Mechanisms for reducing heavy metal toxicity in fertiliser and agrotechnological soil protection systems

Pollution of agricultural soils with heavy metals caused by the activities of industrial enterprises, transport, and intensive use of agrochemicals poses a threat to environmental safety and productivity of agricultural systems. In this regard, the purpose of the study was to evaluate the effectiveness of combined use of green manure and organo-mineral stabilisers (zeolite and biochar) to reduce the bioavailability of heavy metals and phytotoxicity of the soil environment. The research methods included a field block experiment on chernozems southern of Southern Steppe of Ukraine contaminated with cadmium (0.7 mg/kg), using four treatment options (control, zeolite, zeolite + green manure, green manure). The results showed that the most effective option for reducing the bioavailability of cadmium was the option with the introduction of zeolite, which provided a decrease in available cadmium by 58% and a decrease in its total content by 22%. The introduction of green manure alone reduced the bioavailability of cadmium by 31% compared to the control. Biochar in combination with phytoremediation reduced the availability of cadmium and zinc by 50%, and soil removal increased by 40% compared to phytoremediation without biochar. The biomass of the aboveground part of sunflower increased by 24% (up to 35.2 g/plant), the chlorophyll content – by 25%, and the activity of antioxidant enzymes – by 32% and 41%. Mustard and phacelia sideration helped to increase the organic carbon content in the soil by 18%, improve the cation exchange capacity by 11%, and reduce metal leaching by 30%, which indicates an improvement in the overall fixation of toxic elements. All results confirmed a significant reduction in the phytotoxicity of the soil environment and an improvement in the physiological and biochemical state of plants. The practical significance of the results lies in the possibility of using biochar, zeolite, and green manure for reclamation of contaminated soils and reducing the risk of heavy metals entering the food chain