out during the dry season. Burning takes place when the material is
sufficiently dried. Unburned wood is collected and piled around the base of
the large trees left standing. When sufficient fuel is available a fire is started,
which slowly kills the tree. Subsequent disintegration of the canopies
permits crop production underneath the trees.
This typical clearing strategy is less labour-intensive compared to completely
felling the trees. The disadvantage is that over the years branches and
eventually tree trunks come down and damage the perennial crops.
Before soil preparation takes place organic material (leaves, twigs) is
swept together and removed from the field. Farmers see this as a sanitary
measure to avoid the building-up of insect plagues.
Soil preparation is in function of a single crop; the Yam (Dioscorea alata,
D. cayenensis). With the help of a short-handled hoe the relatively fertile
topsoil is scraped together into small hills or mounds. To some extent this
tillage technique destroys soil structure and the root mass in the upper soil
horizon, increasing the possibility of soil erosion.
The number of mounds per unit area varies according to the depth of the
soil. Lena [1984], in a description of immigrant Baoul6 agriculture in the
south-west has found an average of 7,100 hills ha -~. This figure seems to be
on the high side if important quantities of gravel or ironstone are present.
Table 3 gives an average of 4,600 hills for Dj6r6-oula (17 fields observed)
and 5,700 hills in Tiassal6 (20 fields). De Vries (unpublished data) counted
5,600 hills ha-1 on fields near Tai village.