Effects of Fertilizer Rate and Row Spacing on Forage Soybean ( <i>Glycine max</i> [L.] Merrill) Biomass Yield and Quality in the Highlands of Ethiopia

The experiment was conducted with the objective to evaluate the effects of fertilizer level and row spacing on soybean morphological characteristics, forage yield, and nutritive value in the highlands of Ethiopia. A factorial arrangement of randomized complete block design (RCBD) using two factors (row spacing and four fertilizer levels) containing three row spacings of 50, 60, and 70 cm were combined with four 0, 100, 120, and 140 kg ha −1 NPS fertilizer rates. Growth parameters and forage yield data were gathered at the 50% flowering stage, weighed, dried, and ground. Subsamples were then taken for analysis of the following parameters: ash, dry matter (DM), organic matter (OM), in vitro DM digestibility (IVDMD), fiber contents (neutral detergent fiber [NDF], acid detergent fiber [ADF], and acid detergent lignin [ADL]), and metabolizable energy (ME). The collected data were subjected to a general linear model (GLM) for statistical analysis system (SAS) version 9.0. There was significant interaction ( p &lt; 0.05) effect in the fertilizer level and spacing only in the number of nodules among growth parameters, but for nutritional value of forage soybean DM, crude protein (CP), CP yield (CPY), and ME. Both spacing and fertilizer application showed significant effects ( p &lt; 0.001) on the majority of growth characteristics like plant height (PH), number of branches (NBs), number of leaf per plant (NLPP), number of nodule ( N ), DM yield (DMY), and leaf‐to‐stem ratio (LSR). The growth parameters and nutritional quality had better performance in 140 kg ha −1 NPS application and 70 cm row spacing than in lower fertilizer levels. Moreover, significantly ( p &lt; 0.001), maximum DMY (12.2 t ha −1 ) was recorded from 50 cm row spacing. Regarding fertilizer levels, maximum DMY was recorded from high‐level NPS fertilizer application (10.9 t ha −1 ). The row spacing of 70 cm had the highest CP content (16%). The best marginal rate of return (MRR; 859.85%) and largest net profit (40212 birr) were obtained from 140 and 100 kg NPS fertilizer treatments with 50 cm row spacing, respectively. In the current result, forage soybean with a rate of 100 kg ha −1 NPS fertilizer and 50 cm row spacing was chosen among the treatments in the current study and is advised for wider exploitation through irrigation application.