SOIL SOLUTION CHEMISTRY OF SEWAGE-SLUDGE INCINERATOR ASH AND PHOSPHATE FERTILIZER AMENDED SOIL

The chemical composition of the soil solution provides useful informat ion on the feasibility of amending agricultural land with municipal an d industrial waste, because the soil solution is the medium for most s oil chemical reactions, the mobile phase in soils, and the medium for mineral absorption by plant roots. The soil solutions studied in this research were from plots in a 4-yr field experiment conducted to evalu ate the effects of the trace metals and P in sewage-sludge incinerator ash. Treatments compared ash with equivalent P rates from triple-supe rphosphate fertilizer and a control receiving no P application. Ash an d phosphate fertilizer were applied annually at rates of 35, 70, and 1 40 kg citrate-soluble P ha(-1). Cumulative ash applications during 4 y r amounted to 3.6, 7.2, and 14.4 Mg ash ha(-1). Soil solutions were ob tained by centrifugation-immiscible liquid displacement using a fluoro carbon displacing agent. Following chemical analysis, a chemical speci ation model was used to determine possible solubility-controlling mine rals for trace metals and P, and correlations between solution composi tion and plant uptake were analyzed. Ash increased soil solution pH, C d, and Zn, but had no significant effect on solution concentrations of other trace metals. Ash increased soil solution P and S, but P increa ses were less than those from equivalent citrate-soluble P rates of ph osphate fertilizer. Soil solution Ba appeared to be in equilibrium wit h barite (BaSO4). Solubility data did not indicate that any discrete m ineral phases controlled Cd, Zn, Cu, Ni, Pb, or P solubility. Soil sol ution P concentration was strongly correlated (r = 0.92) with P accumu lation in sweet corn (Zea mays L.) plants, but solution trace metal co ncentrations were either weakly correlated (r = 0.49 for Zn and 0.36 f or Cd) or not significantly correlated (r = 0.09 for Ni and - 0.25 for Cu) with plant accumulation.