|Environment, Biodiversity and Agricultural Change in West Africa (UNU, 1997, 141 pages)|
|14: Land use and cover change in the southern forest-savanna transition zone in Ghana: A sequence model|
Abandoned cocoa farm land may be put to food cropping under one of two systems: (1) a bush fallow system; (2) a technologically improved system. The bush fallow system relies on natural fallows for the regeneration of soil fertility. Fire is an important tool for the clearing of land. Fire and the axe eventually eliminate the tree and other woody cover, which leads to the dominance of grasses and increasingly the obnoxious weed Chromolaena odorata (Hall et al. 1972). This process is accelerated by the increasing population and urban concentrations, raising the demand for food and putting pressure on the land and thus leading to a reduction in the fallow period and soil fertility. The present study areas are located in the supply hinterlands of major urban centres: Accra (1,179,484), Koforidua (60,675), Nsawam (25,983) and Suhum (26,436). The soil organic carbon percentage had decreased from an average of 2.7 per cent for uncultivated virgin sites at all sites to an average of 1.2 per cent at sites cultivated in maize and cassava (Gyasi et al. 1994).
Continued pressures lead to the introduction of crop types and varieties that are more efficient in the utilisation of water and minerals, but which may require a more thorough disruption of the cover. In time, the woody root systems in the soil are again removed and hoe cultivation is introduced, which increases the hazards of erosion and further deterioration of the productive capacity of the environment. Hoeing (generally characteristic of the savanna cultivation systems) was common, for example, in the Amanase area.
Over extensive areas, the end state moves in the direction of the dominance of grasses. This is already observable in several locations at all the study sites.
The alternative conversion of abandoned cocoa land into a food crop area may be undertaken with improved technologies, such as an agroforestry system and the use of mineral fertilizers. Official extension policy has introduced and encouraged these technologies. This stage in the development of the land use is yet to be systematically adopted. Indications from the PLEC study, however, show adoption ratios of these strategies at 19.5 per cent for chemical fertilizers and 3.2 per cent for agroforestry (Gyasi et al. 1994).