Variation in Phosphorus Sorption with Soil Particle Size

Phosphorus (P) is considered a primary cause for surface water eutrophication that leads to anoxia. Understanding the relationships between soil particle size and P sorption helps devise effective best management practices (BMPs) to control P transport by erosion, leaching, and overland flow from agricultural land. Consequently, this study examined the effect of surface soil particle size on the sorption of P in five soil series (four Ultisols and one Entisol) from the Mid-Atlantic region. The sorption of P in each soil was assessed by equilibrating (after shaking for 24?h) 5?g soil containing varied amounts of KH₂PO₄ in 20?mL of 0.01?M KCl solution. Phosphorus in solution was determined by the molybdate blue method of Murphy and Riley. The P adsorption characteristics of these soils were described using the Langmuir isotherm. Results indicated that variability in P sorption was related to particle size and soil type. Soil organic matter content contributed a great deal to P sorption in the Entisol. However, soil clay had influence on the P sorption characteristics of each soil. The maximum P retentive capacities of soils (as determined by Sm from Langmuir equation) and P sorbed at 500?mg P kg^?1 addition showed a linear relationship (r2 = 0.94). Therefore, based on the results obtained, the single point method of Bache and Williams may be appropriate to describe the maximum P sorption capacity of non-sandy soils, as observed in this study.