|Pikul Jr, Joseph|
Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: 1/2/2001
Publication Date: 5/10/2006
Citation: Pikul, J.L. Jr. Diurnal freeze/thaw: Temperature and water distribution. In R. Lal, (Ed.) Encyclopedia of Soil Science, 2nd Edition. pp. 485-487. Taylor and Francis, Inc. New York. 2006. Interpretive Summary: In northern climates throughout the world, periodic freezing and thawing of soil is common. Estimates are that approximately 30 percent of the earth's landmass is periodically frozen and that an additional 20 percent of the landmass is underlain by permafrost. Some of the world's most productive soil lies within regions where soil may be seasonally or diurnally frozen. Freezing and thawing of soil exerts a profound effect on soil water distribution, solute movement, soil physical and chemical condition, biological processes, and hydrology. There are very few land-management options available to lessen the effect of freezing weather on the soil thermal environment. But, management that maintains surface cover can reduce the incidence and penetration depth of frozen soil on croplands. Crop residue cover was shown to reduce the incidence and depth penetration of frozen soil. Reduction of soil freezing events could be expected to reduce soil water evaporation, soil surface crusting and undesirable movement of agricultural chemicals.
Technical Abstract: To quanitfy the effect of surface cover on heat and mass transport during diurnal freeze-thaw, field studies included plots that were residue covered and plots that were bare. During one freeze-thaw cycle, the soil did not freeze on plots with residue cover, but froze to about 1.5 cm on plots with having a bare surface. Minimum soil temperature at 0.25 cm was -0.8 degrees C. Soil temperature in residue covered plots hovered near 0.0 degrees C during the night. Concurrent with the decrease in soil temperature to below freezing was an increase of soil water content in the bare surface plot. Soil water content under residue cover remained essentially unchanged throughout the night. On bare surface plots, soil water content of the surface 0.5 cm layer increased from 0.28 kg/kg at 2400 h to 0.45 kg/kg at 0600 h. Soil water content includes both liquid and ice. Both the bare surface and residue covered plots entered the freezing cycle at about the same water content. Surface cover created a unique microclimate affording thermal protection to soil thereby reducing the incidence and severity of frozen soil and associated water movement.