SOIL-WATER PRESSURE MEASUREMENTS IN SUBZERO AIR TEMPERATURES

Air temperatures below freezing often preclude soil water pressure measurements with tensiometers. The use of antifreeze solutions: facilitates tensiometer use in weather when air temperatures are below 0 degrees C yet the soil remains unfrozen, We studied the applicability of methanol concentrations ranging from 100 to 500 cm(3) L(-1). Soil water pressures were measured with ceramic cup tensiometers installed at 15-cm depth within 38-L-capacity buckets, Experimental temperatures were -2, 0, 5, and 15 degrees C. The pressures ranged from 0 to -60 kPa, Readings of the tensiometer with the methanol-water mixture were within 0.6 kPa of that of the tensiometer with pure water, No statistically significant difference (alpha = 0.05) in soil water pressure was found between the methanol-water mixtures and the pure water system using 1:1 lines and the Wilcoxon signed rank test for paired data. The results indicate that field tensiometer data may be collected in unfrozen soils by the use of the appropriate methanol concentration based on the temperature range expected.