Effects of potassium fertilizer rates on growth, tuber yield and quality of sweet potato (Ipomea batatas L) in Ogbomoso, Southwest Nigeria

Abstract

Sweet potato (Ipomoea batatas L) is an important dicotyledonous tuberous staple crop of the Convolvulaceae family. It is valued for its tubers which are either boiled, fried, baked or roasted for human consumption or boiled and fed to livestock as a source of energy. However, the cultivation of sweet potato is constrained by low soil fertility, particularly inadequate potassium, which plays a pivotal role in the growth and tuber development of sweet potato. Therefore, the effects of potassium fertilizer rates on the growth, tuber yield and quality of sweet potato were determined at the Teaching and Research Farm, Ladoke Akintola University of Technology, Ogbomoso during 2022 major cropping season. The treatments were; 0 (control), 60, 90, 120, 150 and 180 kg K2O/ha laid out in randomized complete block design replicated three times. Data collected on length of primary vines, number of leaves, fresh shoot biomass, number of tubers, fresh tuber yield and nutritional contents of the tubers were subjected to analysis of variance and treatment means separated with least significance difference (LSD) at 5% probability level. The application of K fertilizer had significant influence on the performance of sweet potato. At 14 weeks after planting (WAP), plants treated with 180 kg K2O/ha produced the longest mean vine length (p = 0.043, 184.93 cm), highest number of leaves (p = 0.003, 217), highest fresh shoot biomass (p = 0.015, 11.83 t/ha), number of tubers (p = 0.037, 68) and fresh tuber yield (p = 0.0004, 22 t/ha). In contrast, plants that received no fertilizer, had the shortest vine length (133.67 cm), the least fresh shoot biomass (7.1 t/ha) and tuber yield (12.7 t/ha). The least number of leaves (136) was observed with the application of 60 kg K2O/ha while 90 kg K2O/ha produced the least number of tubers (46). The potassium content of sweet potato tuber was significantly influenced by K fertilizer rates, whereas the phosphorus content was unaffected. The highest contents of phosphorus (p = 0.967, 0.10%) and potassium (p = 0.038, 1.26%) were recorded in tubers that received 150 kg K2O/ha and 180 kg K2O/ha, respectively. The carotenoid, carbohydrate, and protein contents of sweet potato tuber decreased as the potassium rates increased. Conversely, the crude fiber content increased (p = 0.044) as the potassium rate increased. In conclusion, application of 180 kg K2O/ha improved the performance of sweet potato better than the other rates in the study area. However, it seems that the maximum yield potential of sweet potato in the study area had not been attained. Therefore, further research with higher than 180 kg K2O/ha may be required to identify the optimal level for cultivating sweet potatoes.