The Improved Phytoextraction of Heavy Metals and the Growth of Trifolium repens L.: The Role of K 2 HEDP and Plant Growth Regulators Alone and in Combination

Heavy metals are among the most widespread pollutants in soil. Phytoextraction technology is used to solve the problem of multi-metal-contaminated soil. The efficiency of this process can be increased by introducing various amendments. A soil amendment is any material added to a soil to improve its physical properties, such as water retention, permeability, water infiltration, drainage, aeration, and structure. Some chemical amendments for enhanced phytoextraction, such as amino polycarboxylates chelators, can be hazardous to the environment and perform poorly at pH > 8. The effect of the potassium salt of hydroxyethylidene diphosphonic acid (K 2 HEDP), plant growth regulators (PGRs), and iron chelate alone and in combination on the phytoextraction by Trifolium repens L. seedlings of Cd, Ni, and Cu was studied in this work. K 2 HEDP works in a wider pH range. The results of this study confirmed that amino polycarboxylate chelators, with the sodium salt of ethylene diamine tetraacetic acid (Na 2 EDTA) as an example, have a pronounced negative effect on the growth and development (organ mass) of Trifolium repens L. seedlings. K 2 HEDP, proposed by the authors instead of Na 2 EDTA, produced a pronounced positive effect on plant growth and development, which was further enhanced by the use of PGRs and with iron chelates. However, it should be noted that K 2 HEDP showed significantly lower efficiency in trials on the Trifolium repens L. seedlings. The highest was the efficiency of K 2 HEDP with PGRs and iron chelates for the phytoextraction of Cd.