Managing Soil Organic Carbon for Multiple Benefits: The Case of Africa - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 308

Population pressures, declining plot sizes and resource constraints in Africa have led to agricultural
intensification and continuous cropping with insufficient inputs, leading to rapid decline in SOC
stocks. Sustainable management of organic resources will require interventions by regional governments
to help farmers access inputs cheaply, as well as educating farmers on sustainable land management
practices.

Introduction

Land-use changes such as conversion of for-
est or grassland to agricultural use have
continued to be of great concern to environ-
mentalists (Lal et al ., 1995). Land-use conver-
sion from forest to annual crop cultivation
and grazing land has been shown to influ-
ence change in soil properties (Kironchi
and Mbuvi, 1996; Gal et al ., 2006). Gal et al .
(2006) have shown that there is consider-
able decline of total organic carbon, SOC
and dissolved organic carbon in the world
carbon stocks. Land-use changes, especially
the cultivation of deforested land, may di-
minish soil quality rapidly, leading to se-
vere land degradation (Kang and Juo, 1986;
Nardi et al ., 1996; Islam et al ., 1999). The
conversion of forest to cropland has been
associated with the reduction in the organic
matter content of the topsoil (Ross, 1993;
Singh and Singh, 1996) and the subsequent
decline in productivity (Sanchez et al .,
1997; Palm et al ., 2001).
Population pressure, decreasing plot
sizes and resource constraints in Kenya and
sub-Saharan Africa have resulted in continu-
ous cultivation that has led to the depletion
of SOM. The manure used in Kenya is gen-
erally of poor quality, due to poor storage
and management. Continuous cropping, re-
moval of field crop residues for feeding ru-
minants and overgrazing between cropping
seasons with little or no external inputs
have reduced the productive capacity of ar-
able lands throughout sub-Saharan Africa
(Onyango et al ., 2000). High input and
transport costs for agrochemicals make the
use of inorganic fertilizers on staple food
crops uneconomical for most smallholder
farmers. Lekasi et al . (2005) report that most
farmers in the Sasumua catchment, a humid
area in Kenya, hardly use fertilizer to re-
plenish the soil nutrients harvested through
crop and animal produce. Most farmers in this
catchment have observed a decline in yields
of food and vegetable crops. This long-term

The distribution of organic matter resources
varies with agroecological zones, land use
in the ecosystems and rainfall within the
continent from the Sahel to the Congo
basin. Due to this variability, the mapping
of soil organic carbon (SOC) is essential for
appropriate land uses and climate mitiga-
tion and adaptation strategies. In the Sahel
and the horn of Africa, soil organic matter
(SOM) has proven to be an indicator of soil
quality and has been severely degraded due
to human activities, which leads to soil
degradation through erosion and loss of
soil fertility, but this trend can be alleviated
through appropriate management. In forest
ecosystems, notably the Congo basin, the
parameter is an indicator of soil health and
ecosystems equilibrium. SOC has been used
for centuries by rural communities to yield
multiple benefits, such as: (i) improve food
security and nutrition with the cropping of
mushrooms and other meso fauna species;
(ii) increase yield and diversity of on-farm
and out-farm crops; and (iii) ensure the re-
sistance of housing using dark rich soils, re-
ducing rainfall penetration.
At subnational, national and regional
levels, increased attention is being given
to SOC in the context of climate change as
a result and indicator of the relevance of
adaptation and mitigation technologies.
Managed appropriately, carbon stocks will
ensure the conservation of multiple benefits
such as the diversification of crops, wild-
life, timber and non-timber, livestock and
fisheries products. To maintain and im-
prove soil productivity and its derived
benefits, organic carbon should be managed
according to a specific context. Among the
biotic factors, biodiversity conservation in
cropping, pastures, water and forest sys-
tems, along with carbon conservation, may
provide a pathway to sustainable development.