Managing Soil Organic Carbon for Multiple Benefits: The Case of Africa - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 307

26 Managing Soil Organic Carbon for
Multiple Benefits: The Case of Africa
Peter T. Kamoni* and Patrick T. Gicheru
Abstract
Organic matter is of great importance in soil, because it impacts on the physical, chemical and biological
properties of soils. Physically, it promotes aggregate stability and therefore water infiltration,
percolation and retention. Biologically, it stimulates the activity and diversity of organisms in soil.
Decomposing organic matter releases nutrients, such as nitrogen (N), phosphorus (P), sulfur (S) and
potassium (K), essential for plant and microbial growth. Sustainable land management practices
enhance carbon sequestration and sustain agricultural productivity, thus mitigating against climate
change. In Western Africa, there is a rapid decline of soil organic carbon (SOC) levels with continuous
cultivation. For the sandy soils, average annual losses may be as high as 4.7%, whereas with sandy
loam soils, losses are lower, with an average of 2%. In the equatorial forest zone with higher rainfall,
abundant moisture favours high biomass production, which in turn brings about higher SOC
(~24.5 g kg - 1 organic C) and nitrogen contents. In the Sudan savannah, organic carbon (~3.3-6.8 g kg -1 )
and total nitrogen are very low, because of low biomass production and high rates of decomposition.
Estimates of SOC stocks and changes made for Kenya using the Global Environmental Facility Soil
Organic Carbon (GEFSOC) Modelling System indicated soil C stocks of 1.4-2.0 Pg (0-20 cm), which
compared well with a soil and terrain (SOTER)-based approach that estimated ~1.8-2.0 Pg (0-30 cm)
of soil C between 2000 and 2030 in Kenya. Direct field sampling and laboratory measurements of soil
carbon in Kenya has been going on for over half a century, and the data exist in the form of numerous
technical and research reports, theses, journal papers and workshop proceedings, Kenya Agricultural
Research Institute annual reports and geographic information system (GIS) databases. A combination
of biomass measurements and empirical equations has also been employed in Kenya to measure
organic carbon stocks. Stratified random sampling of herbaceous standing crop has been carried out at
Nairobi National Park to estimate primary production of the grassland savannah. The Carbon Benefits
Project, developed between 2009 and 2012 by Colorado State University (USA) in collaboration with
Kenya, Nigeria, Niger and China, is able to estimate carbon stocks and greenhouse gas (GHG) emissions.
Increasing soil organic matter content can both improve soil fertility and reduce the impact of drought,
improving adaptive capacity, making agriculture less vulnerable to climate change, while also
sequestering carbon. Agronomic practices in western Kenya include using improved crop varieties,
extending crop rotations, notably those with perennial crops that allocate more C below ground, and
avoiding or reducing the use of bare unplanted fallow among others. Increasing the soil carbon in farms
improves soil fertility, hence improves food security, increases economic returns from carbon revenues
and creates business development opportunities for farmers to diversify income-generating activities.