Effects of different soil amendments on the growth and yield of okra in a tropical rainforest of southwestern Nigeria

This study investigated the effects of different soil enhancers on the growth response of okra [Abelmoschus esculentus (L.) Moench] cultivated on a ‘contaminated’ field with sewage sludge from the two oxidation ponds of the Obafemi Awolowo University (OAU), Ile-Ife, Nigeria. This was with a view to assessing the growth performance and yield of the test crop under different soil amendments. Okra variety, NHAe 47-4 with NPK 12-12-17 (IO), compost organic fertilizer (OR), Glomus mosseae mycorrhiza (MY) and zero fertilizer applications as control (CT) was laid out in a completely randomised block design and each treatment plot (4 x 2 m) was replicated four times. Selected weather parameters were collected from a meteorological station in OAU campus during the period of the experiments. Growth parameters such as plant height, stem girth and number of leaves of okra increased with added soil amendments from four weeks after planting in the order: IO > OR > MY > CT. In 2010, the highest mean yield of 16.3 t ha-1 obtained with 6.0 t ha-1 of MY was not significantly higher than 15.4 t ha-1 obtained with application of 0.2 t ha-1 of IO, but significantly (p < 0.05) higher than 13.1 and 10.4 t ha-1 obtained with applications of 6.0 and zero t ha-1 of OR and CT respectively. Comparative okra yield, though relatively higher with mycorrhizal inoculation, but lower with no soil amendment was obtained in 2011. The study concluded that a direct linear relationship existed between solar radiation and okra productivity. Also, for a moderately ‘treated field’ with sewage sludge from domestic wastes, arbuscular mycorrhizal fungi can be integrated into soil fertility management to achieve low-cost sustainable agricultural systems for enhanced productivity of okra.