Impact of Agroforestry Systems on Mineral Fertility of Soils under Cocoa Trees in Toumodi, Côte D'ivoire

Aims: To evaluate the impact of different agroforestry systems on the mineral fertility of soils under cocoa trees.

Place and duration of study: The experiment was conducted in the field from June to August 2020 in three types of cocoa-based agroforestry systems identified in Toumodi (Côte d'Ivoire) between the northern latitudes 6°19'37 and 6°34'51 and the western longitudes 5°19'58 and 5°20'02. in the forest-savanna transition zone

Methodology: Agroforestry systems define a method of setting up plantations associating various trees with cocoa trees. The choice of cocoa plantations was guided by the density of trees associated with cocoa trees defining a typology of agroforests (simple, mixed or complex). Thus, in each agroforestry system considered, three delimited plots of 100 m2 were randomly placed to make a floristic inventory of the species encountered and each time to take elementary soil samples in the first horizons at 0-20 cm and 20 - 40 cm depth to constitute the composite samples for chemical analyses in the laboratory.

Results: The study identified and recorded floristically, 17 families (Anacardiaceae, Apocynaceae, Arecaceae, Bombacaceae, Caricaceae, Combretaceae, Euphorbiaceae, Invingiaceae, Lauraceae, Meliaceae, Mimosaceae, Moraceae, Musaceae, Myristicaceae, Rutaceae, Sterculiaceae, Verbenaceae) distributed in 27 local plant species of which 55.55% of the species and a density of 55 trees/hectare in SAGS, 70.37% of the species and a density of 155.33 trees/hectare in MAGS and 81.40% of the species 224.33 trees/hectare in CAGS. These arboricultural species introduced or maintained in the plantations are generally species with shade, food, economic or medicinal interests. In terms of the chemical fertility generated, it appears that the contents of major elements and trace elements, as well as the clay-humus complex of the soils under cocoa trees were globally satisfactory and more important in the superficial horizons at a depth of 0-20 cm than in the underlying horizon of 20-40 cm, whatever the type of agroforestry system considered, but much more so in MAGS than in CAGS and SAGS in decreasing order. The different positive (R=0.80) or negative (R=-0.80) correlations established between the mineral elements in the surface horizons contribute to enrich the soil by synergistic or antagonistic effects in the agroforestry systems of Toumodi, Côte d'Ivoire.

Conclusion: The study showed that each forest agroforestry system has distinct characteristics that can be summarized mainly by its floristic diversity and density of associated trees. They are all not only preservers of a certain level of biodiversity and chemical fertility of the soils under cocoa trees, but much more so at 0-20cm than at 20-40cm. However, AGM would be more likely to improve production in a sustainable way by its capacity to establish a nutritional balance in the soil. It can be recommended during the establishment of cocoa plantations in Côte d'Ivoire.