ABSTRACT
Phosphorus is a key nutrient require for high and sustain productivity as it limit plant growth in many soils. Phosphorus sorption capacity of soils is Important in determining the availability of phosphorous for proper crop growth. The study area is located between latitude 06o 36' 59.7"N and longitude 05o 37'15.8” E at an altitude 149.40 m, the study was conducted on soils collected from four (4) depths (0 -30, 30 -60, 60-90, 90 -120cm) in 3 replications from Alagba soil series in Nigeria institute for oil palm research (NIFOR). The P sorption capacity was determined by equilibrating the samples, 3 g soil for six (6) days in 30 ml of 0.01 M calcium chloride (CaCl2) containing various concentrations of P as KH2PO4. The physical and chemical properties of the soils were determined using standard laboratory methods while the Freundlich model was used to express the P sorption capacity at different depths. The data obtained were subjected to statistical analysis using Genstat statistical package. The means were separated at 5% level of probability using Duncan multiple range test. The results from the physical and chemical properties of the soils at the various depths revealed that the sand content decreased with increasing soil depths, the silt content was inconsistent with increased soil depth, while the clay content of the soil increased with increased soil depth and the soil textural class was Sandy loam and loamy sand for all the soil depths. The soils were generally acidic with a mean pH value of 3.94, organic carbon, Nitrogen (N) and Phosphorus (P) decreased significantly with increased soil depths and K, Ca, Mg, Na, EA, ECEC, CEC and % BS did not increase significantly with increased soil depths. The mean values of OC, N, P, K, Ca, Mg, Na, EA, ECEC, CEC and % BS were 6.91 gkg-1 , 0.35 mgkg-1 , 0.39 mgkg-1 , 3.94 cmolkg-1 , 0.29 cmolkg-1 , 0.35 cmolkg-1 , 0.09 cmolkg-1 , 0.84 cmolkg1 , 1.26 cmolkg-1 , 0.41 cmolkg-1 , and 67.20% respectively. The rate of P sorption increased with increase in concentration of P added to the xiv different soil samples. At 20, 40, 60, 80 and 100 mg P L-1 , the mean values of the amount of P adsorbed were 19.69, 37.64, 58.28, 77.49, 93.53 mgkg -1 respectively. The P sorption capacities of the various soil depths considering the Freunlich model decreased in the order of 90-120 cm > 60- 90 cm >30-60 cm >0-30 cm with values of 45.710, 43.750, 38.730 and 26.184 mgg-1 respectively. The result showed that P sorption was least (26.18 mmg1 ) at the top soil (0 -30 cm) considering the freundlich adsorption constant while the R2 value of > of 0.70 shows that the model was robust in predicting phosphorous sorption across the soil depth. Phosphorus sorption determination is important for proper phosphorus management practice.
