Phosphorus Sorption, Desorption, and Buffering Capacity in a Biosolids‐Amended Mollisol

To investigate the impact of biosolids amendments to soil on the sorption, desorption, and buffering capacity of P, laboratory experiments were conducted on soil samples collected from a field study on a Mollisol amended with three levels of biosolids. The potential for sorption of additional P and the binding intensity of P were evaluated by applying the two‐surface Langmuir model to sorption isotherms. Over the range of equilibrium P concentrations in this study, the ability of the soil to sorb added P decreased due to biosolids amendment. Addition of biosolids to the soil also decreased indices of the P‐binding intensity at both the high‐ and low‐affinity sites. The P equilibrium buffering capacity (PEBC) significantly decreased and the equilibrium P concentration (EPC) significantly increased after biosolids amendment. P desorption from soil samples with and without biosolids amendment was investigated for different equilibration periods and at various liquid/solid ratios. The amount of P that could be desorbed from the soil significantly increased after biosolids amendment. The effects of biosolids amendments on indices of soil P sorption–desorption phenomena (binding energy, PEBC, and EPC) imply a large increase in the P concentration of the soil solution. The increase of soluble forms of P in soil solution of this soil, which was heavily amended with biosolids, could enhance the loss of P in runoff and P movement below the root zone.