RESIDUAL EFFECTS OF IRRIGATING CORN WITH DIGESTED SEWAGE SLUDGE

The same corn hybrid (Zea mays L. ) was grown during the last 3 years that Blount silt loam plots were irrigated with liquid, municipal sewage sludge and for the next succeeding 4 years after termination of applications. During the last year in which sludge was applied, leaves from maximum sludge-treated plots contained 112 mg Zn/kg and 7. 1 mg Cd/kg. Four years after sludge applications were terminated, leaves from these plots contained 45 mg Zn/kg and 2. 1 mg Cd/kg. Grain-Zn concentrations decreased from 45 mg Zn/kg during the last year of sludge applications to 27 mg/kg in the 4th year after termination applications. In a similar manner, grain-Cd concentrations decreased from 0. 44 to 0. 07 mg/kg. During the 3rd and 4th years after terminating sludge applications, grain from sludge-treated and control plots could not be distinguised by differences in Zn and Cd concentrations. Soil pH was near neutral throughout the study and was not affected by treatments.