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TECHNICAL NOTES

The Dual Gravimetric Hot-Air Method for Measuring Soil Water Diffusivity

^a Dep. of Biosystems Engineering and Soil Science, Univ. of Tennessee, 2506 E.J. Chapman Dr., Knoxville, TN 37996
^b Agricultural Experiment Station, Univ. of California–Riverside, 770 El Caballo Dr., Oceanside, CA 92057
^* Corresponding author (jtyner{at}utk.edu)

Received 9 June 2006.

The hot-air method provides rapid measurement of a soil's unsaturated hydraulic diffusivity function. The original method consists of blowing hot air across one end of a soil column for a short period, and then quickly extruding, dissecting, and oven drying the soil to provide the soil water content profile, which is used to calculate the soil's unsaturated hydraulic diffusivity. This research presents a novel approach to measuring the soil water content profile during a hot-air test. During the drying process, a soil column is suspended in a horizontal position by a load cell attached at each end. The measured change in force from the two load cells enables calculation of the soil water content profile, without soil extrusion, dissection, and oven drying. Because the test is nondestructive, it permits estimation of the water content profile and calculation of the unsaturated hydraulic diffusivity function at multiple times. Similarity of the diffusivity functions at various times during the drying process provides evidence of proper testing conditions, a utility not available with the destructive approach. We applied the method to a silt loam and a clay loam and both soils achieved a RMSE of 0.012 compared with the traditionally measured water content profile. We also modeled the performance of the new method on previously published hot-air water content profiles and achieved similar results.