Productivity of Solanum potato varieties and their yield responses to nitrogen fertilizer application rates in Eastern Rwanda

Potatoes (Solanum tuberosum L.) is an important crop widely grown in cool and high moist conditions of Rwanda. This study explored the productivity of different potatoes varieties under increasing nitrogen fertilizer application rates in drier agro-climatic conditions of the eastern province of the country. Three potato varieties were mass-selected from locally-grown potato varieties from the areas surrounding three experimental farms of the University of Kibungo (-2.160897o, 30.543591o), namely the Karenge farm in Kibungo town (main Campus) and the Mugesera and Rwamagana farms located 30 km West and 50km North of Kibungo, respectively. The three varieties locally collected were tested in the local experimental farm of the University during the 2015 B agricultural season (March – June 2015). The most performing three varieties from the three farms were tested again in 2016 A season (October – January 2016) at Kibungo and Rwamagana. For each season, and at each farm, four nitrogen application rates were tested: 0, 60, 120, and 180kg N ha-1. Phosphorus and potassium were applied in amounts supplying all treatments, but the control, with 150 kg P2O5 ha-1 and 60 kg K20 ha-1, respectively. The experiment was undertaken in a split plot design with three replicates. Varieties were tested in the main plots while nitrogen factor was in the sub-plots. Total and market potato tuber yields were evaluated at harvesting time. The Four varieties yielded 10 tons ha-1 or more of total potato tuber yields in 2015 B season. Three of them, namely Kirundo, Gasore, and Peko varieties, were retested in 2016 A season. The Kruza variety which yielded 10.6 tons ha-1 of market potato tubers. Over the two agricultural seasons, the Kirundo variety perfect best with 12.5 and 10.5 tons ha-1 of total and marketable tuber yields, respectively. Peko did not maintain the yield levels in 2016 because of important losses that occurred in the fields. Nitrogen application rates in the amount of 60 and 120 kg N ha-1 equally resulted in highest yields. All the varieties significantly responded to nitrogen fertilizer application rates. However, the Kirundo variety yielded 22 tons and 17tons ha-1 respectively for total and market potato tuber yields under 120 kg N ha-1 during the 2016 A season. Potato can therefore be grown and yields well in Eastern Province of Rwanda, provided that nitrogen fertilization is provided and seed quality is maintained.