EQUIPMENT

1. Digital pH meter.
2. Combination pH electrode.
3. 20 mL calibrated soil scoop.
4. 3 ounce wax coated paper cups.

PROCEDURE

1. Scoop 20 mL soil into a paper cup.
2. Add 20 mL deionized water and let stand for 30 minutes.
3. Calibrate the pH meter according to directions given in the instrument manual, using pH 7.00 and pH 4.00 buffers.
4. Immerse the combination electrode in the soil-water suspension.
5. While stirring, read the soil pH to the 0.1 pH unit.
6. If the water pH is less than 6.0, or the soil sample requires recommendations for alfalfa, set the sample aside for later determination of lime requirement.

QUALITY CONTROL

1. The pH of the check soil must be within 0.2 pH units of the established value.
2. The pH of the redip samples must be within 0.2 pH units of the original values.

REFERENCES

1. Peech, M. 1965. Hydrogen-ion Activity. In C. A. Black(ed). Methods of Soil Analysis, Part 2, Chemical and Microbiological Properties #9, Amer. Soc. Agron. Madison, Wisconsin., pp 914-925.
2. Schofield, R. K. and A. W. Taylor. 1955. The Measurement of Soil pH. Soil Sci. Soc. Amer. Proc. 19:164-167.