The Role of Organic Materials in Shaping the Content of Trace Elements in Iron-Contaminated Soil

Iron contamination negatively affects how plants grow and develop, and it has an analogous influence on the health of other organisms. The use of different types of organic soil amendments can be a strategy to reduce the effects of excess iron stress and limit its assimilation by plants. The aim of this experiment was to investigate the possibility of using organic material in the form of humic acids (HAs) to reduce the influence of iron contamination on the content of trace elements (TEs) in the soil. The content of iron in the soil increased linearly (by 14%) as more iron was added. The addition of humic acids to the soil also promoted an increase in soil Fe content (by 12%) in comparison to the series without HAs. The highest dose of iron resulted in a decrease in Cd (by 49%), Pb (by 29%), Cr (by 13%), and Zn (by 10%) and an increase in Mn (by 6%), Cu (by 16%), and Co (by 33%) in the soil in comparison to the object without Fe. However, the first dose of iron increased the lead content, and the first and second dose of Fe also increased the Zn content in the soil. The nickel content in the soil also increased to 500 mg Fe kg^-1 of soil. Thereafter, a decline was observed in the nickel content. The addition of organic material had a different influence on the content of individual TEs in the iron-contaminated soils. The most evident constraining impact of HAs pertained to the level of Cd (reducing it by 14%) and Zn in the soil (only for two of its doses). The content of other TEs in the soil after the addition of organic material was found to be higher than in the series without HAs. This was especially evident for elements such as cobalt (Co) and lead (Pb).