A comparison of measured and theoretical soil acidity diffusion coefficients over a wide range of pH

SUMMARY The soil acidity diffusion coefficients have been measured at two P co2 levels with values in the range 2–70 × 10 −9 cm 2 s −1 . The coefficient passed through an ill‐defined minimum in the pH range 5–6.5. Theoretical values, calculated on the basis that the only significant acid‐base carriers in the soil were the H 3 O + ‐H 2 O and H 2 CO 3 ‐HCO − 3 pairs, agreed well with the experimental values over the whole pH range at P co2 = 0.005 atm. Agreement was not so good however at a CO 2 pressure of 0.0003 atm., especially in the neutralalkaline pH range. This was thought to be due to difficulties in maintaining this level of CO 2 throughout the soil samples.