The unaffordability of chemical fertilizers -- made more unaffordable with every devaluation of the local currency -- leads farmers to adopt improved fallow technologies.
While phosporus replenishment still requires an externally sourced chemical input that may be beyond the reach of the small farmer, this is not necessarily the case for nitrogen. To reverse nutrient depletion of nitrogen in African soils, a second strategy exists, namely an increased use of organic sources of nitrogen nutrients.
The organic sources of nitrogen include: animal manures and compost, biomass transfers of organic matter into the field, and also more efficient use of trees and shrubs whose deep roots capture nutrients from subsoil depths beyond the reach of crop roots and transfer them to the topsoil via decomposition of tree litter. By strategic planting of trees, nitrogen lost over the last 20 years can be replenished with nitrogen from agroforestry innovations.
Whether or not improved fallow technologies can entirely substitute for nitrogen fertilizers, remains to be seen. Most observers agree that the verdict is still out for improved fallow technologies, which may take a decade for farmers to test properly. First farmers plant several small plots of different tree species, then they wait three to four years to see the results of each plot. Because the improved fallow cycle takes so long, farmers’ adoption or adaptation of this technology takes a lot longer than adoption of an improved seed or a new fertilizer. Until the experiment fails, African farmers – like most researchers – are willing to experiment, probably due to the lack of other options available as soil fertility amendments in Africa today.
African Studies Quarterly 6, no. 1&2 (Special Issue: Gender and Soil Fertility in in Africa) (2002)Agroforestry innovations in Africa: can they improve soil fertility on women farmers' fields?
Cameroon Tribune 29/01/08 Cameroon: Fertilizer Programme Revamped