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

Abstract

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 <0.05). The application of a moderate rate of combined NP (40/30) kg N/P2O5 ha-1 and the highest rates of 150 kg ha-1 blended NPSB resulted into the highest number of branches per plant (11.72) and seed yield (1.85 t ha-1 ) of black cumin. The result of partial budget analysis showed that the highest net benefit of 78,137ETB was recorded for the combined application of 40/30 kg N/P2O5 ha-1 and 150 NPSB mineral fertilizers. The third experiment was conducted to investigate the effect of applying mineral and organic fertilizers on seed yield and seed oil content of the crop. The experiment consisted of three rates of combined NP fertilizer (20/15 kg N/P2O5, 40/30 kg N/P2O5, 60/45 kg N/P2O5 ha-1 ) and three rates of blended mineral NPSB (0, 50 and 100 kg NPSB ha–1 ) fertilizer and three rates of vermicompost (0, 3 and 6 t ha–1 ). The experiment was laid out as a randomized complete block design in a factorial arrangement and replicated three times per treatment. The results of the study showed that the combined application of 60/45 kg N/P2O5, 100 kg NPSB, and 3 t ha–1 of vermicompost led to the production of the highest seed yield (2.1 t ha–1 ) and total seed yield per hectare of 0.83 t ha–1 . The highest seed yield obtained at application of 60/45 kg N/P2O5, 100 kg NPSB, and 3 t ha–1 of vermicompost exceeded the minimum seed yield obtained in response to the application of 20/15 kg N/P2O5 ha–1 , nil NPSB, and nil VC by about 93%. But the highest percentage of seed oil content (39.70%) was recorded in response to the application of only 20/15 kg N/P2O5 ha–1 and nil rates NPSB ha–1 and nil rate of vermicompost. The result of partial budget analysis showed that the highest net benefit of from seed yield (82,677 ETB ha–1 ) was obtained at the rate of 60/45 N/P2O5 and 100 kg ha-1 blended NPSB mineral fertilizer and 3 ton ha–1 VC. In general, the seed yield of black cumin obtained in response to the integrated application of 60/45 kg N/P2O5, 100 kg NPSB, and 3 t ha–1 of vermicompost exceeded the seed yield of the crop obtained in response to the application of only 46 kg N ha–1 and 69 kg P2O5 ha–1 by about 20%, and that obtained in response to the application of only 40/30) kg N/P2O5 ha-1 and 150 kg ha–1 blended NPSB fertilizer by 14%. It is concluded that applying 60/45 kg N/P2O5, 100 kg blended NPSB and 3 t ha–1 VC resulted in the highest seed yield of the crop. On the other hand only applying 20/15 kg N/P2O5 ha–1with no application xx of vermicompost and blended NPSB fertilizer resulted in the highest seed oil content of the crop. This implies that integrated application of mineral and organic fertilizers can double the current seed yield of the crop, but a minimal application of only nitrogen and phosphorus fertilizers can also optimize the seed oil content of the crop.