Throughout Sub-Saharan Africa there is a constant threat of famine because of declining crop yields, depletion of soil nutrients, and reduced C stover of soils. The direct subsidy of inorganic fertilizers and nutrient or nutrient recapitalization has been adopted to combat nutrient depletion in smallholder farming systems (Mokwunye, 1995). Nutrient capitalization enhances crop productivity, which then contributes to soil C sequestration from stover, and stubble and root incorporation, as well as applied manures resulting from stover use as livestock feed.
Agroforestry provides fruit and wood fuel, sequesters C in tree biomass, and reduces C emissions through accumulation of C in wood biomass and soil. It has been estimated that agroforestry in Sub-Saharan Africa would accumulate an average of 15 metric tons soil C ha-1 (Woomer et al., 1998) or 59 metric tons C ha-1 (Houghton et al., 1993) in 20 years.
The SOM in tropical soils is of greater agricultural importance than any other soil property except water availability. Nutrient release from leaf litter and SOM accumulated in the underbrush on forest fallow is the main source of nutrients in subsistence cropping systems in the tropics. Soils in Zambia are among the lowest in organic C content; however, the soil C status can be considerably increased through adoption of improved fallowing with the use of agroforestry multipurpose tree planting to sequester C. The rapid release of SOM after clearance and cultivation promotes rapid SOM decomposition, energy availability to microorganisms, and nutrients released for uptake by microorganisms and plants, as well as SOC accumulation.
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