A field study was conducted for two years to assess the spatial and temporal effect of Phosphorus fertilizer on the yield, yield components and yield stability of five soybean genotypes in Umudike and Amakama in eastern Nigeria. The study was laid out as a split-plot in a randomized complete block with three replications. P rates of 0, 10, 20, 30 and 40 kg P/ha as triple superphosphate (TSP, 20% P) was randomly allocated to sub-plots and five soybean varieties (TGX 1440-1E, TGX 1448-2E, TGX 1485-1D, TGX 1835-10E and TGX 1910-14F) to main- plots. Phosphorus rate, year and location were considered as environmental factors in a genotype x environment analysis. Genotype, P rate, year, location and some interactions were significant for most of the traits studied. The Genotypes performed differently across the environments and a high positive and significant association existed between seed yield and number of pods per plant as well as the number of seeds per plant. Hence, these traits can be selected for in the improvement of soybean in this agro ecology. Genotype x environment interactions (GEI) played a significant role in this study and should be given considerable attention in soybean breeding program for development of genetic materials adapted to a wide range of environments. TGX 1910-14F and TGX1440-1E were stable under different P rates.

Key words: Soybean (Glycine max L.) genotypes, yield stability, grain yield, genotype x environment interaction (GEI)