REEVALUATION OF SUSPENSION SOLUTIONS FOR SOIL-PH

Soil pH measurements in salt solutions are often used to provide value s 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 sa lt solution pH measurements are more precise than water for a highly w eathered Plinthic Kandiudult of the Southern Coastal Plain in the Unit ed States. Soil pH measured in water fluctuates by 0.3 to 0.5 units fr om winter to summer, possibly due to varying salts in the soil solutio ns. Comparisons of pH measured in water, 0.01M CaCl2, and M KCl (2 sol ution: 1 soil) were made 9 times in the period 1982 to 1985 to determi ne if some of the seasonal variation could be decreased by a salt-solu tion 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 w ere highly correlated (r = 0.97 to 0.99) and precise [coefficient of v ariability (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 level;. Results indicate that pH in water is equal or superior to pH measured in salt solutions for our soils, thu s eliminating any need to consider a change which would complicate tes t interpretations.