Influence of agroforestry system based on cocoa tree on the physico chemical properties of soils of the Luki Biosphere Reserve in the Democratic Republic of Congo Influence du système agroforestier à base de cacaoyer sur les propriétés physico chimiques des sols de la réserve de biosphère de Luki en République démocratique du Congo

Abstract

Description of the subject. In the Democratic Republic of Congo, cocoa based agroforestry systems in natural forests in general and in the Luki Biosphere Reserve in particular have an impact on the characteristics of cul tivated soils.
Objective. This study examines the impact of the cocoa based agroforestry system on the physico chemical properties of the Luki Biosphere Reserve soils, Democratic Republic of Congo. It seeks to characterize this agroforestry system and asse ss its influence in the soil compared to a natural forest.
Methods. The study was conducted in the Luki Biosphere Reserve (LBR), one of the main cocoa producing areas in the DRC. The climate is tropical humid with two distrinct seasons dry and wet. The agro-forestry system studied include plots established by INERA and farmers between 1961 to 2017. Soil samples were collected and analyzed to determine several soil physico chemical properties, such as: bulk density, granulometry, pH, nitrogen, organic carbon, phosphorus and potassium.
Results. Soils in cocoa based agroforestry system have a pH wich varied between 3.2 to 4.5, while forest soils have a pH around 3.5. The INERA 2017 plot had the highest pH, at 4.5. Nitrogen content is 23.5 mg.kg ¹ in natural fore st, and very low in agroforestry system. However, potassium and phosphorus reach respectively the levels of 31 and 14 mg.kg ¹ in some agroforestry plots, by the way the value recorded for both elements in the natural forest was very low. Carbon stock is higher in the natural forest, 16 g.kg ¹, but lower in agroforestry system 9.23 to 11.54 g.kg ¹.
Conclusion. The natural forest has high nitrogen and carbon levels, while the INERA 1961 plot shows the highest phosphorus and potassium concentrations. Tree dens ity and species diversity significantly impact carbon storage and soil fertility, highlighting the importance of their management in agroforestry system.