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- Author or Editor: Frederick S. Davies x
Reclaimed municipal wastewater has been used to irrigate young and mature sweet orange and grapefruit trees in Florida. In the central ridge area of Florida, trees receiving reclaimed wastewater had greater yields and improved tree vigor compared to trees receiving wellwater. The high level of reclaimed wastewater applied (2.54 cm/week), however, decreased fruit total soluble solids, acids, and their ratio. In contrast, tree vigor and fruit quality were not different for mature grapefruit trees growing in the coastal, flatwoods area of Florida, which received reclaimed wastewater or canal water. Yields, however, were higher for the reclaimed wastewater treatments in one season, but the effect was variable. No adverse effects of applying high levels of reclaimed wastewater were noted at either site. The use of reclaimed wastewater for citrus irrigation has potential benefits for Florida citrus growers in the future.
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.
Abstract
The relationship of root (RLp) and stem hydraulic conductivity (SLp), root electrolyte leakage (EL), and stomatal conductance (gs) to flooding was investigated using 2-year-old ‘Tifblue’ and ‘Woodard’ rabbiteye blueberry (Vaccinium ashei Reade) plants. Soil redox potentials (Eh) decreased to about — 225 mV within 4 to 10 days of flooding, whereas Eh of unflooded soils were always > 400 mV. Root hydraulic conductivity decreased by 44% to 60%, compared to that of unflooded plants after 4 to 6 days of flooding in two of three experiments, decreasing by 29% to 81% by the end of 2 to 3 weeks. Root electrolyte leakage increased and SLp decreased after 6 to 10 days of flooding. Stomatal conductance decreased by 49% to 93% compared with that of unflooded plants after 4 to 6 days of flooding. Decreases in RLp and gs for flooded plants occurred concomitantly and are two of the earliest physiological responses of rabbiteye blueberry plants to flooding.
Abstract
Flooding damage causes millions of dollars in losses to horticultural crops every year. Plantings established on sites with poor drainage and/or an impervious soil layer may flood periodically after heavy rainfall or excessive irrigation. Planting sites with lowlying areas or where site preparation is inadequate for drainage of excess water add to the problem. Poor soil aeration associated with flooding may induce numerous soil and plant changes that adversely affect plant survival, growth, development, and yield. Organic and inorganic soil toxins may accumulate in flooded soils, adversely affecting plant metabolism and physiology.
Abstract
The response of 3-year-old ‘Woodard’ rabbiteye blueberry (Vaccinium ashei Reade) plants to 0, 5,15, 25, and 35 days of flooding during spring and summer of 1984 and 1985 was studied under field conditions. Soil oxygen diffusion rate (ODR) and redox potential (Eh) of flooded plots were significantly lower than those of unflooded plots within 2 days of flooding. After plots were released from flooding, soil Eh recovered to control levels within 10 days but ODR did not. Almost 100% of the plants survived flooding treatments in 1984, whereas plant survival decreased to 83% after 25 days of spring and 67% after 5 days of summer flooding in 1985. Stem elongation and leaf expansion were inhibited after about 15 days of spring and 7 days of summer flooding. The number of flower buds formed during the fall was reduced by about 30% and 70% after as little as 5 days of summer flooding in 1984 and 1985, respectively. Fruit set decreased by 13% and 29% after 25 days of spring flooding in 1984 and 1985, respectively. Yields were not consistently affected by spring flooding, but decreased significantly after 35 days in 1984 and 25 days in 1985.
Abstract
Highbush (Vaccinium corymbosum L. ‘Bluecrop’) and rabbiteye (V. ashei Reade ‘Woodard’) blueberry plants were flooded in the greenhouse to determine how transpiration, stomatal conductance to water and CO2, residual conductance, and C assimilation are affected during flooding and recovery. Carbon assimilation was measured using a portable CO2 analyzer and stomatal conductance using a steady-state porometer. Stomatal conductance and transpiration decreased significantly after 4 to 5 days of flooding, and responses were similar for highbush and rabbiteye blueberries. Carbon assimilation decreased for both species within 9 days and became negative in 11 to 19 days due to decreased photosynthesis, stomatal conductance to CO2, and high leaf temperatures, which increased respiration. Recovery after 24 days of flooding to preflood stomatal conductance values required 18 days for ‘Woodard’ and more than 18 days for ‘Bluecrop’. In laboratory experiments flooded plants were less responsive to changes in ambient CO2 and vapor pressure deficits than unflooded plants, and flooding durations of greater than 9 days significantly decreased residual conductance of the leaves.
Abstract
Whole-tree sprays of gibberellic acid (GA) plus calcium dihydrophosphate Ca(H2PO4)2 increased fruit set of navel orange [Citrus sinensis (L.) Osb.] during 1979 and 1980. Gibberellic acid alone or a combination with Ca(H2PO4)2 or 6-benzylamino purine (BA) increased fruit set in 1980. Benzylamino purine did not increase fruit set or the fruit-setting effectiveness of GA. Calcium dihydrophosphate increased fruit set for approximately 5.5 weeks in 1980 even though leaves did not show signs of calcium deficiency. However, no increase in fruit set was observed 8.5 weeks after application. Fruit sprayed with GA were smaller than untreated fruit initially; however, no size differences were noted 8.5 weeks after full bloom.
Abstract
Moderate and severe water-stress, as determined by decreases in stomatal conductance, resulted in significant reduction of leaf area and plant weight in 1-year-old containerized ‘Bluegem’ rabbiteye blueberry. Drought-tolerance appeared to be intermediate to other plant species based on a number of physiological factors. Critical water potential for stomatal closure was −2.2 MPa, transpiration ratio averaged 222 g of water transpired per g dry matter produced and relative water content changed 6.4% per 1.0 MPa change in water potential.
Abstract
The response of 2- to 3-year-old ‘Tifblue’ rabbiteye blueberry (Vaccinium ashei Reade) plants to periodic flooding of different durations and seasons was studied under field conditions in 1985 and 1986. Soil redox potentials (Eh) decreased to between 0 and −300 mV within 2 days of flooding and recovered to preflood levels (200 to 300 mV) within 8 to 10 days after flooding release. Plants survived 2-day (four periods) and 7-day (two periods) spring flooding treatments, whereas losses of 17% to 100% occurred after two 2- to 15-day summer flooding episodes. Most (83%) plants survived 106 to 117 days of spring flooding, while 33% and 0% survived 78 and 90 days of summer flooding, respectively. Generally, leaf area, percent fruit set, and yields decreased after two 7-day spring flooding periods, whereas the number of flower buds formed decreased by 38% to 70% with as little as two 2-day summer flooding periods. Stomatal conductance and transpiration decreased after the onset and increased after the release of the two 2- and 7-day summer flooding treatments, but remained low for the 15-day (two periods) and 78-day treatments. The effects of periodic flooding on plant survival, stomatal conductance, and the number of flower buds formed were similar to those found for continuously flooded plants in a previous study.
Abstract
Greenhouse-grown potted apple trees (Malus domestica Borkh. cv. Empire) on Malling-Merton (MM) 111 rootstocks displayed much lower water potentials at the end of the season than did similar trees grown outdoors when measured under the same soil moisture and evaporative demand conditions. Differences in water potentials over a wide range of soil moistures were due to the much higher plant and root resistances and the lower leaf capacitances of the greenhouse-grown trees as calculated by using electric analogue circuits. Root resistance differences could not be explained by changes in feeder root percentages or root:shoot ratios.