Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 1996
Publication Date: N/A
Interpretive Summary: As a society we want to reduce runoff of farm chemicals and erosion of soil. A tool called a "tension infiltrometer" makes possible field measurements that many people believe will help determine how much runoff and erosion could occur. We evaluated the tensiometer as it is typically used, and found that it is not a reliable tool for runoff and erosion research. We recommend that the tension infiltrometer not be used as the only tool for determining water movement into soil. Researchers would want to supplement tension infiltrometer measurements with other data so they can determine how much runoff and erosion could occur at a given site.
Tension infiltrometers have been extensively used to determine soil hydraulic properties, but the validity of short-term, quasi steady-state measurements has been questioned. The objective of this study was to determine the validity of short-term measurements by monitoring 100 min of tension infiltration. In September 1991, six replicate measurements were made, without preponding, at each of two negative heads (-30 and -60 mm) using a small base (76 mm) infiltrometer. In August 1992, two replicate measurements were made at the same two negative heads, both with and without preponding, for both 76 and 230 mm base infiltrometers. Measurements were also made at a head of -150 mm using the small base infiltrometers, with no preponding. The infiltration rates across the measurement time were variable, both increasing and decreasing. In two cases, extreme variation in the applied negative head may have contributed to the variation in infiltration rate, but for the other 28 cases, the applied head variation did not influence the infiltration rate variation. Temperature changes during the measurements were small compared with temperature difference between the two measurement dates. Other factors such as poor wettability due to water repellency, heterogeneous soil structure, and/or changes in soil structure during the measurement probably contributed to the transient infiltration rate variations. The magnitude of transient infiltration rate variation should be observed relative to spatial and temporal variations.