Soil-Plant Nutrient Cycling in Old Cocoa Farms in a Part of South Western Nigerian Forest Belt

Abstract

Apart from pests and diseases, a vital issue in the early mature of cocoa crop in Nigeria is soil nutrient degradation in relation to the ageing of the farms and annual mining of nutrients via yield harvests. Indigenous production of cocoa in southwest Nigeria has been on without fertilizer applications. This is the basis for the reduction average lifespan and productive years of the plantation. The aim of this study was to quantify the rates of soil nutrient losses via cycling channels in old cocoa farm using cocoa beans, leaves, litters, and pod husks in south western Nigeria forest belt. Old cocoa farms with an average age of 55 years were selected from Idanre, where nutrients in soil cultivated to cocoa and plant variables were experimentally evaluated. Identified variables were randomly sampled and the composite samples were subjected to laboratory analysis. Results through routine laboratory techniques were subjected to descriptive analysis. Using average and percentage, the results show that inputs from litter falls account for about 29%, pod husks (24%), leaves (28%), beans (13%) and soil (6%) approximately. Soil nutrient balance equation indicates that an average of 1.32% nutrient amounts to loss via annual cycle and the order of nutrient concentrations in old cocoa ecosystem is therefore considered as litter > leaves > podhusks > beans > soil. Results also showed that nutrient cycling in old cocoa farm was high while the loss was low. The study hereby recommends land evaluation, annual relocation and seasonal spreading of pod husks across the farm for redistribution of nutrients to compliment nutrients return through litter fall instead of its usual concentrations where not useful for plant development.

Keywords: Biomass; cocoa; nutrient; degradation; litter;  soil