Abstract:
Soybean (Glycine max (L.) Merrill) is a leading oil and protein crop of the world and can be used as a
source of high quality edible oil, protein, and livestock feed.Declining soil fertility status and poor
agronomic practices, includingminimum use of inorganic fertilizers and inappropriate plant
population are the major reasons for the lower yield of soybean. A field experiment was carried out to
determine the response of soybean to plant population and NP fertilizer in Kersa woreda of Jimma
zone, south western Ethiopia during the 2015/2016 cropping season. The study site is situated at an
altitude of 1740 masl and the texture of the soil is clay. Each four levels of NP fertilizer (23/23, 23/46,
46/46 and 69/69 kg/ha) and plant population (166,667, 200000, 333,333 and 400,000 plants/ha) were
laid out in a factorial experiment in randomized complete block design with three replications. The
released and commonly used soybean variety Clark–63K was used for the study. Data on phenology,
yield and yield components were collected and statistically analyzed to identify the best treatments.
The analysis of variance showed that the interaction of plant population and NP fertilizer
wassignificant for number of pods per plant, pod length, number of nodules per plant, hundred seed
weight, total biomass yield and grain yield. Whereas, plant population had significant influences on
days to 50% flowering, days to 50% maturity, number of branches per plant, number of nodules per
plant, plant height, total leaf area, number of pods per plant, number of seed per pod, hundred seed
weight, total biomass yield and grain yield per plat.Likewise, the main effects of NP fertilizer was
significant for number of pods per plant, number of branches per plant, number of leaves per plant,
total leaf area, plant height, days to maturity, leaf fresh and dry weights, pod length, hundred seed
weight, gran yield and harvest index. The highest grain and biomass yields of 1960 and 5491.7 kg/ha
were recorded at 400,000plant/ha plant population and 23/46kg/ha NP fertilizer. Moreover, the
partial budget analysis also revealed that the highest net benefit and marginal rate of return
(24063.6birr/ ha and 276%) and (25456.4 birr/ha and 623%) were obtained from 400,000plant/ha
plant population and 23/46kg/ha NP fertilizer. However, to generate more reliable information and
technology, further studies need to be conducted by taking into consideration other factors, including
different locations, varieties, fertilizers, plant population, cropping systems and growing seasons in
Jimma zone and other suitable areas in southwestern Ethiopia.
