Nodulating and nonnodulating soybean isolines field‐tested for 7 years produced essentially equal N yields when adequate combined N was available. The amount of N fixed symbiotically depended largely upon the availability of soil N, water, or both, and ranged from 1 to 142 pounds per acre, that is, 1 to 74% of the total N uptake, respectively. The amount of symbiotic N fixation decreased rapidly with increases in fertilizer N. Nodule weight, number, and size were directly related to increased N fixation and inversely related to increased increments of applied N. The correlation of symbiotic N fixation with nodule mass was r = 0.9. Except for a severe moisture stress, the nonnodulating line responded linearly to applied N, with 3.2 pounds of fertilizer N equivalent to 1 pound of plant N. Short‐term rotation studies indicated that, when no fertilizer N was used, the residual effect of a nodulated soybean crop in the previous year was 33 pounds of N per acre.
No takes yet. Share an insight, caveat, or question.
C. R. Weber (1966) studied this question.