Reevaluation of suspension solutions for soil pH

Abstract

Abstract Soil pH measurements in salt solutions are often used to provide values which are reportedly independent of suspension effect errors. Field plots where soil pH levels, measured in water, had been maintained at about 5.7, 6.2, 6.5, and 7.0 for 15 years were used to determine if salt solution pH measurements are more precise than water for a highly weathered Plinthic Kandiudult of the Southern Coastal Plain in the United States. Soil pH measured in water fluctuates by 0.3 to 0.5 units from winter to summer, possibly due to varying salts in the soil solutions. Comparisons of pH measured in water, 0.01M CaCl2, and M KC1 (2 solution: 1 soil) were made 9 times in the period 1982 to 1985 to determine if some of the seasonal variation could be decreased by a salt‐solution measurement. Mean pH for the 576 samples across 4 pH levels was 6.34 in water, 5.62 in CaCl2, and 5.21 in KCl. The three measurements were highly correlated (r = 0.97 to 0.99) and precise [coefficient of variability (CV) = 3.12% for water, 4.06% for CaCl2, and 3.26% for KCl]. The CV for water over time was also less than for the salt solutions for three of the four pH leveu. Results indicate that pH in water is equal or superior to pH measured in salt solutions for our soils, thus eliminating any need to consider a change which would complicate test interpretations.