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Method for estimation of CO 2 (aq) plus H 2 CO 3 °, HCO 3 − and pH in soil solutions collected under field conditions
Author(s) -
Takkar P. N.,
Ulrich Bernhard,
Meiwes KarlJ.
Publication year - 1987
Publication title -
zeitschrift für pflanzenernährung und bodenkunde
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 0044-3263
DOI - 10.1002/jpln.19871500510
Subject(s) - titration , alkalinity , chemistry , analytical chemistry (journal) , titration curve , inorganic chemistry , nuclear chemistry , environmental chemistry
A method for the collection of soil solution and the determination of pH, H 2 CO 3 * (= CO 2 (aq) plus H 2 CO 3 °), HCO 3 − and CO 3 2− , was developed which excluded atmospheric gases during the entire procedure. The soil solution was collected by tension lysimeters without exposure to the atmosphere. Using a closed system, the sample was transferred to a titration beaker for the analysis of pH, H 2 CO 3 * and HCO 3 − . The analysis of CO 2 ‐acidity was done by titration with 0.0454 N Na 2 CO 3 to the end point pH of 8.3. It was immediately followed by an acidimetric titration for the determination of alkalinity using 0.005 N H 2 SO 4 under gentle N 2 flow; the equivalence point was determined graphically from the titration curve. In standard solutions, this method gave nearly 100% recovery of H 2 CO 3 * and HCO 3 − . In soil solutions, the pH markedly increased and H 2 CO 3 * decreased upon exposure to the atmosphere. The values of the sum of CO 2 ‐acidity and alkalinity in soil solutions at a depth > 5 cm agreed well with the values of total inorganic carbon obtained by CO 2 infrared detection following CO 2 degassing. For solutions obtained from 100 cm and 300 cm depth (limestone) the measured distribution of H 2 CO 3 * and HCO 3 − was in agreement with the calculated values based on pH‐measurement and total inorganic carbon. This comparison was unsatisfactory for the concentration of H 2 CO 3 * in solutions of the surface (0–15 cm) soil, possibly because the mathematical model as well as the interpretation of the titration curves did not consider any organic compounds in the solution.