Pedological Study under Cocoa Trees and its Implication on Production in Soubré, Southwest Region of Ivory Coast

Maintaining the fertility of cultivated soils in tropical countries such as Ivory Coast remains a major concern for producers because of crop failures. The aim of this study is to determine the soil characteristics of a cocoa plantation in the Soubré region (southwest of Ivory Coast: 6° - 7° N latitude and 5° - 7° W longitude), in order to improve production. In the centre of the plantation, a section of land (50 m × 50 m) was identified. Five soil pits were opened on this section of land, one at each corner and one in the centre. Soil samples were taken from each of the pits, in the 0-20 cm and 20-40 cm layers. Composite samples were then taken at these two depths for the analytical data. The pH, sum of exchangeable bases (S), cation exchange capacity (CEC), saturation rate of exchangeable bases (V), particle size fraction and organic matter content were measured and compared with threshold values known from the literature. The results show that pH (5.6 - 6.8) and assimilable phosphorus [P ass (130 - 350 ppm)] increase with depth and are in good proportion. Concentrations of potassium (K+ : 2.9 - 2.3 cmol/kg), calcium (Ca2+ : 29.1 - 47.2 cmol/kg) and magnesium (Mg2+ : 2.7 - 22 cmol/kg), as well as chemical properties (S : 35 - 73 cmol/kg, CEC : 48 - 80 cmol/kg and V : 73 - 90 %) are relatively good for cocoa production. However, organic matter (1.38%) and total nitrogen (N = 0.1 - 0.05%) are low. And high levels of clay (48%) and silt (23%) were noted from the first 20 cm depth. Spreading organic matter in the form of compost could therefore be recommended in order to correct the defective characteristics of the soils caused by the abundance of these two mineral particles: clay and silt, on the one hand, and deficiencies in nitrogen and organic matter, on the other.