CALCIUM AND RELATIVE-HUMIDITY EFFECTS ON SOYBEAN SEED NUTRITION AND SEED QUALITY

Reduced seed calcium concentrations have been observed in soybean [Gly cine mar (L.) Merr.] seed lots with reduced seed germination. Soybean plants were grown hydroponically at Ames, IA, 1991, to determine if th e Ca concentration of the root medium and relative humidity (RH) could influence seed Ca concentration and, subsequently, seed quality. Plan ts were grown in solution culture in a controlled-environment growth c hamber, with Ca concentrations of 0, 0.6, 1.2, and 2.5 mM in the root medium from beginning seed (R5) to beginning maturity (R7). In additio n, concentrations of 0.6 and 2.5 mM Ca and RH of 55 and 95% were appli ed from R5 to R7 to plants grown in sand culture in the greenhouse. Tr eatments were arranged in a randomized compete-block design in both st udies, with the blocks replicated in time in the growth chamber study. Seed Ca concentrations increased with increased Ca supply to the plan t. Relative humidity had not effect on either seed Ca concentration or germination. A decrease in the percentage of normal seedlings from 96 .7 to 41.8% coincided with a decrease in seed Ca from 2.37 to 0.87 mg g(-1). Reduced germination of low-Ca seeds was primarily due to an inc rease in the percentage of abnormal seedlings. The percentage of norma l seedlings was significantly and positively correlated with Ca (r = 0 .83) and negatively correlated with the B/Ca ratio and B (r = - 0.97 a nd - 0.83, respectively) in seeds. Results indicate that reduced Ca su pply to the plant may reduce seed Ca concentration in addition to alte ring other seed nutrients. Reduced seed Ca was associated with poorer seed germination, but additional studies are needed to clarify the rol e of Ca and other nutrients in the germination of seeds and seedling e stablishment.