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

B241
Reduction of Water Use for Citrus Cold Protection
Project Type Basin Initiatives
AOR(s)
Water Supply, Water Quality
Basin(s) Alafia River, Peace River, Manasota
Cooperator(s)
University of Florida
Project Manager COHEN, RON
Task Manager(s)
Status Completed
Description
This is a multi-agency agricultural water conservation project to assist citrus producers in reducing water use for cold
protection. The project is an expansion and enhancement of a previously successful Peace River and Alafia Basin
Board project (B137). That project was taken statewide by FDACS, SFWMD and SJRWMD. Florida citrus growers use
low volume irrigation to conserve water and to provide a more effective method of freeze protection. One characteristic
of low volume irrigation used for citrus freeze protection is that the decision to use irrigation must be made prior to the
water in the lateral irrigation lines reaching freezing temperatures of 32 degrees F. This project would develop
site-specific methodology to accurately determine minimum temperatures the next morning based on sunset
temperatures recorded the previous evening. This allows for multiple temperature observations on cold nights from the
growing area providing necessary replication of the Brunt equation. In addition, this project will help disseminate this
information in newsletters and other sources, including FAWN to help the growers conserve water.
Benefits
The water saving would be a function of acres normally protected and gallons of water per acre per hour. Systems
started at 8:00 p.m. and operated to 8:00 a.m. the following morning at 100 trees/acre and 10 gallon/hour emitters
would require 12,000 gallons of water per acre per night of freeze protection. This volume represents a total of 0.44
acre-inches of water used for freeze protection per night. Implementation of this methodology by 10% of the permitted
citrus acreage within the Alafia, Manasota and Peace River Basin Boards (35,526 acres) would result in a water
savings of 424,458,000 gallons of water per non-critical freeze night.
Costs
This three-year project will cost $15,000. About 90% of the permitted citrus acres are within three basin boards and
project costs have been prorated between the Alafia (12%), Manasota (8%) and Peace River (80%) Basin Boards. In
FY2007, FY2008 and FY2009 Alafia will budget $600, Manasota will budget $400 and the Peace River will budget
$4,000 each year.
Additional Information
One characteristic of low volume irrigation used for citrus freeze protection is that the decision to use irrigation must
be made prior to the water in the lateral irrigation lines reaching freezing temperatures of 32 degrees F. Mature citrus
foliage is subject to freeze damage at temperatures below 24 degrees F depending on acclimation and tree condition.
Minimum temperatures above 24 degrees F would result in minimal freeze damage of acclimated mature citrus
foliage. Temperatures that would fall between 32 and 24 degrees F would require no water resources for freeze
protection, since these temperatures would be above critical values for acclimated citrus leaves. There is an
opportunity to determine before a freeze event time the actual need for irrigation to protect citrus trees, thus saving
water resources during a freeze event. Temperature models exist that can help predict minimum temperatures for the
following morning at sunset the previous day under stable freeze conditions and are available through the FAWN
(project B136) weather network. These models need to be enhanced for individual locations to develop a high level of
confidence among citrus growers using the models (Brunt equation to predict minimum temperature methodology has
worked for both advective and radiation type freezes). Leaf freezing methodology was developed in the early 1980's
and late 1990's at the University of Florida Fruit Crops Department. Determinations of KP50 (killing point) of citrus
leaves were made weekly on mature citrus leaves to quantify the level of citrus acclimation to cooler temperatures
experienced in the fall and winter months. Data indicated that these leaf-freezing temperatures were dynamic in nature
and changed throughout the winter in response to previous week's growing conditions. This project would develop
site-specific methodology to accurately determine minimum temperatures the next morning based on sunset
temperatures recorded the previous evening this allows for multiple temperature observations on cold nights from the
growing area providing necessary replication of the Brunt equation. In addition, this project will help disseminate this
information in newsletters and other sources, including FAWN to help the growers conserve water. Historical
temperature data indicates (1941-1970) that there is a 75% chance of temperatures reaching 32 degrees F or lower
during any given winter in Tampa and a 95% chance of 32 degrees F or lower in Lake Alfred during any given winter.
Growers using this methodology in the 2000-2001 season based on historical weather data from the FAWN Dover and
Lake Alfred locations had 6 and 7 nights of minimum temperatures below 32 degrees F, respectfully. Growers run
their irrigation system for cold protection when temperatures were predicted to be 32 degrees F or below. This is in
021 - Manasota Basin 151