Plant 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.

Movement of water remaining in the soil profile at harvest of rice (Oryza sativa L.) from puddled fields in the tropics has not been well documented. This water is used by crops during the dry season. To use it more effectively, however, its behavior during the postrice period must be better understood. Monocrops and intercrops of species differing in rooting habit [cowpea (Vigna unguiculata (L.) Walp.) and sorghum (Sorghum bicolor (L.) Moench)] were compared for effects on zero flux planes in an Andaqueptic Haplaquoll during three postrice seasons in the Philippines. Fallow treatments were included for comparison. Zero flux plane recession was regarded as an indicator of internal drainage. Zero hydraulic head gradients calculated from matric potentials defined the zero flux plane. In all years, the zero flux plane receded most rapidly under monocropped cowpea (to 0.9 m in 36—38 d after planting). The zero flux plane under the intercrop reached 0.9 m 7 d later. Recession under sorghum was less consistent, requiring 43 to 70 d to reach 0.9 m. Under fallow, it receded to about 0.45 m (to the Bt horizon) within 15 to 25 d and remained stationary except when a 30 mm rain 40 d after planting infiltrated and temporarily raised it to 0.3 m. Ten days later, the zero flux plane under fallow again was stationary at 0.45 m. In contrast, under cowpea the 30 mm rain infiltrated the soil under cowpea but was redistributed above the zero flux plane. Monocropped cowpea and the cowpea‐sorghum intercrop were equally effective at arresting drainage of residual water.

Water remaining in the soil after flooded rice (Oryza sativa L.) is a major source for crops grown during the dry season. To develop improved management systems, quantitative information describing water extraction from previously puddled and flooded fields is needed. Water used by monocropped and intercropped cowpea [Vigna unguiculata (L.) Walp.] and sorghum [Sorghum bicolor (L.) Moench] treatments grown on a fine, mixed, nonacid isohyperthermic Andaqueptic Haplaquoll after harvesting flooded rice was compared to water lost from a fallow treatment. Determinations were to 1.1 m. Water used before cowpea harvest was similar within a treatment among years, but among treatments monocropped cowpea used 172 mm, monocropped sorghum 135 mm, the intercrop 162 mm, and fallow 121 mm. Water used between cowpea and sorghum harvests ranged from 22 to 118 mm, varying with rainfall after cowpea harvest. Species were compared by expressing grain yields in Mg glucose hectare−1 required to synthesize grain. Glucose equivalent yields from monocropped cowpea ranged from 1.90 to 1.98 Mg glucose ha−1, monocropped sorghum from 1.99 to 3.66 Mg glucose ha−1, and the intercrop from 1.99 to 4.36 Mg glucose ha−1. Mean water use efficiency by monocropped cowpea, monocropped sorghum, and the intercrop was 11.3, 12.4, and 16.5 kg glucose ha−1 mm−1. Monocropped cowpea and the cowpea‐sorghum intercrop each use about 50% more water than is lost from fallow. Whereas the cowpea monocrop and the intercrop use about the same quantities of water when grown during the dry season after rice, the intercrop will use water more efficiently but yields from it will not be as stable as those from monocropped cowpea.