WATER SENSITIVE PERIODS DURING THE REPRODUCTIVE GROWTH-PHASE OF GLYCINE-MAX L .2. ESTABLISHING WATER-STRESS SENSITIVITY

The water sensitivity of soybeans was determined on a day-to-day basis from the onset of flowering to physiological maturity by correlating daily leaf water potential values of 50 different soil water regimes w ith corresponding grain, vegetative and biomass yields. Days, and cons ecutive days forming periods, during which significant negative correl ations were obtained were regarded as water sensitive periods during t he reproductive growth phase of the soybean crop. Water deficits durin g flowering significantly inhibited vegetative and biomass production but inhibited grain yields only when occurring during early flowering. During pod elongation and seed development the sensitivity of the soy bean plant to water stress was present bur diminished in time with reg ard to vegetative and biomass yields. The effect on grain yields was r estricted to pod elongation and to later seed development stages. Wate r stress affected grain yields to a far greater extent than vegetative growth during seed filling and physiological maturity.