Foliar application of rare earth elements to maize and mungbean

The foliar application of rare earth elements to plants has been reported to increase yields of a range of crops particularly when soils contain low levels of rare earth elements. A rare earth element fertiliser obtained from China was chemically analysed and found to contain 45.3% nitrate plus 8.7% lanthanum and 12.4% cerium; lanthanum and cerium were the most abundant rare earth elements measured. This fertiliser was applied once, as 0, 0.025, 0.05, 0.1, 0.5 and 1.0% (w/v) aqueous solutions to the foliage of 10-day-old maize (Zea mays L. cv. Hycorn 82) and 14-day-old mungbean [Vigna radiata (L.) Wilczek cv. Berken] plants grown in a nutrient-rich potting mix of low total rare earth element status. For comparison, a duplicate set of plants was sprayed with solutions containing analytical grade lanthanum and cerium nitrate at concentrations equivalent to those measured in the rare earth element fertiliser. No beneficial effects of the rare earth element treatments were observed. The shoots of maize and mungbean sprayed with less than or equal to 0.1% rare earth element fertiliser or equivalent appeared completely healthy throughout the experiment, but plants in the 0.5 and 1.0% treatments showed symptoms of leaf burn in maize, and small necrotic spots on mungbean leaves within 1-3 days of treatment. These symptoms became more severe over the next 5-9 days. The shoot dry weight of mungbean sprayed with 0.5 and 1.0% solutions was significantly (P<0.05) reduced by 27%. Symptoms observed on plants sprayed with lanthanum and cerium nitrate solutions were similar to those observed on plants sprayed with the rare earth element fertiliser, and similar growth reductions occurred also.