Phosphorus Adsorption and Fractionation in a Two-phase Olive Mill Waste Amended Soil

Two-phase olive mill waste (TPOMW) is a by-product of olive oil extraction, contains up to 90% organic matter, and maybe used as soil amendment. To investigate the impact of TPOMW amendments to soil on the fractionation, adsorption, and buffering capacity of P experiments were conducted on soils collected from a typical olive grove amended for 5 yr with 0, 30, and 60 Mg ha(-1) of TPOMW. A modified Hedley fractionation scheme evaluated the change in soil P forms while Surface models were used to fit the data. The P fractionation results suggested and increase in HCI-P fraction. Other P pools, such as residual-P, NaHCO3-Pi, NaOH-Pi, NaOH-Po, soluble-P, and NaHCO3-Po increased to lesser degrees. A two-surface Langmuir model fit the adsorption data better than a uniform layer model and underestimation of the P adsorption was observed when the traditional Langmuir equation was used. The TPOMW amendments significantly decreased the P adsorption maxima (alpha = 0.05) and most of the P was adsorbed on low energy sites, independent of the amendment applications received. The TPOMW soil application decreased indices of P-binding intensity at both high and low affinity sites, decreased the P equilibrium buffering capacity, and increased the equilibrium P concentration (EPC). Coupled with the low energy of P binding, results implied an increase in the readily soluble P, and thus runoff P losses could potentially increase in TPOMW amended soil.