Lettuce Grown on Calcareous Soils Benefit From Sewage Sludge

Abstract

The present study aimed to evaluate the effects of sewage sludge, manure and humic acid applications on soil properties and element concentrations of soil and plants. As a field experiment, lettuce was grown on soil amended with 0, 20, 40 and 80 t ha(-1) of sewage sludge or manure. Humic acid was applied on sewage sludge amended plots as 250 kg ha(-1). Addition of sewage sludge and manure increased lettuce yield, head circle, head height and leaf number and N, P, K and Mg levels to same extent. Leaf Cd concentration increased in sludge treated plots more than manure treated plots. Sewage sludge and manure applications increased organic matter, electrical conductivity, total N, available P, exchangeable K, total Cu, Ni and AB-DTPA ( ammonium bicarbonate-diethylenetriaminepentaacetic acid) extractable Mn, Cu and Cd concentrations of topsoil. Extractable Fe, Cr and Zn and total Cd, Cr and Zn increased in soil with added sludge. Soil pH was unaffected by either sludge or manure applications. Lettuce leaf concentrations of Cd from the plots treated with humic acid were lower than those not treated with humic acid. Sludge together with humic acid application significantly increased soil available P, and impeded the increase of the soil AB-DTPA extractable Zn concentration. It may be concluded that sewage sludge can be an alternative to manure to enrich organic matter, and rectify N, P, Fe and Zn deficiencies with high pH and calcareous soils. Also, humic substances can be used, to a limited extent, for controlling the availability of sludge-borne heavy metals.