Phosphate and Trace Metal Availability from Sewage-Sludge Incinerator Ash

Incineration is practiced to reduce sewage sludge volume, but disposal of the resulting ash remains an important waste-management problem. The objectives of a field study conducted from 1987 to 1990 were to evaluate sewage-sludge-incinerator ash as a P fertilizer, determine trace metal availability, and assess the liming potential of the ash. The soil was an Estherville sandy loam (sandy, mixed, mesic Typic Hapludoll) with an initial pH of 5.7. Treatments compared P rates of 35, 70, and 140 kg ha⁻¹ yr⁻¹ from triple-superphosphate fertilizer with equivalent ash rates based on citrate-soluble (available) P. A control receiving no P application was included. Field corn (Zea mays L.) was grown the first 3 yr and sweet corn was grown in 1990. Limited effects on growth occurred the first 2 yr, but in 1989 and 1990 both ash and phosphate fertilizer significantly increased yield. Yield response to ash was equivalent to phosphate fertilizer for 1989 field corn, but significantly less for sweet corn in 1990. Ash and phosphate fertilizer both increased tissue P concentrations, but phosphate fertilizer was the more effective P source. Olsen's soil P extractant provided a more useful measure of plant available P than Bray P-1 for ash-amended soil. Ash increased diethylenetriaminepentaacetic-acid (DTPA) extractable Cu, Zn, and Cd in the 0- to 15-cm soil depth and slightly buffered soil pH. Concentrations of Cu and Zn in plant tissue were consistently higher, and Mn consistently lower, with ash than with phosphate fertilizer. In 1990, ash also significantly increased tissue Cd and Mo in sweet corn. Tissue trace metal concentrations were not in the range of anticipated phytotoxicity or animal health problems. Paper no. 20915 of the Journal Series, Minnesota Agric. Exp. Stn. Research supported by the Metropolitan Waste Control Commission, St. Paul, MN.