ROOT DISTRIBUTION, WATER USE, AND NUTRIENT UPTAKE OF MILLET AND GRAIN SORGHUM ON WEST AFRICAN SOILS

Abstract

Field experiments were carried out in three Sahelian agroecosystems (Kala Pate, N'Dounga, and Chikal) to compare the rooting systems and water and nutrient extraction of millet and sorghum under different levels of water, fertilization, and plant density. Initial soil moisture content was so low (<0.04 m3 m-3) that crop rooting was limited by the maximum depth of the wetting front. Soil acidity (pH 4.5) and aluminum and manganese toxicities reduced the effective crop rooting depth to less than 45 cm at Kala Pate. Millet utilized water more efficiently under less favorable soil conditions, but in most cases it extracted less nutrients and utilized rainfall less efficiently than sorghum. Results from this study suggest that root penetration of both crops was controlled by the seasonal wetting front and soil pH. These factors were most limiting for efficient nutrient and water use. Inputs of water and fertilizer significantly increased rainfall use efficiency and nutrient uptake by both crops.