Field study was conducted at Humera, Kebabo, Banat, Zerbabit, Division and Ruwasa, western zone of Tigray, northern Ethiopia in 2018 under rain fed condition to determine effects of six nitrogen fertilizer levels (0, 11.5, 23.0, 34.5, 46.0 and 57.5 kg Nha-1) applied in the form of urea and four spacing (30, 45, 60 and 75 cm) on growth and biomass yield of Mechello grass (Sorghum aethiopicum). The experiment was arranged in a split-plot design with three replications. Data on dry matter yield

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... Y, tonha-1), onset of flowering date (days), plant height (cm) and the number of tillers at harvest were recorded. A significant difference (p<0.001) due to nitrogen fertilizer was noted on DMY (tonha-1), onset of flowering date (days) and plant height (cm) at harvest. Similarly, spacing had a significant effect on DMY (p<0.001), plant height (p<0.002) and the number of tillers at harvest (p<0.001). Higher values on DMY and plant height at harvest were recorded at 23.0, 34.5, 46.0 and 57.5 kg N ha-1. Similarly, higher values of DMY and number of tillers at harvest were obtained from the denser (30 cm) and less dense (75 cm) spacing's, respectively. The study suggested that application of 23.0 kgNha-1 and 30 cm spacing improved biomass yield of Sorghum aethiopicum under rain fed condition and recommended to be implemented. Therefore, application of 23.0 kgNha-1 and 30cm spacing to boost biomass yield of Sorghum aethiopicum should be demonstrated and popularized in the study area and other similar agro-ecologies of the country.