Diurnal water stress in plants grown on a coarse soil

Abstract

Sorghums were grown on a coarse deep sand under various sprinkler irrigation regimes. Bulk soil water potentials under all treatments remained in the range of 0 to - 1000 cm throughout the experiment. Measurements of leaf water potential showed a rapid diurnal change from no plant water stress at dawn, to large negative potentials in mid-afternoon. It is concluded that, at least in part, this stress was a direct consequence of the unavailability of soil water to meet the potential demand of the plant. Theoretical and experimental evidence suggests that the rate of supply of soil water was limiting. Increased diurnal water stress reduced plant growth and tiller numbers in forage sorghum, and delayed time to flowering in grain sorghum. Less water was evaporated from the treatments showing the greatest levels of diurnal water stress.