CULTIVAR MATURITY AND REPRODUCTIVE GROWTH DURATION IN SOYBEAN

Twenty-seven soybean (Glycine max L. (Merrill)) cultivars from maturity groups (MG) 00 through V were grown in a field at Lexington, Kentucky (38 degrees N latitude), for 2 years, to evaluate the relationship between the duration of reproductive growth and total growth duration. Reproductive growth stages were measured at weekly intervals and dates of R1 (initial bloom) and R5 (beginning seed fill) were estimated by linear interpolation. The dare of physiological maturity (growth stage R7) was based on measurements made at two day intervals. The total growth duration increased from 84 days (averaged across years) for MG 00 to 134 days for MG V. Vegetative growth (planting to R5) increased in direct proportion to the total growth cycle. The flowering and pod set period (R1 to R5) was similar for MG 00 and 0, but increased from MG I to IV. The seed filling period, estimated from R5 to R7 and by the effective filling period, increased from MG 00 to I, but there was no change from MG I through V. These data indicate that the duration of seed fill does not always increase as the total growth cycle increases.