Theses and Dissertations

Title: Pond Soil pH Measurement

Name: Taworn, Thunjai

Degree: MS

Chair: Claude E. Boyd


University: Auburn University

Location: Auburn, Alabama

Date: 2001

Pages: 82

Keywords: pH,water quality,soil


Different methods for determining pH give significantly different results. I attempted to standardize methods, taking into account needs for accuracy and implementation. Dual electrodes (indicating and reference) and a single-probe combination electrode gave similar pH values when inserted into 1:1 mixtures of dry soil and distilled water. There were slight differences in pH between readings with dual and combination electrodes when the dual electrodes were arranged with the indicating electrode in the sediment phase and the reference electrode in the supernatant phase of the mixture. The two-phase method with the dual electrode does not appear warranted because of greater difficulty in making measurements. Dry soil:distilled water ratios of 1:2.5, 1:5, and 1:10 had progressively greater pH readings than obtained at a 1:1 ratio. Measurements made in 0.01 M CaCl2 and 1.0 M KCl had much different values than those made in distilled water. Higher pH resulted when pH was measured without stirring or in filtrates of soil-water mixtures. A 20-min period of intermittent stirring before making measurements was necessary for a stable pH value. Particle size did not influence pH in aliquots passing 0.053 to 2.36-mm sieves. Drying temperature had a strong influence on pH, and measurements made on samples dried at 60 °C are probably most reliable. Measurements of in situ pH in wet soil with standard pH electrode or a portable acidity tester differed greatly from those made in 1:1 dry soil to distilled water mixtures. Pond bottom soil pH measurement should be standardized. Based on findings of this study, the following method is suggested: dry soil at 60 °C in a forced-draft oven: pulverize soil to pass a 2.36-mm sieve: mix soil and distilled water in a 1:1 ratio (weight:volume): stir intermittently with glass rod for 30 min: insert dual electrodes or a combination electrode into the mixture: measure pH while stirring.

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