Fig. 1. Soil iron-oxide-coated filter paper strip–extractable phosphorus (FeO-P) expressed as a percentage of total P analyzed by the USEPA 3050 acid–peroxide digestion method (EPA₃₀₅₀ P) added with biosolids and poultry litter (PL) to the (a) Elsinboro silt loam and (b) Woodstown sandy loam (error bars indicate standard deviation). BNR, biological nutrient removal.