Yield and yield components of potato (Solanum tuberosum L.) as influenced by planting density and rate of nitrogen application at Holeta, West Oromia region of Ethiopia

Four different nitrogen levels and four plant spacing were studied in 4×4 factorial arrangements in randomized complete block design with three replications. The highest yield, number of tuber, number of tuber and dry weight of tuber were obtained with application of jointly 100 and150 kg/ha nitrogen. Increasing plant density resulted in higher tuber yield, dry weight of tuber and total dry matter yield. Increasing nitrogen fertilizer rate 100 up to 150 kg/ha increased mean tuber weight and total dry matter yield. Since, 100 and 150 kg/ha nitrogen had no significant difference to each other producing the highest tuber yield and number of tuber, so in order to prevent environmental pollutions and excessive costs, utilization of 100 kg/ha nitrogen is recommended and any reduction in the planting density lower than 75×30 cm will lower both total yield and % marketable yield. So, 30 cm planting densities' producing the highest yield makes it suitable for planting. The combined effect of different level of nitrogen and plant spacing revealed that the highest nitrogen dose 150 kg/ha applied at the closest 75 cm × 10 cm gave the highest yield of tuber (10377.78 kg/ha). The narrower spacing of 10 cm produced numerous small-sized potatoes. These small-sized potatoes fell in grades that are not commercially accepted. The treatment combination, 150 kgN/ha applied at 75 cm × 20 cm spacing gave the second highest yield of tuber (9214.81 kg/ha). As the spacing increased to 30 cm, and with increasing nitrogen the tuber size increased with more potatoes falling in the acceptable grades. Yield of tuber per hectare was significantly and positively correlated with plant height, number of stem per plant, fresh weight, number of tuber and weight of tuber per plant. The highest marketable tuber yield of 4144.44 per plot was produced at 30 cm spacing, and the lowest marketable tuber yield was obtained at 75 cm × 10 cm (1111.11). Key words: Yield, plant spacing, fertilizer rates.