EFFECT OF HUMIC ACID APPLICATION ON THE REDUCTION OF CADMIUM CONCENTRATION IN LETTUCE (Lactuca sativa L.)

Abstract

Humic acid (HA) applications in soils contaminated by heavy metals and especially cadmium (Cd) based on using phosphorous fertilizers in agriculture are becoming increasingly important as a common method by many researchers all around the world. The aim of this study was to determine the effects of humic acid on the dry matter (DM), Cd content, its uptake and the changing rate in lettuce plants (Lactuca Sativa L.). The lettuce plants were grown with three replicates. Two Cd doses (0 and 40 ppm) and five HA doses (0, 100, 200, 400 and 800 ppm) were applied to soil according to factorial experimental design under greenhouse conditions. In this study, it was found that Cd application in all treatments decreased dry matter (DM) significantly (P<0.01). The highest decrease (-15.21%) in DM of the lettuce plant was obtained with 100 ppm of HA application (P<0.01). On the other hand, 800 ppm HA provided a significant increase (25.11%) in the DM of the lettuce plant (P<0.01). While the Cd content in lettuce plant was increasing at the dose of 100 ppm HA, it was decreasing depending on increasing HA doses (11.57%, -12.92%, -17.78%, -33.97%; 100-200-400-800 ppm, respectively). Similarly, HA applied to the soil with Cd decreased the uptake from 178.33 mu g Cd pot(-1) (control) to 145.68 mu g Cd pot(-1) (800 ppm HA). The decreasing percentage according to increasing HA doses was determined as -6.08%, -7.06%, 9.38%, -18.31%, respectively. At the end of the study, it was found that the amount of HA may be increased to 800 ppm to decrease the harmful effect of Cd in the agricultural soils.