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[Bruce comments] My apologies - this post slipped though a crack somewhere - I hope the trail is not too cold to continue the discussion? Dr. Ioan C. Paltineanu writes Dear Lindsay, In our paper, published in the Soil Sci. Soc. Am J. 61:1576-1585 (1997) on the "Real-time soil water dynamics using multisensor capacitance probes: laboratory calibration" , Dr. J. L. Starr and I reported the results by testing sensors in air and water for a wide temperature range with small linear but opposite effects on the air and water frequencies. Errors associated with frequency readings, at simulated soil temperatures from 10 to 30 deg. C., were calculated to be less than the RMSE for our calibration curve. Nevertheless, we recommended, among others, more calibration research for extremes of soil temperature that can occur diurnally with bare surface soils and seasonally in many climates. As references, we cited Bunnenberg and Khun, 1974, who studied with tritium-labelled vapor the "Movement of water vapor in arid loess soil under conditions of temperature inversion", and Mead, Soppe and Ayars, 1996, "Capacitance probe observations of daily moisture fluctuations". At the recent World Soil Science Congress, held at Montpellier, France, August 1998, Parlange, Cahill, Nielsen, Hopmans and Wendroth presented a "Review of heat and water movement in field soils", published in the Soil & Tillage Research 47 (1998) 5-10. According to their field experiments on the Yolo silt loam of Davis, California, using TDR and platinum resistance temperature detectors (installed at 2, 4, 7, 10, and 15 cm) they demonstrated " the importance of the convective water vapor flux to the mass and energy balances in a diurnally-heated field soil near the land atmosphere interface". Also, they concluded, that: "this convective flux arises from the expansion and contraction of the soil air as it heats and cools over the course of the day"; and that "further measurements of coupled heat and moisture transport in diurnally-heated soils are needed". At the same Congress, another group, Mohanty, Shouse, and van Genutchten, reported experiments conducted at Riverside, California, on the "Spatio-temporal dynamics of water and heat in a field soil" published also in the Soil & Tillage Research 47 (1998) 133-143. In that elaborate experiment the authors used two orthogonal transects comprising 49 regularly spaced (1m) sites on the Arlington fine sandy loam, instrumented with TDR and thermocouple sensors installed horizontally at 2,7, and 12 cm below the soil surface. They concluded that; "a spatio-temporal hysteresis was in soil temperature, while the soil water content exhibited a clustering behavior versus time because of irrigation". As we have now better and much more accurate instruments, I am sure that more work will be reported on this fascinating subject, in order to clarify what is the contribution of the instruments (TDR or capacitance sensors) based on the apparent dielectric constant of the soil-air-water (free and bounded) -chemical elements, and what is the contribution of complex movement of heat and water in unsaturated soil near the land atmosphere interface, particularly under arid and semiarid conditions. If you need some copies of the papers, please give me your address and I will send them by mail. Best regards, Ioan Dr. Ioan C. Paltineanu visiting scientist USDA, ARS, BARC, NRI, ECL Bldg. 007, Room 224, BARC-West 10300 Baltimore Ave. Beltsville, MD 20705-2350 U. S. A. Phone: 301-504-5032 Fax: 301-504-5048 email: ipaltin@asrr.arsusda.gov http://hydrolab.arsusda.gov/ecl