Measuring and Modeling Transpiration in Relation to Citrus Tree Size using Sap Flow Sensors
- canopy volume,
- water use efficiency,
- irrigation scheduling.
The water requirement of citrus trees changes with tree growth and seasonal evapotranspiration. Therefore, estimation of actual water usage by citrus trees at different times of the year is crucial for accurately scheduling irrigation. The relationship between water loss via transpiration and stem sap flow was evaluated for young and mature citrus trees. Actual transpiration was measured with the heat balance method using Dynagage sap flow sensors (Dynamax, Inc., Houston, TX) attached to the tree trunks or branches. Different sized sensors corresponding to stem or branch size of the trees were installed four times in a year (Nov. 2009, Feb. 2010, May 2010, and Sept. 2010). The sap flow data collected from sensors for 15 days were used to estimate the tree water usage. Canopy volume of each branch or the whole tree was measured and weather data (reference crop evapotranspiration, solar radiation, air temperature, and relative humidity) were downloaded from the Florida Automated Weather Network (FAWN) website. The correlation analyses showed that diurnal and seasonal tree water usage were strongly related to the tree canopy volume and weather parameters. Tree canopy volume and reference crop evapotranspiration (ETo) were used to develop predictive models for tree water usage using multiple regression and partial least squares (PLS) regression analyses. The predictive models could explain more than 80% of the variation in the tree water usage for different time periods of the year, suggesting that tree canopy volume and ETo can be successfully used to estimate water usage by citrus trees of any size for accurately scheduling irrigation.