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This article in AJ

  1. Vol. 67 No. 4, p. 487-490
    Received: Aug 5, 1974



Seasonal Development of, and the Effect of Inter-plant Competition on, Soybean Nodules1

  1. R. R. Weil and
  2. A. J. Ohlrogge2



Research suggests that competition for photosynthate between nodules and seeds of soybeans [Glycine max (L.) Merr.] may be responsible for the apparent decline in symbiotic nitrogen fixation during the high N requirement pod-filling period. A study was conducted in eight highly productive commercial fields to characterize the development of nodules during the growing season and to determine the effect on nodulation of thinning to one plant/m2 at a time (end of flowering period) when the response by the reproductive sink would be limited to a small increase in seed size.

The number and size of nodules increased rapidly during flowering, peaked in early pod-filling, and declined thereafter. After flowering, the percentage of red nodulated declined while the percentage of green (inactive) nodules increased. Total nodule volume/plant and active (i.e., red) nodule volume/plant peaked in mid-August and then dropped off rapidly.

The thinned plants showed significantly more nodule volume/plant, a greater percentage of red nodules, and a lower percentage of green nodules during pod-filling, than did the plants growing at normal population densities. During that period, the thinned plants had 2 to 5 times as much active nodule volume/plant. The thinning treatment apparently postponed the decline in the nodules for several weeks. This effect was probably due to an increased supply of photosynthate available to the nodules at the lower plant density.

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