1.  Research Objectives

The aim of this study is to investigate the effect that diurnal temperature changes have on water movement through soil and how that water movement is affected by the presence of rocks on the soil surface.

2.  Approaches, Systems and Experiments

Initial experiments involved using psychrometers which were extremely temperature sensitive and which reduced their usefulness under laboratory conditions.  The use of alternate types of sensors that could be used in the small experimental setup was necessary.  A basic gypsum block was constructed comprised of three electrodes (a micro stereo plug) embedded in a small cylinder of gypsum (Plaster of Paris, CaSO4).  A measurement is taken from a gypsum block by measuring the electrical resistance between the electrodes in the block using an AC-half bridge.  The block transmits water easily and rapidly comes into equilibrium with the soil water. The gypsum block measures soil moisture tension in the 60 to 600kPa range.

3.  Problems Encountered:

Gypsum blocks need to be electrically isolated, although preliminary tests suggest that the low voltage and low conductivity of the soil medium may reduce this problem.  Individual calibration of each sensor will be necessary.

4.  Major Accomplishments:

Tests of the new sensors is still underway but results indicate that the blocks are not very temperature sensitive (top of figure) and can measure water content of sandy soils from near-saturation to almost total dryness, and then quickly respond to increased moisture availability (bottom of figure).

Figure 19 - variation in temperature and water potential over time within heterogeneous soil

5.  Future Goals and Objectives:

Measurements of water movement through soil in the cylindrical tank will resume after 60 of the new sensors have been constructed and they have been calibrated.

PEOPLE

Faculty:

Philip Rundel

Staff:

Eric Graham