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Comparison of Soil pH Methods on Soils of North America
Author(s) -
Miller Robert O.,
Kissel David E.
Publication year - 2010
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2008.0047
Subject(s) - soil water , soil ph , chemistry , soil test , nutrient , environmental chemistry , soil science , environmental science , organic chemistry
Soil pH, one of the most routine measurements performed, is used to interpret chemical reactions, nutrient availabilities, and the rates of many biological processes in soils. Predominantly, soil pH is measured in soil–water suspensions using a glass H + ‐sensing electrode and a reference electrode. Soil/water ratios of the suspensions ranging from saturated paste to 1:5 are used in research and commercial soil testing laboratories. The objective of this study was to evaluate relationships between pH measured in saturated paste extract (pH sp ), 1:1 and 1:2 soil/water suspensions (pH 1:1w and pH 1:2w ), and 1:1 and 1:2 soil/0.01 mol L −1 CaCl 2 suspensions ( pH 1 : 1 CaCl 2andpH 1 : 2 CaCl 2 ) . In addition, the effects of soil suspension electrical conductivity (EC 1:1w ) on measured values of soil pH were assessed. Analytical results for 120 agricultural soil samples from a laboratory proficiency program database indicated that the relationship between pH 1:1w andpH 1 : 1 CaCl 2was highly significant (r 2 = 0.984). Similar regressions were found between pH sp andpH 1 : 1 CaCl 2, and between pH 1:2w andpH 1 : 2 CaCl 2The EC 1:1w explained 85.1% of the variation in the difference between pH 1:1w and pH 1:1CaCl A model comprised of a linear term of pH 1:1CaCl and a nonlinear term EC 1:1w explained 99.5% of the variation in soil pH 1:1w , with the estimated pH of 88% of the soils between ±0.10 pH units of the measured pH 1:1w Results for individual soils indicated that a nonlinear function using matrix EC explained >98% of the variation in soil pH across a range of soil/water ratios and suspension matrices ranging from 0.00 to 0.01 mol L −1 CaCl 2 It is our assertion that the current practice of determining soil pH in soil–water suspensions of low ionic strength results in a significant analytical measurement error associated with liquid junction potentials of a glass reference–H + electrode system. For soil diagnostic analysis purposes, we concluded that the measurement of soil pH using 0.01 mol L −1 CaCl 2 solution at a soil/water ratio of 1:1 is a more robust measurement for soils of North America.