Abstract
Water requirements of citrus trees depend on tree characteristics (size and health) as well as weather parameters (temperature, humidity, and wind velocity). During extended droughts, the typical combination of warmer than average temperatures, lower than average humidity, and often times higher wind velocities tend to result in higher than normal evapotranspiration (ET) rates. As a result, calculations based on monthly averages tend to under estimate water use during dry periods. This paper summarizes important factors relating to water use by citrus trees grown on flatwoods soils: soil physical properties, root systems, rainfall patterns, irrigation uniformity and application efficiency, upflux from the water table, and salinity. The daily historical rainfall records at the Indian River Research and Education Center over the last 50 years were evaluated to determine frequency and extent of droughts. There were 33 periods of 4 weeks or more that had less than 0.25 inch of rainfall, 34 periods with less than 0.05 inch of rain, and 52 periods with less than 1.0 inch of rain. Rainfall analysis of the spring dry season revealed that 34% of the years had periods of 4 weeks or longer during March-May that received 0.25 inch of rain or less. In addition, 48% of the years had periods of 4 weeks or more with 0.5 inch or less, and 68% with 1.0 inch or less. Calculations show that the combination of shallow root systems, sandy soils, and lack of perched water table during the dry season results in an irrigation frequency of 1-2 d during peak ET periods to provide adequate soil moisture for optimum production. Therefore, irrigation systems for citrus should be designed for complete ET replacement during the critical March to mid-June period. If saline irrigation water is used, additional water will be required for frequent irrigations to leach salts below the root zone.
