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Effects of Night Temperature on Dry Matter Partitioning and Seed Growth of Indeterminate Field-Grown Soybean¹

Dry matter allocation, and thus productivity, within soybean plants (Glycine max (L.) Merr.) is affected by night temperature. The indeterminate soybean cultivar S09-90 of Maturity Group O was grown in the field at Oregon State University in 1981 and 1982 to assess the effect of night temperature on dry matter partitioning and seed growth through out the growing season. Mean minimum night temperature used as treatments included check (noncontrolled, ca. 10°C), 16, and 24°C. Night temperatures for 16 and 24°C treatments were raised by enclosing plots with polyethylene-covered chambers at night and increasing chamber temperature with electric heaters. The chamber covers were removed each morning to provide natural field conditions during the daylight hours. Treatments were applied from 2 weeks after crop emergence until physiological maturity. Higher night temperatures enhanced early vegetative growth, advanced reproductive development and physiological maturity, and increased seed yield. Although higher night temperatures increased crop growth rate during the vegetative period, final vegetative dry matter, pod weight, and leaf area generally decreased as night temperature increased. Net assimilation rates were similar among the treatments. Seed growth duration (SGD) did not vary considerably among the treatments except for 24°C plants in 1982 whose SGD was 6 days longer than the check plants. Increased seed yield of the 16°C plants over the check was associated with 31 and 38% increases in seed growth rates (SGR) in 1981 and 1982, respectively. Seed growth rate of 24°C plants also was 24% higher than the check in 1981. Increased seed yield of 24°C plants in 1982 was primarily due to their longer SGD. Increased seed growth along with reduced vegetative growth and pod wall growth of plants at higher night temperatures resulted in higher harvest indices in these plants compared to the check. Harvest index was increased above the check by 27 and 33% in 1981 and 16 and 23% in 1982, for 16 and 24°C plants, respectively. These data support the conclusion that SGR of early maturing soybeans is responsive to night temperatures. Low night temperatures restrict SGR that, in turn, favors partitioning of photosynthates to vegetative organs and pod walls.

Key Words: Crop growth rate • Net assimilation rate • Seed growth duration • Harvest index • Environmental stress • Cold tolerance • Thermoperiodicity • Glycine max (L.) Merr.

² Former graduate research assistant, currently post-doctoral research associate, and associate professor of crop science, Dep. of Crop Sci., Oregon State Univ., Corvallis, OR 97331.

Received for publication May 31, 1983.