Soil Titratable Acidity to pH = 7 by Filtering the Extract and Controlling the pH with Electrode

Authors

  • Andrés Beretta INIA La Estanzuela, Laboratorio de Suelos, Plantas y Aguas. Ruta 50, km 11, 70.000 Colonia, Uruguay
  • Daniel Bassahum INIA La Estanzuela, Laboratorio de Suelos, Plantas y Aguas. Ruta 50, km 11, 70.000 Colonia, Uruguay
  • Deborah Torres INIA La Estanzuela, Laboratorio de Suelos, Plantas y Aguas. Ruta 50, km 11, 70.000 Colonia, Uruguay

DOI:

https://doi.org/10.31285/AGRO.20.1.8

Keywords:

base saturation, buffered soil extraction, phenolphthalein

Abstract

Whwn measuring the titratable acidity to pH=7 (AT_pH7) the soil is placed down with a buffer solution of pH=7 and the amount of acidity released is quantified with alkali. There is no comparative information about different analytical methods used in Uruguay. The AT_pH7 was measured by three methods: a) the mixture calcium acetate:soil was stirred and allowed a 16 hours rest, the extraction was filtered, and titration at pH = 7 was controlled by electrode (AT_pH7_fil); b) the same as the previous method, but after a 16 hours rest the supernatant was titrated unfiltered (AT_pH7_sob); c) four successive extractions with barium acetate buffered to pH = 7 were done, the extract was filtered and titrated to pH = 7 using phenolphthalein (AT_pH7fen) as an indicator. The AT_pH7fen values were considered as reference. When comparing AT_pH7_sob with AT_pH7_fil the first were considered as reference values. The fit between AT_pH7_fil and AT_pH7_sob was satisfactory. The average difference was 0.36 meq.100g-1 but differences from -1.00 to 1.70 meq.100g-1 were observed. There was no bias in the differences. Some sources of acidity may have remained in the sediment and were not evaluated when titrating the supernatant. The AT_pH_fil overestimated the average AT_pHfen values in 0.73 meq.100g1. The average values of AT_pH_sob and AT_pHfen did not differ. The samples had the same classification according to their base saturation regardless of the method used. Neither the measurement of pH = 7 with electrode instead of phenolphthalein, nor the longest extraction time, or the use of calcium acetate as extractant introduced significant errors of interpretation. The AT_pH_fil method had acceptable precision and accuracy.

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Published

2016-06-01

How to Cite

1.
Beretta A, Bassahum D, Torres D. Soil Titratable Acidity to pH = 7 by Filtering the Extract and Controlling the pH with Electrode. Agrocienc Urug [Internet]. 2016 Jun. 1 [cited 2024 May 22];20(1):45- 50. Available from: https://agrocienciauruguay.uy/index.php/agrociencia/article/view/227

Issue

Section

Soil and Water
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