MANASOTA & PEACE RIVER BBDs Meeting Notebook 10-21-09.docx

B265
Optimizing Irrigation For Shade Tree Production
Project Type Basin Initiatives
AOR(s)
Water Supply, Flood Protection, Water Quality
Basin(s) Alafia River, Hillsborough River, Withlacoochee River, Peace River, Manasota
Cooperator(s)
University of Florida
Project Manager COHEN, RON
Task Manager(s)
Status Ongoing
Description
There are over 5,000 acres of nursery production in the central part of the District and typically they are permitted for
about 1.7 million gallons of water per acre. With the increase of urban development, it is anticipated that the number of
nursery acres will increase and landscape water use will too. This project will investigate ways to reduce nursery and
landscape irrigation by studying the relationships between moderate water stress, photosynthesis and shoot growth of
trees. The goal of the project is to develop irrigation management strategies that take advantage of gas exchange
properties occurring at moderate water stress. These strategies would be linked to the ongoing projects modeling tree
water use based on ETo, further increasing the level of irrigation precision of non-production situations beyond that
which will come from the ETo projects. Plant growth is a two stage process. First, new cells are produced by
meristematic tissues. Second, these cells enlarge. The first phase mainly requires new cellular components which are
derived from photosynthesis and absorbed minerals. The principal requirement for the second phase of growth, cell
enlargement, is hydrostatic (turgor) pressure. Plant water status, mainly as it affects cell turgor pressure, is the primary
driving force in this second phase. In pecans, nearly all leaf expansion occurred at night (Anderson, 1989). This is the
time when water stress in plants is the lowest, and water status and turgor pressure are the highest. This is
hypothesized as the primary reason cyclic irrigation of containerized plants accelerates growth, in that it results in
higher turgor pressures during the night by making more water available in the root ball late in the day. While this
information on leaf expansion was reported in the scientific literature over 10 years ago, it was never pursued much
further and will be investigated in this project.
Benefits
Information from this project will help nursery producers, commercial landscapers and homeowners reduce water use.
The amount of water saved will be a function of the number of acres planted and their water use, which will change
annually based on market and climatic conditions. Assuming an annual 5% water savings from only nursery
production, there would be a total of about 1.9 mgd savings on permitted water use. In addition, information form this
project can be used by the District's FARMS program to help promote water conservation.
Costs
This four year project will cost the District a total of $83,875. Funding for this project is prorated between five Basin
Boards (Peace River - 23%, Hillsborough River 22%, Alafia - 18%, Manasota 18% and Withlacoochee 11%) based on
the number of permits for nursery production in their watershed. In FY2009, FY2010, FY2011, and FY2012 the Basin
Boards will budget each year: Peace River $5,159, Hillsborough River $5,008, Alafia River $4,103, Manasota $4,103
and Withlacoochee River $2,595.
Additional Information
Recently, data collection of a project at MREC supported by the Southwest Florida WMD, Horticultural Research
Institute and others quantified the daily water use of live oak and red maple to 7-inch calipers, and Nellie R. Stevens
holly to 5-inch calipers. Preliminary modeling of red maple reported a high correlation of predicted and actual water
loss based on a algorithm incorporating reference evapotranspiration (ETo) and trunk cross sectional area just below
the first major branch (Beeson, 2007). A project with a similar goal using D.D. Blanchard magnolia, Aliee, Chinese elm
and slash pine is currently in the second year. Maximum plant growth occurs when transpiration is maximum because
transpiration and photosynthesis are tightly linked. Reductions in stomata aperture reduce the flow of carbon dioxide
into leaves and water out of leaves. However, for the limited number of tree species studied, slight to moderate
reductions in stomatal aperture cause no to small reductions in photosynthesis, but resulted in relatively large
reductions in transpiration. Thus under moderate water stress, trees and woody plants, in general, tend become more
water efficient with little reduction in photosynthesis (Noble, 1999).
021 - Manasota Basin 166