Effect of Urea Fertilizer and Maize Cob Ash on Soil Chemical Properties, Growth, Yield, and Mineral Composition of Okra, Abelmoschus esculentus (L.) MOENCH

Field experiments were carried out at the Teaching and Research Farm, Landmark University, Omu-Aran, Kwara State, Nigeria, in the cropping seasons of 2015 and 2016. The soil at the site of the experiment is an Alfisol classified as an Oxichaplustalf or a Luvisol. The trial consisted of sole and combined applications of urea fertilizer (U) applied at 0, 60, and 120 kg·ha⁻¹ and maize cob ash (M) applied at 0, 3, and 6 t·ha⁻¹. The results showed that U and M alone or in combinations increased the soil chemical properties, growth, yield, and mineral composition of okra compared with the control. M alone at 3 t·ha⁻¹ produced optimum soil chemical properties, yield, and mineral composition of okra fruit. U alone at 60 kg·ha⁻¹ produced optimum yield of okra, while growth and mineral composition were increased when urea fertilizer was applied at 120 kg·ha⁻¹. The treatment with U applied at 60 kg·ha⁻¹ in combination with M applied at 3 t·ha⁻¹ (U₆₀M₃) produced the highest values of okra yield, while U applied at 120 kg·ha⁻¹ in combination with M applied at 3 t·ha⁻¹ (U₁₂₀M₃) has the highest growth and highest N, K, Ca, Cu, and Fe contents of okra fruit. Compared with the control and using the mean of the two years, U₆₀M₃ increased okra fruit yield by 93.3%. Therefore, for viable production of okra in low nutrient soil of the Nigeria derived savanna or similar soils elsewhere, 60 kg·ha⁻¹ U + 3 t·ha⁻¹ M (U₆₀M₃) is recommended. However, for improved mineral quality of okra, 120 kg·ha⁻¹ U + 3 t·ha⁻¹ M (U₁₂₀M₃) is recommended.