Comparison of Stresses Which May Limit Soybean Yields1

Abstract
Hydroponically grown ‘Dare’ soybeans (Glycine max L.) were exposed to a number of discrete stresses at the time of flowering. Effects on initial pod set, subsequent pod abscission, and ovule growth were assessed. Lodging, when not associated with shading, did not lower pod set. Severe short‐term deficiency of calcium and nitrogen decreased pod set by one‐third. Temperatures above 40C caused severe pod abscission. Shading (63% of ambient) also caused abscission of half the pods. If plants were returned to short‐night conditions after 18 or 22 longnight cycles, flowering and initial pod set were similar to controls but ovule growth was markedly retarded. Thus, yield may be limited by high temperatures and by low light intensities, which cause pod shedding, or by inadequate night lengths which retard seed filling.

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