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Laboratory Simulation of Temperature and Hydraulic Head Variations under a Soil Ridge

USDA-ARS National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011

D. C. Reicosky and W. B. Voorhees

USDA-ARS North Central Soil Conservation Research Lab, Morris, MN 56267

*Corresponding author.

ABSTRACT

Temperatures and water content under soil ridges vary temporally and spatially in a complex manner and are difficult to measure under field conditions. A controlled laboratory lysimeter experiment was conducted to study soil temperature and water patterns under sinusoidal ridges. A large soil container was packed with the 2-mm fraction of a Barnes loam (fine-loamy, mixed Udic Haploboroll) to a uniform bulk density of 1.2 Mg/m³. Banks of heat lamps and fans were positioned and computer controlled to simulate solar radiation and wind. A colling plate was installed near the bottom of the lysimeter to induce a thermal gradient throughout the soil profile. For each of three experimental runs, hydraulic heads were measured each morning and afternoon using 170 miniature spring-loaded tensiometers installed at 5-cm grid spacings in the front wall of the lysimeter. Soil temperatures were measured hourly with 64 copper constantan thermocouples buried in a similar grid pattern. Soil started drying most rapidly near the peak and upper slopes of the ridges. Significant rewetting of dried soil occurred during the night period until the hydraulic head (referenced to the furrow height) was less than –300 to –400 mm. After the first few days, most evaporation occurred through the slopes and furrow areas, as evidenced by salt bands that formed on the soil surface. Surface soil temperatures were maximum at the ridge peak or on the upper portion of the south slope.

Received for publication June 3, 1992.