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The purpose of this experiment was to determine the extent to which the number of pods per node (“sink Size”) controls the accumulation of mineral nutrients, carbohydrate, and total dry matter in soybean plants (Glycine max (L.) Merrill). A quantitative description of the relationship between sink size and nutrient accumulation will help to identify nutrients which might limit yield at higher reproductive loads. Plants were grown in the field and various numbers of pods were removed as they formed to give an average of 0, 0.8, 1.1, 1.9, 2.4, or 2.7 pods per node. Leaf blades, stems plus petioles, pods, and seeds from mature plants were analyzed for N, P, K, Ca, Mg, and carbohydrate concentration. Increasing the sink size resulted in decreases in N and P concentration in leaves, stems, pods, and seeds and in Mg concentration in stems plus petioles. Conversely, K concentration in all plant parts and Ca concentration in leaf blades increased in response to increasing sink size. These increases in K and Ca concentration appeared to be due to a greater decline in the matter content than in K and Ca content as sink size increased, resulting in concentration of K and Ca. As sink size increased from zero to 2.7 pods per node: 1) carbohydrate content of leaf blades decreased 64%; 2) carbohydrate content of stems plus petioles decreased 40%; 3) mineral nutrient content of leaves plus stems decreased as follows, N — 72%, P — 64%, K — 28%, Ca — 18%, and Mg — 55%; and 4) total dry weight of leaves plus stems decreased 37%. When nutrient content of leaves and stems was plotted against sink size the result was a nearly perfect fit to a straight line for all nutrients except potassium. A comparison among nutrients of the slopes of these curves suggested that maximum reduction of N and P content in leaves and stems would occur at sink sizes smaller than required for maximum reduction of other mineral nutrients. Total Mg and Ca accumulated by above‐ground plant parts was not dependent on sink size, whereas total N, P, and K accumulated was strongly dependent on sink size.

Investigations with exogenous test solutions showed that abscisic acid (ABA) inhibited germination of nondormant seeds and that gibberellins (GA) promoted the germination of yellow foxtail (Setaria lutescens (Weigel) Hubb.) The effect of the promoters was much more readily demonstrated with excised caryopses than with intact seeds. Cytokinins reversed ABA inhibition of germination; GA did not, but the two promoters in combination were more effective than the cytokinin alone. The reversal occurred only at one end of the embryonic axis, the shoot end. An endogenous inhibitor was extracted from dormant and nondormant yellow foxtail seeds and compared with ABA by chromatography, electrophoresis, and bioassays. The extracted inhibitor was very similar to ABA in six paper-chromatography solvent systems, three paper electrophoresis runs at different pH values, and three bioassays. Paper electrophoresis was an effective means of separating the two plant hormones, ABA and gibberellic acid (GA3).

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