Use of Humic Acids, Zeolite and Bentonite to Mitigate Iron Toxicity and Improve Growth Parameters and Chemical Composition in Maize (Zea mays L.)

Soil contamination with metals is a significant environmental problem that can adversely affect the growth of crops and the quality of yields. Among potentially toxic elements, iron plays a particularly important role, as excessive amounts of it disrupt physiological processes and plant nutrition. The aim of the study was to assess the impact of varying levels of iron contamination in the soil and the effectiveness of selected neutralising substances in mitigating iron stress on the growth, mass, SPAD index and chemical composition of maize biomass. In the absence of additives, excessive iron content (750 mg Fe kg−1 of soil) significantly restricted plant growth, causing a 62% reduction in plant height and a reduction in fresh and dry matter mass of 92% and 94%, respectively, compared to the control. However, the lowest dose of iron (250 mg Fe kg−1 of soil) in without additions series exhibited a stimulating effect, resulting in an increase in maize height and fresh matter mass. Among the tested neutralising substances, bentonite proved to be the most effective, significantly mitigating the negative effects of iron by increasing plant height by average 92% and fresh and dry matter mass by 167% and 193%, respectively, compared to the series without additives. Bentonite and humic acids also limited the decline in the SPAD index during subsequent growth stages. Soil contamination with iron significantly altered the chemical composition of maize biomass, with the additives used correcting these changes to varying degrees.