B. Ludwig et al., USE OF A COUPLED EQUILIBRIUM-MODEL TO DESCRIBE THE BUFFERING OF PROTONS AND HYDROXYL IONS IN SOME ACID SOILS, Zeitschrift fur Pflanzenernahrung und Bodenkunde, 161(5), 1998, pp. 547-554
The buffering of protons and hydroxyl ions in acid soils was studied b
y the addition of small amounts of HCl, H2SO4, and NaOH in consecutive
batch experiments using surface soils and subsoils from two Cambisols
and one Podzol. A chemical equilibrium model was used to study the ma
in buffer processes. The model included inorganic complexation and mul
tiple cation exchange, and also the solubility of jurbanite and Al(OH)
(3) for the subsoils. Buffering of protons was predicted quite well by
the model for the surface soil of the Spodi-Dystric and Spodic Cambis
ols, suggesting that multiple cation exchange was the main buffer proc
ess. For the Podzol surface soil, however, the model overestimated pro
ton buffering by cation exchange considerably. Hydroxyl buffering in a
cid surface soils could be described well by the model for the Podzol
soil only. For the Cambisols, hydroxyl buffer reactions included not o
nly cation exchange, but also solubilization of large amounts of organ
ic matter and presumably deprotonation of dissolved organic carbon (DO
C). Modelling proton and hydroxyl buffering in subsoils suggested that
equilibrium with Al(OH)(3) was not maintained for the Podzol and spod
ic Cambisol. Sulphate sorption had to be considered to describe titrat
ion experiments in all three soils. The assumption of jurbanite being
in equilibrium with soil extracts was useful only for the Spodi-Dystri
c Cambisol.