Plant Density and Soybean Yield

The spacial distribution of plants in a crop community is an important determinant of yield. However, the mechanisms responsible for the observed responses to changing plant density are not well understood. Field experiments utilizing a systematic design that made it possible to evaluate a wide range of plant densities in a single experiment were conducted with an indeterminate (‘Cumberland’‐ 2 yr) and a determinate (‘Pixie’‐1 yr) soybean Glycine mar (L.) Merrill. Population densities used in the analyses varied from 0.6 to 24 plants m −2 . At low population densities, where there was no interplant competition, yield increased in direct proportion to increases in plant density. At plant densities providing interplant competition, the rate of yield increase was reduced. Yield of the indeterminate cultivar increased as plant density increased above the density required for 95% insolation interception at growth stage R5. The increase in yield was a result of increases in seed m −1 in both years along with seed size in 1985. However, the determinate cultivar exhibited maximum yield at the plant density that provided 95% insolation interception at growth stage R5. The data for the indeterminate cultivar confirms a recently published theoretical analysis of soybean yield responses to plant density. The data suggest that plant densities higher than those required to maximize insolation interception by growth stage R5 may be required for maximum yields of indeterminate cultivars.