The study seek to identify and explain the effects of some soil factors on the productivity of Cocoa in farmers' fields. Thirty trees were sampled from each of the 36 farmers’ plot across 9 randomly selected villages in the South Cameroon low plateau agro ecological zone. Productivity per plot was calculated by computing a Cocoa Pod Index (CPI). Soil samples were collected at two horizons : 0-20 cm and 20-40 cm, around the selected trees. The pods collected per tree per farmers' plots where soil samples were taken were categorized into the following three Performance Weight Classes (PWC): PWC≤5000g, PWC>5000g≤10000g and PWC>10000g. The results obtained based on the Duncan mean separation test with generalized linear procedure in SAS 9.0, showed that for composite soil samples in the B-horizon, there was a significant difference between the levels of potassium and bean yields per pod by tree. It was also observed that there is no significant difference for phosphorus in all horizons in samples by soil horizon within the threshold of α = 5%. The mean levels of potassium is 0.32 Cmol/kg and 14.36 ppm of phosphorus in the two horizons, which are that, in this soil, the main components of fruits are very low in soils as well as the minimum and a maximum requirements for P205 (25-50kg/ha) and K20 (55-75kg/ha), which are the main components of fruits are very low in soils. The Pearson correlation coefficients linking the beans weight class (Prdta, Prdtb, PRdtc) and the soil elements (potassium and phosphorus) in the A-horizon are 82% and 6% respectively for PRdta, 31% and -43% for Prdtb, 11% and 3% PRdtc respectively. Yields per plot are very low: Talba has an average yield of 1,11t-ha, followed by Bokito (0,91t-ha), Obala (0,73t-ha) and Nkomedzap (0,45t-ha). Based on these results the situation of poor yields can be mitigated by providing additional nutrients to this effect. To mitigate this situation K+Na/Mg+Ca should be within the treshold of 1/50 to ensure good growth. On the other hand an optimal organic matter content of >3% as well as Ca >8, Mg >2 and K>0.24 meq/100g of soil, guarantees high production.
Keywords: Soil chemical factors, cocoa farm productivity, agro-ecology, soil sampling, South Cameroon low plateau
