Effect of mineral fertilization on the physicochemical properties of soils in the region of Go and the vegetative behaviour of immature trees of clone PB 235 of Hevea brasiliensis in South- Western Côte d'Ivoire

Abstract The effect of mineral fertilization on the physicochemical properties of the soil and the vegetative behaviour of clone PB 235 of Hevea brasiliensis has been studied in the Go experimental plantation of San Pedro in south-western Côte d'Ivoire. On that respect, the fertility of soil treated with different doses of complete fertilizer and the vegetative behaviour of rubber trees were assessed from soil samples and measurements of parameters of vegetative growth before and seven years after the establishment of rubber trees. The different doses of fertil izer spread changed from zero to four times the dose used in industrial plantations. The rate of fines (clay and silt) decreased from unfertilized soils those treated with high doses of fertilizer. We noticed a gain of organic matter, carbon and a stability of surface horizons whose maximum is expressed by the treatment fertilized with half-dose. However, the almost constant loss of nitrogen was independent of doses of manure. The rates of exchangeable Ca and Mg decreased from unfertilized soils to those treated with the standard dose and whose values were the lowest, unlike the cationic exchange capacity (CEC) which increased with the same amount of manure. Despite the potassium application at the opening of rubber trees, the loss of exchangeable K and the increasing deficiency of available phosphorus were independent of fertilizer doses. Nevertheless, a constant application of high-doses of phosphorus ensures its availability in soil. Fertilization by half dose of fertilizer leads on the long-term to a stable soil, physically improved. The vegetative behaviour of PB 235 was satisfactory and showed that an application of manure beyond the half dose was not necessary.