Optimizing blended (NPSB) and N fertilizer rates for the productivity of Durum wheat (Triticum turgidum L.var. durum) in Central Highlands of Ethiopia

Durum wheat is one of the major cereal crops produced in East Shewa Zone, Oromia Regional state for the purpose of both home consumption and market. However, its productivity is low due to low availability of soil nutrients. Therefore, field experiment was carried out in 2017–2019 cropping seasons to determine economically feasible rate of blended NPSB and N fertilizes for increase the productivity of durum wheat. The treatments consisted of four levels of blended (0, 50, 100, and 150 kg NPSB ha⁻¹) and five levels of nitrogen (0, 46, 69, 92, and 115 kg N ha⁻¹) fertilizers. The experiment was laid out in a randomized complete block design in a factorial arrangement and replicated three times per treatment. Combined analysis of the results revealed that chlorophyll content, days to heading, days to maturity, plant height, harvest index, thousand kernels weight, and lodging index were highly significantly (p < .01) affected only by the main effect of N. However, total tillers (TT), productive tillers (PT), spike length (SL), number of kernels per spike (NKPS), aboveground biomass yield (AGBY), grain yield (GY), and straw yield (SY) were significantly (p < .05) affected by the interaction effect of blended NPSB and nitrogen fertilizers. The highest TT (421.33 plant m⁻²), AGBY (17,383 kg ha⁻¹), and SY (12,349 kg ha⁻¹) were recorded at combined application of 150 kg blended NPSB with 115 kg N ha⁻¹ while the highest PT (375.67 plant m⁻²), SL (6.67 cm), NKPS (50.07), and GY (5,666 kg ha⁻¹) were obtained at combined application of 150 kg blended NPSB with 92 kg N ha⁻¹. The result of economic analysis showed that combined application of 100 kg NPSB and 92 kg N ha⁻¹ gave economic benefit of 2,032.13 US$ ha⁻¹ with acceptable marginal rate of return (97.77%). Therefore, it could be concluded that application of 100 kg blended NPSB with supplement of 92 kg N ha⁻¹ fertilizer rates were economically profitable yield of durum wheat production in the study area.