Water Stress Effects On Physiological Processes And Yield Of Soybeans

Download or read book Water Stress Effects on Physiological Processes and Yield of Soybeans written by Mahmoud Fadl El Mula Ahmed and published by . This book was released on 1983 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Soybeans [Glycine max (L.) Merr.] cv. Bragg were grown in field lysimeters for the study of water stress effects on certain physiological characteristics during different growth periods. A second objective was to study changes in plant water relations of well-irrigated soybeans during the growing season. Mid-day measurements were taken for soil water potential, leaf water potential components, stomatal diffusive resistence, transpiration, and leaf temperature. In well-irrigated plants, leaf osmotic potential began to decline with the onset of flowering, causing a considerable decrease in the leaf water potential. Mid-day turgor potential maintained hight values (5 to 8 bars) throughout the growing season. Diffusive resistence, transpiration rates, and leaf-to-air temperature differential (leaf temperature minus air temperature) were also constant util after R[indice]5, when diffusive resistance began to increase, transpiration rates decreased and temperature differential increased. This was related to plant aging as the crop approached the late reproductive growth stages. As estomatal diffusive resistance increased, transpiration cooling was less resulting in increased temperature differentials. During the drying cycles, leaf water potential componentes of the stressed plants were, in most cases, lower than teh control plants. Transpiration rates and stomatal conductance were also lower in the stressed plants while leaf-to-air temperature differential was greater. A high correlation was observed between osmotic potential and leaf water potential during drying cycles and was most likely associated with dehydration effect which resulted in increased concentrations of the osmotic components. However, osmotic potential at full turgor (leaf water potential equal to zero), showed progressive decreases during the season, giving values of -9.4, -10.9, -11.6 and -15.1 bars at V[indice]5, R[indice]1, R[indice]5 and R[indice]6 stages, respectively. This reflects changes in osmotic potential of soybeans as they grow from vegetative to reproductive phases. The slope of [phi][indice][pi] versus [phi][indice]L also declined from 0.437 at V[indice]5 to 0.233 at R[indice]6, suggesting reduced plasticity during late reproductive stages. Moisture strees during R[indice]6 resulted in significant diferences in harvest index, 100-seed weigth, percent empty pods, and shelling percentage as compared to the well-watered control. No significant differences in seed yield were observed; however, the data suggests yield reductions of 12%, 13% and 14% due to water withholding during V[indice]5, V[indice]5 plus R[indice]5, and R[indice]6 growth periods, respectively.