In the absence of counter-measures such as liming, the natural process is for soil to become gradually more acid if for no other reason than the fact that rainfall is weakly acidic.
Oni ddefnyddir mesurau megis calchu i wrthweithio’r broses, y broses naturiol fydd i’r pridd ddod yn fwy asidig dros amser gan bod glaw ei hun yn asid gwan iawn.