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  • Author or Editor: Lawrence R. Parsons x
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Abstract

Virtually all land plants are exposed to water stress at some time during their life cycles, yet it has been stated that interest in water stress rises and falls inversely with the rainfall. As Webb stated (60), “A good rain is the only quick solution to the problem of drought.. Unfortunately, a good rain washes away more than the drought, it washes away much of man’s interest in providing for the next one, and it washes the supports from under those who know that another dry cycle is coming and who urge their fellows to make ready for it.”

Open Access

We determined whether the ability of sour orange seedlings to withstand saline irrigation water could be improved by the addition of calcium to the water. Sour orange (Citrus aurantium L.) seedlings were treated for 4 months with a nutrient solution containing either no NaCl, 40 mm NaCI, or 40 mm NaCl plus various concentrations of CaSO4, CaCl2, or KCl. After 4 months, the NaCl alone reduced root and shoot dry weights by ≈ 30% with no leaf necrosis. Addition of 1, 5, or 7.5 mm CaSO4 to solutions containing 40 mm NaCl significantly inhibited the NaCl-induced reductions in shoot dry weight. Addition of 7.5 mm CaCl2 or 7 mm KCl to the NaCl solution reduced leaf Na, but increased Cl to the toxicity level; hence, growth was not improved. The beneficial effect of CaSO4 was mainly attributed to a reduction in the accumulation of Na and Cl below the toxicity level in the leaves (0.4% and 0.5%, respectively) without a major increase in total dissolved salts. This study demonstrated that the beneficial effect of adding Ca depended on the anion associated with the Ca salt. Calcium sulfate, but not CaCl2, was able to overcome the damaging effect of NaCl to sour orange seedlings.

Free access

The development of improved equipment for measuring soil water content has created the need for a better understanding of soil water drainage and movement. Without this understanding, it is impossible to know if an observed decrease in soil water content at a particular depth is due to evapotranspiration and/or continual drainage. This study was designed to determine the length of time for different soil depths of a Florida Candler fine sand to reach field capacity. A field site with no vegetation on it was saturated with water and covered with a plastic tarp to prevent evaporation. At 6- to 24-hour intervals, soil water content was measured gravimetrically in the top 15 cm (6 inches) and with the neutron probe from 30 to 150 cm (12 to 59 inches). The 15-cm depth reached field capacity after one day, but it took 4 days for the 30- to 150-cm depths to reach field capacity because of rewetting by water draining form higher horizons. The time required for drainage to stop must be considered when evaluating changes in soil water status at a particular depth. This is important for distinguishing between plant water uptake and drainage for different soil layers.Soil water characteristic curves of undisturbed soil samples, bulkdensity, porosity, and field capacity in situ were also determined for this soil. Field capacity values found in situ were compared to those found using the pressure plate technique. Laboratory values were higher than field values because the laboratory data were closer to hydrostatic conditions than the field data and the degree of saturation provided during wetting of the cores was higher in the laboratory. Water was not readily retained in Candler fine sand because the soil was very porous, infiltration rates were high, drainage was rapid, and water storage capacity was limited. Using field measurements, field capacity values of soil at different depths ranged from 4.8% to 6.2% volume for Candler fine sand. These are considered to be low values when compared to other types of soil.

Full access

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.

Open Access

Abstract

Water relations responses of 21-year-old grapefruit trees (Citrus paradisi Macf.) irrigated by three types of irrigation systems were compared. Drip, undertree microsprinkler, and overhead sprinkler with application levels of 150 and 450 mm of water per year were compared. Leaf water potential, stomatal conductance, and soil water status were measured under field conditions on a deep, well-drained sandy soil in central Florida. In the early part of a dry spring period, there were no differences in midday or early morning leaf water potential, but, by the end of this period, significant differences in leaf water potential were found among all three irrigation treatments. Highest leaf water potential and stomatal conductance values were maintained in the overhead sprinkler blocks. No midday stomatal closure was observed under the conditions of this study. Relationships among diurnal leaf water potentials, vapor pressure deficits, and stomatal conductance showed hysteresis; this affected the correlations among these factors. Greater water stress occurred in trees irrigated with drip than in trees irrigated with overhead sprinkler systems, but responses to microsprinklers were generally intermediate between the overhead sprinkler and the drip treatments. In an area with high rainfall and sandy soils, increased irrigation coverage can reduce leaf water stress.

Open Access

Abstract

Fruit and vegetative growth of 21-year-old grapefruit (Citrus paradisi Macf.) trees on well-drained sandy soil was studied in central Florida. Drip, microsprinkler, and overhead sprinkler irrigation was compared at two levels of irrigation (150 and 450 mm·year−1). Significant differences in leaf area, fruit size, fruit growth, new flush growth, and canopy area were found with different irrigation systems applying similar amounts of water. Growth was improved by irrigation even in a year of high rainfall (1410 mm). With mature trees, drip systems promoted the least growth, while overhead sprinkler systems promoted the most. Leaf fresh and dry weights and individual leaf areas in the overhead sprinkler treatments were 40% to 50% greater than in the drip or nonirrigated treatments, while specific leaf weight and leaf water content per unit dry weight were similar for all treatments. Final fruit size and tree canopy area were 9% to 20% greater in the overhead sprinkler treatments than in the corresponding drip or nonirrigated treatments. Responses to microsprinklers were generally intermediate between the overhead sprinkler and the drip treatments. Because of the low soil area coverage, applying water at the higher rate with the drip system did not improve growth as well as the overhead system at the lower rate. With mature grapefruit trees under central Florida conditions, systems providing greater soil area coverage gave better leaf and fruit growth than systems providing less soil coverage.

Open Access

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.

Free access

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.

Free access

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.

Free access

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.

Open Access