EFFECTS OF BLENDED NPSB FERTILIZER RATES AND INTRA-ROW SPACING ON YIELD AND YIELD RELATED TRAITS OF POTATO (Solanum tuberosum L.) UNDER IRRIGATION IN DEBRE LIBANOS DISTRICT, CENTRAL HIGHLANDS

Potato is one of food and cash crop in Debre Libaanos District of central highlands of Ethiopia. However, the yield of the crop is low due to various constraints of which poor soil fertility and lack of proper plant spacing recommendation specific to the District. Therefore, a field experiment was conducted to asses’ effects of blended NPSB fertilizer rates and intra-row spacing on yield and yield related traits of potato and to estimate cost-benefit of NPSB fertilizer for potato production in Debre Libaanos District during 2019 off-season under irrigation. The treatments consists of five rates of blended NPSB fertilizer (0, 150, 200, 250 and 300 kg ha-1) and three intra-row spacing (20, 30 and 40 cm). The experiment was laid out as a Randomized Complete Block Design in a 5 x 3 factorial arrangement and replicated three times. The results of analysis of variance revealed that the main factors, intra-row spacing and Blended NPSB fertilizer had significant effect on phenology, growth, yield components, yield and tuber quality related traits except number of main stem hill-1 and Blended NPSB fertilizer had non-significant effect on tuber dry matter content (%) and specific gravity of tubers as well as proportion of medium size tubers did not significantly influenced by intra-row spacing. Interaction of NPSB fertilizer and intra-row spacing significantly influenced average tuber mass, average tuber weight, marketable tuber yield (t ha-1), unmarketable tuber yield (t ha-1), and total tuber yield (t ha-1). The plants at intra-row spacing of 40 cm had significantly delayed days to 50% flowering and days to 90% maturity at about 60 and 113 days after planting, respectively, while the application of highest rates of NPSB fertilizer (300 kg ha-1) significantly delayed 50% of plants flowering and 90% maturity at about 61 and 114 days after planting, respectively. The tallest plants were observed at wider intra-row spacing (30 and 40 cm) and higher rates of NPSB fertilizer (250 and 300 kg ha-1). The highest tubers dry matter and specific gravity of 27.04% and 1.095, respectively, were estimated from plants at 40 cm intra-row spacing. The higher marketable tuber yield of 42.19 and 41.47 t ha-1 obtained from plants at 30 and 20 cm intra-row spacing, respectively, with the application of 250 kg ha-1 NPSB fertilizer and significantly higher total tuber yield of 44.6 and 43.32t ha-1 obtained at 20 and 30 cm intra-row spacing, respectively, with the application of 250 kg ha-1 NPSB fertilizer. The higher agronomic efficiency at ratio of 93.07:1 and 82.22:1 total tuber yield to applied NPSB fertilizer were estimated from plants at 30 and 20 cm intra-row spacing, respectively, with application of 250 kg ha-1 NPSB fertilizer. Moreover, the maximum net benefit of (249291.50Birr ha-1) with highest marginal rate of return (7861.33%) was obtained from the application of 250 kg ha-1 blended NPSB fertilizer rates and 30 cm intra-row spacing. Therefore, it can be concluded that 250 kg ha-1 blended NPSB fertilizer rates and 30 cm intra-row spacing could be provisionally recommended for potato growers in study area.