ZINC AND CADMIUM UPTAKE BY BARLEY IN FIELD PLOTS FERTILIZED SEVEN YEARS WITH URBAN AND SUBURBAN SLUDGE

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Abstract
Barley plants grown in 2.4− × 3.0-m field plots were fertilized annually with two sources of sewage sludge for 7 consecutive years. One sludge originating, from a suburban area, was composted and applied dry. The concentrations of N, Zn, and Cd were low and over the years averaged 1.1%, 496 mg kg-1, and 5.2 mg kg-1, respectively. The other sludge came from an industrial, urban area and was applied as a slurry. It had an N content three times as high, a Zn content that averaged 5 to 10 times as high, and a Cd content 5 to 20 times that of the suburban sludge. The applied sludge rates ranged from 0 to 225 metric tons (t) per hectare in increments of 45 t. Yields in each year peaked at 90 t with the suburban and at 45 t with the urban sludge. Yields increased during the first 4 years and remained stable for the last 3. No toxic effects were observed on any of the plants. During the first 2 years, little or no increase in concentrations of Zn and Cd in grain of barley was found with either sludge. In the last 4 years, Zn and Cd concentrations in grain and straw increased where urban sludge was used. In all cases, straw accumulated more Zn and Cd than did grain. A chemical fertilizer treatment of NPKS produced grain with Zn and Cd content comparable to that from an agronomic rate of suburban sludge over the entire 7-year period.