Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2000
Publication Date: N/A
Interpretive Summary: Evaporation of water from the soil (E) is an important component of crop water use. It is commonly measured using isolated volumes of soil called lysimeters, which are weighed periodically, and E determined by change in mass. Materials used to construct lysimeters can differ in thermal properties, which may affect energy distribution, soil temperature, and E of lysimeters. We compared soil temperature and E of small steel and plastic lysimeters at locations in Nebraska and Texas, which were filled daily with undisturbed soil, to determine if there was an effect of wall material. When the soil surface was wet and E was high, there was little difference in either soil temperature or E between the steel and plastic lysimeters at both locations. Steel lysimeters showed 14% more E compared with plastic lysimeters at Nebraska when the soil surface was dry. No differences in E were observed at Texas. At Nebraska, as the soil dried, the steel-walled lysimeters conducted heat downward during the day, so tha the soil surface was cooler and the bottom of steel lysimeters was warmer, compared with plastic lysimeters. The opposite was observed during the night. At Texas, as the soil dried, steel lysimeters were warmer than plastic at the surface and bottom. Non-conductive, plastic bottom caps were a barrier to heat flow out the bottom of lysimeters. Additional energy may have been added to steel lysimeters, possibly at the exposed steel wall at the surface. It is recommended that scientists use less conductive material for lysimeter side walls and more conductive material for bottom caps in order to minimize the effects of construction material on soil temperature and soil water evaporation in small, daily replaced lysimeters.
Technical Abstract: Small volumes of isolated soil used to measure soil water evaporation (E) are sensitive to size, construction materials, and replacement frequency. Steel and plastic are commonly used materials, but they have different thermal characteristics. Our objective was to investigate how wall material affects E and soil temperature distribution of small lysimeters which were filled daily with undisturbed soil during two studies in Nebraska and Texas. Plastic and steel lysimeters were 76 mm long, with inside diameters of 82 and 86 mm. Evaporation from steel lysimeters at Nebraska (soil with 14% clay and 47% silt) averaged 14% more than E from plastic lysimeters on four of ten days. There were no significant differences in E at Texas (soil with 30% clay and 53% silt) due to wall material. Daytime temperatures of steel lysimeters at Nebraska were cooler on the surface and warmer at the bottom than those of plastic lysimeters; nighttime temperatures of steel lysimeters were warmer on the surface and cooler at the bottom. At Texas, daytime temperatures of steel lysimeters were slightly cooler on the surface and warmer on the bottom compared with plastic lysimeters when soil was wet and E high, but surface and bottom temperatures became warmer as soil dried and E decreased. Nighttime surface temperatures of steel lysimeters were warmer than those of plastic. Temperature differences due to wall material were smallest when most energy was consumed as latent heat and increased as soil dried and E decreased. Wall material should have low thermal conductivity to minimize heat transfer, and bottoms should have high conductivity and good contact with field soil to allow heat transfer out of the lysimeter.