Productivity of Irish potato varieties under increasing nitrogen fertilizer application rates in Eastern Rwanda

Irish potatoes are an important crop only promoted in cool and high moist conditions of Rwanda. This study explored the productivity of Irish potatoes varieties under increasing nitrogen fertilizer applications in drier agro-climatic conditions of the eastern Rwanda. Potato seeds mass-selected from locally-grown varieties in the region surrounding Kibungo town (-2.160897°, 30.543591°) were planted under rain-fed conditions, during the March to June agricultural season of 2015, in the three experimental farms of the University of Kibungo at Karenge, Mugesera and Rwamagana, respectively located in Kibungo town, 30 km West and 50 km North of Kibungo town. The most performing three varieties were tested again in 2016A season (October to January, 2016) at Kibungo and Rwamagana. For each season, and at each farm, four nitrogen application rates (0, 60, 120, and 180 kg N ha-1) were tested. Phosphate and potash were supplied in sufficient amounts of 150 kg P2O5 ha-1 and 60 kg K20 ha-1, respectively. No fertilizers were applied on the control treatment. A split plot design and three replicates were used with varieties in main plots and nitrogen in sub-plots. Plant growth rate, shoot counts, tuber calibration, and total and market potato tuber yields were monitored. Four varieties yielded 10 tons ha-1 or more of total potato tuber yields in 2015B season. Three of them, namely Kirundo, Gasore, and Peko varieties, were re-tested in 2016. Over the two seasons, Kirundo variety stood out with 12.8 and 10.5 tons ha-1 of total and marketable tuber yields, respectively. All the varieties significantly responded to nitrogen fertilizer. However, Kirundo variety, respectively yielded 22 tons and 17 tons ha-1 of total and market potato tuber yields under 120 kg N ha-1 during the 2016A season. Irish potato can therefore be grown and produce substantial yield in eastern Rwanda, provided that appropriate nitrogen fertilization and seed quality are available. Key words: Irish potatoes, varieties, nitrogen, yields, fertilizer, rates.