Response of Potato (<i>Solanum tuberosum</i> L.) to NPSB Fertilizer Rate and Inter Row Spacing at Buno Bedele Zone

Potato is one of the most important tuber crops grown in Ethiopia as it plays a crucial role in Ethiopian agriculture, contributing to food security and livelihoods of majority of farmers. However, Ethiopia's Potato production and productivity lag behind other countries due to various constraints faced by the farmers of the country, notably among them improper application rate of NPSB fertilizer and inter row spacing for potato production. Thus, study was conducted to determine the effect of NPSB fertilizer rates and inter row spacing on tuber yield and yield components of potato during 2022-2023 cropping season. The experiment consisted of four levels of NPSB (50,100,150 and 200 kg ha<sup>-1</sup>) fertilizer and three (65, 75 and 85cm) inter row spacing with control treatment. The experiment was laid out in 4x3 factorial plus control arrangements in randomized complete block design with three replications. The analysis of variance showed that the main effect of NPSB application rates and inter row spacing were significantly affected all studied parameters. However, interaction effect showed non-significant. Hence, application of 200 kg ha <sup>-1 </sup>NPSB resulted maximum marketable tuber yield (51.36t ha<sup>-1</sup> while lower yield was obtained from control treatment. Furthermore, the highest marketable tuber yield (45.16 t ha <sup>-1 </sup>were obtained from the inter-row spacing of 85cm whereas the lowest result for these parameters were recorded at 65 cm. Conversely, the highest value of agronomic efficiency 152.4 kg kg<sup>-1 </sup>was obtained at lowest NPSB rate 50 kg ha <sup>-1</sup> while lowest agronomic efficiency 142.65kg kg<sup>-1</sup>was obtained from highest NPSB 200 kg ha <sup>-1</sup>. The result of correlation analysis showed that there is positive and significant correlation among tuber yield and yield components, such Marketable tuber yield was strolgly correlated with tuber number (r=0.49**), total tuber yield (r=0.99***), Average tuber weight (r=0.92***), large tuber size (r=0.92***), Medium tuber size (r= 0.46**) and small tuber size (r=0.46**). <i>Besides, </i>the partial budget analysis revealed that the highest net benefit obtained (1231355 birr ha<sup>-1</sup>) with acceptable marginal rate of return (3823.92%) and (2120240 birr ha<sup>-1</sup>) with acceptable marginal rate of return (11444.83%) from NPSB kg ha<sup>-1</sup> and 85cm inter row spacing respectively. Therefore, the production of potato with 150 kg ha <sup>-1</sup>NPSB fertilizer rate and 85cm inter row spacing is most productive and economically profitable and can be recommended for the study area for further scaling up.