Response of Medium and Late Maturing Sweetpotato (Ipomoea batatas L.) Varieties to Application of N and P Fertilizers in Halaba Area of Southern Ethiopia

Abstract

A two-year field study was conducted during the growing seasons of 2013 and 2014 in Halaba, southern Ethiopia to evaluate the response of two improved sweetpotato varieties (Kulfo and Awassa-83) to four  rates of N and three rates of P₂O₅. Factorial combinations of the treatments were arranged into a randomized complete block design with three replications. Results showed that averaged over P₂O₅ and Nitrogen rates, Awassa-83 (late maturing and white fleshed) had longer vines (longer by 47 cm) than Kulfo variety (medium maturing and orange fleshed). However, Kulfo variety had significantly higher (p<0.05) branches than Awassa-83. Increment in phosphorus levels from 0 to 92 P₂O₅ did not result in significant (P<0.05) variation in root length, root width, number of roots/plant, number of branches/plant and root yield/unit area. In fact, most sweetpotatoes growth and yield components responded significantly (P<0.05) to application of nitrogen, and the two varieties responded differently to its application. Significantly higher (P<0.01) root yield of Awassa-83 variety was obtained due to application of 46 kg/ha P₂O₅ and 92 kg/ha N. Similarly, significantly higher (P<0.01) root yield of Kulfo variety was obtained with the application of 92 kg/ha P₂O₅ and 92 kg/ha N. However, root yield of Kulfo variety due to 46 kg/ha P₂O₅ and 92 kg/ha N, and 46 kg/ha P₂O₅ and 46 kg/ha N were not significantly different (p<0.05). Moreover, economic analysis depicted that fertilizer rates that produced agronomic optimum have also resulted in highest marginal rate of return. Hence application of 46 kg/ha P₂O₅ and 46 kg/ha N would be agronomic and economic optimum for Kulfo variety production in Halaba areas, and other warm sub moist lowlands of the country with similar soil types and soil fertility status. It can be concluded that the response of white and orange fleshed medium and late maturing varieties were different to application of chemical fertilizers within a given locality.

Keywords: Maturity groups, Nitrogen, Phosphorus, Vine length, Root yield