Root morphology and potassium supply to pearl millet roots as affected by soil water and potassium contents

Pearl millet is usually grown in periods when water is deficient in soil, a fact that possibly affects the K uptake. The experiment in Botucatu, Sao Paulo State, Brazil, was conducted to evaluate the effects of soil water content (-0.03;-0.05,-0.10 and -0.50 MPa) associated with K rates(15 and 120 mg dm(-3) of K) on the K mass flow and diffusion to pearl millet (Pennisetum glaucum (L.) Leek) roots in greenhouse conditions. In pots with soil from the arable layer of a Red Latosol, pearl millet was grown for 28 days after plant emergence, when the plants were harvested and the shoot and root dry matter, K contents, as well as the root morphology determined. K mass flow and diffusion to roots were estimated. Irrespective of soil K level and water content, diffusion was the main mechanism of K supply to the roots. There was a larger relative contribution of mass flow at the K lowest rate, which amounts to 12% of the total K uptake, compared to 4% at the highest K rate. No effect of the soil water content on the mechanisms of K supply to pearl millet roots was established.