Response of Current Midwestern Soybean Cultivars to Late Planting
- P. L. Raymer and
- R. L. Bernard
Soybean [Glycine max (L.) Merr.] is grown in the Midwestern USA primarily as a full-season crop and only to a limited extent as a double crop following small grains. Development of cultivars specifically adapted to later planting dates commonly associated with double-crop production has been suggested as a means to expand double-crop hectarage in this area. To determine if currently used soybean cultivars differ in their adaptation to late planting and if any specific plant traits are related to improved performance under late-planted conditions, 16 soybean cultivars were evaluated at both conventional (May) and late (late June to early July) planting dates in 1979, 1980, and 1981. Cultivar by planting date interactions were found for days to maturity, height at maturity, seed quality, and seed mottling, but not for yield, days to flowering, height at flowering, lodging, and weight per 100 seeds. All cultivars suffered substantial and similar yield reductions when planted late. Phenotypic correlation coefficients of cultivar performance between the two planting dates were positive and highly significant for all plant traits measured. The relationship of yield with various plant traits varied greatly from year to year and no differences in these relationships were observed between the two planting dates. These results do not furnish any evidence to justify a separate breeding program for the development of double-crop cultivars adapted to the Midwest. The lack of a strong cultivar by planting date interaction for yield and the lack of any strong associations of specific plant characteristics with yield in a late-planted environment imply that testing in a conventional early-planted environment will be effective in identifying lines that perform well in either full-season or double-crop environments.
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