Uniformity of Plant Spacing Effect on Soybean Population Parameters

Soybean Glycine max (L.) Merr. plant population experiments often are conducted by thinning stands to a predetermined density in equidistant spacings. Results are used to make recommendations to producers whose stands are more irregular due to less uniform seed placement by mechanical planters and random emergence. Field experiments were conducted in central Louisiana on a Norwood silt loam soil fine‐silty, mixed (calcareous), thermic Typic Udifluvent in 1988 and 1989 to determine effects of equidistant and nonequidistant plant spacings on seed yield, plant height, lodging, seed size, and seed quality of ‘Hartz 5171’ soybean grown at low, medium, and high plant densities in rows spaced 97 cm apart. Yields were slightly higher both years when plants were spaced equidistantly. Yields were low due to stress in 1988 and plants in equidistant spacings produced only 157 kg ha −1 more soybean than those in nonequidistant spacings. Yields were higher in 1989 than 1988, and plants in equidistant spacings increased yield by 257 kg ha −1 . There was no interaction between plant spacing and plant density on yield, which indicates that the optimum density for soybean is not dependent on plant spacings. Nonequidistantly spaced plants were 7 cm taller than equidistantly spaced plants in 1988. Less lodging occurred both years when plants were uniformly spaced. Seed size increased slightly when plants were spaced equidistantly in 1988. The results of this study indicated that although yields increased slightly under good conditions, soybean responded to plant density in the same way under either equidistant or random spacings.