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- Author or Editor: T. Adair Wheaton x
Highly treated sewage effluent water increasingly is being used for agricultural irrigation. This reclaimed water is presently being used in a large citrus irrigation project in central Florida. The purpose of this study was to determine the effects of high application rates of reclaimed water on growth and leaf mineral content of young citrus trees. High application rates (1270 and 2540 mm per year) of reclaimed wastewater were compared to a normal recommended rate of 406 mm per year of either reclaimed or well water. Tree growth was greater at the higher application rates, but these rates also promoted greater weed growth. With reclaimed water, leaf Na, Cl, and K contents generally increased with increasing irrigation rate, but these levels remained well below levels that would cause plant damage. Leaf Cl accumulation was much higher in `Hamlin' orange than `Orlando' tangelo. Rootstock also affected leaf Na and Cl accumulation. Reclaimed water appears to be a useful alternative to well water for citrus irrigation.
Undertree microsprinkler irrigation has protected 1 or 2 year old trees to a height of 1 meter during severe advective freezes. During the severe December 1989 freeze, microsprinklers elevated to 0.9 meter protected 5 year old citrus trees to a height of 2 meters. Limb breakage due to ice loading was negligible. Protection was achieved with water application rates less than half that required by some overhead sprinkler models. Survival is attributed to 1) continuous spray from the microsprinkler rather than periodic spray from a rotating overhead sprinkler, and 2) effective localized application rate on branches intercepting spray is more than average overall spray application rate. Elevated microsprinklers provide freeze protection to a greater height and allow for more rapid post-freeze recovery.
Wraps of fiberglass or other insulating material have frequently been used in Florida for cold protection of young citrus tree trunks. Traditional wraps were compared to a foil-covered plastic bubble material formed into cones. The base of the cone on the ground trapped soil heat and the apex was secured around the trunk at a height of 40 cm. Cones with base diameters of 15, 30, 45 and 60 cm were compared to a cylindrical wrap of the same material and other traditional wraps. A major freeze in Dec. 1989 killed unprotected control trees to the rootstock. Cones provided better freeze protection than other wraps. Temperatures inside the cones were generally warmer as cone diameter increased. By trapping soil heat, cones of this material can provide better freeze protection of young trees when irrigation or other heat sources are not available.
Abstract
Microsprinkler irrigation has proved effective in providing frost protection for young citrus trees, but there can be a risk of damaging trees during advective or windy freezes. The objectives of this study were to monitor evaporative cooling and to determine if height of young tree protection cold be increased to include the major scaffold branches. Microsprinklers were evaluated during a severely damaging advective freeze that occurred in central Florida in Jan. 1985. Trunk temperatures were measured at 15-, 30-, 45-, and 60-cm heights. By positioning the sprinkler at a 45° or higher angle, microsprinkler spray was aimed up into the young tree. This treatment was compared to the normal 15° low-angle spray pattern. Application rates on the wetted area were estimated to be 7 mm·hr−1 for high-angle treatment and 8.8 mm·hr−1 for low-angle treatment. With high-angle spray, trees were protected to a height of 85 cm, which was significantly higher than low-angle spray. Evaporative cooling below air temperature was not seen on irrigated trees. Continuous microsprinkler spray helped reduce evaporative cooling, but cooling did occur on a nearby tree that received only intermittent spray. Microsprinkler irrigation directed at an upward angle protected the trunk and scaffold branches of young trees in this particularly severe freeze and enhanced tree recovery.
`Hamlin' oranges and `Orlando' tangelos on four rootstocks have been irrigated since planting in 1987 with highly treated reclaimed effluent water at application rates of ≈500, 1250, and 2500 mm/year. Reclaimed water treatments have been compared to a well water control at 500 mm/year. Tree growth, yield, and fruit quality have been satisfactory for all irrigation treatments. Growth and yield of `Orlando' tangelos was greatest at the 2500 mm rate and yield was highest on `Swingle' citrumelo and `Carrizo' citrange rootstocks. `Orlando' tangelos benefited more from the high irrigation rates than `Hamlin' oranges. Dilution of soluble solids in the juice by high irrigation rates has diminished as trees matured. Leaf nutrient content was influenced by irrigation, variety, and rootstock. Reclaimed water supplied all the phosphorous and boron needed for citrus production. Soil pH increased due to irrigation with reclaimed water. No disease problems have resulted from the high irrigation rates. Irrigation with high rates of reclaimed water on deep well-drained sands is not detrimental and has benefited citrus production.
Hamlin orange trees on Swingle rootstock planted in 1991 were subjected to six different rates of irrigation with approximately the same amounts of water applied either daily (1-day), every other day (2-day), or every 4th day (4-day). Rates provided from 0.43 to 1.95 of historical daily evapotranspiration (ET) applied to the wetted area. Irrigation was delayed following rainfall. The effects of irrigation rate and frequency on trunk and canopy growth, yield, soil water content, root distribution, and total water use were studied. There was little effect of irrigation rate or frequency during the first 2 years after planting. However, tree growth improved with increasing irrigation rate during the 3rd and 4th years, and growth in these years was greater when irrigation was scheduled daily. Effects of rate and frequency on growth were not as great as expected. Yield increased as irrigation increased in 1994. Leaf nitrogen was generally higher at the lower irrigation rate. Soil water content varied with depth. Extraction of soil water was more rapid in the top 45 cm of soil. Roots after 4 years did not extend below 45 cm with 60% of the roots in the top 15 cm and 90% in the top 30 cm. Roots were concentrated closer to the trunk for trees at the lower irrigation rates.
Abstract
A diluting and dispensing system is described for providing concentrations of ethylene as low as 0.1 ppm to a number of different chambers in a continuous flow system for treatment of plant tissue. Several concentrations can be provided simultaneously. The system eliminates the need for routine recharging of the ethylene reservoir.
A water use simulation for citrus (Citrus sinensis) was used to estimate the effects of climate, soil-available water, rooting depth, allowable depletion of available water, and partial coverage irrigation on the annual irrigation requirements. The soil in the study was excessively drained Candler sand (hyperthermic, uncoated Typic Quartzipsamments) of the Central Florida Ridge. Variation of annual rainfall from 667 to 1827 mm had a relatively small impact on annual irrigation requirements. Soil-available water, depth of root zone, and allowable depletion of available water all affected irrigation management and the number of irrigations annually. Simulated annual irrigation requirements varied over a wide range depending on the allowable depletion of soil-available water, irrigation depth, and the fraction of the land area that is irrigated. Effective rain estimated by the TR21 method during months of high rainfall was higher than estimates by the water budget. Monthly irrigation requirements varied seasonally and peaked in normally dry spring months of April and May. The irrigation simulation is a useful tool for examining the range of management strategies that can be considered for citrus.
Abstract
The effectiveness of microsprinkler irrigation for frost protection was examined during several cold nights in central Florida in 1981. Air temperatures ranged from 0 to 2.8°C warmer in the irrigated area above the spray zone than in the non-irrigated area, and were generally 0.5 to 1.5°C warmer. By irrigating under the tree, microsprinklers avoid some of the disadvantages associated with overhead sprinklers. Overhead sprinklers are not practical for freeze protection of large evergreen citrus trees because of limb breakage due to ice loading. During calm radiation cold nights, microsprinkler irrigation can provide some protection and is one alternative to burning petroleum products for citrus cold protection.