Effects of a rare earth element-based feed additive on growth of selected crop species

Aims Rare earth elements (REEs), particularly lanthanum (La) and cerium (Ce), are increasingly used in agriculture. However, their effects on crops under contrasting soil moisture conditions remain unclear. This study investigated the effects of a La and Ce based feed additive on seed germination, growth, and nutrient status of maize, wheat, bean, and radish under two soil moisture conditions, identifying the thresholds at which beneficial effects shifted towards phytotoxic effects. Methods A greenhouse pot experiment using an LD80-sand substrate was conducted under dry and moist conditions. A commercial feed additive containing La and Ce as citrate complexes was applied at different additive concentrations, together with a control and a NaCl control treatment to account for potential Na and Cl effects associated with the feed additive. Plant performance was assessed by seed germination, leaf area, dry mass, and element concentrations. Results Lower treatment levels (0.375 and 0.75 g kg −1 ) stimulated seed germination and total biomass in maize and wheat. In contrast, high treatment levels (6 and 12 g kg −1 ) significantly inhibited plant growth and in some cases prevented seedling establishment. Radish biomass was reduced by up to 88% under the highest treatment level. Biomass was generally higher under moist than dry conditions, particularly in maize and radish. Conclusions The REE-containing feed additive induced hormetic responses, stimulating plant growth at lower treatment levels but inhibiting growth at high levels. Soil moisture modified these responses, particularly in maize and radish. Dose–response relationships and EC50 values were determined for the studied species, providing quantitative thresholds for phytotoxicity.