Yield and yield components of early maturing soybean genotypes in the mid-south

Maturity group (MG) IV soybean [Glycine max (L.) Merr.] cultivars are planted in April through June in the mid-south. April plantings are used to avoid mid-season droughts, though seed quality from April plantings of MG IV cultivars is often poor. Thus, a late June planted seed quality nursery is required for breeding material. This range of planting dates for MG IV Lines may affect yield, plant morphology, and produce genotype x planting date interactions that affect cultivar selection. Our objectives were to study yield, yield components, and the relationships between traits in MG IV genotypes planted in April and June in the mid-south. Twenty-seven indeterminate and nine determinate genotypes were planted in mid-April and late June in 1992 and 1993 in Arkansas. Data were collected on yield, yield components, height, and days to R2 and R8. Neither planting date nor stem termination affected yield. Genotype x date interactions were significant for many traits in indeterminate but not in determinate lines. Plant height was reduced in April plantings for both types, yet for indeterminate types, main stem node number increased. Number of branches, pods per branch, and percentage of total yield derived from branches were greater in April than in June plantings. These trends were more pronounced in indeterminate than in determinate lines. Few strong associations between yield and its components were noted for determinate lines or June-planted indeterminate lines. For the April-planted indeterminate lines, yield was strongly associated with a complex of components that was dominated by number of main stem nodes. Number of main stem nodes and plant height may be useful selection criteria for improving seed yield of MG IV cultivars.