Effect of different phosphorus rates to soybean [Glycine max (L) Merril] varieties in yayo district ilubabor zone, Southwestern Ethiopia

Soybean [Glycine max (L) Merril] is among the most important legume crops produced in western Ethiopia. However, declining soil fertility as well as poor soil fertility management practices has limited its yields. A field experiment was conducted in Yayo District on a farmer’s training centre to investigate the effect of phosphorus on yield and yield components of soybean varieties. The treatments included factorial combinations of six phosphorus rates (0, 11.5, 23, 34.5, 46 and 57.5 kg P2O5 ha-1) and three soybean varieties [Clark-63k, Ethio-Yugoslavia and Jalale (AGS-217)]. The experiment was laid out in RCB design with three replications. Highly significant (P<0.01) variations in days to emergence, days to flowering, days to physiological maturity, plant height, number of nodules per plant, number of branches per plant, above ground biomass yield, stand count after establishment, stand count at harvest, number of seeds per pod, hundred grain weight, grain yield and harvest index were observed among the varieties. Similarly, days to flowering, days to physiological maturity, number of nodules per plant, number of branches per plant, above ground biomass yield, number of seeds per pod, hundred grain weight, grain yield and harvest index were highly significantly (P<0.01) affected by phosphorus rates whereas days to flowering, days to physiological maturity, number of nodules per plant, number of seeds per pod, grain yield and harvest index were highly significantly (P<0.01) influenced by the interaction effect of variety and phosphorus rates. Among the varieties, Ethio-Yugoslavia had the highest value for days to emergence (7.49), plant height (71.71cm), number of branches per plant (9.02), above ground biomass yield (7550 kg/ha) and hundred grain weights (14.3 g). Regarding the phosphorus rates, maximum responses were obtained at rate of 46 kg phosphorus ha-1 for plant height (62.26 cm), number of pods per plant (61.9) and hundred grain weight (13.97 g) whereas 57.5 kg phosphorus/ha resulted in the highest number of branches per plant (9.01) and above ground biomass (7734 kg/ha). Considering the interaction between phosphorus rates and varieties, application of 46 kg phosphorus ha-1 on variety clark-63k led to production of the highest number of nodules per plant (14.367), grain yield (2730 kg/ha) and harvest index (0.4) whereas, 11.5 kg phosphorus/ha on variety Jalale (AGS-217) resulted in the highest number of seeds per pod (2.63). Accordingly, the grain yield ranged from 2113.3 to 2406.7 kg ha-1 depending on phosphorus fertilizer rates and varieties. In conclusion, application of the highest rate of phosphorus (46 kg/ha) on variety Clark-63k resulted in the best performance in grain yields (2730 kg/ha) under the agro-ecology of Yayo district from among the three varieties and six phosphorus rates.