Evaluation of soybean breeding lines by examining their responses to sowing date and row spacing

Abstract

Seven genotypes, including 5 in the final stages of cultivar selection, were evaluated for their phenological development, yield, seed size, oil concentration and protein concentration in response to changes in sowing date and row spacing over 3 seasons, 1982-83, 1983-84and 1984-85. Genotype x sowing date interactions were detected for both phenological development and yield, particularly with the cultivar Sxy 59. This genotype was most affected by temperature during the pre-flowering phase of early November sowings. It was lower yielding in November sowings but was the highest yielding genotype in January sowings. Its adaptation to January sowings was unexpected because this genotype also showed high photoperiod sensitivity and flowered and matured rapidly in the late sowings. With early sowing, yield of the other cultivars was equivalent, or superior to (P=0.05), that obtained with the recommended early December sowing date, depending on the season. Late sowings caused yield reductions of about 34%. Increases in yield with narrow rows (50 v. 100 cm) were significant (P = 0.05) in 1 season and averaged 5% overall. Genotypexrow spacing interactions were only detected in 1 season, but no genotype was superior to the standard cultivar, Forrest, in adaptation to narrow rows. Thus this study revealed genotype responses which would affect adoption of newly released cultivars. It was concluded that this type of study is valuable in the final stages of a selection program and that these studies should include both early and late sowing dates and be conducted over several seasons.