Propagation of pH Changes Through Soil

Changes in pH are propagated by the movement of protons. Bnt because free protons do not exist they must move by transfer between proton donors and acceptors, i.e. Bronsted acids and bases  

Consider the balance of acid, HS, between two imaginary planes of unit cross-section at X and x - - 5x in the soil. The general reaction of the acids and bases with the soil may be written 

It is assumed that the impedance factor, /l, is the same for all mobile acids and bases. It is also assumed that the solid equilibrates rapidly with the adjacent solution in cases where it does not, terms for the rates of reaction can be added to the equation. 

The term 9[HB]/9x in Equation (2.27) is expressed in terms of 9[HS]/9x as follows. The pH buffer power of each acid-base pair is defined as  

However, because in general there is no net flux of component B, d[B ] = -d[HB] and 

---