In this study, the effects of ethylenediaminetetraacetic acid (EDTA) and humic acid (HA) chelate applied to soils contaminated with heavy metals on the development, antioxidant defence system, and phytoremediation of forage turnip (Brassica rapa L.) were investigated for the first. Three doses of EDTA (E 1 : 5 mmol/kg, E 2 : 10 mmol/kg, E 3 : 15 mmol/kg) and three doses of HA (HA 1 : 500 mg/kg, HA 2 : 1 000 mg/kg, HA 3 : 2 000 mg/kg) were applied to soils contaminated with heavy metals (Cd, Pb, Zn, and Cr) in the pot. According to experiment results, HA application as chelate to the polluted soil caused a significant increase in the growth of forage turnip. Phytoremediation values of the plant for Cd heavy metal were found to be BCF shoot , BCF root > 1, and translocation factor > 1. This result proved that forage turnip has Cd accumulating properties. Also, HA application caused a decrease in H 2 O 2 (46%) and malondialdehyde (6%) levels and antioxidative enzyme activity in polluted soil. It has been concluded that humic acid improves the oxidative stress conditions in the plant and is more effective in the development and growth of the plant than EDTA, so that it can be used effectively in phytoremediation studies.

Rapeseed has been cultivated to produce non-edible and edible oil for thousands of years. It is known as the second-largest oilseed plant in the world with 24.6 million tons of oil production in 2021. The interventions that can be carried out during the cultivation of a plant with such a high production value are quite significant. Growth, enzymatic activities, and phytoremediation of rapeseed grown under heavy metal stress supported by humic acid (HA) and ethylenediaminetetraacetic acid (EDTA) applications were investigated for the first time in this study. Three doses of EDTA (EDTA1:5 mmol/kg, EDTA2:10 mmol/kg, EDTA3:15 mmol/kg) and three doses of HA (HA1:500 mg/kg, HA2:1000 mg/kg, HA3:2000 mg/kg) were applied in heavy metal treated pots. According to experiment results, HA1 and HA2 applications increased plant dry and fresh weights, root dry and fresh weights. However, EDTA applications caused a decrease in shoot length, a number of leaves, shoot fresh and dry weights, root fresh and dry weights. Bioconcentration factor (BCF) values for Zn, Cr and Cd we found higher than in both shoots and roots of rapeseed. For all levels of EDTA, the values of BCF (shoot) and BCF (root), transfer factor (TF) and translocation factor (TLF) increased compared to HA applications. On the other hand, in comparison to heavy metal polluted soils alone (PS), all levels of HA resulted in significantly reduced APX and CAT enzyme activity, and hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents. We concluded that humic substances exert a significant influence on plant growth and reduce heavy metal toxicity in polluted soils. At the same time, HA could be more effective than EDTA in terms of phytoremediation of Cr. HA can increase phytoremediation in polluted soils as it improves plant growth and oxidative stress due to its organic nature. The results provide remarkable information for rapeseed cultivation in polluted regions.

The aim of this study was to investigate the effects of humic acid (HA) applications on rapeseed (Brassica napus L.) growth, heavy metal uptake, bioconcentration factor (BCF), translocation factor (TF), tolerance index (TI), catalase (CAT), ascorbate peroxidase (APX) enzyme activities and hydrogen peroxide (H2O2) content in polluted soil with lead (Pb), chromium (Cr), cadmium (Cd), and zinc (Zn). Three doses of HA (Control, HA1:500 mg kg-1, HA2:1000 mg kg-1, HA3:2000 mg kg-1) were applied in pots. HA1, HA2, and HA3 applications increased plant growth parameters compared to polluted soil. Compared to the control, HA applications in polluted soil increased the Pb, Cr, Cd, and Zn concentrations in the plant. However, HA applications in polluted soil significantly decreased the heavy metal content in roots and shoots of the plant compared to polluted soil. BCF in both roots and shoots of the plants were greater than 1 for Pb, Cr, Cd, and Zn. However, specifically HA2 application decreased the shoot and root BCF values in polluted soil. TF was smaller than 1 in Pb, Cr, Cd, and Zn in polluted soil. On the other hand, HA applications for Cd increased TF values. Shoot TI decreased 17.37 %, and root TI decreased 9.09% in polluted soil. CAT and APX enzyme activities and H2O2 increased significantly in polluted soil. However, HA applications decreased CAT and APX enzyme activities and H2O2 content in rapeseed. It is concluded that HA application in Pb, Cr, Cd, and Zn polluted soil has a remedial effect on the development of rapeseed by reducing heavy metal content and oxidative stress.

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.

The objective of this study was to determine the effects of nitrogen fertilizer sources of ammonium sulphate and municipal sewage sludge on yield, N content and uptake of the maize (Zea mays L.). Nutrient and heavy metals were determined in soil and plant. The experiment with three sludge rates (256, 513 and 1026 kg total N ha⁻¹ or 9.5, 18.0 and 38.1 t ha⁻¹ sludge), two nitrogen rates (80 and 160 kg N ha⁻¹) and zero-N control were conducted on a clay loam soils under irrigated conditions in Eastern Anatolia region in Turkey. Treatments were arranged in a randomized complete block design with four replications. Yield, N content and total N uptake of maize increased significantly with sludge application. 9.5 t and 19.0 t ha⁻¹ sewage sludge applications did not significantly affect heavy metal content of leaf and grain. However, 38.1 t ha⁻¹ sludge applications increased leaf Pb and Zn. DTPA-extractable Cd, Cu, Fe, Pb and Zn concentrations of the soil increased at applications of 38.1 t ha⁻¹ sewage sludge, whereas applications of 9.5 t and 19.0 t ha⁻¹ sludge only resulted in elevated levels of Cu and Zn, We conclude that if sewage sludge is to be used in production of maize, applications rate up to 19 t ha⁻¹ could be accepted. However, this means also that the N requirement of maize crop is not covered by the sludge; therefore, the rest of nitrogen could be supplied as inorganic N.

The objective of this study was to determine the effect of the increasing doses of sewage sludge and different application times on DTPA (diethylenetriaminepentaacetic acid) extractable nutrients and heavy metal concentration in calcareous soil for three years. For this purpose, sewage sludge was applied at different rates (0, 4.1, 8.2, 16.4 t ha-1) and periods (spring and autumn) to meet the nitrogen fertilizer requirement of grass-legume mixtures. Experiment results showed that cumulative sludge applications significantly increased DTPA extractable metal concentrations for 0-20 cm. Sludge application in spring period reduced the soil pH and increased the extractable metal concentrations compared to the autumn. Sludge application doses increased DTPA-Zn concentration for all soil depths and years. At the end of the experiment, it was determined that the heavy metal contents in the soil did not reach the levels that would have a negative effect on plant production. The fact that Van soil is rich in lime and alkaline pH of the soil, where the experiment was carried out, caused the solubility of heavy metals from sewage sludge to be low and toxic effect not to be seen. However, long-term sludge application should be followed in soil.