Yield Response of Common Bean (Phaseolus vulgaris L.) Varieties to Combined Application of Nitrogen and Phosphorus Fertilizers at Mechara, Eastern Ethiopia

A field experiment was conducted in 2012 cropping season to determine the optimum rates of nitrogen and phosphorus fertilizers for maximum yield of common bean and to select the best combination of varieties and fertilizer levels for optimum yield on nitisols at Mechara research station. The treatment consists of four common bean varieties (Awash Melka, Awash 1, Chercher and Red Wolayita) and five combined nitrogen and phosphorus rates [0,0; 9,23; 18,46; 27,69; and 36,92 kg N and P2O5/ha) laid out in randomized complete block design with three replications. The main effect of common bean varieties and NP rates were significant (P<0.05) on days to 50% flowering, 90% physiological maturity, number of pods per plant, seeds per pod and hundred-seed weight. Similarly, the interaction effect of variety and NP rate was significant (P<0.05) on days to 50% emergence, number of nodules, and grain yield, biological yield, and harvest index, nitrogen and phosphorus concentration of shoot tissue. Accordingly, variety Awash Melka with the application of 27 kg N: 69 kg P2O5 ha-1 gave the highest value for grain yield (3127 kg ha-1), biological yield (7446 kg ha-1). The highest number of seeds per pod (4.60) and the highest nitrogen content (3.89%) of the shoot tissue also recorded from Awash Melka and application of 27 kg N: 69 kg P2O5 ha-1. Whereas, the lowest grain yield (574 kg ha-1) was recorded for variety Awash 1 in response to no fertilizer application. Thus variety Awash Melka with the application of 27 kg N: 69 kg P2O5 ha-1 was found to be the best combination under Mechara's agro-ecology as it gave higher values for yield and most of yield related traits.