
Contents
2.8.02
AOAC Official Method 994.17
pH Measurement of Saline-Sodic Soils
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Published:January 2023
Cite
pH Measurement of Saline-Sodic Soils', in Dr. George W Latimer, Jr. (ed.), Official Methods of Analysis of AOAC INTERNATIONAL, 22nd Edition (
Extract
First Action 1994
Final Action 1997
[Applicable to pH measurement of saline-sodic soils (i.e., containing large amounts of soluble salts and sufficient exchangeable sodium to interfere with growth of most crop plants).]
See Table 994.17 for results of the interlaboratory study supporting acceptance of the method.
Interlaboratory study results for pH measurements in soil paste
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Principle
Water is added to air-dried soil until saturated paste is obtained and pH is measured. For determination of sodium adsorption ratio, salt analysis is performed on saturation extract from paste.
Apparatus
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Reagents
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Calibration
Calibrate pH meter to appropriate setting using two standard buffers, C(b), depending on type of laboratory sample. If reading of second standard buffer is not within 0.05 pH unit after adjusting to first standard buffer, follow manufacturer’s instructions for recalibration.
Preparation of Standard Soils
Use three different standard soils (air-dried) of known pH, covering pH range of test samples. Weigh 50–250 g air-dried soil into paper cup or glass beaker. (Note: Use smaller amounts of soil for pH measurement only; use larger amounts to obtain sufficient volume of saturation extract for other measurements.) Wet soil with H2O, C(a), while stirring with spatula. [Note: Calibrated volume of soils may be substituted for weighing. Alternatively, add sufficient amount of soil to known volume of H2O to obtain saturated paste. Moisture content in soil may vary (25–100%) depending on soil texture, clay mineralogy, and content of organic matter.]
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