Residual Effects of Irrigating Corn with Digested Sewage Sludge

Abstract 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 of 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 distinguished by differences in Zn and Cd concentrations. Soil pH was near neutral throughout the study and was not affected by treatments. Except for the decrease during the first year after which sludge applications were terminated, total N and organic‐C concentrations in previously sludge‐amended soil remained fairly constant at levels markedly higher than in control plots. The cation exchange capacity of the soil was increased in proportion to the amount of organic‐C remaining in the soil after termination of sludge applications.