RESPONSE OF ROOT BRANCHING AND SHOOT WATER POTENTIALS OF FRENCH BEANS(PHASEOLUS-VULGARIS L) TO SOIL-MOISTURE AND FERTILIZER POTASSIUM

Extensive branching patterns of roots and the maintenance of adequate water within shoots enables plants to overcome water stress. However, information on the relationship between fertilizer potassium, root bra nching patterns and shoot water potentials of food legumes grown under different soil moisture regimes is scarce. Thus, an experiment was co nducted in a phytotron to ascertain the effect of fertilizer potassium on root branching patterns and shoot water potentials of a popular tr opical food legumes (Frenchbeans Phaseolus vulgaris L). The plants wer e grown in a sand medium with 0.1, 0.8 or 3.0 mM of potassium under a suboptimal and optimal soil moisture regime. Root lengths and dry weig hts were enhanced by potassium, especially under a suboptimal soil moi sture regime. The branching patterns changed due to potassium, where t he numbers of second and third order roots increased under both soil m oisture regimes, although the impact was greater in plants grown with low soil moisture. Plant water contents measured in terms of shoot wat er potential, relative water contents, turgid weight:dry weight ratio and water uptake capacity were also increased by potassium. A positive relationship was observed between root branching patterns and water p otentials with increasing potassium levels especially in plants grown under suboptimal soil moisture conditions. Shoot growth and nodulation was also promoted by potassium. The ability of plants to develop a mo re extensive branching pattern of roots by inducing a greater number o f second and third order roots and changing the root branching habit f rom a herringbone to a dichotomous type to maintain a greater shoot wa ter potential especially under low soil moisture regimes is presented.