A radiometric sensing approach to measure turfgrass evapotranspiration

A method which accurately and efficiently measures turfgrass evapotranspiration is necessary for proper evaluation of water use characteristics for germplasm screening. Chapter 2 evaluates the current methods of measuring small plot scale turfgrass water use and an energy based evapotranspiration mapping algorithm method based upon surface temperature to determine instantaneous evapotranspiration. Our analysis showed that the energy budget method correlated well to the Bowen Ratio, a standard in evapotranspiration measurement, and has potential for use in turfgrass research. However, soil heat flux, a significant part of the energy budget, is required to determine instantaneous evapotranspiration and can be difficult to measure. Chapter 3 evaluated the relationship between net radiation and soil heat flux and proposes a method of soil heat flux prediction from net radiation. This researched indicated that daytime hourly linear relationships can be used to predict soil heat flux for instantaneous measurements within five percent mean absolute difference of available energy. Chapter 4 evaluates the use of the instantaneous ET method to measure turfgrass water use during and induced drought period. Phenotypic responses were also measured. This study showed there are differences in drought response between species and cultivars. Tall fescue cultivars retained green color longer than fine fescue or Kentucky bluegrass. Instantaneous evapotranspiration measurements indicated grasses which have greater instantaneous evapotranspiration show better drought response, according to retaining green canopy color. This research also suggests grasses which have greater instantaneous evapotranspiration after only a few weeks of drought may also have greater water use later in a drought and better green color retention in the canopy. This relationship may make germplasm screening for drought response easier by minimizing the need for extended droughts and rainout shelters. This research offers a new approach to measure turfgrass evapotranspiration in the field on a small plot compared to micro-lysimeters which often provided inaccurate measurements. It also provides a rapid and energy efficient method to measure instantaneous evapotranspiration during a drought period for analyzing drought response between turfgrasses species and cultivars.