Effect of foliar application of red large onion (Allium cepa L.) peel solution on growth and yield of cowpea (Vigna unguiculata L. WALP)

Cowpea (Vigna unguiculata L. Walp.) is a significant food and grain legume in the semi-arid tropics. Red onion peels are used to make organic potassium-rich fertilizer for growing plants. The effect of foliar application of red onion peel solutions on growth and yield of cowpea cv dhawala were studied in a pot experiment at the home garden, Mailapitiya, Kandy, Sri Lanka, from May to September 2021. This study was designed in a randomized complete block design with six treatments. They were as follows: T1 – control (distilled water), T2 – 20% onion peel solution, T3 – 40% onion peel solution, T4 – 60% onion peel solution, T5 – 80% onion peel solution, T6 – 100% onion peel solution applied at two weeks interval. Foliar application of onion peel solutions led to significant (P<0.05) effects on tested parameters over the control. The application of 40% concentration onion peel solution increased the plant height, number of leaves, number of branches, number of trifoliate leaves and number of internodes per plant at 9th WAP and also root length, number of nodules and weights of stem, leaves and root after harvesting pods. Among the treatments, the application of 100% concentration onion peel solution gave the highest values in many measured yield parameters. There were no significant differences in these parameters between plants applied with 80% and 100% onion peel solutions (T5 and T6). Therefore, it could conclude that 80% - 100% concentrations of onion peel solution could be used to enhance the seed yield of Vigna ungiculata L.