Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2004
Publication Date: 5/5/2005
Citation: Ochsner, T.E., Horton, R., Kluitenberg, G.J., Wang, Q. 2005. Evaluation of the heat pulse ratio method for measuring soil water flux. Soil Science Society of America Journal. 69:757-765. Interpretive Summary: Researchers have difficulty determining the rate of water movement beneath the ground surface. This difficulty introduces uncertainty in efforts to describe or predict subsurface water and chemical movement. This paper verifies the potential of a recently proposed heat pulse method for measuring water flow and identifies key research needs to further develop this method. These findings will benefit the growing number of researchers working to develop and apply this method. Ultimately, the application of this method may enable researchers to better measure the environmental impact of land management practices and to develop improved land management practices to enhance surface and ground water quality, thus benefiting the general public.
Technical Abstract: Soil water flux (J) is an important parameter in many research endeavors, yet few techniques for measuring J in situ are available. In this paper we evaluate the heat pulse ratio method for measuring J. We conducted heat pulse measurements of J in packed laboratory columns of sand, sandy loam, and silt loam soil. Water fluxes were calculated from the heat pulse data following both a traditional temperature increase difference method and a new temperature increase ratio method. Both methods yielded similar estimates of J, agreeing to within 0.87 cm h-1 on average. However, the ratio method permitted simpler calculations and exhibited two to three times greater precision. The ratio method was able to detect J as low as 0.10 cm h-1. We found strong linear relationships (r2>0.98, SE<0.4 cm h-1) between J estimated by the ratio method and J determined from column outflow up to 40 cm h-1. The slopes of these relationships were less than one indicating that the sensitivity to J was less than predicted by the standard conduction'convection model. We propose an empirical reduced convection model which closely matches the measured data. The results of this study suggest that with proper calibration the heat pulse ratio method can be used to accurately estimate J in the range of 0.1 to 40 cm h-1.