Agricultural Settlement and Land Use in Mountains - Mountain Geography: Physical and Human Dimensions - page 556

fertility with animal fertilizers and mulch. The problem of waterlogging is particularly
acute in clay soils with limited permeability, such as those in the highlands of Ethiopia
and Sudan. In these situations, farmers add gravel to improve soil texture and infiltra-
tion capacity, employ contour plowing, and block small channels to reduce the chance
of slope failure. Permanent cropping and conservation techniques like these represent
an advanced stage of land use, and may have evolved from shifting cultivation once the
population became too great to support itself through this method.
FIGURE 11.9 Plowing rice terraces in the Hoang Lien Mountains, northwest Vietnam. (Photo by S. F.
Cunha.)