RESPONSE OF BLACK CUMIN (NIGELLA SATIVA L.) TO APPLICATION OF MINERAL AND ORGANIC FERTILIZERS AND ROW SPACING IN AMBO AND DANDI DISTRICTS, CENTRAL HIGHLANDS OF ETHIOPIA

Black cumin (Nigella sativa L.) is one of the most important spice and medicinal herb which is produced mainly by smallholder farmers in Ethiopia. However, the seed yield of the crop is low due to a number of constraints out of which low soil fertility, random plant spacing, and sowing of the seeds by broadcasting are the major ones. Therefore, field experiments were conducted in Ambo and Dandi districts in West Shewa Zone of Central highlands of Ethiopia to investigate the effect of applying mineral and organic fertilizers and inter-row spacing on yield components, seed yield, and seed oil contents of the crop. One experiment was conducted in 2016/17 and the two exponents were conducted in 2017/18 main cropping seasons. The first experiment consisted of three rates of nitrogen fertilizer (0, 46, and 69 kg ha–1 N), three rates of phosphorus fertilizer (0, 46, and 69 kg P2O5 ha–1 ), and three inter-row spacing (20 cm, 25 cm, and 30 cm). The experiments were laid out as a randomized complete block design in a factorial arrangement and replicated three times per treatment. The results revealed that yield related parameters and seed yield were significantly (P < 0.05) affected by the interaction effects of N and P fertilizer. The highest number of branches per plant, number of capsules per plant, aboveground biomass yield, and seed yield were recorded in response to the application of 46 kg N and 69 kg P2O5 ha-1 . Row spacing also significantly affected yield components and the highest aboveground biomass yield, and seed yield were recorded on row spacing of 20 cm. The highest seed yield of 1.75 t ha–1 was obtained in response to the application of 46 kg N ha–1 and 69 kg P2O5 ha–1 . This yield exceeded the minimum seed yield obtained from the control treatment by about 68%. However, the partial budget analysis revealed that application of 69 kg N and 69 kg P2O5 ha-1 resulted in the highest net benefit (77,425 ETB ha–1 ) with a MRR 1572.08% was found superior of the other treatments. The second experiment was undertaken to determine the effect of NP and blended NPSB mineral fertilizer on seed yield and yield components of black cumin. The treatments comprised three rates of combined nitrogen and phosphorus fertilizers (20 kg N ha–1 and 15 kgP2O5 ha–1 , 40 kg N ha–1 and 30 kg P2O5 ha–1 , and 60 kg N ha–1 and 45 kgP2O5 ha–1 ) in the form of Urea and triple xix super phosphate, and four rates of blended NPSB fertilizer (0, 50, 100 and 150 kg ha–1 in the form of NPSB. The experiments were laid out as a randomized complete block design in a factorial arrangement and replicated three times per treatment. The experiment was undertaken during the 2017/18 main cropping season. The results of study indicated that NP and blended NPSB interacted to influence yield and yield related parameters of black cumin significantly (P