Poind Soil pH Measurement

Abstract

Soil pH often is measured in samples from the bottoms of aquaculture ponds. Several different techniques for soil pH are used. This study considered the differences in pH obtained by the different methods and determined which methods appeared most useful. 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 40 to 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‐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.

Lime application methods, water and bottom soil acidity in fresh water fish ponds

“…Soil samples were oven dried at 60 o C in a mechanical convection oven and pulverized through a 40-mesh screen (0.425-mm openings). Soil pH was measured in 1:1 mixtures of dry soil and distilled water (Thunjai et al, 2001). The exchangeable acidity was measured by the change in pH caused by adding 5 g soil to 10 mL of a p-nitrophenol buffer solution (Adams & Evans, 1962).…”

A New Calibration Free pH‐Probe for In Situ Measurements of Soil pH

“…The values obtained by the in situ measurements and the moistened samples do not differ significantly. This indicates, that the drying process does not play such an important role for the measurement of these arable soils with a glass electrode as was described by [10,14] for measurements in pond soil samples. On the other hand, the suspension effect influences strongly the pHvalues obtained with the glass electrode, as it was described in the literature [10].…”

“…This indicates, that the drying process does not play such an important role for the measurement of these arable soils with a glass electrode as was described by [10,14] for measurements in pond soil samples. On the other hand, the suspension effect influences strongly the pHvalues obtained with the glass electrode, as it was described in the literature [10]. In contrast to the findings for the glass electrode, the pH-values determined with the soil pH-probe do not differ significantly in case of all the measurement procedures.…”

“…To obtain soil solutions, a treatment was followed as suggested by Thunjai et. al [10]: The samples were dried at 60 8C for 48 hours in a drying oven and then sieved through a 2 mm mash. The dry material of each sample was homogenized, and 25 g were suspended in distilled water in a 1 : 2.5 weight ratio.…”

“…Until now there is no single and general accepted method for measuring the pH of soils or sediments [8,9]. Several studies have shown that the measured pH values depend strongly on the analytical conditions such as soil to solution ratio, the way and time of suspending the soil (stirring or shaking), the way of pH measurement (suspension effect) and the nature and concentration of the salt solution [10,11]. The most commonly accepted procedure is to collect a certain amount of soil sample, dry and sieve it in laboratory, suspend the dried material in water or salt solutions (KCl, CaCl 2 ) and measure the pH with a standard glass electrode [10].…”