|WILLIAMS, MARK - Pennsylvania State University|
|LIN, HENRY - Pennsylvania State University|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2010
Publication Date: 9/1/2010
Citation: Williams, M.R., Feyereisen, G.W., Folmar, G.J., Lin, H.S. 2010. Experimental system for simulating a natural soil temperature profile during freeze-thaw cycles. Applied Engineering in Agriculture. 26(5):843-848.
Interpretive Summary: In the mid-to-northern latitudes, wintertime daily low temperatures are rising, which is increasing the number of freeze-thaw cycles. The greater number of freeze-thaw cycles has heightened the need to study agricultural soils and the potential change in nutrient losses to surface water, groundwater, and the atmosphere. Laboratory methods are often used to study the effects of freeze-thaw cycles on soil and nutrient losses, but often the methods used do not establish a temperature gradient from the soil surface to the deeper layers of the soil that is similar to field conditions. This paper describes a system that mimics soil temperature gradients that are found in the field by placing an insulated box containing soil into a walk-in freezer. The insulated box held four, 6-in diameter PVC pipes filled with soil that were surrounded by sand. A heating cable was buried in the sand at the bottom of the insulated box to create an upward heat flux. Soil temperatures for the laboratory system were recorded during a period where air temperature changed from 25 to 50°F, then compared to soil temperatures from a field installation for a day with similar air temperatures. The system did a reasonable job of replicating freeze-thaw rates and the temperature gradient observed in the field. This system has also been used to compare nutrient losses from soil after dairy manure was applied under winter conditions. This information will benefit other researchers, policy makers, and producers attempting to minimize nutrient losses to natural waters and maximize use of manure as a fertilizer.
Technical Abstract: The controlled manipulation of freeze-thaw cycles has varied widely among studies and despite their value in demonstrating the mechanisms of freeze-thaw action in soils, many methodologies do not replicate actual field conditions. A simple soil thermal cycling system was developed to address several of the methodological weaknesses observed in previous laboratory experiments and to better assess the effects of freeze-thaw cycles on soil physical properties, water and pollutant transport, and microbial activity. The experimental system consisted of a 61 by 61 by 61-cm insulated bin containing four 15-cm diameter PVC lysimeters encased in sand, with a commercially-available heating cable located in the bottom of the sand mass. The completed assemblage was rolled on a cart into a walk-in freezer and subjected to a range of air temperatures below and above freezing. The heating cable created an upward heat flux representative of heat flow in soil under field conditions. In order to test the system, the heating cable temperature was set to temperatures ranging from 0 to 5 deg C in 1 deg C increments. Observed hourly air and soil temperatures as well as soil temperature gradients and freezing and thawing rates were reported for three freeze-thaw cycles and compared to field values. The experimental system was able to produce a vertical temperature gradient in the soil of 0.08 deg C cm**-1 compared to a 0.07 deg C cm**-1 gradient observed under similar conditions in the field, as well as minimize large fluctuations in subsurface soil temperatures relative to changes in air temperature.