Tuesday, 8 November 2005
10

This presentation is part of: Biogeochemistry of Agricultural Soils

Influence of Selected Soil Properties on the Kinetics of Soil Acid-Base Buffer Reactions.

Mark Rékási, Imre Czinkota, Mária Csubák, and Peter Czanik.

Our work discusses the background of soil acid-base buffer reactions. We investigated the kinetics of acid and base neutralisation - the rate of proton transfer reactions – that alters with the soil properties and characteristics of soil colloids. To describe the kinetics of buffer reactions we applied pH-stat titrations. 25 acidic soil samples were used from different regions of Hungary. Titration at a given pH level (pH8.2 and pH3) was achieved with an equipment and software combination built for this purpose. The measurements were carried out in a 1:40 soil / 1 M KCl solution suspension. For the titration 0.1 M HCl and 0.1 M NaOH solutions were used. To evaluate results the time and added base or acid quantities are extrapolated to infinite time using a function fitted on these data. The duration of measurement was 8 hours. The applied function is the following:

y = C + a1 • (1 - e-k1t)+ a2 • (1 - e-k2t)

Where: C — amount of base or acid to reach the given pH, cmol/kg

y — amount of fed base or acid, cmol/kg

t — time, sec

a1 — base or acid consumption of faster process, cmol/kg

a2 — base or acid consumption of slower process, cmol/kg

k1 — rate constant of faster process, s-1

k2 — rate constant of slower process, s-1

Our aim was to find and describe the relations among parameters of this function and selected properties of soils: pH, clay+silt content, organic matter, hydrolytic acidity, CEC and exchangeable cations. To reveal the connection of these properties with kinetics of acid-base buffer reactions we used stepwise linear regression analysis an correlation analysis.


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