We don't have synonyms for planosol yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are latosol and palaeosol.
(n) :
A soil with a light-coloured, coarse-textured surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon.
(n) :
A soil with a light-coloured, coarse-textured surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon.