Effect of Soil Reduction on Phosphorus Sorption of an Organic-Rich Silt Loam.

Phosphorus flux from agricultural landscapes to surface waters may cause eutrophication. In the northeastern United States, P transport largely depends on P sorption of soils in variable source areas or in land treatment systems. Soil redox fluctuation commonly occurs in these areas. Nevertheless, the effect of soil redox on P sorption has been variable in the literature. This study investigated P sorption of an organic-rich northeastern glaciated silt loam (Langford) under air-dried, field-wet, and reduced conditions using batch P sorption experiments. Additionally, the influence of farm wastewater on soil P sorption was studied. Major results indicated that soil reduction increased the maximum amount of P that can be sorbed (S_max) and decreased the aqueous P concentration at which P sorption and desorption are equal (EPC₀), both determined from a modified Langmuir isotherm model. The slightly reduced field-wet soils had no significant difference in S_max due to limited soil reduction. Using the diluted wastewater as the sorption solution matrices instead of 0.01 mol L^-1 KCI solution, the soils generally exhibited greater S^max and lower EPC₀ except for the EPC∅ of a reduced surface soil, implying more complex P sorption in the field. Identified P sorption mechanisms include phosphate precipitation, ligand exchange with organic matter, and adsorption onto Fe hydroxides. Transformation of Fe compounds during soil reduction is primarily responsible for the changes in soil P sorption. [ABSTRACT FROM AUTHOR]