CHEMICAL AND PLANT EXTRACTABILITY OF METALS AND PLANT GROWTH ON SOILS AMENDED WITH SLUDGE

Abstract

The addition of sludge to a Fox sandy loam (sl), Granby sl and Rideau clay (c) soil increased soil pH, total C, NaHCO3-extractable P, cation exchange capacity and exchangeable Ca. Sludge application increased DTPA-extractable Cd 2 to 5 times, Pb 2 to 3 times, Cu 3 to 7 times and Zn 7 to 31 times. Metal extractability in Granby and Fox sl soils was not greatly changed after 11 mo incubation but extractable Zn, Cu, Pb and Cd were reduced in the clay soil following incubation. Cropping to lettuce reduced the quantity of metal extracted from Fox sl soil and to a lesser extent from Rideau c soil but not from Granby sl soil. Lettuce (Lactuca sativa L.) yields were significantly reduced for the first crop grown on sludge + fertilizer-treated Rideau c and Granby sl soils and for all three harvests from similarly treated Fox sl soil compared to harvests from soils treated with fertilizer only. Yield reduction for the first crop was attributed to a salt effect, as subsequent yields on Rideau c and Granby sl soils were similar to harvests from fertilized treatments. Saturation extract conductivities for all sludge treatments were higher for incubated than for cropped soils. Generally Zn, Cu and Pb tissue concentrations in lettuce harvested from sludge + fertilizer-treated Fox and Granby sl soils were significantly increased but total uptake was only increased for Zn. Metal uptake and tissue concentrations for lettuce grown on similarly treated Rideau c soil were equal to or less than those found in lettuce harvested from the fertilizer-only treatment. To a lesser extent similar trends were observed with the tomato (Lycospersicon esculentum Mill.) crop.