Characterization of drinking water treatment residuals for use as a soil substitute

The beneficial use of drinking water treatment residuals (WTRs) as a potential source of topsoil for land reclamation was evaluated. Seventeen WTRs were characterized for use as soil substitutes by comparing chemical and physical properties and plant nutrients of the WTRs with soil. A tomato (Lycopersicon esculentum) bioassay was performed to determine the ability of soil chemical tests to measure WTR phosphorus (P) adequacy. The WTR chemical and physical properties were typically adequate for crop growth. None of the WTRs were considered unsuitable as soil substitutes based on plant nutrients, with the exception of P. Tomato vegetative yield and tissue P were poor either because of phytotoxic nitrite-nitrogen (NO2-N) (> 10 mg/kg) generated during the bioassay or because of WTR P deficiency. Limited data suggest that WTRs with NO2-N less than 10 mg/kg and Olsen P greater than 50 mg/kg, water soluble P greater than 580 micrograms/L, or Mehlich III P greater than 54 mg/kg support growth but still produce inadequate tissue P in tomatoes.