WATER-UPTAKE BY PEARL-MILLET IN A SEMIARID ENVIRONMENT

Crops during drought may not utilize water at depth. This under-utiliz ation of deep water may result from slow rates of root extension, low root density, or a decline in soil water potential or associated pheno mena. The importance of several of these factors on pearlmillet (Penni setum glaucum (L.) R. Br., cv. CIVT) water uptake and growth from pani cle initiation to flowering was studied on a sandy soil in northern Ni geria during two dry seasons. Half of the crop was irrigated while the other half received no water after panicle initiation. Soil water con tent, stomatal conductance and stem extension were measured periodical ly. A potential-driven water uptake model, which assumes a static, exp onential distribution of roots and couples transpiration to leaf water potentials, described in both seasons the observed pattern and timing of water uptake, as well as predawn leaf water potential and actual t ranspiration. As the soil dried, estimated transpiration declined belo w potential transpiration and modeled and measured predawn leaf water potential declined. There was close agreement between observed and mod eled predawn leaf water potential and soil water uptake. Analysis usin g the model indicated that decreased water uptake at depth was attribu table to root distribution throughout the soil profile, as well as to low root length density at depth.