ADHERENCE OF SPRAY-APPLIED LIQUID DIGESTED SEWAGE SLUDGE TO TALL FESCUE

Liquid anaerobically digested sewage sludge was spray-applied on field plots of mowed and unmowed tall fescue (Festuca arundinacea Schreb) at rates of 0, 51, and 103 m3/ha in mid-September 1975. Forage samples were periodically cut to a 7-cm height following rainfall events for 80 days, and again the following spring. The concentrations of Fe, Cu, Zn, Pb, Cd, and Ni were markedly increased by sludge spraying, with a greater increase at the higher sludge rate. The levels of Fe, Pb, and Cu in samples of healthy plants were so high (37,800 mg Fe, 140 mg Pb, and 115 mg Cu/kg dry forage) that absorption-translocation by the roots could not have supplied them. The %-sludge in/on the forage was calculated for each element based on the proportion of increased metal content in/on the forage to the metal content of the sludge. The %-sludge estimates for 6 elements were in close agreement, confirming sludge contamination rather than metal uptake from soil. Adhering sludge was not removed by washing in 0.1% Na lauryl sulfate. Adhering sludge comprised 22 to 32% of the forage on the day of application; sludge content decreased with time but was not related to rainfall events (27 cm during 15 days following sludge application). Sludge content declined more rapidly in the mowed treatment, apparently because less forage was contaminated and rapid growth diluted contaminated forage. Sludge was no longer found in/on forage samples grown after spring mowing. Adhering sludge could increase exposure of forage consumers to heavy metals and other sludge constituents.