Calcium effects on soybean seed production, elemental concentration, and seed quality

Soybean [Glycine max (L.) Merr.] plants produce fewer and lower quality seeds when grown in conditions that decrease seed Ca concentration. Indeterminate soybean was gown in modified hydroponic culture to ascertain the effects of Ca deficiency on leaf dry matter, seed production and elemental concentration, and the effect of pod position on seed elemental concentration in 1992 and 1993. Treatments consisted of 2.0 (Control), 0.2 (Low), 0.1 (Very Low) mM Ca in the nutrient media. Some Control plants were switched to Low or Very Low (Con/L, VL) Ca levels at beginning seed growth stage (R5), and some plants grown at the Very Low Ca level were switched to the Control (VL/Con) Ca level at R5. At harvest, plants were divided into four sections: top-third (T/3), middle-third (M/3), and bottom-third (B/3) of the mainstem and branches (Br). Low and Very Low treatments produced 65 and 10% as much seed mass, respectively, as Control in both years. Low and Very Low treatments retained significantly less total leaf dry matter at R5 in both years. Seed Ca levels were 25 to 300% higher in treatments that included the Control Ca level during any part of reproductive growth compared to other treatments in both years. Seed Ca concentration was highest in the T/3 and Br sections in both years. Germination was reduced in treatments not including the Control solution during part of the reproductive growth period in both years. Decreased Ca levels in the nutrient medium reduced soybean leaf dry matter during seed fill, seed production, seed Ca concentration, and seed germination, and increased the incidence of seedling disorders such as watery hypocotyl and epicotyl necrosis.