Soybean Growth and Yield as Affected by Row Spacing and by Seasonal Water Supply 1

Previous experiments have shown that soybeans [ Glycine max (L.) Merr.] grown in narrow rows often out‐field those grown in the more traditional 102‐cm row spacings. Those experiments often have been conducted where early season leaf area development and synthesis rate, rather than seasonal water, control crop yield. The present research was conducted to test the hypothesis that wide row soybeans will yield as much as, or more than, narrow row soybeans during years of low seasonal water supply. ‘Wayne’ soybeans were grown in 25, 50, 75, and 100‐cm row widths at Castana, Iowa during the 1975, 1976, and 1977 growing seasons. All plots were thinned to 16 plants/m 2 about 3 weeks after planting. Data were collected on leaf areas, leaf water potentials, stages of development, dry weights of plant parts, numbers of pods, root length densities, soil water contents, and yield. There were wide differences among the 3 years in seasonal water supply for soybean growth. During 1977, a year when water supply was high, narrow row soybeans (25‐cm rows) yielded 17% more than those in the 100‐cm rows. During the 2 years with the lower seasonal water supplies, there were no significant differences in yield (P = 0.05) among the 25, 50, 75, and 100‐cm row spacings. Plants growing in the 75 and 100‐cm row widths, however, had higher (wetter) daytime leaf water potentials, grew taller, had larger leaf areas, and set more pods than those growing in the 25‐cm rows. An intriguing question remains about the reason that the wide row plants yielded no more than the narrow row plants during dry years.