THE EFFECT OF DIFFERENT MOISTURE AND LIGHT REGIMES ON PRODUCTIVITY, LIGHT INTERCEPTION AND USE EFFICIENCY OF COMMON BEAN

Abstract

The response of common bean (Phaseo/us <rulgans L.) fo different moisture. and light
regimes was examined in a 5 x 2 factorial field experiment in Ethiopia. The soil moisture levels were: (1)
well watered throughout (2) stress during the vegetative phase (3) stress during the flowering phase (4)
stress during the seed filling phase and (5) stress throughout. The two light levels were: (1) full light
and (2) 50% shade. The highest seed yield loss due to water stress was observed for the seed filling
phase followed by the flowering and vegetative phases. There were significant interactions between
.moisture availability and light intensity for seed yield. Shading reduced seed yield under full water
supply or early drought while it increased it under terminal and season-long drought. Seed yield was
Significantly correlated to pod number per plant, under both light regimes. Plants under full light
produced 34% less pods on the main stem but 158 % more on the branches <;ompared to shaded plants.
Water use efficiency was significantly decreased by water stress while shading increased it. The lowest
total leaf area duration and total light interception occurred from water stress during seed filling. Water
stress reduced radiation use efficiency (RUE) by 33% while shading increased it by 27%. Under full light,
total intercepted PAR and RUE accounted for 90% of the variation in seed yield while it is 83% in the
shade. Ught intercepted during seed filling contributed 56% and 33%.of the explained variation in seed
yield under full light and shade, respectively