Technical Abstract: Large quantities of byproducts and increased costs for land fill have heightened interest in using byproducts on agricultural lands as soil amendments. There are concerns of potential negative environmental impacts of byproducts-amended soils when the fields are taken out of agricultural production. The objectives of this study was to determine the effects of lowering soil pH and cropping on the solubility of P immobilized by water treatment residue (WTR) and coal combustion bed ash (BA). Two high P soils were mixed with two WTRs and a BA and incubated for 15 weeks using several wetting and drying cycles. Soil pH was reduced to levels that are found in the wooded area adjacent to agricultural fields using elemental sulfur and 1N H2SO4. Byproducts reduced extractable P in both soils. Phosphorus concentrations reduced 50 to 90% of the control in both soils at the lowest rate of WTRs, while soil Al concentrations increased < 18% of that in the control. BA was not as effective as WTR in reducing soluble P. Phosphorus concentration was further reduced with initial pH reduction; however, after five monthly harvests of Bermuda grass, P levels increased to original levels. Although soil Al, Ca and Fe concentrations increased under acidification and cropping, concentrations were not at levels that would negatively impact the environment. Phosphorus immobilized by WTR before pH reduction did not become soluble under acidic and cropping conditions for both soils.