Potato (Solanum tuberosum L.) is one of the most important tuber crops produced in Ethiopia. However, production and productivity of the crop is far below the world average due to poor crop, soil fertility and water management practices. An experiment was therefore conducted to study the effect of different Nitrogen (N) and Phosphorus (P) levels on growth, yield and quality of potato. Treatments consisted of four levels of N (0, 55, 110 and 165 kg N ha-1) and four levels of P (0, 45, 90 and 135 kg P ha-1) laid out in Randomized Complete Block Design (RCBD) in a 4x4 factorial arrangement with three replications. Data were collected on growth and yield parameters and analyzed using SAS 9.2 software. Results revealed that application of N and P fertilizer significantly (P<0.05) influenced plant height, days to 50% flowering, main stem number, days to physiological maturity, total tuber number, marketable tuber number, total underground stem yield, marketable tuber yield, average tuber weight and tuber dry matter percentage. Combined application of 0N and 90P and 55N and 90P shorten the days to 50% flowering. Combined application of 165 kg N/0 kg P ha-1and control treatment delayed the days to flowering. Increasing P application from 0 to 135 kg ha-1(the highest level P) significantly increased main stem number per hill (from 3.63 to 5.19). Increasing rate of P from 0 to 135 kg ha-1 increased the main stem number by 42.97%. The highest plant height (71.6cm) was measured at the combination of 165 kg N ha-1 and 135 kg P ha-1, while the lowest plant height (44 cm) was recorded from the control. Increasing p application from 0 to 135 kg ha-1 shortens number of days to physiological maturity by 9 to10 days as compared to the control. The maximum total tuber number was recorded for the highest level of nitrogen and phosphorus (13.7/hill), and the minimum total tuber number (8.53/hill) was obtained from the control. The highest marketable tuber number (9.79) per hill was obtained for the combined application of 165 kg N1and 135 kg P ha-1while the lowest (5.03) was recorded for the control. Increasing level of nitrogen from 0 to 165 kg ha-1 increased average tuber weight by 50.56%. The highest total tuber yield was recorded for combined application of 165 kg N and 135kg P ha-1 (42.27 t ha-1) and the lowest (12.91 t ha-1) was obtained at the control plot. Combined application of 165 kg and 135 kg P ha-1 gave the highest marketable tuber yield (36.13 t ha-1) and the lowest value (19.18 t ha-1) was recorded for the control. The highest average tuber weight (78.97g) was observed for 165 kg N ha-1 while the lowest (52.45g) was obtained from the control. The highest dry matter (27.27%) percentage of potato tuber was recorded from plots that received the combination of N 110 kg ha-1 and P 90 kg ha-1, while the lowest (22.17%) tuber dry matter percentage was obtained at the combination of highest (165 kg ha-1) level of nitrogen and zero level of Phosphorus. In conclusion the results of this study showed that different nitrogen and phosphorus rates and their interactions have sound and promising impact on growth and yield of potato. Therefore, on the basis of the results of the present study, farmers can be more benefited from using 110 kg ha-1of nitrogen in combination with 135 kg phosphorus.
Keywords: Nitrogen, Phosphorus, Potato, Yield Parameters, Quality Parameters