Soil test levels of potassium, yields, and seed size in soybean cultivars

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Abstract
The effect of soil test levels of K (1 N, NH4OAc) on yields of soybean (Glycine max Merr) reproductive growth, seed size and numbers were evaluated for early, medium, and late maturing cultivars on a Maury silt loam (Typic Paleudalf). Relative yields were near maximum when extractable K was approximately 210 pp2m. Concentrations of K in uppermost, fully expanded leaves at flower initiation at the high production level were approximately 2.0 to 2.15%. Neither dates of flower initiation nor pod maturation of the three cultivars, Bonus, Cutler 71, and Williams, were altered by K nutrition. Either seed size or seed number were approximately equally capable of serving as a mechanism for increasing yield in response to improved K nutrition. Among cultivars, Bonus tended to have more smaller seeds, whereas Cutler 71 tended to have larger seeds with fewer seeds being produced.