P Sorption Characteristics in Hevea Supporting Soils of Coastal Plain Sand Origin in Southern Nigeria

Phosphorus (P) is a macronutrient element that plays a number of important roles in plants and soils including Hevea brasiliensis (Natural Rubber). Adequate P nutrition in rubber will result in improved latex production, crop quality, root growth and early maturation. Thus, a study of the relevant indicator of P sorption across depth of rubber supporting soils is necessary. Therefore, this study is aimed at evaluating the P sorption capacities of Coastal plain sand classified at the series level (Ahiara series) in RRIN, Iyanomo rubber stations. The study was conducted on soil samples collected from the representative profile pit in the soil mapping unit of Ahiara series, which were bulked samples from the six (6) different horizons of the profile pit, 5 samples were collected from each horizon amounting to 30 soil samples and were analysed for physic-chemical analysis and P sorption studies. The Phosphorus (P) concentrations differential of 53.28, 85.61, 120.89, 173.06 and 216.49 mg/l from KH2PO4 were used as P added. Furthermore, the sorption data were fitted into the Isotherm models of Freundlich, Langmuir and Temkin models and thereafter used to correlate the physical and chemical characteristics of the soils in Ahiara series respectively. The results of the P sorption capacity showed that all the soil horizons exhibited different affinity to sorb P but horizons with higher clay content and organic carbon showed higher mean P sorbed values of 85.03 in the Bt3 horizon with a depth of 140 – 180 cm and 82.49 in the A1 horizon with a depth of 0 – 20 cm. The soil series showed an EPR of 2.34mg/kg at 0.2mg/l P equilibrium concentration, which implies that it is a low P sorbing soil. Also, Freundlich model best describes P sorption capacity in Ahiara soil series based on the smallest RMSE values its showed when compared to the other models used in this study. However, the correlation co-efficient between some soils physical and chemical properties with the Freundlich indices showed negative and positive correlation r = -0.746 and -0.427 in clay and r= 0.541 and 0.376 in organic carbon.