EFFECT OF ORGANIC-MATTER INPUT ON THE WATER-BALANCE AND YIELD OF MILLET UNDER TROPICAL DRYLAND CONDITION

In Senegal, rainfed millet production is influenced by the combination of scarce and unpredictable rains and falling soil fertility. In orde r to analyse the interaction between the water and fertility factors u nder conditions of low rainfall, the water use by a millet crop (Penni setum glaucum L.) was studied under different organic matter input sit uations. Water balance was evaluated using a model and in situ soil mo isture measurements. Application of manure raised the crop water requi rements without substantially increasing the water supply of the soil. At the end of the crop cycle, the soil dried faster where manure was applied than without manure. The consequences of this on growth and pr oduction were studied: changes in the pattern of evolution of the soil water content induced by manuring limited the depth of root penetrati on, and promoted post-flowering water constraint that can cancel the p ositive effect of manure on growth and production. As a result, the us e of manure increases the risks taken by the farmer and should therefo re be taken into consideration for the analysis of existing cropping s ystems or the definition of possible new ones.