Can the application of rare earth elements improve yield and decrease the uptake of cadmium in ryegrass-dominated pastures?

Rare earth elements (REEs) have been linked to increases and decreases in plant growth and the uptake of biotoxic metals such as Cadmium (Cd). We hypothesised that under the right soil and climatic conditions the application REEs to soil may improve yield of ryegrass-dominated pasture and inhibit Cd uptake in foliage. A soil survey measuring REEs concentrations in soils from across New Zealand showed that REEs were enriched in Volcanic compared with Sedimentary-derived soils, and in soils used for dairying compared with those used for sheep and beef. From a range of REEs applied to ryegrass with and without N, lanthanum (La) showed minor yield improvement under glasshouse conditions, but only for Sedimentary (not Volcanic) soils low in REE concentration and at 40% available soil moisture or less. A similarly mixed yield response occurred in a field trial. Decreases in the Cd concentration of ryegrass (mgkg-1) only occurred in the harvests after application (40% at 20kg La ha-1 for one soil) and did not translate into an annual effect. We conclude that there was insufficient evidence to recommend the use of La (screened from a range of REEs as the most promising) to increase annual dry matter yield or decrease Cd uptake from ryegrass-dominated pastures