GROWTH AND YIELD RESPONSES OF SOYBEAN (GLYCINE MAX L. MERRIL) TO HYDROTHERMAL REGIMES IN A HUMID ZONE OF NIGERIA

Abstract

The responses of growth, development and seed yield of ten lines of soybean «(ilycine max, L, Merrill) were investigated in the late cropping season of 2002 and 2003 under field condition in Akure, a humid rainforest zone of Nigeria. The objectives of were to evaluate differences among the selected soybean cuItivars in terms of duration of phenological phases and seed yield and genotypic differences in the responses to the hydrothermal conditions of the late season. The cuItivars were: TGX191O-5F, 191O~8F, 1910-12F, 1910-15F, 19 18-22F, ]9]8-17F, 1844-4E, 1844-]8E, ]440-IE, 923-2E. The weather conditions of the pre and post-flowering growth affected the growth, developmental phases and seed yield of soybean. In particular, stresses \occurred at late vegetative and reproductive growth (flowering to physiological maturity; Rl to R7). There were differences among genotypes in duration from emergence to first flowering.' Across soybean lines, the average durations from emergence to flowering' were from 20.6 and 24.2 days. Differences were aslo noted in the duration of the critical period of pod and seed number determination: the attainment of anthesis (Rl ), days to 50% flowering (R2), beginning of podding and pod filling (R3) and physiological maturity (R3-R7). The relative performance of the cultivars in terms of shoot and seed yield production varied. TGX 1918-22F and 1440-1p out yielded other varieties with respect to shoot biomass yield. However, cultivars TGX 1918-12F, 923-2E and 1440-] E produced significantly higher seed yield in both years (2002 and 2003). The selected soybean cultivars exhibited different sensitivities to the prevailing environmental conditions' during growth and hence growth and seed yield adaptation to the of the late cropping season. Regression equations were· established for duration of reproductive growth, and seed yield. The reproductive growth duration were negatively associated with seed yield • and the relationships yielded higher r2. The sensitivity of reproductive phases to supraoptimal temperatures has implications for seed yield and adaptation of soybean to late season.