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Effect of Hastened Flowering on Seed Yield and Dry Matter Partitioning in Diverse Soybean Genotypes¹

Optimization of relative vegetative and reproductive dry matter accumulation may provide a means of enhancing soybean [Glycine max (L.) Merr.] productivity. This 2-year field study measured the effect of artificially hastened flowering on the accumulation of dry matter and nitrogen in the seed and stover of eight soybean cultivars. Exposure to short- photoperiod treatment (10-h photoperiods from 18 June through 8 July at Urbana, IL) hastened flowering and physiological maturity by an average of 5 and 17 days, respectively. Despite this decrease in season length, short-photoperiod treatment resulted in lower seed yield only in the relatively short-season cultivars Wells and Corsoy in each of the 2 years, and in the early isoline of Clark (L62-1932) in 1 year. In five later-maturing cultivars, seed yield potential was maintained despite the abbreviation of season length in response to treatment. Dry matter harvest index was increased by treatment in six of the eight cultivars, and contributed to yield retention in all but the earlfiest cultivars. Total N accumulation was decreased by treatment in the early-maturing cultivatars Wells, Corsoy, and L62-1932 and unaffected in the latermaturing cultivars. Photoperiod treatment had no effect on nitrogen harvest index in any of the cultivars evaluated. Efforts to optimize the partitioning of dry matter in soybean through genetic or chemical means may be most successful if directed towards reproductive timing in late-maturing genotypes where vegetative duration is excessive.

Key Words: Glycine max (L.) Merr. • Harvest index • Oil • Photoperiod • Protein • Vegetative duration • Reproductive duration

² Assistant professor, Dep. of Agronomy, Purdue Univ., West Lafayette, IN47907 (formerly graduate research assistant, Dep. of Agronomy, Univ. of Illinois), and plant physiologist, USDA/ARS, Urbana, IL 61801.

Received for publication August 31, 1984.