- Grain yield, Plant population density, Quality protein maize and fertilizer.
Field studies were conducted in 2015 and 2016 under rain fed conditions in south western Ethiopia, Jimma zone to determine optimum plant population density and NP fertilizer on Maize. The experiment had four NP fertilizer rates; 69/52, 92/69, 115/86, and 138/104 N/P2O5 kg ha-1 and four plant population density; 44,444(75cm*30cm), 53,333(75cm*25cm), 66,666(75cm*20cm) and 88,888(75cm*15cm) plants per hectare. Each treatment was assigned to each plot in split plot design. Grain yield and above ground biomass significantly increased as plant populations and NP fertilizer rates increased. The number of ears per plant was significantly decreased as plant population density increased and increased with the increased rate of NP fertilizer. The greater lodging was recorded in 2015 cropping season when compared with that of 2016 cropping season. The highest grain yield 8752 kg ha-1 and above ground biomass 18.33 ton ha-1 were recorded from 138/104 N/P2O5 fertilizer. Regarding plant population density the highest grain yield 9401 kg ha-1 and above ground biomass 19.90 ton ha-1 were recorded from 88,888 plants ha-1 (75cm*15cm). The highest net benefit 30,669ETB ha-1 with highest MRR 164% was recorded from 115/86 N/P2O5 kg ha-1. Concerning plant population density the highest net benefit 36,705 ETB ha-1 with acceptable MRR 585% was obtained from 88,888 plants ha-1 (75*15cm). Therefore, plant population density 88,888 plants ha-1 (75*15cm a plant hill-1 or 75 x 30 cm two plants hill-1) with N/P2O5 fertilizer rate of 115/86 kg ha-1 can be advisable for farmers in the study area and adjacent woredas’ with similar agro-ecologies.