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W.A. Dozier Jr., A.W. Caylor, D.G. Himelrick, A.A. Powell, A.J. Latham, J.A. Pitts, and J.A. McGuire

Own-rooted, 4-year-old kiwifruit plants [Actinidia deliciosa (A. Chev.) C.F. Liang et R. Ferguson var. deliciosa] protected by a Styrofoam insulation wrap with a water-filled pouch (Reese clip-on trunk wrap) or by microsprinkler irrigation sustained less freeze injury than unprotected plants under field conditions at temperatures as low as -17.8C. Trunk splitting occurred on the plants, but no injury was detected on canes, buds, or shoots in the canopy of the plants. Unprotected plants had more trunk splitting and at greater heights than protected plants. New canes developed from suck- ers of cold-injured plants and developed a trellised canopy the following season.

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Mark Rieger and Stephen C. Myers

“The feasibility of using an over-tree microsprinkler irrigation system for spring freeze protection of `Loring' peach trees [Prunus persica (L.) Batsch] was evaluated under a range of meteorological conditions during Winter 1988-89. Microsprinklers were attached to the underside of polyethylene laterals 2.5 m above ground level and centered over the tree rows. Irrigation rates of 0, 27, 36, and 44 liters/hour per tree were tested on trees trained to an open-center habit using microsprinklers that produced a circular wetting pattern. Microsprinkler irrigation maintained average bud temperature above -2C and 2 to 5C above those of nonirrigated trees under calm conditions, but provided no protection under windy conditions. Flower bud temperatures of irrigated trees were similar for 36 and 44 liters·hour-1, but were slightly lower for 27 liters·hour-1 under conditions typical of spring freezes. Limb breakage due to ice loading was negligible for all application rates, even under advective freeze conditions. Calculated water and energy consumption were reduced by at least 50% and 88%, respectively, by the microsprinkler system, compared to a typical overhead sprinkler system.

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Thomas E. Marler and Frederick S. Davies

Growth responses of young `Hamlin' orange [Citrus sinensis (L.) Osbeck] on sour orange (C. aurantium L.) trees to microsprinkler irrigation were studied under field conditions from 1985 to 1987 to determine the most-efficient irrigation rates and duration. Trees were irrigated when available soil water depletion (SWD) reached 20% (high frequency), 45% (moderate frequency), and 65% (low frequency). Trees at the moderate and low levels received 49% and 13%, respectively, as much irrigation water as the high treatment. Canopy volume, trunk cross-sectional area, dry weight, shoot length, leaf area, total root dry weight and volume, and new root dry weight were similar for the high and moderate levels in 2 of 3 years, but were significantly reduced at the low level. Summer and fall growth flushes were delayed or did not occur at the moderate and low levels. More than 90% of root dry weight was within 80 cm of the trunk at the end of the first growing season.

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Mark Rieger

Spring frost events reduce fruit production in the southeastern United States more than any other factor, with some losses occurring in 5 out of 7 years. Orchard heaters, wind machines, and overhead irrigation are sound methods of reducing losses, but their relatively high cost is a major deterrent for fruit growers (Castaldi, 1990). A potentially leas-costly and more water- efficient approach to frost protection is overtree microsprinkling. Microsprinkler irrigation was applied either beneath or onto canopies of 4-year-old `Loring' peach [Prunus persica (L.)] trees at a rate of 38 liters/h per tree to evaluate the relative efficacy of low-volume undertree and overtree microsprinkling for frost protection. Overtree microsprinkling maintained flower bud temperatures 2C during a calm, radiative frost on 20-21 Mar. 1990 (minimum air temperature -4.4C), whereas undertree sprinkling provided 0.5C of air temperature elevation at a comparable height in trees (2 m). Twelve days later, fruit set was lower for nonirrigated and undertree-irrigated trees (none to one fruit/m of shoot length) than for trees irrigated with overtree microsprinklers (eight to nine fruit/m of shoot length). Economic analysis showed that capital costs of overtree microsprinkler systems increased annual costs of peach production by 8% to 13%, which required increased yield (or price per unit yield) of 17% to 20% before profits exceeded those of nonirrigated orchards, assuming all else equal. The estimated 1% increase in annual production costs of overtree microsprinkling compared to undertree microsprinkling appears to be justified by the increased efficacy of the overtree system.

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D.G. Himelrick, W.A. Dozier Jr., and A.W. Caylor

Own-rooted four-year-old kiwifruit plants (Actinidia deliciosa) protected by a Reese clip-on styrofoam insulation trunk wrap, or microsprinkler irrigation, sustained less freeze injury than unprotected plants under field conditions at temperatures as low as -17.8C. Trunk splitting occurred on the plants but no injury was detected on canes, buds, or shoots in the canopy of the plants. Unprotected plants had more trunk splitting and at greater heights than protected plants. New canes developed from suckers of cold-injured plants and developed a filled canopy the following season.

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C. Chen, R.J. Roseberg, D. Sugar, and J.S. Selker

A study was undertaken to determine if microsprinkler irrigation (MI) can provide sufficient water and produce similar yield and quality of pear (Pyrus communis L.) fruit as flood irrigation (FI) in a cracking (shrinking-swelling) clay soil. Soil water content and fruit quality attributes were measured under MI and FI in 2 years. Water potential of the upper 120 cm (47 inches) of soil was maintained at 0.1 to 0.3 MPa (14.5 to 43.5 lb/inch2) through most of the growing season in both MI and FI treatments. MI and FI treatments did not differ in their effect on fruit size, yield, or firmness decline during cold storage. No consistent effect on fruit susceptibility postharvest fungal decay related to irrigation treatment was observed. MI has the potential to reduce chemical and water movement to groundwater, while providing sufficient water to produce satisfactory yield and fruit quality in a cracking clay soil.

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Monte L. Nesbitt, N.R. McDaniel, Robert C. Ebel, W.A. Dozier, and David G. Himelrick

Several microsprinkler treatments were tested on 5-year-old satsuma mandarin orange (Citrus unshiu Marc.) trees to compare survivability of trunks and scaffold limbs in severe freezes. Three damaging freeze events occurred during winter, with two in 1995–96 and one in 1996–97. Air temperature dropped to –9.4, –5.6, and –6.7 °C, respectively. Almost 90% of the foliage was dead on the control plants after the first freezing event and 98% after the second. A single microsprinkler 1.6 m high in the canopy delivering 90.8 L·h–1 reduced injury; only 54% of the canopy was dead after the first freeze and 71% after the second. There was slightly more shoot-tip dieback on the plants in the microsprinkler treatments than on the control plants after the first two freezes. The amount of limb breakage by ice was minor. The third freeze killed 34% of the canopy in the control plants, but only 26% in the plants in the microsprinkler treatments. Use of microsprinklers increased yield in 1996, but yield for all treatments was very low. Yield for all treatments fully recovered in 1997, averaging 153 kg/tree. Although no death of scaffold limbs or trunks occurred, these results demonstrate that microsprinkler irrigation reduces damage to foliage and increases yield somewhat in severe freezes.

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Monte L. Nesbitt, N.R. McDaniel, Robert C. Ebel, W.A. Dozier, and David G. Himelrick

Several microsprinkler treatments were tested on 5-year-old satsuma mandarin orange (Citrus unshiu Marc.) trees to compare survivability of trunks and scaffold limbs in severe freezes. Three damaging freeze events occurred during winter, with two in 1995-96 and one in 1996-97. Air temperature dropped to -9.4, -5.6, and -6.7 °C, respectively. Almost 90% of the foliage was dead on the control plants after the first freezing event and 98% after the second. A single microsprinkler 1.6 m high in the canopy delivering 90.8 L·h-1 reduced injury; only 54% of the canopy was dead after the first freeze and 71% after the second. There was slightly more shoot-tip dieback on the plants in the microsprinkler treatments than on the control plants after the first two freezes. The amount of limb breakage by ice was minor. The third freeze killed 34% of the canopy in the control plants, but only 26% in the plants in the microsprinkler treatments. Use of microsprinklers increased yield in 1996, but yield for all treatments was very low. Yield for all treatments fully recovered in 1997, averaging 153 kg/tree. Although no death of scaffold limbs or trunks occurred, these results demonstrate that microsprinkler irrigation reduces damage to foliage and increases yield somewhat in severe freezes.

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Robert C. Ebel, Monte Nesbitt, William A. Dozier Jr., and Fenny Dane

, the principle limitation for long-term production is still the threat of freezes. However, freeze protection measures that did not exist in the early 1900s, especially microsprinkler irrigation ( Bourgeois and Adams, 1987 ; Bourgeois et al., 1990

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Michael A. Maurer and Frederick S. Davies

Two field studies conducted from 1990 to 1991 evaluated the effects of reclaimed water on growth and development of 1- and 2-year-old `Redblush' grapefruit (Citrus paradisi Macf.) trees on Swingle citrumelo [Citrus paradisi (L.) Osb. ×Poncirus trifoliata (L.) Raf.] rootstock. Treatments were arranged as a3 (water sources) x 3 (irrigation levels) factorial at two locations on an Arredondo (well drained) and Kanapaha (poorly drained) fine sand near Gainesville, Fla. Irrigation treatments included 1) reclaimed water, 2) reclaimed water plus fertigation, and 3) well water plus fertigation. The reclaimed water was formulated to simulate that of a sewage treatment plant at Vero Beach, Fla. Irrigation was applied at 20% soil moisture depletion, or at 19 or 25 mm·week regardless of rainfall. In both experiments, visual ratings of tree vigor, and measured tree height and trunk diameter, were significantly lower for trees watered with reclaimed water without fertilizer than for the others in both years. Moreover, there was no fourth leaf flush in 1991 with reclaimed water. There was a significant increase in leaf Na, Cl, and B concentrations for the reclaimed water and reclaimed water plus fertigation treatments in 1990; however, in 1991 only leaf B concentrations showed a similar trend. In 1991, there were no significant differences in leaf Cl concentrations. Visual symptoms of N deficiency were observed by the end of the first season in trees grown with reclaimed water. Irrigation levels generallv did not affect tree growth.