Foliar levels of rare earth elements and thorium in coconut palm in relation to root (wilt)-disease

Concentrations of major nutrients and micronutrients, rare earth elements (REEs), Th and nutrient/REE ratios in the leaves of diseased and apparently healthy coconut palms of the root (wilt)-disease-affected tract and healthy palms of the disease-free tract, covering three major soil types of Kerala, namely alluvial (entisols), laterite (ultisols), and sandy (entisols), were examined in relation to the disease. Accumulation of major nutrients, especially K, was generally observed in the leaves of diseased palms. Mg content of leaves of palms growing on laterite soil in disease-affected tract was lower than than of palms in the disease-free tract. The leaf concentrations of La, Ce, Pr, Nd, Sm, Gd and Th did not show significant differences between healthy and diseased palms. The only exception to this trend was Gd whose concentration was less in the diseased and apparently healthy palms growing on laterite soil of the disease-endemic area than that in the healthy palms of the disease-free area. Some of the essential plant nutrients (EPN)/La, and EPN/Ce ratios were significantly different in palms of the disease-affected tract compared to that in palms of the disease-free tract indicating imbalances in the relative concentrations of EPNs and REEs. These results call for more detailed study of the geochemical differences between the disease-affected and disease-free tracts for identification of the soil chemical factors associated with the incidence of the disease. (author)