|Horton, Robert - IOWA STATE UNIVERSITY|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 24, 2006
Publication Date: June 5, 2006
Citation: Ochsner, T.E., Sauer, T.J., Horton, R. 2006. Field tests of the soil heat flux plate method and some alternatives. Agronomy Journal. 98:1005-1014. Interpretive Summary: Environmental and agricultural scientists often need to measure rates of heat flow in soil. This information is utilized in studies of crop water use and carbon sequestration. Heat flux plates are commonly used to measure soil heat flow. This manuscript demonstrates the inaccuracies in the plate method and describes some promising alternative methods. Summertime soil heat flow was measured with plates and with alternative methods at each of three sites. The standard plate method underestimated the soil heat flow at all sites. The underestimates ranged from 18 to 66%. Agreement between the alternative methods was good with discrepancies ranging from 2 to 6%. The data show that the three needle gradient method is a viable successor to the plate method. The self-calibrating plate method also shows potential. Scientists who measure heat flow in soil will benefit from these findings. Our results may help them improve the accuracy of data on, not only soil heat flow, but also the related processes of crop water use and carbon sequestration.
Technical Abstract: Heat flux plates are commonly used to measure soil heat flux, a component of the surface energy balance. The plate method is simple and precise, but several previous studies have demonstrated the potential for relatively large errors. Here we present the results of in situ tests of the plate method, and we describe some promising alternative methods. Summertime soil heat flux was measured with heat flux plates and with two alternative methods at each of three sites. In total, three alternative methods were used: a single probe gradient method, a three needle gradient method, and a self-calibrating plate method. The standard plate method underestimated the magnitude of the heat flux at all sites. The underestimates ranged from 18 to 66% for the four types of plates we tested. Agreement between the alternative methods was good with discrepancies ranging from 2 to 6%. The plates underestimate flux apparently due to a combination of low plate thermal conductivity, thermal contact resistance, and latent heat transfer effects. The three needle gradient method for measuring heat flux performed well at all three sites, providing a good alternative to the standard plate method. The self-calibrating plate method performed well at the one site where it was tested and may also be a good alternative. Increased adoption of these methods should lead to more accurate soil heat flux and surface energy balance data.