Indeterminate and Determinate Soybean Responses to Planting Date 1

Determinate and indeterminate soybean [ Glycine max (L.) Merr.] strains respond differently to planting date in the northern United States. The objectives of this study were to compare performance of closely related determinate and indeterminate strains in response to planting date. Five pairs of determinate and indeterminate isolines or related cultivars were evaluated at three planting dates for 1 yr, and five planting dates for two succeeding years at West Lafayette, IN. Dates were recorded when plants reached stages V1 to V5 and all reproductive stages. Additional data were recorded on agronomic characteristics of the isolines. Planting delays resulted in fewer days between stages V1 to V5 in 2 of the 3 yr and in stages R2 through R8 in all 3 yr. Determinate and indeterminate strains responded the same to planting delays in the vegetative stages V1 to V5 but not in the reproductive stages. Indeterminate strains were shorter and had fewer nodes with planting dates after May 24. Determinate strains either increased or were the same in plant height and number of nodes with successive planting dates after May 24. When lodging was moderate to severe, strains of both types lodged more severely when planted in June than in May. In general, determinate strains yielded more when planted late May or early June; indeterminate strains produced maximum yields when planted from early to late May. Determinate strains responded similarly to planting date regardless of the source of the dt 1 gene.