Sewage sludge incinerator ash effects on soil chemical properties and growth of lettuce and corn

Incineration reduces sewage sludge volume, but management of the resulting ash is an important environmental concern. A laboratory incubation study and greenhouse pot experiments withlettuce (Lactuca sativa L.) and corn (Zea mays L.) were conducted to examine the potential for recycling elements in sewage sludge incinerator ash in agricultural systems. Ash rates in both the laboratory and greenhouse were 0, 0.95, 3.8, 15.2, and 61.0 g/kg soil (Typic Hapludoll). Ash was also compared to equivalent rates of citrate soluble P from superphosphate fertilizer in a soil-less growth medium. During soil:ash incubation, Olsen P and DTPA extractable copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) increased with incubation time at the higher ash rates. Release rates diminished rapidly, however, and the limited release of these elements after 280 dayswas associated with decreasing pH. In the greenhouse ash amendment increased extractable soil P, plant tissue P, and the growth of lettuce and corn. Ash was a less effective P source than superphosphate fertilizer in the soil-less growth medium and Olsen P levels were more consistent withthese differences than Bray P. Ash increased extractable soil levels and plant tissue concentrations of calcium (Ca), magnesium (Mg), sodium (Na), Cu, and Zn, but extractable soil manganese (Mn) and plant tissue Mn decreased. Ash increased soil pH and extractable SO₄-S. DTPA extractable Cd and Pb increased, but chromium (Cr) and nickel (Ni) decreased. Lettuce accumulated higher amounts of these trace metals than corn, but tissue concentrations were at control levels or below detection limits in both crops.