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Comparison of the Nodal Distribution of Yield Components of Indeterminate Soybeans under Irrigated and Rain-fed Condition¹

Although the response of soybeans (Glycine max. L. Merr.) to soilmoisture stress has been studied extensively, information on the vertical distribution of yield and yield component responses is limited. Therefore, an experiment was conducted in 1978 which included two soil-moisture treatments and seven cultivars with differing maturity growing in a cumulic hapludoll. In 1978, early soil-moisture levels were near normal, and much of the growing season received adequate rainfall. Periods of warm, dry weather in August and September, however, reduced seed yield.

The response of these soybeans under these conditions varied considerably in their expression of seed yield and the vertical display of yield components. Soil-moisture levels, atmospheric demand, and physiological stage of development differences among cultivars led to significant yield and yield component interactions. Seed yield reductions due to soil-moisture stress varied from 20% to 50%, depending on cultivar. The reductions for individual components of yield (ie., 100-seed wt, seedslpods, podslnode, and nodeslplant) varied considerably over all cultivars. These decrements ranged from 0% to 30%

Key Words: Cultivar comparisons • Yield compensation • Plant stress • Maturity • Vertical yield distribution

² Professor and Curtiss Distinguished Professor of Agricultural Climatology, Agronomy Dep., Iowa State Univ., Ames, IA 50011.

³ Formerly graduate student, Agronomy Dep.

Received for publication August 31, 1981.