Date of Award
Doctor of Philosophy
Thomas C. Kaspar
An automated tension infiltrometer useful for a range of water tensions from 0.02 to 0.50 m and for infiltration rates of 1 x 10[superscript]-8 to 5 x 10[superscript]-4 m s[superscript]-1 is described. Infiltration rates are calculated from the change in water height in a Mariotte column. Water height is automatically measured by using the difference in tension between two pressure transducers, one installed at the top, and the other at the bottom, of the Mariotte column. Using two transducers increased precision of water height measurement as compared to measurements made with only one transducer. This occurred because tension fluctuations or 'noise' caused by bubbling in the Mariotte column is part of measurement error when only one transducer is used. The new design incorporates several features used or suggested by other workers, including a bubble tower for tension regulation and interchangeable Mariotte columns with different diameters. The latter enables users to match column volume with expected cumulative infiltration. Advantages of the new device include (i) quick and accurate tension control at low tensions, (ii) improved measurement precision at low flow rates, and (iii) automatic measurement and data collection, which increases measurement speed and eliminates bubbling-induced variability. The tension infiltrometer was used in the field to measure unconfined steady-state infiltration rates at three tensions (30-, 60-, and 150-mm water tension) into no-till and chisel-plow tillage systems. Measurements were made on trafficked and untrafficked interrows for each system. The saturated unconfined infiltration rate was determined by using an infiltrometer designed for ponding water on the surface. The infiltrometers accurately measured steady-state infiltration rates from 2 to 300 [mu]m s[superscript]-1. Increasing tension resulted in decreasing infiltration rates for both tillage and traffic treatments. Wheel traffic caused large decreases in infiltration rates for both tillage systems, especially at low tensions. This implies that compaction destroyed more large macropores than small ones. The tension infiltrometer was also used on restructured cores in the laboratory to unsaturated infiltration. The Philip and Swartzendruber infiltration equations were evaluated for their ability to estimate sorptivity and hydraulic conductivity. The Swartzendruber infiltration equation yielded estimates of unsaturated hydraulic conductivity similar to directly measured values of conductivity, while the Philip equation did not.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Mark Dwight Ankeny
Ankeny, Mark Dwight, "Characterization of soil macropores by infiltration measurements " (1988). Retrospective Theses and Dissertations. 8821.