Water Relations and Growth of Snap Beans as Influenced by Differential Irrigation

Abstract

Abstract Two field experiments were conducted to evaluate the effects of differential irrigation on plant growth, development, and water status of 2 snap bean cultivars, ‘Oregon 1604’ and ‘Galamor’ (Phaseolus vulgaris L.). Plants were grown at various irrigation levels ranging from a well-watered control to a dry treatment which received only one irrigation to establish plants. Measurements on plants sampled weekly at 6 times during the growing season showed that total plant dry weight, total leaf dry weight, total leaf area, average area per leaf, and number of leaves per plant were reduced by water deficits in both cultivars. Also, for both cultivars, total leaf area per plant was reduced more by a decrease in area per leaf than by a reduction in leaf number. Specific dry leaf weight was higher in the drier treatments. During each year, a significant difference between treatments occurred earlier in the season for total leaf area per plant than for total plant weight. At predawn, leaf water potential (ψ) always was more negative in the dry treatment than in the control. Early in the season, there was no significant difference in midday ψ between the control and dry treatment. Later, as soil water became limiting, the dry treatment had a more negative ψ than the control. Near the end of the season, after the dry treatment had been subjected to a long period of water stress, midday ψ was more negative in the control than in the dry treatment. Although some osmotic adjustment occurred in the dry treatment, leaf turgor potential (ψp) was generally lower than in the control throughout the day. As ψ decreased from early morning through midday, transpiration rates increased due to an increase in evaporative demand on the leaves. Leaf diffusive resistance also increased with decreasing ψ but a “threshold value” for stomatal closure was not demonstrated.