STARTER NITROGEN AND GROWTH HABIT EFFECTS ON LATE-PLANTED SOYBEAN

In the Gulf Coast region of the southeastern USA, soybean [Glycine max (L.) Merr.] is often planted in a double-cropped system following cor n (Zea mays L,), In this system, soybean planting date is delayed from the optimal range (mid-May to mid-June) to late July, causing a subst antial yield reduction. Potential grain yield response has led to incr eased interest in indeterminate growth habit and N application for lat e-planted, double-cropped soybean systems. Our objective was to determ ine the interactive effects of growth habit (determinate and indetermi nate stem termination types) and starter N (0 and 50 kg ha(-1)) on soy bean growth and yield when planted following corn in a double-crop sys tem. Three Maturity Group VIII soybean genotypes [thr near-isolines Au 86-23971 (Dt(1)Dt(1), indeterminate) and Au86-2397D (dt(1)dt(1), deter minate) and a determinate check cultivar, Cook] were planted in late J uly in seven Alabama environments during 1995 and 1996, Starter N Incr eased R1 dry matter for both Au86-2397D and Au86-2397I by 0.50 Mg ha(- 1). Au86-2397I had 1 cn greater average plant height at the Ri develop mental stage and 14 cm greater height at Rs than Au86-2397D. Au86-2397 I yielded 0.16 Mg ha(-1) more than its determinate near-isoline, Appli cation of starter N decreased the number of nodules per root, but incr eased plant N concentration and dry matter yield. Grain yield was incr eased on average by 0.15 Mg ha(-1) with addition of starter N, In this study, an indeterminate genotype soybean coupled with application of starter N promoted greater soybean growth and yield in a late-planted, double-cropped system.