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This article in AJ

  1. Vol. 68 No. 4, p. 583-587
    Received: Apr 17, 1975

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Components of Soybean Seed Yield as Influenced by Canopy Level and Interplant Competition1

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



Recent work with genetic manipulation of the shape of the canopy and investigations of the source-sink relationships in soybeans [Glycine max (L.) Merr.] have emphasized the need for more information on hew various canopy levels and yield components contribute to the whole plant seed yield. A study was conducted to determine the vertical distribution of seed yields within the canopies of eight highly productive commercial soybean fields. Also, by thinning the stands to one plant/m2 at the beginning of the pod-filling period, the effect of decreased interplant competition on weight/seed was studied independently from other seed-yield components. Plants thus thinned yielded 12.5% more per node with 11.5% higher seed weights than the normal density plants.

The plant canopies were divided into five horizontal strata or canopy levels: canopy level 1 being the lowest 20% of the nodes, and so on. For the normal density plants, canopy levels 1, 2, 3, 4, and 5 contributed 19.51, 27.51, 26.51, 17.47, and 8.76% of the whole plant seed-yields, respectively. The thinning treatment had its greatest effect at the top of the canopy, with progressively diminishing effects toward the bottom. Thus, in the uppermost canopy level the weight/seed was 23.9% greater on the thinned than on the unthinned plants, while weight/seed in the lowest canopy level was unchanged. This interaction between canopy level and plant density during the pod-filling period may have been due to an alteration in the pattern of translocation and an inability of the lowest leaves to respond to increased light intensity.

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