EFFECTS OF NPS FERTILIZER RATES AND INTER ROW SPACING ON GROWTH, YIELD COMPONENTS AND YIELD OF COMMON BEAN (Phaseolus vulgaris L.) AT YABELO, SOUTHERN ETHIOPIA

Common bean is one of the most important food and export pulse crop in Ethiopia. However, its yield is limited by a number of constraints, which include poor agronomic practices such as low soil fertility management, inappropriate plant spacing, low and erratic rainfall and diseases. Hence, a field experiment was conducted at Yabelo during the 2018-2019 main cropping seasons to assess effect of rates of NPS fertilizer and inter row spacing on growth, yield components and yield of common bean; and to evaluate the cost-benefit of NPS fertilizer rates for production of common bean. The treatments consisted of factorial combinations of five rates of NPS (0, 50, 100, 150 and 200 kg ha-1) that contain 19% N, 38% P2O5 and 7% S and four inter row spacing of common bean (20, 30, 40, 50 cm) with uniform intra-row spacing of 10 cm. The experimental design used was randomized complete block design with three replications. The interaction of inter-row spacing and NPS rates had significant effect on harvest index and aboveground dry biomass where the highest harvest index (43.10%) was obtained at combination of 100 kg NPS ha-1 with 40 cm row spacing while the highest aboveground dry biomass (11333 kg ha-1) was obtained at 200 kg NPS ha-1 with 20 cm row spacing. Results of the main effects of NPS fertilizer indicated significantly the highest days to flowering (40.83), days to maturity (83.17), leaf area (2202 cm2), leaf area index (4.5 ), total number of nodules per plant (70.91), effective number of nodule (37.78 ), plant height (57.09 cm), number of primary branches per plant (7.66), and number of total pods per plant (12.14),were obtained at the highest rate of 200 kg NPS ha-1 while significantly highest hundred seeds weight (54.21 g), agronomic efficiency (16.04 kg grain kg-1 of NPS), grain yield (2881 kg ha-1) were recorded at 100 kg NPS ha-1. Among the inter-row spacing, 50 cm gave significantly the highest number of total pods per plant (12.39) and number of seeds per pod (3.56) while the highest grain yield (2491 kg ha-1) was obtained at 40 cm inter row spacing. The partial budget analysis also showed the highest net benefit (25617.00 Birr ha-1) with marginal rate of return of 1109.6% was obtained from combination of inter-row spacing of 40 cm with application of 100 kg NPS ha-1. Thus, it can be concluded that combined application of 100 kg NPS ha-1 with inter row spacing of 40 cm proved to be superior and can tentatively be recommended for study area.