Shoot Growth Rate of Soybean as Affected by Drought Stress
1987
Hoogenboom, Gerrit | Peterson, Curt M. | Huck, M. G.
Shoot size at time of flowering has a strong effect on final yield and can be significantly reduced by drought stress. Studies were performed at the Auburn rhizotron from 1981 through 1983 to investigate the effects of drought stress on daily shoot growth rates of soybean [Glycine max (L.) Merr. ‘Braxton’]. Plants were grown in a Marvyn loamy sand (fine-loamy, siliceous, thermic Plinthic Paleudult) and received only rainfall (NI) or rainfall and supplemental irrigation (IR) during each growing season. Irrigation was controlled by tensiometers installed 0.4 m deep, and water was added when soil water potential (Ψ ₛₒᵢₗ) fell below −15 kPa. Shoot growth patterns, e.g., stem elongation, leaf formation, and leaf area increase, followed characteristic exponential growth curves during early vegetative development when no moisture stress was evident. Sensitivity to water stress (Ψ ₛₒᵢₗ < −15 kPa) increased as total leaf area and resulting transpiration demand increased. Stem elongation and leaf area expansion rates decreased significantly for the NI treatment during periods of water stress. During periods of moisture stress, leaves formed on NI plants were smaller than leaves at comparable nodes on IR plants (0.0075 vs. 0.010 m²). After periods of rainfall, shoots of NI plants grew more rapidly than those of IR plants (0.025 vs. 0.020 m/day), and most of the growth reduction during the previous stress period was regained. Accumulated growth over time, i.e., total leaf area (0.22 m2), number of nodes (17), final internode lengths (e.g., 0.08 m), and mainstem height (1.15 m), was comparable between NI and IR treatments. Thus, no long-term differences were observed between IR and NI treatments because significant short-term reductions in shoot growth rate due to drought stress were followed by compensatory growth during periods of rainfall.
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