Foliar application of rare earth elements on soybean (Glycine max (L)): Effects on biometrics and characterization of phytotoxicity

Abstract This study aimed at investigating the effects of foliar application of aqueous solutions of La3+ and Ce3+ nitrates on soybean plants (Glycine max). First, we observed that Triton HW 1000 surfactant at 0.01 vol% reduced droplets contact angle and increased their drying time. Under greenhouse conditions, the foliar treatments did not affect chlorophyll content, plant height, number of leaves, number of pods, number of seeds per pod and average seed weight. However, the treatments induced phytotoxicity since foliar injuries appeared after the spraying. Microprobe X-ray fluorescence spectroscopy combined to scanning electron microscopy showed that the leaf lesions were positively correlated to accumulation of Ce and La on the leaf surface and also promotes structural alteration to the epidermal cells. X-ray absorption near edge structure showed the La and Ce nitrates were partially bio transformed into oxides by the leaves which might explain the harmful effects.