A 2-year study was conducted to quantify the actual evapotranspiration
(ETa) of three woody ornamental trees placed under three different leaching
fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow
[Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana
Mill.) (nursery seedling selection) were planted as 3.8-,18.9-, or 56.8-liter container
nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances
were maintained. Weekly storage changes were measured with a portable hoist-load
cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25
(theoretical) based on the equation irrigation (I) = ETa/(1-LF). Tree
height, trunk diameter, canopy volume, leafarea index, total leaf area (oak only) and dry
weight were monitored during the experiment or measured at final harvest. Average
yearly ETa was significantly influenced by planting size (oak and willow, P
<= 0.001) and leaching fraction imposed (P <= 0.001). Multiple regressions
accounting for the variability in average yearly ETa were comprised of different growth
and water management variables depending on the species. LF, trunk diameter, and
canopy volume accounted for 92% (P <= 0.001) of the variability in the average yearly
ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on
data from non-water-deficit trees, such that LF, trunk diameter, and canopy volume
accounted for 92% (P <= 0.001) of the variability in the average yearly ETa
of oak. Monthly ETa data were also evaluated, with multiple regressions
based on data from nonwater - deficit trees, such that LF could be ignored. In the
case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P <=
0.001) of the variability in the monthly ETa. Results suggest that
irrigators could apply water to arid urban landscapes more efficiently if irrigations were
scheduled based on such information.
