What is ionic exchange ? How does it occur between root and soil?

Ionic exchange is the exchange of ions between a cell or root and the external medium. It occurs between root and soil by two methods :
(a) Carbonic acid exchange : C02 produced in { respiration dissolves in water to form carbonic acid. Carbonic acid dissociates into hydrogen ions (H+) ; and bicarbonate ions (HC03)
H02 + C02 H2C03 H+ + HC03
Contact exchange : H+, OH’ or HC03_ ions adsorbed over the surface of root can directly get exchanged with similarly charged ions present over the surface of soil particles of oscillatoria volumes overlap