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This article in CS

  1. Vol. 19 No. 5, p. 607-610
    Received: Oct 18, 1978

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Implications of Genotype ✕ Planting Date and Row Spacing Interactions in Double-cropped Soybean Cultivar Development1

  1. T. E. Carter and
  2. H. R. Boerma2



Soybeans (Glycine max (L.) Merr.) are grown in the southeastern U.S. as both a full-season crop and a double crop. The cultivars currently grown in the doublecropped environment were developed and released based on performance in full-season environments. To determine the need of a breeding program for double-cropped cultivars, 10 genotypes were evaluated at two row spacings (48 and 96 on) in an early (21 May and 3 June) and late (28 June and 30 June) planting date in 1975 and 1976.

The genotype ✕ planting date interaction was significant for seed yield, lodging, flowering date, and height at flowering and maturity over years. For seed yield, this interaction resulted hi changes in rankings of genotypes and differences in the results of the L.S.D. means test. The genotype ✕ row spacing interaction was significant for seed yield, seed size, and number of pods/ms over years. The interaction for seed yield was large enough to cause changes in rankings of genotypes and differences hi the results of L.S.D. means test. The genotype ✕ planting date ✕ row spacings interaction was significant for seed yield. Comparison of the yield of the 10 genotypes in the early-wide and late-narrow environments, the common planting date-row spacing combination for full season and double-cropped soybeans, respectively, indicated that the two highest yielding genotypes hi the early-wide environment ranked ninth and 10th in the late-narrow environment. The correlation for yield or rank order based on yield of the genotypes between the two environments were negative, but nonsignificant.

The relationships between yield and various plant traits were different in the various planting date-row spacing environments. A later flowering date, more seeds/pod, longer internodes, and shorter reproductive period were associated with increased yield in the late-narrow but not the early-wide environments. Since double-cropped soybeans are usually planted in late June in narrow rows, the magnitude of the interactions among genotypes, planting date, and row spacing for yield and the different relationships between plant traits and yield in the fullseason and double-cropped environments would indicate that development and testing of double-cropped cultivars should be practiced in a late-planted, narrow-row environment for maximum progress.

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