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Larry R. Parsons and T. Adair Wheaton

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.

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Larry R. Parsons and T. Adair Wheaton

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.

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Larry R. Parsons and T. Adair Wheaton

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.

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Larry R. Parsons and T. Adair Wheaton

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Larry R. Parsons and T. Adair Wheaton

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.

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Larry R. Parsons and T. Adair Wheaton

`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.

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T. Adair Wheaton, Lawrence R. Parsons and K.T. Morgan

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.

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Larry R. Parsons, T. Adair Wheaton and William S. Castle

Citrus trees in an experimental planting responded well to high application rates of reclaimed water. Irrigation treatments included annual applications of 400 mm of well water and 400, 1250, and 2500 mm of reclaimed water. The effects of these irrigation treatments on two citrus cultivars (`Hamlin' orange and `Orlando' tangelo) combined with four rootstocks were compared. Growth and fruit production were better at the higher irrigation rates. The concentration of soluble solids in juice was diluted at the highest irrigation rate, but total soluble solids per hectare increased due to the greater fruit production. Average soluble solids/ha production was >15% higher at the 2500-mm rate than the 400-mm reclaimed water rate. While fruit soluble solids were usually lowered by higher irrigation, the reduction in fruit soluble solids observed on three of the rootstocks did not occur in trees on Carrizo citrange. Trees on Cleopatra mandarin grew similarly at the different irrigation rates, but canopy volume of trees on Swingle citrumelo was significantly smaller at the 400 mm rate than at the 2500 mm rate. Fruit peel color score was lower but juice color score was higher at the highest irrigation rate. Weed pressure increased with increasing irrigation rate, but was controllable. Both juice and fruit soluble solids were higher on Swingle citrumelo and lower on Cleopatra mandarin rootstock. Total soluble solids/ha, solids/acid ratio, and juice color were higher on Swingle rootstock. Reclaimed water, once believed to be a disposal problem in Florida, can be an acceptable source of irrigation water for citrus on well drained soils at rates up to twice the annual rainfall.

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Lawrence R. Parsons, T. Adair Wheaton and George Yelenosky

Handwarmers placed inside conventional insulating tree wraps increased trunk temperatures and improved tree survival under freeze conditions. Handwarmers generate heat by oxidation of Fe powder. In freeze-chamber tests with air temperature as low as –7.1C for 4 hours, wraps plus handwarmers kept trunk temperatures above freezing. Handwarmers increased minimum temperatures by 7C during a one-night freeze. Benefit of the handwarmer decreased the second night of a simulated two-night freeze but still increased minimum temperature by 1.3C. Tree survival was significantly improved by handwarmers in the freeze-chamber tests. In a field test during a mild freeze, handwarmers increased the minimum temperature by 3.5C the first night but provided no benefit the second night.

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Lawrence R. Parsons, T. Adair Wheaton and William S. Castle

Conversion of wastewater to reclaimed water for crop irrigation conserves water and is an effective way to handle a growing urban problem: the disposal of wastewater. Water Conserv II is a large reclaimed water project developed by Orlando and Orange County, Fla., that presently irrigates ≈1900 ha of citrus. The project includes a research component to evaluate the response of citrus to irrigation using reclaimed water. Citrus trees in an experimental planting responded well to very high application rates of reclaimed water. Irrigation treatments included annual applications of 400 mm of well water, and 400, 1250, and 2500 mm of reclaimed water. The 2500-mm rate is excessive, and since disposal was of interest, this rate was used to determine if citrus could tolerate such high rates of irrigation. The effects of these treatments were compared on `Hamlin' orange [Citrus sinensis (L.) Osb.] and `Orlando' tangelo (C. paradisi Macf. × C. reticulata Blanco) combined with four rootstocks: Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.], Cleopatra mandarin (C. reticulata Blanco), sour orange (C. aurantium L.), and Swingle citrumelo (C. paradisi × P. trifoliata). Growth and fruit production were greatest at the highest irrigation rate. Concentration of soluble solids in the juice was usually lowered by the highest irrigation rate, but total soluble solids per hectare were 15.5% higher compared to the 400-mm rate, due to the greater fruit production. While fruit soluble solids were usually lowered by higher irrigation, the reduction in fruit soluble solids observed on three of the rootstocks did not occur in trees on Carrizo citrange. Fruit peel color score was lower but juice color score was higher at the highest irrigation rate. Crop efficiency (fruit production per unit of canopy volume) was usually lower at the 2500-mm rate and declined as trees grew older. Weed cover increased with increasing irrigation rate, but was controllable. Irrigation with high rates of reclaimed water provided a satisfactory disposal method for treated effluent, benefited growth and production of citrus, and eliminated the need for other sources of irrigation water. Reclaimed water, once believed to be a disposal problem in Florida, is now considered to be one way to meet irrigation demands.