EFFECT OF GROWTH HABIT ON YIELD AND AGRONOMIC CHARACTERISTICS OF LATE-PLANTED SOYBEAN

Seed yield of double-cropped soybean [Glycine mar (L.) Merr.] in the southeastern USA is reduced compared with full-season soybean, and most agronomic traits are affected. This study was initiated to determine the effects of determinate (dt(1)) and indeterminate (Dt(1)) growth habit genes on yield and agronomic characteristics of late-planted near-isogenic soybean lines (near-isolines) in the southeastern U.S. Twenty-three determinate and 23 indeterminate near-isogenic soybean lines from three populations were compared in the field at two locations (Brewton and Tallassee, AL) in 1991 and three locations (Shorter, Tallassee, and Brewton, AL) in 1992. Growth habit had no effect on seed yield, but growth habit x location effects were large. At Brewton, indeterminate lines yielded more than determinate lines; at Tallassee, both types yielded equally; and at Shorter, determinates yielded more. Flowering and reproductive periods were longer for indeterminates than for determinates at all locations. Determinates were shorter at Growth Stages R1 and R8 and produced fewer mainstem nodes per plant after initiation of flowering than did indeterminates. Seed oil percentage was lower and protein content higher for indeterminates than for determinates. We concluded that growth habit x location interactions play a large role in determining the yield advantage of either growth habit in double-cropped, late-planted cropping systems.