ABSTRACT

Field experiments were conducted in 2017 and 2018 cropping seasons to determine the effects of Genotype and Fertiliser Rates on Growth and Yield Parameters of Soybean (Glycine max L. Merrill) in the Rainforest (represented by Amakama) and Derived-Savannah (represented by Ishiagu) agro-ecological zones of South-East, Nigeria, using eight genotypes (TGX 1951-3F, TGX 1987-10F, TGX 1835-10E, TGX 1988-5F, TGX 1987-62F, TGX 1989- 19F, TGX 1448-2E, TGX 1990-67F)  collected from International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. Compound fertiliser (NPK15:15:15)  rates  of  0 kg ha^-1  (F₁ ),  93.75 kg ha^-1  (F₂), 125.0 kg ha^-1  (F₃) and 156.25 kg ha^-1  (F₄); equivalent to 0%, 75%, 100% and 125%, respectively, of recommended (125.0 kg ha^-1) were used. Studies were carried out to determine Nitrogen Uptake (NU), Dry Matter Accumulation (DMA), Growth and Yield Parameters in the selected genotypes, in the study locations. Greenhouse study was also carried out, in 2017, in the facility of College of Crop and Soil Sciences, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria, using the eight genotypes and same fertiliser levels, to validate the Field Experiments.  Data collected were subjected to variability and correlation analyses, followed by stability analysis using additive main effects and multiplicative interaction (AMMI) and genotype (G) and genotype × environment (GE) interaction effects (GGE) bi-plot models. This study showed that wide variations exist among the collections of Soybean genotypes in many of the characters studied. In 2017 Field Experiment, Analysis of Variance (ANOVA) for DMA showed significant differences (p<0.05) for the 2 locations, genotypes and  Location x genotype (LOC.GEN) interactions at 4 weeks after Planting (wap;WAP), 6wap,8wap and10wap while ANOVA, from the Field experiments, for both years (2017  & 2018) showed significant differences (p<0.05) among the genotypes for NU8WAP. ANOVA from the Greenhouse experiment also showed significant differences (p<0.05) for NU for all the attributes and their interactions at 4WAP, 6WAP, 8WAP and 10WAP. The relative contributions of Pod length, Number of Seeds per Pod, 100 seed weight, Dry Matter Yield and the production of more seeded-pods per plant, among others were highlighted. This is without prejudice to the role of DMA and NU. Cluster analyses based on Principal Component (PC1) and Seed yield per hectare revealed the closeness of the genotypes and the different environments as PC1 scores could effectively represent genotype effect. From this study, it may be concluded  that TGX 1951-3F, TGX 1987-10F, TGX 1988-5F ,TGX 1989- 19F and TGX 1448-2E were the more important Soybean genotypes studied and Nitrogen has positive effect on nutrient uptake  and yield of these  genotypes. Application of compound fertilizer (NPK  15:15:15) at the rate of 125.0 kg ha^-1 is recommended in the Derived Savannah region of South-East, Nigeria, as represented by Ishiagu, for TGx1988-5F. NPK 15:15:15 rate of 156.25 kg ha^-1 is recommended for TGX 1951-3F in the Rainforest agro-ecological zone of South-East, Nigeria, as represented by Amakama. The soybean genotype, TGX 1989-19F is recommended for both locations, at NPK 15:15:15 rate of 156.25 kg ha^-1, for optimum, more stable production. These recommendations are for rain-fed field conditions. It is also advised that the fertilizer (NPK 15:15:15) be applied at 4 and 8WAP for optimum N uptake and subsequent utilisation.