WEIGHING LYSIMETERS FOR EVAPOTRANSPIRATION RESEARCH IN A HUMID ENVIRONMENT

Abstract

Three weighing lysimeters were developed for evapotranspiration research at the University of Florida, Instituteof Food and Agricultural Sciences, Plant Science Research and Education Unit near Citra, Florida. The lysimeter designfollowed accepted procedures as well as aspects unique to the study site, including a foundation designed for a perched watertable outside the lysimeters, fetch distance, deep drainage, and lightning protection. Each lysimeter has a planted surfacearea of 2.32 m2 and a soil depth of 1.37 m. The soil in each lysimeter is reconstructed sandy soil originally from theexperimental site. The lysimeter facility includes monitoring wells, an automatic pumping system, and additional lightningprotection system for load cells and soil moisture sensors. The construction materials and installation cost (excluding labor)were $63,443 for the three lysimeters. Lysimeter on-site maintenance, operation, and performance are discussed. Four loadcells with an accuracy of 0.02% (0.12 mm) are used to weigh the average 5.8 Mg lysimeter mass, including the steel lysimetertank and soil. Initial data show that the three lysimeters provided a consistent hourly evapotranspiration (ETc) measurementover a five-day period in the summer season, although many field activities and precipitation events occurred. An additional30 days of daily bahiagrass ETc resulted in a 0.82 ratio between the ETc and Penman-Monteith reference evapotranspirationin November 2003.