Drought Response of Grain Legumes Under Irrigation Gradient: III. Plant Growth1

Abstract

AbstractPlant growth in semiarid and tropical regions is often limited by variations in the amount and duration of rainfall. Four food legumes, mungbean (Vigna radiata L.), cowpea (Vigna unguiculata L.), soybean (Glycine max L.), and peanut (Arachis hypogeae L.) were subjected to different moisture gradients in the field on a medium‐deep Tropudalf soil. Water stress effects on the shoot and root growth were analyzed to determine relationships with seed yield and plant growth and to evaluate possible drought avoidance mechanisms. Water stress was created with a line‐source sprinkler irrigation system. Plant growth analyses were computed from samples taken at frequent intervals during the vegetative and reproductive phases. Increasing moisture stress resulted in progressively less leaf area, leaf area duration (LAD), crop growth rate (CGR), and shoot dry matter. Conversely, specific leaf weight increased with increasing levels of water stress. The four seed legumes differed in their ability to maintain leaf area expansion rate, leaf area index, LAD, CGR, and shoot dry matter at high levels of water stress. Cowpea and peanut had higher root densities at 0.4 to 0.8 m soil depths than soybean or mungbean and this appeared to be a major adaptive mechanism for their drought tolerance.