However, when you look at the amount (per unit area) of leaf litter and soil nutrients they still don't compare to the amount of nutrients we pour onto our plants during routine "feeding"......except in a cornfield.
Consider that there may be more "clay"
in (not under) the leaf litter than the reports show. Also clay particles collect in the root area of epiphytes.
Fine dust particles settle on the canopy foliage and wash down through epiphytic plants and on to the litter. When it does not rain in the rainforest leaves are covered in dust.This is probably not really considered by the investigators because it is almost invisible, but is is there. These minute clay particles may contribute a lot to ionic exchange of orchid roots. Or maybe not, but it should be considered.