Abstract
Effects of three irrigation regimes (50, 75 and 100% of field capacity) on leaf area, biomass production and growth patterns of maize and sunflower were determined in pot culture experiments. Total shoot dry matter (TOM) was linearly associated with culm weight, leaf weight and leaf area and the amount of the irrigation water applied during the growth period. TOM produced during the vegetative stage (0-21 days after emergence) at the 75% regime, in both crops, was significantly (P ? 0.01) higher than that produced under either the 50% or the 100% irrigation regimes. In the pre-flowering (21-42 days) and the flowering (42-64 days) stages, TDM attained under the 100% irrigation regime, in both crops, was significantly (P ? 0.01) the highest; whereas, in the post-flowering stage (64-86 days) differences between the 75% and the 100% regimes, in this respect, were not significant. The irrigation regime also significantly affected absolute growth rate, relative growth rate, net assimilation rate, leaf area ratio, leaf weight ratio and specific leaf area. The magnitude of this effect and its direction, however, varied with both the crop and. its stage of growth. Drought avoidance in both maize and sunflower is apparently partially due to low transpiration resulting from the significant reductions in leaf area at high or moderate moisture stress. Increase in leaf thickness (reduced SLA) appeared to be an adaptive mechanism to drought used by maize but not by sunflower.
