From Past to Present: Environmental Stewardship through Irrigation Methods and Cold Protection

The northeastern citrus production never fully recovered from the Great Freeze of 1894-95 and during their rehabilitation another damaging freeze occurred in 1899. The crippling devastation forced growers 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 preservation and the research of citrus began to gain momentum. Studies being developed focused on passive and active practices necessary against freeze events. Already, the Riverside Horticultural Club and the U.S. Weather Bureau had begun pioneer studies into active freeze 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 locations, 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. Some other passive aids discovered include ground maintenance, efficient pruning, trunk wraps or ground covers, and cold air drainage. Heat radiates to the upper atmosphere, causing the temperatures nearest the ground to cool by heat radiating outward. On calm nights temperatures fall rapidly, since cold air is heavier than warm, it settles nearer the ground, increasing the risk for frost. Elevated sandy soils of the Florida Ridge lose heat quickly but allow for better air drainage due to elevation changes. Large bodies of water radiate heat outward, thereby providing warmth to nearby property.

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 at reducing radiant heat loss. Due to environmental concerns these open burning methods of cold protection are no longer used. Return stack heaters, which recycle smoke and vapor, burn cleaner, but are rarely used today due to the cost of fuel.
• Wind machines: Brought to use in the 1950s, wind machines raise the grove’s temperature by mixing the warmer upper air with the cold air that is near the ground. 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 to mix the air when temperature inversions occur on nights that lack wind to mix the atmosphere. The rotations of the blades push the warm air down, thus warming the air near 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 more frequently 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 it where it was needed and maintaining the required amounts of fog 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 a method of cold protection. Strong positive results with water as a method of 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 is the amount of water being applied based on environmental conditions and ensuring adequate coverage. 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. During this time, water conservation concerns and sustainability remained a top priority, which would bring about in the future the creation of drip irrigation (for watering crops) and microirrigation, accompanied with data that found them to be highly effective. Microirrigation is more cost effective and uses less water than conventional sprinklers with equivalent frost protection when water is applied correctly.

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 for cold protection and when to apply water for irrigation.

Irrigation was not an organized practice of citrus production until the 1950s. Initially, young newly set 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 have a low water-holding capacity. The flatwood soils of coastal and southern Florida are poorly drained with typically a high water table. Different types of Florida soils and climates require unique systems of irrigation. March through April is the tender stage of fruit set and early fruit development, while May through June is the dry season. The supplementation of water during this period assists in enhancing yields.

In the 1940-50s, portable galvanized and aluminum perforated pipe systems were first used. Seepage irrigation worked well in groves with nearly level land. Carefully engineered furrows were pumped with water and the water seeped horizontally.

In the 1960s, the east coast and 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 the 1970s, prolonged drought saw the founding and legislation of the Florida Water Resources Act. As constant seekers of solutions, environmental stewards of the citrus industry would adapt a newly developed low-volume drip system for Florida’s groves, and soon thereafter microirrigation. Overhead and traveling guns became widely unpopular due to high-volume water use and a higher energy requirement. New farms installed microsprinkler systems while many established groves began to convert from overhead irrigation to the new under tree microsprinkler method.

In the 1980s, another drought season successfully cemented drip systems as staples for irrigation and microirrigation for use in cold protection at a fraction of the water use. Fuel costs cut back significantly the use of traditional heating systems that used fossil fuel for crop cold protection.

From 1990 to present day, microirrigation is used in most groves. 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.

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CREDITS

story by J.P. SMITH
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