Effects of Sewage Sludge and Humic Acid Applications on Yield, Nutrients and Heavy Metal Contents of Maize and Some Soil Properties
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In this study, it was aimed to investigate the effects of different sewage sludge (0, 10, 20 and 30 %) and humic acid applications (0, 1000, 1500 and 2000 ppm) on growth, nutrient and heavy metal contents of maize (Zea mays L.) grown on a calcareous soil, and also some properties, nutrients and heavy metal contents of the soil remained after harvest. The increasing concentrations of sewage sludge applications significantly decreased the pH and lime contents in soil after harvest, while salt contents, organic matter, P, Ca, Mg, Fe, Mn, Zn, Cu, Cd, Ni, Pb and Co contents of soil after harvesting were increased. Sewage sludge doses caused significant increases in shoot and root dry or wet weights and plant height of corn. With increased sewage sludge applications, significant increases in P, K and Zn contents of root and P, K, Ca, Mg, Fe, Mn, Zn, Cu, Cd, Ni, Pb and Co contents of shoot were recorded, but Fe, Mn, Cd, Ni, Pb and Co contents were significantly decreased. The increasing concentrations of humic acid applications increased organic matter, P, Ca and Mg contents of soil, but did not significantly affect the other soil properties. Plant height, dry and wet weights of root and shoot were significantly increased up to 1000 ppm of humic acid application, but higher levels had no beneficial effects. Micro nutrients of root of maize were numerically decreased by applications of humic acid. As a result, application 20% of sewage sludge and 1000 ppm of humic acid for maize is the most appropriate levels.