Soil temperature and water evaporation of small steel and plastic lysimeters replaced daily

Soil water evaporation (E) measured by small, weighable lysimeters is affec ted by their size, construction materials, and replacement frequency. Steel and plastic are commonly used nlaterials, but they have different thermal characteristics. Our objective was to investigate how wall material affects E and soil temperature ofstllall. lysimeters filled daily with undisturbed soil. Research was conducted during 5 days in August 1995 at Bushland, Tex as, where the soil is a Pullman silty clay loam (fine, mixed, thermic Torre rtic Paleustoll, 30% clay, 53% silt). Plastic and steel lysimeters 76 mm lo ng, with inside diameters of 82 and 86 Nm, respectively, were filled each m orning by pressing them into undisturbed soil, and E was determined by mass change. Soil temperatures inside additional steel and plastic lysimeters w ere measured by thermocouples. No significant differences in E due to wall material were measured. For lysimeters of both wall materials, daily E rang ed from 2 to 5 mill, daytime and nighttime E averaged 2.7 mm and 0.5 mm,, r espectively, and total cumulative E was 15.5 mm, Evaporation front small ly simeters was within 5% off from a nearby large, precision, weighing lysimet er. Steel lysimeters were wanner at night near the surface, with significan t differences from 0.5 to 0.9 degreesC, and warmer during the day at the bo ttom, with significant differences from 0.5 to 2.8 degreesC, Plastic lysime ters had greater vertical soil temperature differences than steel lysimeter s, Significant differences inside plastic lysimeters ranged from about 2.0 to 3.5 degreesC greater than those of steel lysimeters during the daytime, and 0.5 to 1.0 degreesC greater during the nighttime, Measured temperature differences were consistent with greater thermal conductivity and enhanced heat transfer in steel sidewalls compared with plastic. Wall material affec ted temperature distribution, but not evaporation, of small lysimeters that were replaced daily.