RESPONSE OF POTATO (Solanum tuberosum L.) TO NPS FERTILIZER AND FARMYARD MANURE UNDER SUPPLEMENTAL IRRIGATION AT DAMOTA, HARAMAYA DISTRICT, EASTERN ETHIOPIA

Potato (Solanum tuberosum L.) is one the most important food and cash generating crops in the eastern parts of Ethiopia, particularly East Harerghe zone, where it is grown three times per year. However, the average yield of potato is low, due to low soil fertility and poor ferti lizer management practice. Therefore, a field experiment was conducted in 2021 at Damota, Haramaya district, with the objectives of assessing the influences of integrated use of Farm yard manure and NPS blended fertilizers on growth, yield and yield components and to estimate cost-benefit of NPS and Farmyard manure for potato production. Factorial combina tions of four levels of NPS rate (0, 50, 100 and 150kgha-1 ) and four levels of Farmyard manure (0, 10, 20 and 30 t ha-1 ) were laid out in a Randomized Complete Block Design with three replications using improved potato variety Bubu as a test crop. Results of the research revealed that both the main and interaction effects of mineral NPS fertilizer and Farmyard manure significantly influenced all phenology, growth, yield and yield related parameters of the crop except unmarketable number of tubers and unmarketable tuber yield. The plants that supplied 30 t ha-1 FYM and 150 kg ha-1 NPS fertilizer had significantly delayed days flower ing, significantly highest number of main stems, leaf area, proportion of large and medium sized tubers, specific gravity, dry matter and starch contents of tubers. The interaction of 150 kg ha-1 NPS with 20 and 30 t ha-1 FYM significantly delayed maturity of potato and the inter action of 150 kg ha-1 NPS fertilizer with 10, 20 and 30 t ha-1 FYM significantly increased the height of plants. The interaction of 100 kg ha-1 NPS fertilizer with 30 t ha-1 FYM significantly increased marketable and total tuber number per hill while the interaction of 150 kg ha-1 NPS with 30 t ha-1 FYM significantly increased tuber mass per hill. The variety produced highest total and marketable tuber yield of 41.63 and 40.36 t ha-1 , respectively, due to the interaction effect of 150 kg ha-1 NPS fertilizer with 30 t ha-1 FYM. The highest net benefit of 378302 Birr ha-1 with acceptable marginal rate of return of 1276.5% was obtained from the application of 150 kg ha-1 NPS +30 t ha-1 FYM. Therefore, the combined application of 150 kg ha-1 blended NPS fertilizer and 30 t ha−1 Farmyard manure could be provisionally recommended forʻʻBubu ̓ ̓ variety production in the study area