a first solution to restrict erosion is to plant living hedges of grass (Setaria) and
leguminous bushes (Leucaena leucocephala or L. diversifolia and Calliandra cal-
Zothirsus, better on acid soils) every 10 m and to dig a big ridge covered with
permanent sweet potatoes or leguminous forage crops every 5 m to stop the runoff
energy;
. mulching with crop residues (mainly with banana leaves, sorghum stalks and various
tree leaves) is the best solution under banana, tea, coffee and cassava plantations;
- leguminous cover crops are also useful under permanent plantations.
Finally, reforestation with Pinus kessia (very good litter) and other forest species
growing above a dense soil cover will reduce runoff and erosion risks under acceptable
level after 2 to 5 years.
Fig. 1 (Duchaufour and Bizimana, 1992) and Fig. 2 (Kiinig, 1992) show that many
biologic antierosive systems are efficient to reduce erosion risks sufficiently even on
fragile sandy ferrallitic topsoil of the mountains: they associate a source of biomass