Response of Soybean (<i>Glycine max</i>. L.) to Different Rates of NP Fertilizer and Plant Population Densities at Jimma Zone, South Western Ethiopia

Abstract

Declining soil fertility status and poor agronomic practices, including minimum use of inorganic fertilizers and inappropriate plant population per hectare are the major reasons for low productivity of soybean. Therefore, the field experiment was conductedto evaluate the response of soybean to different rates of NP fertilizer and plant population density at Jimma South Western Ethiopia during 2015-2017 main cropping seasons. The experiment was laid out in RCBD with 4x4 factorial arrangements with four plant population densities; 333,333, 400,000, 200,000 and 166,666 plants ha^-1, and four NP fertilizer rates; 23/23, 23/46, 46/46, 69/69 kg ha^-1 N/P₂O₅. An interaction effect of plant population densities and NP fertilizer rates was observed for all parameters. The results indicated that as plant population density increased plant height, pod height, grain yield and above ground biomass significantly increased but number of pods per plant was decreased. As NP fertilizer rate increased slightly plant height, number of pods per plant, grain yield and significantly above ground biomass was increased. Significanthighest mean grain yield of 3724 kg ha^-1 was obtained from the highest plant population density of 400,000 plants ha^-1 (50x5cm). Further research must done to conclude the yield response of the crop to plant population density because the yield is significantly increasing up to 400,000 plants ha^-1. Regarding the effect of NP fertilizer rates, the highest grain yield of 3477kg ha^-1 was obtained from 69/69 kg ha^-1 N/P₂O₅ which was statically at par with 46/46 kg ha^-1 N/P₂O₅ fertilizer. In conclusions, plant population density of 400,000 plants ha^-1 (50 cm inter row with 5 cm intra row spacing) with 46/46 kg ha^-1 N/P₂O₅ fertilizer rate were determined for optimum production of soya bean in Jimma area and similar agro-ecologies of the country.