Effect of level and timing of moisture stress on soybean plant development and yield components

Abstract

Field studies were conducted in 1984 and 1985 using non-weighing lysimeters of 1 m² to determine the effect of level of soil moisture stress (L) and timing of moisture stress (T) on reproductive phenology, plant characteristics, and yield components of Maple Amber soybean [Glycine max (L.) Merr.]. The study incorporated the most probable combinations of moisture stress in order to provide a basis for planning and managing irrigation for optimum soybean production. The effect of L was consistent over T and Year. Neither L nor T affected days to full bloom stage (R2). Increases in L linearly (r² = 0.71) increased days to beginning seed stage (R5), but decreased (r² = 0.93) days to full maturity stage (R8). L was related quadratically to plant height (r² = 0.88) and number of pod-bearing nodes (r² = 0.98), and linearly to number of pods (r² = 0.75) and total dry matter (r² = 0.91). No consistent effect of T on the timing of R5 to R8 stages was found, mainly because of the presence of a Year X T interaction (P = 0.05). Withholding irrigation during the R5 stage from previously adequately watered crops caused significant reduction in plant height (7%), number of pod-bearing nodes on the main stem (13%), number of pods (18%), number of seeds (20%), total seed weight (25%), and total dry matter (23%), indicating the importance of irrigation during this stage. It was concluded that, if irrigation water is limiting, with-holding irrigation at R2 may be acceptable, but irrigation at R5 is essential for optimizing yield components and thus yield.