Application of Dry Cocoa Bean Shell Ash and NPK 15:15:15 for Improvement of Soil Fertility and Maize Yield on a Degraded Humid Tropical Alfisol, Southwestern Nigeria

The application of dry cocoa bean shell ash (DCBSA) and NPK 15:15:15 for the improvement of soil fertility and yield of maize (Zea mays L.) was studied on an Alfisol South Western Nigeria, located at Joseph Ayo Babalola University Ikeji-Arakeji, Ilesa Osun State, Nigeria Teaching and Research Farm from April to July 2017 and from August to November 2016. Four treatments of dry cocoa bean shell ash (DCBSA) at 5 tonsha-1, NPK 15:15:15 at 300 kgha-1, dry cocoa bean shell ash (DCBSA) at 2.5 tonsha-1, mixed NPK 15:15:15 at 150 kgha-1 and control (C) were used in a Randomized Complete Block Design (RCBD) with three replications. The data collected were subjected to analysis of variance (ANOVA) and the means were compared by the use of Duncan multiple range test (DMRT) at 5% significance level. The study showed that dry cocoa bean shell ash (DCBSA) used alone can serve as a suitable alternative to inorganic fertilizer in the south western Nigeria, Especially, DCBSA has higher organic carbon than NPK dry cocoa bean shell ash (DCBSA) at 5 t ha-1, NPK 15:15:15 at 300 kg ha-1, dry cocoa bean shell ash (DCBSA) at 2.5 t ha-1, mixed NPK 15:15:15 at 150 kg ha-1 produced higher values for plant height, leaf area, chlorophyll, plant diameter, cob length, cob diameter and grain yield against the control that recorded the lowest value. Also. DCBSA improves soil pH as well as increases minerals such as Ca, Mg, Na and in particular, made available phosphorous due to its increment on soil pH. pH increased fro 5.3 to 7.8 DCBSA, N levels in the soil increased from 0.06g kg-1 to 2.61g kg-1 (DCBSA) and 2.10 g kg-1 (DCBTA + NPK). Organic carbon (OC) increased from 0.07 g kg-1 to 2.87g kg-1 DCBSA plot. P level decreased from 3.7 mg dm-3 to 1.09 mg dm-3 (DCBSA) and 1.81 mg dm-3 (NPK) and 1.42 mg dm-3 (DCBSA + NPK) which was an indication of P availability to crop during growing season. Maize grain yield increased from 0.77 tonsha-1 in the control plot to 1.25 t ha-1 in DCBSA plot, 1.22 t ha-1 a in NPK plot and 1.26 t ha-1. in DCBSA + NPK plot. The study recommends an application rate of 5 t ha-1 of dry cocoa shell ash (DCBSA) alone or 2.5 t ha-1 combination each of (DCBSA + NPK) for maize yield and fertility improvement on this type of soil in this agro - ecology.