
SOC:
soil organic carbon
SOM:
soil organic matter
SSA:
sub-Saharan Africa
REFERENCES
African Development Bank. 2012. Abuja declaration on fertilizer for the African green development.
mechanism/abuja-declaration/
(accessed July 14, 2012).
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