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Yield of Indeterminate Soybeans in Response to Multiple Periods of Soil-Water Stress During Reproduction¹

Yield potential of soybeans [Glycine max (L.) Merr.], which are grown under nonlimiting soil-moisture conditions, has been greatly improved through breeding and management practices in recent years. Much improvement, however, is still needed in the development of high yielding soybeans grown under suboptimal soil-moisture conditions. To better understand limiting soil-water effects on yield, four indeterminate soybean cultivars were grown in restricted rooting mediums of Nicollet Loam soil (fine-loamy, mixed, mesic Aquic Hapludolls) in the field, and single and multiple periods of soil-moisture stress were induced during the reproductive stage by withholding hand watering at appropriate times and covering the plots during periods of rainfall.

Seed yield reductions for all soil-water treatments and cultivars varied from 2% (NS) to 27% ( = 0.01). Two of the cultivars, ‘Ottilie 7270’ and ‘Beeson’, were less affected by soil-water stress (12% yield loss) than the other cultivars (18% yield loss), ‘Hodgson’ and ‘Corsoy’, averaged over stress treatments. Soil-water stress during the first of three stress periods reduced yield by 12% ( = 0.01). A second and third period of soil-water stress reduced yield additionally 5% (NS) and 4% (NS), respectively. Treatments receiving soil-water stress for the first time during period 2 or period 3 had 11% ( = 0.01) or 12% ( = 0.01) yield reductions, respectively. The plants subjected to three periods of soil-water stress produced fewer but heavier seeds than plants stressed only during the third period. The response of yield components, nodes/plant, pods/node, seeds/pods, and weight per seed, varied extensively between cultivars and treatments. The magnitude of individual decrements in these parameters was dependent on the timing of soil-water treatments and the state of development of the soybeans.

Under the conditions of this experiment, all the cultivars exhibited similar yield response to single periods of stress. Preconditioning soybeans for later stress resulted in less yield reduction than if the plants were unconditioned. Seed yields of later maturing cultivars, Ottilie 7270 and Beeson, were greater and were less affected by multiple stress during reproductive growth than the cvs. Corsoy and Hodgson. Soil-water stress imposed on plants early in their reproductive periods appeared to change dry matter partitioning by increasing their harvest index, and this was most notable with the later maturing cultivars.

Key Words: Glycine max (L.) Merr. • Components of yield • Water relationships • Yield compensation • Harvest index • Preconditioning

² Formerly graduate assistant in agronomy, now extension biometeorologist, Dep. of Land, Air and Water Resources, Univ. of California, Davis, 95616; professor; and distinguished professor, Agronomy Dep., Iowa State Univ., Ames, IA 50011.

Received for publication March 25, 1981.