A Look at Irrigation Methods and Cold Protection from Past to Present
The northeastern citrus productions never fully recovered from the Great Freeze, and during their rehabilitation another damaging freeze occurred in 1899. The crippling devastation forced growers and orchardists to relocate to Central Florida and southward, seeking out warmer climates in what is known today as the citrus belt, including the counties of Hillsborough, Polk, Indian River, and others, in the hopes to rebuild the citrus industry. New institutions specialized in the preservation and research of citrus began to gain momentum. Studies being developed focused on passive and active practices necessary against frost. Already, the Riverside Horticultural Club and the U.S. Weather Bureau had begun pioneer studies into active frost protection, including tests in windward placed smoldering matter, also known as smudging, and burning coal in wire baskets. [emember_protected custom_msg=”Click here and register now to read the rest of the article!”]
Passive components of cold protection that growers adapted early were, 1) locating the grove in warmer temperatures, preferably close to water, and 2) the healthy fertilization and spraying of the groves. New studies conclusively proved that deficient trees are at greater risk to cold damage and loss. Other passive aids discovered include ceasing soil cultivation, ground maintenance, efficient pruning, trunk wraps or ground covers, maintaining pests and bacteria, and cold air drainage. Heat radiates to the upper atmosphere, causing the soil nearest the ground to cool by contact or convection. If the air cannot move downward, since cold air is heavier than warm, it sits stagnant, increasing the risk for frost. Elevated sandy soils of the Florida Ridge lose heat quickly but allow for better air drainage. Large bodies of water provide adequate air drainage and warmer soil.
Active frost protection required elaborate formulas, and some of these methods are still used in modern citrus production today. These formulas help groves adjust to crucial elements and variables, and include the following methods:
Heaters: The historical use of heat for frost protection, such as open fires, was practiced for more than 2000 years. The placement of heaters is essential in replacing energy loss. Charles Froude introduced the first oil heater in 1890, but the costly fuel kept it from broad use until after the turn of the century. Wood burning was an affordable, thus popular active method, rather than the expensive fuels of oil, coal, and coke (a residue from coal’s destructive distillation). Smoke from these methods was believed to also aid in warming crops; however, later it was determined to have no effect towards retaining heat for crop radiation and convection. Today, these pollutant-heating methods are banned in the U.S.A. for environmental reasons. Return stack heaters, which recycle smoke and vapor, and clean-burning heaters are approved and used in some areas today.
Wind machines: Brought to use in the 1950s, wind machines are larger and more expensive than heaters. They raise the grove’s temperature by mixing the warm air with the cold air. The formulas for the type, rotation, and strength of the wind machine requires precise figures for inversion strength that vary for individual groves.
Helicopters: In the latter half of the 20th century, helicopters became another tool for citrus growers. The rotations of the blades push the warm air down, thus warming the surface in downward heat transfer. Thermostats monitor the grove and are signaled to the pilot with lights, which indicate where warmth is necessary or when they’ve attained temperatures safe from frost. They pass over groves in 30-minute intervals for mild frosts and longer for more severe frosts, though the length of passes will vary with the size of the crop as well.
Fog generators: Also in the mid- to late-20th century, fog generators came into use for frost protection. The higher density of fog (because of present water droplets) acts as ground coverage that keeps radiation loss minimal. The problem with fog was containing where it was needed and maintaining the required amounts in density.
Sprinklers, surface irrigation, and microirrigation: Precision water application was implemented around the 1950s to provide crop cold protection. Humidity concepts and water principles are essential to the use of water as cold protection. Strong results with water as cold protection were not present until research data was produced much later. Misapplication of water can result in ice loading with destruction of limbs and possibly killing the tree. Key elements that are critical for success are timing of release and amount of water distributed evenly and efficiently. Soil that is moistened prior to a frost can elevate the temperature by 2 degrees F and provide continual warmth from deeper under the surface. Today, new technology enables systems to be set to precise calculations and timings. A psychrometer is used to detect atmospheric humidity that measures the temperature of ambient air, called dry bulb, and simultaneously the wet surface temperature, called the wet bulb. Dew point is the temperature when water condenses. These gauges aid farmers in knowing when and how and for how long to apply water. Water conservation concerns and sustainability took priority, thus drip irrigation and microirrigation were created, accompanied with data that found them to be highly effective. Microirrigation is affordable and uses 80 percent less water than conventional sprinklers with equivalent frost protection.
In present day, technological advances from the Florida Automated Weather Network (FAWN) and the National Weather Service (NWS) provide an integrated Internet tracking application that has interactive tools in cold protection. Irrigation can be set to turn off and on based on real-time temperatures set by the growers’ critical temperature for their grove, a 7-day Point Forecast and fruit frost station forecast are available, as well as an irrigation scheduler for assistance to growers determining when to apply water protection and regular water supply.
Irrigation was not an organized practice of citrus production until the 1950s. Initially, trees were watered by water wagons and only when absolutely necessary. The subtropical Florida citrus belt is characterized by sandy rolling hills with an average 48-59 inches of rain annually. The Ridge soils are sandy and of a low water-holding capacity. The flatwood soils of coastal and southern Florida are poorly drained high water table. Different types of Florida soils and climates require unique systems of irrigation. May through June is the dry season and also the tender stage of fruit set and early fruit development. The supplementation of water during this period assists in preserving yields and fruit quality.
In the 1940-50s, portable galvanized and aluminum perforated pipe systems were first used. Seepage irrigation worked well in groves with poorly leveled land. Carefully engineered furrows were pumped with water and the water seeped horizontally underground.
In the 1960s, southwest Florida continued broad use of seepage as well as a similar method called “crown flooding.” Also in this era, overhead sprinklers were commonly used for irrigation in groves, in addition to their use for cold protection. However, the use of overhead sprinklers for cold protection when not used properly can meet with devastating results, such as during the major freeze of 1962, which caused ice loading, bringing about the collapse and breakage of trees and limbs.
In the 1970s, prolonged drought saw the founding and legislation of the Florida Water Resources Act. This inspired the first low-volume drip system, already in use in Israel and South Africa, and soon thereafter microirrigation. Overhead and traveling guns became widely unpopular due to high-volume water use. New farms installed drip systems while many established groves began to convert to the new method.
In the 1980s, another drought season and air pollution concerns successfully cemented drip systems and microirrigation as staples for irrigation and cold protection at a fraction of water use. Fuel costs and environmental trends also cut back use of traditional heating systems for crop cold protection.
From 1990 to present day, microirrigation is used in most groves on the Ridge. Many factors contribute towards this system’s positive reception and success, including drought and water shortage regulations, frost protection, production benefits, and environmental sustainability awareness.
“The Birth of an Industry” is an exclusive preview for what will be a permanent outdoor exhibit of the Florida citrus industry. The exhibit will be hosted at Circle B Bar Reserve in Lakeland, Florida, and is being built in partnership with Polk County, Parks and Natural Resources Division; Polk County Farm Bureau; Polk County History Center; and Central Florida Media Group. The unveiling is projected to take place in the fall of 2013.
story by J.P. Smith
photography courtesy of Florida Department of Agriculture and Consumer Services