Rare Earth Elements (REEs) Rich-Phosphate Fertilizers Used in Brazil are More Effective in Increasing Legume Crops Yield Than Their REEs-Poor Counterparts

Rare earths elements (REEs) can affect plant growth positively. Besides their intentional agricultural use, REEs have also been involuntarily applied to soils through phosphate (P) fertilizers. This study aimed to evaluate the effects of REEs contained in P fertilizers on increasing legume crops yield in Brazilian agroecosystems. Field experiments were conducted with Phaseolus vulgaris L. and Glycine max (L.) Merrill with four sources of P (a pure ammonium phosphate with no REEs and three single superphosphates—SSP—with varying REEs contents) applied to the soil at four P rates (0, 17.5, 35, 70 kg ha −1 ). Irrespectively of the rate, the SSP—Catalão (richest in total and soluble REEs among the sources tested) consistently increased the yield of common bean (~ 30%) in relation to the control (ammonium phosphate). Single superphosphate Araxá (intermediate REEs content) also increased common bean yield. For soybean, the SSP-Catalão, at the 70 kg P ha −1 rate, was superior to the control (at the same level of P) and to the treatment without P addition. Our results showed that the REEs, present as impurities in phosphate fertilizers, increase their effectiveness on legume crops yield. These findings are relevant, as producers could enhance yield with REEs-rich P-fertilizers, especially in tropical agroecosystems, where high application rates are required.