Nodulating and Nonnodulating Soybean Isolines: I. Agronomic and Chemical Attributes1

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Abstract
Agronomic and chemical attributes for a pair of nodulating and nonnodulating soybean isolines were field‐tested under varying environmental and soil conditions for 6 years. The nonnodulating line usually gave large increases in the following attributes with increased amounts of applied N: seed and dry matter yields, seed size, protein in seed and dry matter, plant height, and lodging suceptibility. Maturity date was delayed. Oil content was the only attribute that decreased. The nodulating line gave very small responses in these attributes with increasing N under the same conditions.With adequate N, yield and all other attributes in the isolines were essentially alike except for the nodulating character. Elemental N obtained through fixation by the nodulating line supplemented soil N; in contrast, the nonnodulating line used only available soil N.With moisture limiting, the attributes of the isolines were equalized at 50 pounds per acre of applied N; with favorable moisture, the isolines were not quite equalized in their attributes with 150 pounds per acre of applied N. When corncobs were used to partly immobilize soil N, the isoline traits were essentially equalized with 600 pounds per acre of applied N.Nonseed dry matter to seed yield ratios for the nonnodulating line increased with stresses for moisture, N, or both. Consistently smaller ratios for the nodulating line compared with the nonnodulating line may indicate that symbiotic N may be more biologically suitable for seed production than combined N.

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