mold

blackland, clay, gault [chiefly British], gley, guck (or gook), gumbo, kaolin, muck, mud

dust, gravel, sand

humus, loam, topsoil

alluvium, colluvium, detritus, loess, marl, sediment, shingle, silt

duff, mull

subsoil, substratum

sour, turn, turn off [British]

contaminate, defile, pollute, taint

addle, curdle, ferment

mortify

rust

crumble, decline, degenerate, descend, deteriorate, dilapidate, sink, wither