Modelling pH buffering and aluminium solubility in European forest soils

Citation
S. Lofts et al., Modelling pH buffering and aluminium solubility in European forest soils, EUR J SO SC, 52(2), 2001, pp. 189-204
Citations number
39
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Agriculture/Agronomy
Journal title
EUROPEAN JOURNAL OF SOIL SCIENCE
ISSN journal
1351-0754 → ACNP
Volume
52
Issue
2
Year of publication
2001
Pages
189 - 204
Database
ISI
SICI code
1351-0754(200106)52:2<189:MPBAAS>2.0.ZU;2-9
Abstract
The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation ac idity. The chemistry of sail organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Neverth eless, models of humic substance chemistry have been developed, one of whic h is WHAM-S, which contains a model (Model V) of proton and metal binding a t discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAMS to model so lution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting t he amounts of soil aluminium and humic substances within defined limits, ta king the contents of copper chloride-extractable Al and the base-extractabl e organic matter as starting values. The model simulated both pH and dissol ved Al well with optimized amounts of aluminium and humic substances within the defined Limits (root mean squared error for pH from 0.01 to 0.22, for p[Al](aq) (total dissolved Al) from 0.03 to 0.49, five data points). Contro l of dissolved Al by dissolved organic matter was important particularly at above-ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)(3). The optimized model also gave reas onable predictions of pH and dissolved Al in supernatants obtained by repea ted leaching of the soil horizons. The results show that humic substances d ominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)(3) occurs but is the exception.