Evaluation of Soil Quality under Cocoa Trees in the Marahoué Region (Central-Western Côte d’Ivoire)

Abstract

This study, which assesses the quality of soils under cocoa trees in the Marahoué region of Côte d’Ivoire, is being carried out against a backdrop of declining crop yields due to a number of factors, including the loss of soil fertility. The aim was to identify homogeneous groups of soils in terms of fertility and propose sustainable management methods for each group. The study was carried out on twenty-four cocoa orchards belonging to the SCOOP KAPATCHIVA cooperative, spread over eight sectors. A morphological characterisation of the soils was carried out in the field, followed by physico-chemical laboratory analyses of soil samples taken in the field. Soil fertility was analyzed on the basis of these two groups of data. The results showed that soil depths were generally high, except in some high altitude areas, where soils were often enriched in ferromagnesian elements and compacted. The texture of the soils varied between loamy and sandy-loamy, influencing cocoa production. Indeed, the soils of the plots with high production were looser and without ferromagnesian concretions, while those of the plots with low production were more gravelly and compact. Biological activity in the upper soil layer (0 - 30 cm) was notable with an abundance of termites and earthworms. The organic matter and nitrogen content varies considerably between sectors, directly impacting soil fertility. The soils were slightly acidic and showed significant differences in the levels of exchangeable magnesium and potassium, and not at all for phosphorus which appeared at very low doses. Chemical analysis also revealed that nutrient balance was a key factor in orchard productivity, with varying ratios of calcium, magnesium and potassium. Knowledge of these results made it possible to make recommendations for soil management with a view to improving cocoa yields in the study area.