Canopy Response of Soybean Affected by Growth Habit and Late Season Competition
- R. R. Weil and
- N. Khalil
Soybean [Glycine max (L.) Merr. J isolines that differ only in regard to determinacy have been developed as tools for better understanding the differential responses of determinate and indeterminate types to environmental factors. This study was conducted to investigate the effect of growth habit on soybean yield components at different canopy levels, and on the response of these yield components to environmental conditions during critical reproductive growth stages. Three pairs of near-isogenic lines (determinate and indeterminate) were grown at three Maryland (USA) locations and subjected to a thinning treatment at the R4 growth stage to release the plants from competition for light, water, and nutrients after pod set was completed. In each plot, six plants were divided into four canopy levels at maturity and hand harvested. For unthinned soybean there was no consistent difference in yield between growth habits. Under low-moisture conditions at the Beltsville site, the determinates responded more to release from competition than did the indeterminates, indicating that the latter are more buffered against unfavorable growing conditions. Generally seed yield and seed size near the bottom of the canopy was greater in determinates than in indeterminates, but the opposite was true near the top. Thus, the determinate growth habit shifted yield production toward the bottom canopy level. The effect of thinning was nearly uniform at all canopy levels for both stem termination types, increasing the yield of determinates by 38.2 and indeterminates by 13.8%.
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