Determining Minimum Irrigation Coefficients for Landscape Trees Based on Evapotranspiration and Public Opinion

The objective was to determine the minimum amount of water required to maintain aesthetically pleasing landscape trees. Beginning in 2009, 63 trees produced in 27 L containers were transplanted into a sand soil under a double polyethylene covered, open-side gutter-connected greenhouse in Apopka, Florida. The first species were Quercus virginiana, and Ulmus parvifolia. Trees were transplanted in late August with abundant irrigation and allowed 6 months for root establishment. In late February the following year, irrigation volumes were estimated based average on trunk cross-sectional measured 30 cm above ground level, using models previously determined for each species derived from 5 to 6 years of weighing lysimeter data and daily ETo. Irrigation was based on ETo measured inside the structure and at 3 reduced percentages below 100%, to 55%. In late August tree farmers, municipal arborist, extension agent, master gardeners and homeowners rated 8 trees of each irrigation rate randomly distributed with the greenhouse.  This was repeated in 2010 with Magnolia grandiflora and Acer rubrum; and in 2011 with Pinus elliottii and Ilex opaca ‘East Palatka’ species.  Most species were rated aesthetically acceptable at irrigation rates of 55% of ETo. However shoot growth was greatly reduced.  Acer rubrum trees all died.