FREEZE-THAW AND WINTER TEMPERATURE OF AGRICULTURAL SOILS IN INTERIOR ALASKA

Freeze-thaw and winter temperature of soil influences the viability of perennial plants, yet the thermal regime of agricultural soils is virtually unknown in interior Alaska. The frequency of daily freeze-thaw events in the spring and fall, winter temperature minima, and the duration of critically-low winter temperatures in the plant root zone (0.05 to 0.40 m depth) were ascertained from daily air and soil temperature data collected from September 1987 through May 1992 at Fairbanks (64-degrees-51'N) and Delta Junction (63-degrees-55'N). Soil freeze-thaw events at both stations occurred more frequently in spring than in fall and were influenced in part by snow cover. At Delta Junction, where persistent winds result in thin snowpacks, the lowest soil temperature observed during this study was -29.1-degrees-C. Temperatures at 0.05 m were lower than 0-degrees and -15-degrees-C (lethal temperature of winter grains and legumes) for 169 and 14 consecutive days, respectively. At At Fair-banks, the lowest soil temperature was -12.3-degrees-C. This study suggested that snow management on agricultural fields in interior Alaska can influence the frequency of soil freeze-thaw and the occurrence of lethal winter temperatures.