EFFECT OF SEED RATE AND MINERAL NP FERTILIZERS ON YIELD COMPONENTS, YIELD, AND SEED OIL CONTENT OF BLACK CUMIN (Nigella sativa L.) IN GORO DISTRICT, SOUTH EASTERN ETHIOPIA

Abstract

Black cumin is a seed spice cultivated in Ethiopia for a long period of time. It is also cultivated in Goro district of Bale Zone by small land holder farmers. However, expected benefit of this crop is not being obtained by farmers since they are using in-appropriate agronomic practices such as inappropriate seed rate without any fertilizer application. Therefore, a field experiment was conducted in Goro district, south Eastern Ethiopia. The objective of the experiment was to determine the effect of different seed rate and mineral nitrogen and phosphorus fertilizer on yield, yield component, and essential oil contents of black cumin. The treatments consisted of three seed rates (15, 20, 25 kg ha-1), three of nitrogen fertilizer levels (0, 46, 92 kg N ha-1), and three phosphorus fertilizer levels (0, 46, 92 kg P2O5 ha-1). The experiment was laid out in Randomized Complete Block Design and replicated three times per treatment. Analysis of variance showed that, the main effect of seed rate significantly (P <0.05) influenced Days to flowering (DF), number of capsule per plant (NCPP) and number of seed per capsule (NSPC). Accordingly, highest DF (86.7 days), highest NCPP (12.59) and highest NSPC (76.1) were obtained with 15 kg ha-1 seeding rate. Similarly, the main effect of nitrogen fertilizer rate significantly influenced DF, days to maturity (DM), NCPP, number of primary branches (NPBPP), NSPC and thousand seed weight (THSW). Highest DM (127.3 days), highest NPBPP (4.95), highest NCPP (14.14), highest NSPC (76.51), highest THSW (2.34 g) was obtained with 92 kg ha-1 nitrogen fertilizer rate. The interaction effects of seeding rate, nitrogen fertilizer, and phosphorus fertilizer significantly influenced plant height (PH) where, the maximum PH (53.13 cm) was recorded at the seeding rate of 20 kg ha-1 combined with the application of 46 kg N ha-1 and 46 kg P2O5 ha-1. The interaction effects of seeding rate and phosphorus fertilizer significantly (P < 0.01) influenced aboveground biomass (BM) and the seed yield (SY). As a result the highest BM (3.98 ton ha-1) and highest SY (1152 kg ha-1) was obtained with 20 kg ha-1 seeding rate combined with 46 kg ha-1 P2O5 fertilizer rate. Essential seed oil content of the crop was affected neither by the main nor the interaction effects of all factors. Partial budget analysis showed that, the treatment with 20 kg ha-1 seeding rate xiii combined with 46 kg P2O5 ha-1 resulted in the highest marginal rate of return (1263%) and maximum net benefit (75060 ETB ha-1). Thus, it could be concluded that establishing black cumin plants with the seeding rate of 20 kg seed ha-1 and application of 46 kg P2O5 ha-1 resulted in the best growth and seed yield of the crop with optimum economic benefits.