Microsprinkler irrigation of mature, reset, and young grapefruit (Citrus paradisi MACF.) trees with reclaimed wastewater

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Title:
Microsprinkler irrigation of mature, reset, and young grapefruit (Citrus paradisi MACF.) trees with reclaimed wastewater
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xiii, 204 leaves : ill. ; 29 cm.
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English
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Maurer, Michael Alvin, 1962-
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1994.
Bibliography:
Includes bibliographical references (leaves 185-203).
Statement of Responsibility:
by Michael Alvin Maurer.
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Typescript.
General Note:
Vita.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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notis - AKN0382
oclc - 33293221
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Full Text










MICROSPRINKLER IRRIGATION OF MATURE, RESET,
AND YOUNG GRAPEFRUIT (CITRUS PARADISI MACF.)
TREES WITH RECLAIMED WASTEWATER









By

MICHAEL ALVIN MAURER


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


1994














ACKNOWLEDGEMENTS


Sincere appreciation is extended to Dr. F.S. Davies, committee

chairman, for his supervision, counsel and patience during this study and

preparation of this manuscript. Appreciation is also extended to Dr. D.A.

Graetz, Dr. KE. Koch, Dr. J.G. Williamson and Dr. H.K. Wutscher for serving

on the committee and for assistance and guidance in this research.

Thanks go to the following who contributed to the research project in

Vero Beach, Fla. the St. Johns Water Management District for funding of this

research, Indian River County for providing funding and the grove to conduct

the project and Arapaho Citrus Inc. for grove management. Special thanks go

to Joseph 'Mike' Rinehart for his assistance and maintaining the daily

operations of the project.

Thanks go to Leonard 'Rip' Rippetoe for his help and friendship during

my stay here at the University. In addition, thanks go to the personnel in the

laboratories of Dr. Graetz, Dr. Locasio and the Analytical Research Laboratory

for their help and assistance in this research.
















TABLE OF CONTENTS


Page


ACKNOWLEDGEMENTS .........

LIST OF TABLES ..............

LIST OF FIGURES ..............


. v


. . . . ix


ABSTRACT ................................


. . x


CHAPTERS


I INTRODUCTION ..........


. . . . 1


II REVIEW OF THE LITERATURE ........................

Irrigation .. . . .. .
Fertilization .................................
Reset Citrus Trees ............................
Reclaimed Wastewater .........................
Freeze Hardiness .............................

III RECLAIMED WASTEWATER IRRIGATION AND FERTILIZATION
OF MATURE 'REDBLUSH' GRAPEFRUIT TREES ON
FLATWOODS SOILS ...............................

Introduction ................................
Materials and Methods .........................
Results and Discussion ........................

IV RECLAIMED WASTEWATER IRRIGATION OF RESET 'MARSH'
GRAPEFRUIT TREES ................. .............

Introduction .................................
Materials and Methods .........................
Results and Discussion ........................


.... 34

.... 34
.... 36
.... 57


.... 99

.... 99
... 101
... 109









V RECLAIMED WASTEWATER AND WELL WATER IRRIGATION OF
YOUNG 'REDBLUSH' GRAPEFRUIT TREES ................. 127

Introduction .................................... 127
Materials and Methods ............................ 129
Results and Discussion ........................... 137

VI LEAF NITROGEN CONTENT EFFECTS ON FREEZE HARDINESS
OF YOUNG 'REDBLUSH' GRAPEFRUIT TREES ............... 156

Introduction .................................... 156
Materials and Methods ............................ 158
Results and Discussion ........................... 161

VII CONCLUSIONS ..................................... 179

APPEN D IX .............................................. 183

A. MONTHLY HISTORICAL AND 1991-93 RAINFALL AND
TEMPERATURE DATA FOR VERO BEACH, FLA .............. 184

LITERATURE CITED ....................................... 185

BIOGRAPHICAL SKETCH ................................... 204














LIST OF TABLES


Table Page

3.1. Total water applied via irrigation to 'Redblush' grapefruit trees at
Vero Beach, Fla., 1990-91 ............................... 38

3.2. Total water applied via irrigation to 'Redblush' grapefruit trees at
Vero Beach, Fla., 1992 ................................. 39

3.3. Total water applied via irrigation to 'Redblush' grapefruit trees at
Vero Beach, Fla., 1993 ................................. 40

3.4. Four and five day schedules and amounts of reclaimed
wastewater irrigation for 'Redblush' grapefruit trees, Vero Beach,
Fla 1990-93 ....................................... 41

3.5. Average chemical analysis of reclaimed wastewater and canal
water from Vero Beach, Fla .............................. 47

3.6. Influent and effluent analyses of enterovirus levels, Vero Beach,
Fla. 1990-93 ................................... ..... 48

3.7. Reclaimed wastewater and canal water effects on vegetative
growth and development of 'Redblush' grapefruit trees at Vero
Beach, Fla., 1989-93 ................................... 60

3.8. Reclaimed wastewater and canal water effect on trunk diameter of
'Redblush' grapefruit tress at Vero Beach, Fla., 1990-9 .......... 61

3.9. Reclaimed wastewater and canal water effects on leaf tissue
nutrient concentration of 'Redblush' grapefruit trees in Vero
Beach, Fla. 1990 ...................................... 63

3.10. Reclaimed wastewater and canal water effect on leaf tissue
nutrient concentration of 'Redblush' grapefruit trees in Vero
Beach, Fla. 1991 ...................................... 64








3.11. Reclaimed wastewater and canal water effects on leaf tissue
nutrient concentration of 'Redblush' grapefruit trees in Vero
Beach, Fla. 1992 ................................

3.12. Reclaimed wastewater and canal water effects on leaf tissue
nutrient concentration of 'Redblush' grapefruit trees in Vero
Beach, Fla. 1993 ................................

3.13. Reclaimed wastewater and canal water effects on yield of
'Redblush' grapefruit tress at Vero Beach, Fla., 1990-94 ...


...... 65



...... 66


. .. 92


4.1. Total water applied via irrigation to 'Marsh' grapefruit trees at Vero
Beach, Fla., 1990-91 ..................................

4.2. Total water applied via irrigation to 'Marsh' grapefruit trees at Vero
Beach, Fla., 1992 ....................................

4.3. Total water applied via irrigation to 'Marsh' grapefruit trees at Vero
Beach, Fla., 1993 ....................................


4.4. Four and five day schedules and amounts of reclaimed
wastewater irrigation for 'Marsh' grapefruit trees, Vero Beach, Fla.,
1990-93 .. .. . . . .

4.5. Reclaimed wastewater and canal water effects on vegetative
growth and development of reset 'Marsh' grapefruit trees planted
Nov. 1990 at Vero Beach, Fla., 1991-93 ...................

4.6. Reclaimed wastewater and canal water effects on tree height of
reset 'Marsh' grapefruit trees planted Nov. 1990 at Vero Beach,
Fla 1990-93 .......................................

4.7. Reclaimed wastewater and canal water effects on trunk diameter
of reset 'Marsh' grapefruit trees planted Nov. 1990 at Vero Beach,
Fla., 1990-93 ......................................

4.8. Reclaimed wastewater and canal water effects on trunk diameter
and tree height of reset 'Marsh' grapefruit trees planted June
1993 at Vero Beach, Fla., 1993 .........................

4.9. Reclaimed wastewater and canal water effects on leaf tissue
concentrations of reset 'Marsh' grapefruit trees planted Nov. 1990
at Vero Beach, Fla., 1991 ..............................


103


104


105


.107



S110



. 111



S112



S113



S115







4.10. Reclaimed wastewater and canal water effects on leaf tissue
concentrations of reset 'Marsh' grapefruit trees planted Nov. 1990
at Vero Beach, Fla., 1992 ............................... 116

4.11. Reclaimed wastewater and canal water effects on leaf tissue
concentrations of reset 'Marsh' grapefruit trees planted Nov. 1990
at Vero Beach, Fla., 1993 ............................... 117

4.12. Reclaimed wastewater and canal water effects on leaf tissue
concentrations of reset 'Marsh' grapefruit trees planted June 1993
at Vero Beach, Fla., 1993 ............................... 121

5.1. Nutrient concentration and pH of well-water and simulated
reclaimed wastewater at Fifield (Arredondo fine sand)(Ridge) and
Horticultural Unit research farms (Kanapaha fine sand)
(flatwoods), 1990-92 .................................. 131

5.2. Visual rating, tree height and trunk diameter measurements of
young 'Redblush' grapefruit trees as affected by water source and
irrigation level in 1990-92, Expt. 1 (Arredondo sand, Ridg ....... 138

5.3. Visual rating, tree height and trunk diameter of young 'Redblush'
grapefruit trees 1990-91 as affected by water source and irrigation
level, Expt. 2 (Kanapaha sand, flatwoods) ................... 139

5.4. Visual rating, tree height and trunk diameter of young 'Redblush'
grapefruit trees as affected by water source and irrigation level,
Expt. 3 1991-92 and Expt. 4 1992 (Kanapaha sand, flatwoods) ... 140

5.5. Leaf tissue nitrogen analysis for young 'Redblush' grapefruit trees
1990-92 as affected by water source and irrigation level, Expts. 1-
4 . . . . . . 14 3

5.6. Leaf tissue phosphorus analysis for young 'Redblush' grapefruit
trees 1990-92 as affected by water source and irrigation level,
Expts. 1-4 .......................................... 146

5.7. Leaf tissue potassium analysis for young 'Redblush' grapefruit
trees 1990-92 as affected by water source and irrigation level,
Expts. 1-4 .......................................... 147

5.8. Leaf tissue sodium analysis for young 'Redblush' grapefruit trees
1990-92 as affected by water source and irrigation level, Expts. 1-
4 . . . . . . 14 9








5.9. Leaf tissue boron analysis for young 'Redblush' grapefruit trees
1990-92 as affected by water source and irrigation level, Expts. 1-
4 . . . . . . 15 1

6.1. Effects of leaf nutrient content on leaf killing point (LKP) of
'Redblush' grapefruit leaves determined by the electrolyte leakage
m ethod, 1991-92 ..................................... 162

6.2. Effects of leaf nutrient content on leaf killing point (LKP) of
'Redblush' grapefruit leaves determined by the visual rating
m ethod, 1991-92 ..................................... 164

6.3. Effects of leaf nutrient content on leaf killing point (LKP) of
'Redblush' grapefruit leaves determined by the electrolyte leakage
m ethod, 1992-93 ..................................... 165

6.4. Effects of leaf nutrient content on leaf killing point (LKP) of
'Redblush' grapefruit leaves determined by the visual rating
m ethod, 1992-93 ..................................... 167

6.5. Visual rating of 'Redblush' grapefruit trees following minimum air
temperatures of -6.5 C on 17 Jan. 1992 .................. 175

6.6. Leaf tissue analysis of 'Redblush' grapefruit trees following
minimum air temperatures of -6.5 C on 17 Jan. 1992 .......... 176














LIST OF FIGURES


Figure Page

3.1. Mean soil moisture content determined by neutron probe
readings taken at a depth of 23 cm (A). Daily rainfall (B) for 1991,
Vero Beach, Fla. ...................................... 52

3.2. Mean soil moisture content determined by neutron probe
readings taken at a depth of 23 cm (A). Daily rainfall (B) for 1991,
Vero Beach, Fla. ...................................... 54

3.3. Mean soil moisture content determined by neutron probe
readings taken at a depth of 23 cm (A). Daily rainfall (B) for 1991,
Vero Beach, Fa. ...................................... 56

3.4. Reclaimed wastewater and canal water effects on fruit growth of
'Redblush' grapefruit at Vero Beach, Fla., 1990 (A) and 91 (B) ..... 73

3.5. Reclaimed wastewater and canal water effects on fruit growth of
'Redblush' grapefruit at Vero Beach, Fa., 1992 (A) and 93 (B) ..... 75

3.6. Reclaimed wastewater and canal water effects on fruit and juice
weight and peel thickness of 'Redblush' grapefruit at Vero Beach,
Fla., 1991-92 ......................................... 77

3.7. Reclaimed wastewater and canal water effects on fruit and juice
weight and peel thickness of 'Redblush' grapefruit at Vero Beach,
Fla., 1992-93 ......................................... 79

3.8. Reclaimed wastewater and canal water effects on fruit and juice
weight and peel thickness of 'Redblush' grapefruit at Vero Beach,
Fla., 1993-94 ......................................... 81

3.9. Reclaimed wastewater and canal water effects on fruit total
soluble solids (TSS), titratable acidity (TA), and TSS:TA ratio of
'Redblush' grapefruit at Vero Beach, Fla., 1991-92 ............. 84







3.10. Reclaimed wastewater and canal water effects on fruit total
soluble solids (TSS), titratable acidity (TA), and TSS:TA ratio of
'Redblush' grapefruit at Vero Beach, Fla., 1992-93 ............. 86

3.11. Reclaimed wastewater and canal water effects on fruit total
soluble solids (TSS), titratable acidity (TA), and TSS:TA ratio of
'Redblush' grapefruit at Vero Beach, Fla., 1993-94 ............. 88

3.12. Reclaimed wastewater and canal water effects on weed growth in
the tree row for 'Redblush' grapefruit at Vero Beach, Fla., 1992
(A) and 93 (B) ........................................ 96

4.1. Reclaimed wastewater and canal water effects on weed growth in
the tree row for 'Marsh' grapefruit at Vero Beach, Fla., 1992 (A)
and 93 (B) ......................................... 124

6.1. Average, maximum and minimum daily temperatures (A), Leaf
killing point (LKP) determined by the electrolyte leakage method
(B), Leaf killing point (LKP) determined by the visual rating
method (C), in 1991-92 ................................ 170

6.2. Average, maximum and minimum daily temperatures (A), Leaf
killing point (LKP) determined by the electrolyte leakage method
(B), Leaf killing point (LKP) determined by the visual rating
method (C), in 1992-93 ................................ 172













Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

MICROSPRINKLER IRRIGATION OF MATURE, RESET,
AND YOUNG GRAPEFRUIT (CITRUS PARADISI MACF.)
TREES WITH RECLAIMED WASTEWATER

By

Michael Alvin Maurer

December, 1994


Chairman: Frederick S. Davies
Major Department: Horticultural Sciences


Several experiments were conducted on mature, reset and young

grapefruit trees to determine the effect of reclaimed wastewater on growth,

development and yield in Florida.

An experiment was designed to determine the effects of canal water and

reclaimed wastewater on growth and yield of mature 'Redblush' grapefruit

(Citrus paradisi Macf.) trees. Trees receiving low (23.1 mm-wk1) and moderate

(30.7 mm-wk1) levels of reclaimed wastewater had the largest tree canopies,

trunk diameters and highest yields. Fruit growth rate, size, juice weight, total

soluble solids (TSS), titratable acidity (TA), and TSS:TA ratio were similar

among treatments 2 of 3 years. Peel thickness was similar for all treatments.







Leaf boron (B) levels were similar for all reclaimed wastewater treatments, but

were lower for the canal water treatment. Heavy metal concentrations in the

reclaimed wastewater were low or non-detectable. Similarly, enteric viruses in

the effluent were always < 0.003 plaque-forming units per liter. Weed growth

increased as irrigation levels increased.

Two field studies were designed to determine the effects of canal water

and reclaimed wastewater on reset 'Marsh' grapefruit trees. Tree growth and

development was similar for all treatments during the first 3 years after

planting. Leaf B levels were significantly higher for trees receiving reclaimed

wastewater compared to those receiving canal water, however; no B toxicity

was observed. Reclaimed wastewater again increased weed growth compared

to the canal water treatment.

Four field studies were designed to determine the effects of well water

and reclaimed wastewater at 3 irrigation levels and 3 water and fertilization

sources on growth and development of newly planted 'Redblush' grapefruit

trees. Trees receiving reclaimed wastewater plus fertigation were more

vigorous and larger than trees receiving other treatments and had greater

yields in the third year. Trees receiving reclaimed wastewater alone were less

vigorous and visually N deficient. Leaf Na and B levels increased in trees

receiving reclaimed wastewater, but were below toxic levels.

Reclaimed wastewater irrigation of citrus has several potential

advantages, with increased weed growth being the only major disadvantage.







Nevertheless, proper drainage and grove design are necessary when regularly

applying reclaimed wastewater to citrus groves.













CHAPTER I


INTRODUCTION



Citrus is the most economically important fruit crop grown in Florida with

more than 300,000 ha planted and annual production of 11.1 million tons in

1992-93. (Florida Dept. of Agr., 1992). In recent years increased urbanization

and planting of citrus in South Florida has put ever- increasing demands on

the water supply. Urbanization also causes problems with efficient and

environmentally safe disposal of reclaimed wastewater (Katterman and Day,

1987). Previously, disposal of reclaimed wastewater was into waterways, but

passage of the Federal Water Pollution Control Act of 1972 and the Clean

Water Act of 1977 discouraged the direct discharge of reclaimed wastewater

into surface waters (Gleason et al., 1984). Presently, about 41% of all water in

Florida is used for agricultural purposes (Fernold and Patton, 1984) and 34%

of this water is used to irrigate citrus (Smajstrla et al., 1992). Irrigation of citrus

trees with reclaimed wastewater provides a means of wastewater disposal and

a water and nutrient source for citrus trees. However, only about 2% of









growers in Florida are currently using reclaimed wastewater to irrigate citrus

groves (Ferguson and Taylor, 1993).

Citrus trees require irrigation in Florida to achieve optimum growth and

production (Koo, 1963). The low water holding capacity of Ridge and flatwoods

soils makes trees susceptible to drought during periods of low rainfall.

Conversely, flatwoods soils are also poorly drained due to the presence of a

relatively impermeable subsurface layer which may result in flooding during

periods of heavy rainfall. Reclaimed wastewater treatment facilities require the

frequent disposal of effluent throughout the year, even at times when citrus

trees may not need irrigation. It is important to determine the volume of

reclaimed wastewater that can be applied to the grove without causing drought

or flooding stress.

Citrus trees in Florida are generally grown on sandy soils of low native

fertility, which require fertilization for optimum tree growth and production.

Fertilization requirements for citrus trees are well defined for mature and young

citrus trees (Ferguson and Davies, 1989; Koo et al., 1984). Reclaimed

wastewater contains many essential plant nutrients, especially N, P and K, and

irrigation with reclaimed wastewater may have an effect similar to that of

frequent fertigation with a dilute concentration of plant nutrients (Neilsen et al.,

1989a). Moreover, the use of reclaimed wastewater may reduce or eliminate

the need for additional fertilization. In addition, citrus trees irrigated with








3
reclaimed wastewater may reduce contamination of surface and ground water

by taking up plant nutrients contained in reclaimed wastewater.

Reclaimed wastewater also has some potential drawbacks due to the

presence of heavy metals, salinity, viruses and bacteria. Heavy metals are

typically associated with industrial wastewater and may be detrimental to plant

growth and human health; however, non-industrial wastewater generally has

low or non-detectable levels. Likewise, elements such as Na, Cl and B in

reclaimed wastewater may reduce citrus tree growth if toxic levels occur. In

addition, viruses and bacteria present in reclaimed wastewater may pose a

potential hazard to workers and consumers. However, the level of heavy

metals, salinity, viruses and bacteria vary depending on the location and

source of reclaimed wastewater. Vital to the use of reclaimed wastewater is the

understanding of how frequently applied reclaimed wastewater influences the

growth and development of mature, reset and young citrus trees.

Citrus tree freeze hardiness has been associated with nutrient levels and

fertilization rates for many years. Field observations of post-freeze damage

from numerous fertilization studies indicate that high N levels increase freeze

hardiness of citrus trees. However, no replicated field studies have been

conducted to determine the effects of leaf N concentrations on freeze

hardiness of young citrus trees throughout the winter.

The results of these experiments may be useful to optimize the use of

reclaimed wastewater for mature, reset and young citrus trees, potentially








4
reducing irrigation and fertilization costs. Determining the potential effects of

leaf N levels on young citrus tree freeze hardiness may influence fertilization

programs for young trees. This research should enable growers to efficiently

and safely use reclaimed wastewater for irrigation of citrus trees and may lead

to an increase in reclaimed wastewater use.














CHAPTER II


REVIEW OF THE LITERATURE



Irrigation and fertilization are two important factors essential for

achieving optimum citrus tree growth and production. The use of reclaimed

wastewater for irrigation of citrus trees is also a potential source of water and

nutrients. Reclaimed wastewater provides a consistently available water source,

but disposal of large quantities of reclaimed wastewater may cause flooding of

the grove during periods of heavy rainfall. Reclaimed wastewater also contains

many essential plant nutrients (Berry et al., 1980; Bielorai et al., 1984; Feigin et

al., 1984; Neilsen et al., 1989a) which reduce fertilization rates. The uptake of

plant nutrients from reclaimed wastewater by citrus trees may prevent surface

and/or ground water contamination (Sanderson, 1986). In addition, reclaimed

wastewater may be used for freeze protection (McMahan et al., 1989).

Potential disadvantages of reclaimed wastewater use include the presence of

heavy metals (Kirkham, 1986; Omran et al., 1988), salinity (Basiouny, 1982;

Kirkham, 1986) and health risks associated with viruses and bacteria in

reclaimed wastewater (Basiouny, 1982; Berry et al., 1980; Brenner et al., 1988;









Gleason et al., 1984; Rose and Gerba, 1991). Understanding the influence of

reclaimed wastewater on the growth and development of mature, reset and

young citrus trees is critical for the safe and efficient use of reclaimed

wastewater.



Irrigation

Irrigation is essential for citrus trees to achieve maximum growth and

production (Koo, 1963) and reclaimed wastewater is a potential source of low

cost, useable irrigation water. Although Florida's climate is characterized by an

average annual rainfall of 1300-1500 mm, rainfall distribution occurs in irregular

patterns. Rainfall distribution is characterized by periods of heavy rainfall in the

summer and low rainfall during the winter and spring. Low rainfall particularly

in the spring combined with the low water holding capacity of most Florida

soils requires the use of irrigation to maintain optimum soil moisture levels for

tree growth.

The low water holding capacity of Ridge and flatwoods soils makes

trees susceptible to drought during periods of low rainfall. The extensive root

system of trees on the Ridge provides a large volume of soil with which to

obtain available water (Ford, 1952; Reitz and Long, 1955). In contrast, trees on

flatwoods soils have a small root system and soil volume (Calvert et al., 1967;

Calvert et al., 1981; Ford, 1952; Reitz and Long, 1955; Young, 1951). Graser

and Allen (1987) found that transpiration and soil evaporation can deplete









available soil moisture to 75% in 2 days, 50% in 4 days and to less than

permanent wilting point in 8 days. However, the upward flux of water from the

water table helps meet the water needs of citrus trees grown on flatwoods soils

(Graser and Allen, 1987; Obreza and Admire, 1985). In addition, irrigation

frequencies and durations are different for citrus trees on flatwoods and Ridge

soils. Trees grown on flatwoods soils require more frequent irrigations of

shorter duration compared to trees grown on the Ridge (Parsons, 1989).



Mature citrus tree irrigation

The objective of citrus tree irrigation is to obtain maximum production

with the least quantity of water (Koo, 1985b). Irrigation of citrus trees increased

tree growth and production in many citrus regions (Chilembwe, 1985;

Constantin et al., 1975; Hilgeman, 1966; Hilgeman and Sharp 1970; Huberty

and Richards, 1954; Koo, 1963; Koo, 1969; Koo, 1975; Koo, 1979; Koo, 1985b;

Koo and Sites, 1955; Koo and Smajstrla, 1984; Koo et al., 1974; Levy et al.,

1978a; Metochis, 1989; Sites et al., 1951; Wiegand and Swanson, 1982a;

Wiegand and Swanson 1982b; Zekri and Parsons, 1989; Ziegler, 1955). The

increase in tree size from irrigation may account for the increase in yield (Koo

1969; Levy et al., 1978a; Sites et al., 1951). However, maintaining high soil

moisture levels throughout the entire year failed to induce fruit setting and yield

proportional to tree size (Boman, 1992; Chilembwe, 1985; Hilgeman and

Sharpe, 1970; Koo 1963; Koo, 1969). Metochis (1989) in Cyprus found that









irrigation in excess of the crop requirement had no affect on fruit growth or

production of 'Marsh' grapefruit trees. Irrigation is particularly critical during

specific times of the year for increasing fruit set (Constantin et al., 1975;

Hilgeman and Sharpe, 1970; Koo, 1963; Koo, 1969; Koo and Sites, 1955; Sites

et al., 1951) reducing number of 'off bloom' fruit (Koo and Sites, 1955; Reese

and Koo, 1976; Sites et al., 1951), increasing fruit size (Hales et al., 1968;

Hilgeman, 1966), and reducing fruit drop (Boman, 1992; Koo, 1963; Koo,

1969).

Irrigation of mature citrus trees in Florida is currently recommended at

one-third soil water depletion from Jan.-June and two-thirds soil water

depletion from July-Dec. Irrigation at these levels provided the most efficient

use of water while maintaining tree growth and production (Koo, 1963). In a

similar study on the flatwoods, navel orange trees irrigated at 30% soil water

depletion throughout the year had similar tree growth and production as trees

irrigated at 50% soil water depletion (Boman, 1992). Although high soil

moisture content (one-third depletion) throughout the year on flatwoods and

Ridge soils increased production, the increased number of irrigations required

was not economically justified (Boman, 1992; Koo, 1963).



Fruit quality and development

Irrigation of mature citrus trees affects fruit growth and quality. However,

limited information is available on fruit growth and quality of trees irrigated







9
above optimum levels as would be the case when using reclaimed wastewater.

Sites et al. (1951) found that irrigated trees had greater fruit size than fruit from

nonirrigated trees. In addition, dry periods 3 months after fruit set decreased

fruit size which could not be regained by subsequent irrigation. Hales et al.

(1968) found that soil moisture tension correlated with average fruit volume

increase and that greater soil moisture tension decreased fruit size. In addition,

fruit size is a function of fruit set with less fruit per tree producing larger fruit

sizes (Hilgeman, 1966; Hilgeman and Sharpe, 1970). In contrast, Boman

(1992) found that fruit weight and fruit size distribution of navel oranges were

similar for trees irrigated at 30% or 50% soil water depletion.

Fruit juice content is also influenced by irrigation. Increases in juice

content of fruit for irrigated vs. nonirrigated citrus trees are well documented

(Bielorai, 1982; Calvert et al., 1967; Koo, 1963; Koo, 1969; Sites et al., 1951).

However, Cruse et al. (1982) in Texas found no difference in juice content for

trees irrigated at 40% and 60% soil water depletion, but juice content was

greater than trees receiving irrigation at 80% soil water depletion. Hilgeman

and Sharpe (1970) also found no difference in juice content for trees receiving

1.72 and 1.35 m of water annually, but juice content was greater than for trees

irrigated with 0.95 m of water. In Florida, Graser and Allen (1987) found no

difference in juice content of trees irrigated at intervals of 2-3 days vs. 14 days,

but juice content was significantly greater than nonirrigated trees. Boman

(1992) found no difference in juice content for trees irrigated at 30% and 50%







10
soil water depletion. The results of these irrigation studies clearly indicate that

trees receiving irrigation had increased fruit juice content compared to

nonirrigated trees. However, irrigation at greater than 50% soil water depletion

did not increase fruit juice content.

Peel thickness is primarily influenced by climate (Reuther, 1973) and K

levels (Embleton et al., 1973). Increases in peel thickness from irrigation have

also been reported by Constantin et al. (1975); however, the increase in peel

thickness (10%) was associated with a 30% increase in fruit size. Metochis

(1989) in Cyprus found no difference in peel thickness for trees irrigated at

39%, 55% and 63% of pan evaporation. In contrast, Hilgeman and Sharpe

(1970) in Arizona found a decrease in peel thickness for trees receiving 1.72

and 1.35 m of water compared to trees receiving 0.95 m of water. Omran et al.

(1988) in Egypt reported that peel thickness increased during the years that

reclaimed wastewater was used. However, this may be attributed to an

increase in soil K levels from long-term use of reclaimed wastewater.

Reductions in fruit total soluble solids (TSS) resulting from irrigation are

well documented (Bielorai, 1982; Cruse et al., 1982; Graser and Allen, 1987;

Hilgeman and Sharpe, 1970; Koo, 1963; Koo, 1969; Koo, 1985b; Koo and

Reese, 1976; Koo and Sites, 1955; Metochis, 1989; Sanchez Blanco et al.,

1989; Sites et al., 1951; Ziegler, 1955) with irrigation in the fall affecting TSS

more than at other times due to dilution of TSS (Cruse et al., 1982; Koo, 1963;

Koo and Sites, 1955). Similarly, Zekri and Koo (1993) found a dilution of TSS








11
for trees irrigated with reclaimed wastewater which received a larger volume of

water than well water irrigated trees. Fruit TSS was similar for navel orange

trees irrigated at 30% and 50% soil water depletion (Boman, 1992).

Titratable acidity (TA) generally decreases as levels of irrigation increase

(Bielorai, 1982; Cruse et al., 1982; Graser and Allen, 1987; Hilgeman and

Sharpe, 1970; Koo, 1963; Koo, 1969; Koo, 1985b; Koo and Sites, 1955; Levy

et al., 1978b; Metochis, 1989; Sanchez Blanco et al., 1989; Sites et al., 1951).

Zekri and Koo (1993) observed a reduction in fruit TA from reclaimed

wastewater irrigation which was applied at higher rates than well water. Koo

and Smajstrla (1984) found that fruit TA was similar for 3 of 5 years for trees

receiving 0.3 and 0.6 m of water annually. Fruit TA was similar for trees

irrigated at 30% soil water depletion compared to 50% for 2 of 3 years for

navel orange fruit (Boman, 1992).

The effects of irrigation on fruit TSS:TA ratios are variable. Sites et al.

(1951) found a significantly higher fruit TSS:TA ratio for irrigated 'Duncan'

grapefruit trees compared to nonirrigated trees, but no difference in fruit

TSS:TA ratio for 'Marsh' grapefruit trees. Many other irrigation studies have

reported no difference in fruit TSS:TA ratios (Bielorai, 1982; Graser and Allen,

1987; Hilgeman and Sharpe, 1970; Koo and Smajstrla, 1984; Metochis, 1989).

For example, Boman (1992) found similar fruit TSS:TA ratios for trees irrigated

at 30% and 50% soil water depletion. However, in the Conserv II project fruit









TSS:TA ratio was increased in 4 of 6 years for trees receiving reclaimed

wastewater compared to well water trees. (Zekri and Koo, 1993).



Youna citrus tree irrigation

Irrigation of young citrus trees is substantially different from that of

mature citrus trees. Young citrus trees because of their limited root zone are

more susceptible to water stress than mature citrus trees and require more

frequent irrigations. In Florida 68% of growers use microsprinklers to irrigate

young citrus trees (Taylor et al., 1989). Smajstrla (1993) reported that

microirrigation increased young tree growth compared with conventional

irrigation methods and the return on investment is often realized 1- to 2-years

earlier using microirrigation.

In Arizona, trickle and basin irrigation systems provided the greatest

growth and reduced water use for young orange trees compared to flooding

and sprinkler irrigation (Roth et al., 1974). In Texas, Leyden (1975) compared

strip, ring and drip irrigation on newly planted grapefruit trees. Tree growth

was similar during the first 2 years for all three irrigation methods. Similarly,

Swietlik (1992) for 'Ray Ruby' grapefruit found that tree growth was similar for

trees trickle or flood irrigated at 16% and 50% soil water depletion,

respectively, but flood irrigated trees used 90% less water. In Florida, 'Valencia'

orange trees irrigated at 45% soil water depletion were more vigorous than

trees irrigated at 30% or 55% soil water depletion on an Arredondo fine sand.









In addition, the soil was continuously wet for trees irrigated at 30% soil water

depletion (Smajstrla et al., 1985). Marler and Davies (1990) found that

microsprinkler irrigated 'Hamlin' orange trees at 20-45% soil water depletion

were more vigorous than trees irrigated at 65% soil water depletion on a

Kanapaha fine sand. Maintaining high soil moisture levels required irrigation 2

to 3 times per week during periods of no rainfall.



Flooding

Flatwoods soils are poorly drained due to low elevation and the

presence of a relatively impermeable subsurface layer, which often leads to

periods of flooding. Frequent irrigations required with reclaimed wastewater

use may lead to flooding or increase the level of the water table. Irrigations or

rainfall of 3.8 mm have been shown to influence the level of the water table on

flatwoods soils (Obreza and Admire, 1985). Flooding results in reduced

photosynthesis and growth, dieback and sometimes death of citrus trees in the

flatwoods (Ford, 1964; Reitz and Long, 1955; Young, 1943; Young, 1951).

Plant responses to flooding have been reviewed by Kozlowski (1984)

and Schaffer et al. (1992). Flooding tolerance is most often defined as the

plant's ability to grow and survive in soils when water content is above field

capacity (Andersen et al., 1984). However, growth reductions are often not

apparent until long after the period of flooding (Kozlowski, 1984). Most plant

responses to flooding result from a reduction in oxygen in the root zone









(Bradford and Yang, 1981). Citrus trees are characterized as flood sensitive

compared to other fruit crops (Kozlowski, 1984; Schaffer et al., 1992), but

flooding tolerance varies among citrus rootstocks. For example, 'Hamlin'

orange trees on sour orange rootstock flooded for 30 days resulted in dieback

or death of 90% of the trees, whereas trees on rough lemon rootstock after

flooding for 60 days, only 20% of trees had dieback or were dead (Vu and

Yelenosky, 1991; Vu and Yelenosky, 1992).

Flooding affects several physical, physiological and biochemical

processes in the soil and the plant. Flooding restricts pore space and limits

oxygen diffusion to the roots (Graser and Allen, 1988; Kramer, 1951; Stolzy

and Letey, 1965). Decreases in soil oxygen resulted in decreased root and top

growth of apples (Childers and White, 1942), prunes, peaches (Boynton and

Compton, 1943), and citrus (Bevington and Castle, 1985; Syvertsen et al.,

1983). Roots of citrus seedlings growing in soil with an oxygen diffusion rate

(ODR) of less than 0.11 ug*-cm-.min-' stopped growing and were damaged. In

contrast, citrus roots grew in soil with an ODR of 0.22 to 0.24, but at a reduced

rate when compared to soils with an ODR above 0.63 (Stolzy et al., 1965).

Shoot growth and root health of citrus seedlings declined within 8 days of

flooding due to anoxic soil conditions (Syvertsen et al., 1983). Similarly, shoot

growth and root health of field grown citrus trees declined after 14 days of

flooding (Graser and Allen, 1988). Low oxygen levels reduced root permeability

and restricted water uptake (Graser and Allen, 1987). Schaffer and Moon









(1990) found that 'Tahiti' lime trees exposed to flooding for 7 days had

reduced net CO2 assimilation and transpiration, but net CO, and transpiration

generally recovered to pre-flooding levels after 7 days of nonflooding. Citrus

trees under flooded conditions resulted in decreases in leaf water potential

(Ford, 1984; Graser and Allen, 1987; Phung and Knipling, 1976; Syvertsen et

al., 1983), stomatal conductance (Ford, 1984; Graser and Allen, 1987; Vu and

Yelenosky, 1991), transpiration (Phung and Knipling, 1976; Schaffer and Moon,

1990), and net CO, assimilation (Phung and Knipling, 1976; Schaffer and

Moon, 1990; Syvertsen et al., 1983; Vu and Yelenosky, 1992).

Nutrient uptake by plants is also affected by flooding. Levels of N, P, K,

Ca, Mg, Mn and Zn were reduced in avocado leaves for trees grown in flooded

soils with 02 levels of <2% (Slowik et al., 1979). Concentrations of N, P, K, Ca

and Mg decreased while Na increased in citrus seedlings under flooded

conditions (Labanauskas et al., 1966). Similarly, B, Cu, Fe, Mn and Zn levels

decreased as oxygen decreased, but Na and CI levels increased in the foliage

of citrus seedlings (Labanauskas et al., 1971).



Fertilization

Citrus trees in Florida are generally grown on sandy soils of low native

fertility (Koo et al., 1984), therefore fertilization is necessary to attain acceptable

growth and production. Reclaimed wastewater has the potential to reduce or

eliminate the need to fertilize citrus trees. Applications of macronutrients are








16

generally required on an annual basis to avoid nutrient deficiencies (Koo et al.,

1984), but micronutrients are required less frequently (Koo, 1988; Wutscher

and Obreza, 1987).



Fertilization methods

Fertilization methods and timing are changing due to the use of

irrigation systems to apply fertilizer ('fertigation'). Nitrogen uptake was affected

by method of irrigation with trickle irrigated citrus trees having higher leaf N

concentrations than flood-irrigated trees (Roth et al., 1981; Wutscher et al.,

1975). Fertilizer efficiency is associated with soil moisture with high soil

moisture levels increasing nutrient uptake (Bravdo et al., 1992; Koo, 1979). Koo

(1980) found that fertilization of 60% to 70% of the root zone was critical for

adequate mature tree growth in Florida. In addition, tree growth was similar for

trees receiving fertigation 3- or 10-times/yr or granular fertilizer at comparable

rates (Koo, 1980). Likewise, there was no advantage or disadvantage to the

combination of granular fertilization and fertigation at 15% and 30% of the total

N requirement (Koo and Smajstrla, 1984). However, Dasberg et al. (1988) on

mature 'Shamouti' orange trees in Israel observed an increase in yield for trees

fertigated at 160 kg N/ha compared to trees receiving broadcast fertilization,

but no difference in tree growth or yield between fertilization methods at 280

kg N/ha. Similarly, for young trees Smajstrla (1993) reported that fertigation

increased tree growth compared to granular fertilizer. However, Willis et al.









(1991) found no difference in tree growth between fertilization methods

(granular vs fertigation) for young 'Hamlin' orange trees. However, fertigation at

30 times/yr increased trunk diameter of 'Hamlin' orange trees on a Carrizo

citrange rootstock grown on Arredondo fine sand, but not on a Kanapaha fine

sand (Willis et al., 1990).

The loss of nutrients by leaching is a growing concern due to the

potential contamination of waterways and ground water. Frequent fertilizer

applications ensure that nutrients are being supplied to the tree and reduce

losses from excessive rainfall or irrigation (Ferguson and Davies, 1989). Rainfall

or irrigation above field capacity are major causes of nutrient leaching (Mansell

et al., 1980). Willis et al. (1990) found that for young citrus trees most N

leaching occurred when recommended levels (0.22 kg N/tree per yr) of

fertilizer were applied 5 times/yr, but N leaching was significantly reduced with

more frequent applications. Similarly, for mature citrus trees leaching

accounted for < 50 kg N/ha for trees fertilized at 100 and 180 kg N/ha, but

leaching resulted in losses of > 50 kg N/ha for tree receiving 280 kg N/ha.

Significant quantities of N were unaccounted for and may be incorporated in

the soil organic matter (Dasberg et al., 1984).



Mature citrus tree fertilization

Fertilization of mature citrus trees is essential to maintain a highly

productive grove. Fertilization rates have been established for many citrus









producing areas (Calvert and Reitz, 1964; Dasberg et al., 1983; Hume et al.,

1985; Koo et al., 1984; Reese and Koo, 1976; Reitz and Koo, 1959; Sites et al.,

1953; Sites et al., 1961). In Florida, current fertilizer recommendations for

mature citrus trees are based on the previous seasons yield. Nitrogen rates are

based on 0.14 and 0.18 kg N/box of fruit for grapefruit and orange trees,

respectively (Koo et al., 1984). Mature citrus trees require 100 to 340 kg N/ha

per yr however rates above 225 kg N/ha are rarely justified.

Numerous field studies have been conducted to determine the optimum

number and timing of N fertilization for mature citrus trees. Leyden (1966) in

Texas found that fertilizer applied prior to bloom resulted in higher yield than

applications after bloom. In contrast, Dasberg et al. (1983) in Israel found that

leaf growth of the spring flush was dependent mainly on tree N reserves and

not uptake from the soil. In Florida, frequency and timing of fertilization had

minimal effects on tree growth compared to fertilization rate (Calvert and Reitz,

1964; Reuther and Smith, 1954; Sites et al., 1961). Tree growth was similar for

trees receiving 1- or 2-fertilizations a year, but more frequent applications were

unwarranted under normal conditions. However, trees planted on coarse or

shallow soils may require 3- or 4-applications a year because of leaching or a

restricted root system. Likewise, more frequent applications may be necessary

in years of heavy rainfall or following hurricanes (Koo et al., 1984).









Young citrus tree fertilization

Nutrient requirements have been established for young citrus trees

grown on the flatwoods (Calvert, 1969) and Ridge areas of Florida (Rasmussen

and Smith, 1961). Current fertilizer recommendations range from 0.14-0.27,

0.25-0.41, and 0.35-0.58 kg N/tree per yr applied 5-6, 4-5 and 3-4 times/yr for

1-, 2-, and 3-year old trees, respectively (Ferguson and Davies, 1989; Koo et

al., 1984). In addition, it is recommended that fertilization include nutrients in

the following ratios 8N-8P-8K-1.6Mg-0.4Mn-0.2Cu-0.05B. Willis et al. (1991)

found that trees fertigated at recommended rates (0.22 kg N/tree per yr)

produced the most vigorous growth compared to trees receiving 0.06 and 0.11

kg N/tree per yr. However, Marler et al. (1987) found no difference in tree

growth for trees receiving 0.07 or 0.22 kg N/tree per yr. Lkewise, Guazzelli

(1994) found no difference in tree growth related to fertilization rate in the first

year. Recent research indicates that fertilization at one-half (0.11 kg N/tree per

yr) the recommended rate (0.22 kg N/tree per yr) produced trees of similar

vigor (Ferguson et al., 1990; Obreza, 1990; Obreza and Rouse, 1993). In

addition, newly planted citrus trees may have considerable N reserves from the

nursery, which may account for similar tree growth in the first year.



Reset Citrus Trees

Uterature on reset citrus trees is limited and most information on reset

management comes from young tree studies. Resets are defined as trees 1- to








20
3-years old planted to replace dead or unproductive trees within an established

grove (Florida Dept. of Agr., 1992). Reset management is essential in

maintaining a highly productive and economically viable grove with over 50%

of growers planting resets annually (Ferguson and Taylor, 1993).

Tree losses in Florida are associated with climatic conditions and the

increased incidence of disease. Annual losses of mature citrus trees typically

average 4% to 5% a year (Ferguson and Taylor, 1993; Muraro, 1988; Muraro

and Holcomb, 1993) and losses of 4% to 6% of resets in the first year after

planting (Jackson et al., 1986; Taylor et al., 1989). Tree losses are often

accelerated by diseases such as foot rot and blight or the occurrence of

severe freezes.

The care and management costs of resets are significantly higher than

for solid plantings of young citrus trees (Jackson et al., 1986; Muraro and

Niles, 1976) because resets are typically scattered throughout an established

grove. Fertilization and irrigation of resets is likewise difficult as resets must

compete with mature citrus trees and weeds for available soil nutrients and

moisture. Reset fertilization is important to prevent nutritional deficiencies and

stimulate growth (Jackson, 1981). In addition, weed control is particularly

important as weeds compete for available soil moisture and nutrients and can

significantly reduce young tree growth (Smajstrla et al., 1985). Resets having a

limited root zone often do not receive adequate water when irrigated on a

mature tree schedule or irrigation system (Jackson, 1981). Currently, about








21
70% of reset acreage is irrigated with microsprinklers with 57% of the irrigation

systems designed for fertigation (Ferguson and Taylor, 1993). However,

fertigation or granular materials applied at mature grove rates may be

inadequate to meet the nutritional requirements of resets because of their

limited root zone, thus supplemental fertilization may be necessary. The use of

controlled release fertilizers may be particularly useful for fertilization of resets

to reduce application frequency and reduce leaching of the fertilizer (Obreza,

1990).



Reclaimed wastewater

Reclaimed wastewater has been successfully used to irrigate many

agronomic crops, such as sorghum (Day and Cluff, 1985), cotton (Bielorai et

al., 1984; Feigin et al., 1984; Oran and DeMalach, 1987; Papadopoulos and

Stylianou, 1988a), bermuda grass (Day et al., 1984; Hayes et al., 1990;

Mancino and Pepper, 1992), Kentucky bluegrass, reed canary grass, orchard

grass, tall fescue (Clapp et al., 1984; Marten et al., 1979), smooth bromegrass,

quackgrass, Timothy (Marten et al., 1979), rye grass (Hayes et al., 1990), corn,

alfalfa (Campbell et al., 1983; Marten et al., 1979), sunflower (Papadopoulos

and Stylianou, 1991), wheat (Campbell et al., 1983; Tripathi et al., 1990),

vegetables (Neilsen et al., 1989c; Schalscha and Vergara, 1982; da Costa

Vargas et al., 1991) and forest trees (Hopmans et al., 1990; Stewart and Flinn,

1984; Stewart et al., 1990). Reclaimed wastewater has also been used for








22
irrigation of fruit crops such as grapes (Neilsen et al., 1989b), cherries (Neilsen

et al., 1991), peaches (Basiouny, 1984), apples (Neilsen et al., 1989a), and

citrus (Kale and Bal, 1987; Koo and Zekri, 1989; McMahan et al., 1989; Omran

et al., 1988; Overman et al., 1987; Parsons and Wheaton, 1992; Wheaton and

Parsons, 1993; Wood, 1988; Zekri and Koo, 1990; Zekri and Koo, 1993).

Reclaimed wastewater composition and treatment costs vary

considerably with location. Water quality is dependent on three major

variables; 1) quality of the original water source; 2) type of use; and 3)

renovation treatment (primary, secondary or tertiary treatment of the influent)

(Berry et al., 1980). However, reclaimed wastewater composition varies locally

and temporally even within the same treatment facility (Basiouny, 1982).

Treatment facilities with secondary treatment filtration and disinfection produce

reclaimed wastewater which can be used for non-restricted irrigation (Rose and

Gerba, 1991) and can become a permanent component in an integrated water

supply system (Asano and Tchobanoglous, 1991). The cost of reclaimed

wastewater depends on whether the local treatment facility personnel view the

reclaimed wastewater as a disposal problem or as the marketing of a natural

resource (Berry et al., 1980). In Florida, reclaimed wastewater at the Conserv II

project is an inexpensive water source as compared to pumping ground water

because water and pumping costs are free to the grower (McMahan et al.,

1989).








23
Treated reclaimed wastewater contains many plant nutrients in varying

concentrations (Berry et al., 1980; Bielorai et al., 1984; Feigin et al., 1984).

Plant nutrients in reclaimed wastewater are typically considered pollutants, as

N and P can cause eutrophication of streams and lakes when disposed of into

waterways (Sanderson, 1986). Conversely, the presence of a crop on land

used for reclaimed wastewater disposal could remove unwanted materials

(Terry and Tate, 1981) and the use of plant nutrients may prevent pollution of

surface and ground waters (Sanderson, 1986). In addition, irrigation with

reclaimed wastewater may be similar to continuous fertigation with a dilute

concentration of plant nutrients, particularly N, P and K (Berry et al., 1980;

Neilsen et al., 1989a).

Reclaimed wastewater use has been associated with increases in

growth and production of many agronomic crops (Campbell et al., 1983; Day

et al., 1984; Hayes et al., 1990; Marten et al., 1979; Neilsen et al., 1989c; Oron

and DeMalach, 1987; Papadopoulos and Stylianou, 1988b; Papadopoulos and

Stylianou, 1991). Similarly, proper management of reclaimed wastewater

irrigation for fruit crops may produce economic gains of 25-30% (Basiouny,

1982). Increases in growth and production from reclaimed wastewater irrigation

have been reported for peaches (Basiouny, 1984), apples (Neilsen et al.,

1989a), cherries (Neilsen et al., 1991), grapes (Neilsen et al., 1989b) and citrus

in India (Kale and Bal, 1989), Egypt (Omran et al., 1988), and Florida (Koo and








24
Zekri, 1989; Parsons and Wheaton, 1992; Wheaton and Parsons, 1993; Zekri

and Koo, 1993).

Reclaimed wastewater has the potential to add considerable quantities

of plant nutrients to the crop. In Chile, untreated reclaimed wastewater added

an estimated 780 kg N/ha per yr to vegetable crops via irrigation with 160-290

kg N/ha removed by the crop (Schalscha and Vergara, 1982). However,

current regulations in Florida require that reclaimed wastewater released from

the treatment facility contain < 10 mg- liter"1 NO3 (Florida Dept. of

Environmental Regulation, 1982). The volume of reclaimed wastewater used

and concentration of elements within the reclaimed wastewater determine the

amount of each element applied. Reclaimed wastewater limited the amount of

N and P fertilizer necessary to obtain high yields for sunflowers (Papadopoulos

and Stylianou, 1991) and vegetables (Neilsen et al., 1989c). Turfgrass irrigated

with reclaimed wastewater showed signs of over-fertilization when N levels

were not reduced (Hayes et al., 1990). Nitrogen concentrations increased in

cotton plants receiving reclaimed wastewater compared to plants receiving well

water (Papadopoulos and Stylianou, 1988a). Likewise, N from reclaimed

wastewater was efficiently taken up by sudax (Sorghun vulgare x S.

sudanense)(Papadopoulos and Stylianou, 1988b). In Australia, Stewart et al.

(1990) estimated that river red gum, flooded gum, Sydney blue gum, river she-

oak, radiata pine and poplar trees accumulated about one-third of the N

applied in reclaimed wastewater. Leaf N, P and K concentrations were








25
increased in fruit crops receiving reclaimed wastewater for cherries (Neilsen et

al., 1991), grapes (Neilsen et al., 1989c), apples (Neilsen et al., 1989a), and

peaches (Basiouny, 1984). For citrus Omran et al. (1988) found increases in

leaf N content for trees receiving reclaimed wastewater, but Zekri and Koo

(1993) found no difference in leaf N concentration due to high rates of N

fertilization for trees receiving reclaimed wastewater and well water. Similarly,

leaf K levels were the same for all treatments possibly due to yield. However,

leaf P was significantly increased for trees receiving reclaimed wastewater

compared to well water trees (Zekri and Koo, 1993).

Fruit growth and quality characteristics are also influenced by reclaimed

wastewater. Fruit from peach trees irrigated with reclaimed wastewater reached

maturity 7 to 10 days earlier than trees receiving well water. Titratable acidity

(TA) levels were reduced, but total soluble solids (TSS) increased (Basiouny,

1984). In contrast, fruit TA was not affected, but pH and TSS were increased

for grapes irrigated with reclaimed wastewater (Neilsen et al., 1989b).

Reclaimed wastewater irrigation of 'Mclntosh' and 'Red Delicious' apple trees

increased fruit number compared to trees receiving well water, but fruit size

was increased only for 'Red Delicious' apples (Neilsen et al., 1989a). In Egypt,

Omran et al. (1988) found increases in fruit weight, peel thickness and yield for

'Valencia' orange trees irrigated with reclaimed wastewater, but juice quality

was not affected compared to well water irrigated trees. In Florida, reclaimed

wastewater increased fruit size, juice content and TSS:TA ratio, but decreased









TSS and TA as compared to trees receiving well water for 'Valencia' and

'Hamlin' oranges and 'Orlando' tangelos (Zekri and Koo, 1993).

Heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni and Zn) are potential hazards

associated with reclaimed wastewater irrigation (Aboulroos et al., 1991;

Basiouny, 1982; Campbell et al., 1983; El Nennah et al., 1982; Omran et al.,

1988; Waly et al., 1987). Toxic levels of heavy metals may limit plant growth

and present a health risk to humans. However, Cd, Cu, Ni and Zn at low levels

are essential elements for humans (Kirkham, 1986). Heavy metal content varies

depending on the source of water. Non-industrial wastewater typically has

lower levels of heavy metals than industrial wastewater. Soluble heavy metals

in the soil solution typically increase with duration of reclaimed wastewater use

and may with time reach phytotoxic levels (El Nennah et al., 1982). Aboulroos

et al. (1991) found that heavy metals were primarily in nonexchangeable forms

and therefore not available for plant uptake. However, non-exchangeable and

exchangeable heavy metals are in equilibrium in the soil and non-

exchangeable heavy metals may become available for plant uptake. In Utah,

where reclaimed wastewater was applied to agricultural land for 20 years, soil

heavy metal concentrations were not significantly increased from the control as

reclaimed wastewater and well water had similar heavy metal concentrations

(Campbell et al., 1983). In Egypt, concentrations of heavy metals in the soil

after irrigation with reclaimed wastewater for up to 70 years were within

permissible limits for plant growth (Waly et al., 1987). Citrus trees grown on








27
these soils had the highest levels of heavy metals in the leaves followed by the

peel and juice (Omran et al., 1988), but were below levels causing any toxic

affects in plants or humans. In Florida, at the Conserv II project heavy metals

have not been a concern due to pretreatment of industrial wastewater and

trace or non-detectable levels in the reclaimed wastewater (McMahan et al.,

1989).

Elements such as Na, Cl and B in reclaimed wastewater may limit plant

growth if allowed to accumulate to phytotoxic concentrations. However, in

areas of high rainfall and soils with low cation exchange capacity allow for the

use of irrigation water with higher salinity levels than is generally considered

safe (Basiouny, 1984). Salinity is generally of concern only in arid regions in

which accumulated salts are not flushed from the soil by precipitation

(Kirkham, 1986). In Florida, where rainfall is plentiful soluble salts from

reclaimed wastewater may not accumulate to levels which limit plant growth.

Increases in Na and Cl concentrations from reclaimed wastewater irrigation

have been reported for many agronomic crops (Mancino and Pepper, 1992;

Stewart et al., 1990; Tripathi et al., 1990; Waly et al., 1987). However, in some

locations reclaimed wastewater may have a lower salinity level than alternative

water sources and thus provide a higher quality of irrigation water (Kale and

Bal, 1987). Reclaimed wastewater applied through overhead irrigation systems

may cause foliar injury; therefore under tree irrigation systems are

recommended (Basiouny, 1982). Reclaimed wastewater typically contains B









levels ranging from 0.5 to 1.0 mg liter' (Kirkham, 1986). Boron is used in

household cleaners and detergents (Basiouny, 1982). Increases in leaf B from

reclaimed wastewater use have been reported for peaches (Basiouny, 1984),

cherries (Neilsen et al., 1991), and citrus (Zekri and Koo, 1993). In Egypt,

prolonged reclaimed wastewater irrigation resulted in a slight increase in soil

Na levels, but soil Cl levels remained unchanged (Waly et al., 1987). In the

Conserv II project leaf Na and Cl levels increased for trees receiving reclaimed

wastewater compared to well water treated trees (Zekri and Koo (1993).

However, in all these experiments with reclaimed wastewater no adverse

effects on plant growth from B, CI or Na were reported.

A major concern in the use of reclaimed wastewater is the possible

presence of pathogenic microorganisms and potential health risk to workers

and consumers. Untreated sewage contains many pathogenic microorganisms

including over 120 enteric viruses (Rose and Gerba, 1991). After secondary

treatment filtration and disinfection there is no evidence of increased risk to

workers or consumers from reclaimed wastewater irrigation (Basiouny, 1982;

Berry et al., 1980; Brenner et al., 1988; Rose and Gerba, 1991); however,

conventional systems cannot guarantee completely pathogen-free reclaimed

wastewater (Gleason et al., 1984). In Portugal, lettuce which was sprinkler-

irrigated with low quality reclaimed wastewater met standards for viruses and

pathogens within 5 days after ceasing irrigation (da Costa Vargas et al., 1991).

Lkewise, citrus fruit dipped directly into untreated reclaimed wastewater had









no enteric viruses in the fruit or on the peel following washing with standard

packinghouse procedures (A. Lewis, Florida State Dept. of Health and

Rehabilitative Services, personnel communication). Pathogenic contamination

of fruit trees by treated reclaimed wastewater is very unlikely because

pathogenic organisms are not present in the effluent. (Basiouny, 1982). In

Florida, reclaimed wastewater from the Conserv II project had no detectable

enteric viruses after treatment. In addition, regulations prohibit overhead

sprinklers for reclaimed wastewater irrigation to prevent direct contact of fruit

with the reclaimed wastewater (McMahan et al., 1989).



Freeze Hardiness

Freeze hardiness of citrus trees has been associated with various plant

nutrients. Trees receiving high rates of phosphate were more severely injured

by freezing temperatures than trees receiving low rates of phosphorus

(Spencer, 1958; Spencer, 1960). However, Smith and Rasmussen (1958),

found no effect of leaf P concentration on freeze damage of citrus, while Zekri

and Koo (1990) observed that leaves with higher P levels had less freeze

damage. High levels of K have also been reported to decrease freeze

hardiness of citrus trees (Koo, 1985a; Smith and Rasmussen, 1958). In

contrast, Jackson and Gerber (1963) found no relationship between leaf K

concentration and freeze hardiness. Low or deficient Mg levels increased

freeze damage (Lawless, 1941), and Zekri and Koo (1990) observed that trees









with high leaf Mg levels survived better than trees at lower leaf Mg levels. In

Texas, Swietlik and LaDuke (1985) observed that low Mn levels were

associated with groves receiving extensive freeze damage. Lawless (1941)

observed that Zn and Cu deficiencies greatly decreased freeze hardiness.

However, Smith and Rasmussen (1958), observed no differences in trees

freeze hardiness related to Cu, Mn or Zn levels.

Leaf N levels have long been associated with freeze hardiness of citrus

trees. Sharpies and Burkhart (1953) observed low N leaves (1.7%) were less

freeze tolerant than leaves with 2.0% N. Smith and Rasmussen (1958)

observed that ammonium sulfate increased freeze damage compared to

calcium nitrate and ammonium nitrate, but that there was a clear tendency for

high N rates (1.6-1.8 kg N/tree per yr) to reduce freeze damage. Similarly, in

Korea Cheong and Moon (1989) found that among the various leaf nutrients

tested, N was the only element that showed a correlation with leaf freezing

tolerance. Nitrogen fertilization up to twice the standard level increased freeze

hardiness, whereas three times the standard level did not further increase

freeze hardiness. Conversely, Koo (1981) observed no difference in freeze

damage related to leaf N in the freeze of 1977, but in the 1981 freeze branch

dieback was greatest in high N (290 kg N/ha per yr) vs. low N plots (112 kg

N/ha per yr). Smith and Rasmussen (1958) found less freeze damage on

'Marsh' grapefruit trees with leaf N levels of 2.86% compared to 2.64% and a

similar trend for 'Valencia' oranges. Likewise, Koo (1985a) observed increased








31
freeze damage when leaf N content was below 2.5% than when leaf N content

was 2.5-2.8%.

Fertilization practices have a relatively small affect on freeze hardiness of

citrus when obvious deficiencies are absent (Lawless and Camp, 1940; Smith

and Rasmussen, 1958). However, tree size and foliage density appear to be

important parts of citrus tree freeze hardiness as healthy trees reduced

radiation losses (Lawless, 1941; Smith and Rasmussen, 1958; Spencer, 1960),

but smaller less vigorous trees may have had nutrient deficiencies (Lawless

and Camp, 1940). Increased tree vigor and canopy size may function to

prevent radiation losses as temperatures within the tree canopy can vary up to

2 C (Davies et al., 1981). For young nonbearing citrus trees high N levels

increased freeze hardiness (Smith and Rasmussen, 1958), however, late

applications of N that may promote active growth or delay nonapparent growth

reduced freeze hardiness of young citrus trees (Smith and Rasmussen, 1958).

In contrast, Maxwell and Shull (1963) found no effect of fertilization timing on

tree freeze hardiness.

Freeze hardiness of citrus trees is related to many other factors such as

leaf water content (Davies et al., 1981; Husain and Cooper, 1958; Koo, 1981;

Yelenosky and Guy, 1989), leaf solute levels (Purvis and Yelenosky, 1983;

Sharpies and Burkhart, 1953; Yelenosky, 1978; Yelenosky, 1982; Young and

Peynado, 1965), soil temperature (Wilcox et al., 1983), air temperature

(Hutcheson and Wiltbank, 1970; Rouse and Wiltbank, 1972; Yelenosky and








32
Young, 1977), rootstock (Rouse et al., 1990; Wutscher, 1979; Yelenosky and

Wutscher, 1985; Yelenosky et al., 1981) and level of dormancy (Cooper, 1959;

Young, 1961; Young and Peynado, 1962; Young et al., 1960). Acclimation of

citrus trees is dependent on both soil and air temperature (Hutcheson and

Wiltbank, 1970; Rouse and Wiltbank, 1972; Wilcox et al., 1983; Yelenosky and

Young, 1977). Yelenosky and Young (1977) found that freeze hardiness began

to increase 2 weeks after night temperature below 10 C in a growth chamber.

However, citrus trees began to deacclimate within 1 week of 24/18 C day/night

temperatures (Young and Peynado, 1965). In Florida, fluctuating temperatures

may cause trees to acclimate and deacclimate multiple times during the winter

(Wiltbank and Oswalt, 1983).

Freeze hardiness of citrus trees has been determined by many methods.

Freeze chambers in the field (Cooper, 1959; Young et al., 1960) or growth

chambers (Young and Peynado, 1962) have been used to determine citrus tree

freeze hardiness based on tree damage and regrowth. Freeze hardiness has

also been determined by the leaf freezing point method of attached and

detached citrus leaves (Gerber and Hashemi, 1965; Jackson and Gerber,

1963). Jackson and Gerber (1963) found the leaf freezing point was similar for

attached and detached citrus leaves. Likewise, leaf freeze hardiness was

similar regardless of location of the leaf on the tree (Gerber and Hashemi,

1965; Hutcheson and Wiltbank, 1970). More recently leaf killing points using

the electrolyte leakage method have been used to determine freeze hardiness









of citrus (Anderson et al., 1983; Wiltbank and Oswalt, 1983). The electrolyte

leakage method resulted in similar leaf freeze hardiness levels as previous

methods and was similar to freeze hardiness from regrowth test.

The focus of this literature review has been on the potential advantages

and disadvantages of using reclaimed wastewater for irrigation. Reclaimed

wastewater may be a source of water and plant nutrients which are essential

for plant growth. However, potential hazards such as heavy metals, salinity,

bacteria and viruses from reclaimed wastewater have also been discussed.

Understanding how these factors may influence mature, reset and young citrus

tree growth, development and production are important to the scope of this

research.














CHAPTER III

RECLAIMED WASTEWATER IRRIGATION AND FERTILIZATION
OF MATURE 'REDBLUSH' GRAPEFRUIT TREES
ON FLATWOODS SOILS


Introduction



In Florida, 34% of agriculturally available water is used to irrigate citrus

trees (Smajstrla et al., 1992). Competition for limited water resources is

increasing between urban, industrial and agricultural interests. This competition

is especially acute in the coastal areas of Florida where salt water intrusion is

often a problem due to excessive demand on the ground water supply. In

addition, urban growth in the coastal areas of Florida has increased the need

for efficient and environmentally safe disposal of municipal reclaimed

wastewater. Currently, about one-half of all citrus is grown in flatwoods areas

of Florida (Florida Dept. of Agr., 1992). The use of reclaimed wastewater for

irrigation of citrus is potentially beneficial to both urban and agricultural

interests. Reclaimed wastewater could provide an economical means of

irrigating, decrease pollution of surface waters and provide ground water

recharge.









Reclaimed wastewater has been used to irrigate apples (Nielsen et al.,

1989a), cherries (Nielsen et al., 1991), grapes (Nielsen et al., 1989b), peaches

(Basiouny, 1984) and citrus (Kale and Bal, 1987; Koo and Zekri, 1989; Omran

et al., 1988; Wheaton and Parsons, 1993; Zekri and Koo, 1990; Zekri and Koo,

1993). The use of reclaimed wastewater for irrigation of citrus trees has several

potential advantages. Reclaimed wastewater contains many essential nutrients

for plant growth and its application may reduce fertilizer application rates

(Neilsen et al., 1989a). The uptake of plant nutrients in reclaimed wastewater

and reduction in fertilizer use may prevent surface and/or ground water

contamination (Sanderson, 1986). In addition, reclaimed wastewater may be

used for freeze protection (McMahan et al., 1989). Potential disadvantages of

using reclaimed wastewater include accumulation of phytotoxic levels of heavy

metals (Omran et al., 1988), salinity (Basiouny, 1982; Kirkham, 1986) and

concern over the health risk associated with viruses and bacteria in the water

(Basiouny, 1982; Berry et al., 1980; Brenner et al., 1988; Gleason et al., 1984;

Rose and Gerba, 1991).

Reclaimed wastewater has been used for irrigation of citrus on the deep

sandy soils of the Ridge area of Florida (Wheaton and Parsons, 1993; Zekri

and Koo, 1993), but no in depth studies have been conducted on the east

coast flatwoods where soil type and drainage patterns vary considerably due

to the presence of hard pans and a high water table. The objective of this

experiment was to evaluate the effects of various irrigation rates with reclaimed









wastewater on the growth and development, fruit quality and yield of mature

'Redblush' grapefruit trees on flatwoods type soils. In addition, the effects of

reclaimed wastewater on soil moisture levels throughout the year were also

studied. The overall goal of this study was to determine whether citrus growers

can safely and economically use reclaimed wastewater for citrus irrigation on

flatwoods-type soils.



Materials and Methods

The experimental site consisted of an 8.1 ha block of 25-year old

'Redblush' grapefruit trees (Citrus paradisi Macf.) on sour orange (C. aurantium

L.) rootstock. The study was conducted from 1 Oct. 1990 to 16 Apr. 1994. The

site was located adjacent to the Indian River County municipal wastewater

treatment facility located near Vero Beach, Fla. Trees were planted on double

beds 18.3 m wide and 177 m in length. The crest of the bed was ca. 1 m

above the bottom of the water furrows. Trees were spaced 9.15 m between

and 6.1 m within rows (29 trees/row). The soil type was predominantly a

Wabasso fine sand (sandy, siliceous, hyperthermic Alfic Haplaquods) with

areas of Chobee loamy fine sand (fine-loamy, siliceous, hyperthermic Typic

Argiaquolls) and EauGallie fine sand (sandy, siliceous, hyperthermic Alfic

Haplaquods) occurring in portions of the block. The soil had a volumetric field

capacity of 9.95%, a permanent wilting point of 2.48% and a mean bulk density

of 1.61 g-cm3.








37
Four treatments were arranged in a completely randomized design with

each double bed representing a replicate (four replicates/treatment). Irrigation

treatments were arranged in this manner to assure statistical validity and

because it was impractical to irrigate an area smaller than an entire bed.

Treatments consisted of a control (canal water) irrigated based on soil water

depletion of one-third from Jan.-June. and two-thirds from July-Dec. (Koo,

1963) and reclaimed wastewater (secondary treated municipal wastewater)

applied at low (23.1), moderate (30.7) and high (38.6 mm wk') rates (Tables

3.1-3). Trees were irrigated using 56.8 liter/h, 3600 Maxijet microsprinklers

(two/tree) located within the tree row. The wetting pattern was 4.3 m in

diameter at 101 kPa pressure. The arrangement of the microsprinklers

overlapped sufficiently to provide coverage of the entire grove floor within the

tree rows. The drive and furrow rows between tree rows were not irrigated.

Trees receiving the low and moderate-reclaimed wastewater treatments were

irrigated 2 days/wk and the high-reclaimed wastewater treatment 3 days/wk.

Reclaimed wastewater for all treatments combined were applied 4- or 5-

days/wk during each year, with the exception of times when the water furrows

were being cleaned in December 1991 (Table 3.4).

All treatments received about 135 kg N/ha per yr. The control treatment

was fertilized two times/yr (12 on 15 Feb, 1990, 1/2 on 15 Aug, 1990) using a

12N-2P-16K analysis granular fertilizer. Since reclaimed wastewater contains N,

P, K and other nutrients, fertilizer rates were adjusted for these treatments to













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N N







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0 0
0 0 -1 m









Table 3.4. Four and five day schedules and amounts of reclaimed wastewater
irrigation for 'Redblush' grapefruit trees, Vero Beach, Fla., 1990-93.z

Five day irrigation schedule.
Treatments Mon. Tue. Wed. Thur. Fri.
(mm/day)
Low 23.1 mm wk1' 7.7 15.4
Mod. 30.7 mm -wk' 15.4 15.4
High 38.6 mm. wk'1 15.4 15.4 7.7
Four day irrigation schedule.
Treatments Mon. Tue. Wed. Thur. Fri.
(mm/day)
Low 23.1 mm-wk-' 23.1
Mod. 30.7 mm-wk' 23.1 7.7
High 38.6 mm wk' 23.1 15.4

z Amount of reclaimed wastewater applied to 'Redblush' grapefruit trees.








42
standardize nutrient levels among treatments. In 1991, granular fertilizer (10N-

2P-15K) was applied on 15 Mar. at 67, 51, 28 and 0 kg N/ha for the canal

water, low, moderate and high-reclaimed wastewater treatments, respectively.

The second application was not made in 1991 due to excessive rainfall which

prevented fertilizer spreaders from entering the grove. In 1992, granular

fertilizer (12N-0P-0K) was broadcast in the tree row on 11 Mar. at 67, 67, 45

and 23 kg N/ha for the canal water, low, moderate and high-reclaimed

wastewater treatments, respectively. A second application of granular fertilizer

(10N-0P-15K) was made on 7 July and consisted of 67 kg N/ha applied to the

canal water treatment. The remaining 70, 95 and 112 kg N/ha was provided in

the reclaimed wastewater for the low, moderate and high-reclaimed wastewater

treatments, respectively. In 1993, granular fertilizer (12N-0P-15K) was applied

on 18 Feb. at 67, 51, 28 and 0 kg N/ha for the canal water, low, moderate and

high-reclaimed wastewater treatments, respectively. The second application of

granular fertilizer (12N-2P-12K) was made on 30 Aug. at 67 kg N/ha to the

canal water treatment. The high-reclaimed wastewater treatment received low

levels or no granular fertilizer and received from 107 to 129 kg N/ha per yr

from the reclaimed wastewater alone depending on the season.

Soil moisture was monitored with a Troxler 4300 neutron probe (Troxler,

Raleigh, N.C.) once a week for the reclaimed wastewater treatments and twice

a week for the control treatment. One aluminum access tube was placed at the

drip-line about half-way down in the tree row of each bed in 1990-92. In 1993,










additional tubes were placed at the east and west ends of the control beds

because of variations in soil moisture content along the bed. Soil moisture

content in the control treatment was then determined by taking the average of

the three lowest readings from the 12 tubes. These tubes were selected so that

trees would be irrigated based on the driest soil conditions to ensure that the

control trees would not be under water stress. Neutron probe readings were

taken at a depth of 23 cm from the crest of the bed because most of the roots

were located in this region and the water table fluctuated between a 30-40 cm

depth.



Growth and development

Tree vigor was rated visually prior to imposing irrigation treatments in

1989 and each subsequent year. The grove had been irrigated using flooding,

but was converted to microsprinkler irrigation in the fall of 1989. Visual

evaluations were made on 17 Nov. 1989, 13 Dec. 1990, 11 May 1991, 14 Sept.

1992 and 23 Dec. 1993. Twelve trees/bed were randomly selected as

subsamples for further data collection. Trees were rated from 1 (poorly

growing, unhealthy) to 8 (vigorous, healthy) tree. In addition, trunk diameter

measurements were taken about 30 cm above ground level each year from

1990-93.

Fruit growth was determined by randomly selecting and tagging eight

fruit/tree (two fruit from each quadrant) from four trees/bed and measuring the








44
fruit equatorial diameter each month. Measurements began on 13 Mar. 1990,

18 Apr. 1991, 14 May 1992 and 11 June 1993 after the initial fruit drop period.

Dates varied seasonally due to differences in bloom date. Full bloom occurred

in early-Feb. 1990, early-Mar. 1991, mid-Mar. 1992 and mid-April 1993. Fruit

growth was measured monthly until harvest, which also varied seasonally.



Leaf tissue analysis

Leaves for mineral nutrient tissue analysis were collected in Aug. 1990

and 91 and Sept. 1992 and 93. In 1990 and 91, 100 mature spring flush leaves

from non-fruiting branches were selected from the 12 sample trees in each bed

and four beds/treatment. In 1992 and 93, five leaves from four sample trees

were collected with three samples/bed and four beds/treatment. This sampling

technique permitted us to determine the amount of tree-to-tree variation within

a bed. Leaves were then washed in detergent (Dreft; Proctor and Gamble,

Cincinnati), rinsed once with running tap water and four times in deionized

water, dried at 70C for 48 h and then ground to pass through a 0.5 mm (40

mesh) screen. Total Kjeldahl N was determined by the micro Kjeldahl

procedure (Wolf, 1982) using a rapid flow analyzer (Alpkem Corp., Clackamas,

Ore). Leaf P, K, Ca, Mg, Na, B, Cu, Fe, Mn and Zn were determined by ashing

a 0.5 g sample in a muffle furnace at 550C for 8 h using Quartz crucibles. The

ash was then brought to a volume of 50 ml with 1N HCI and filtered. Samples

were than analyzed by the Analytical Research Laboratory, Univ. of Florida,









Gainesville on an Inductively Coupled Argon Plasma Spectrometer (Thermo

Jarrell Ash Corp., Boston, MA).



Fruit quality

Fruit weight, juice weight, peel thickness, total soluble solids (TSS),

titratable acidity (TA) and TSS:TA ratio were measured monthly beginning in

Aug., Sept. and Oct. in 1991, 92 and 93, respectively. This starting date varied

yearly based on date of full bloom. Fruit samples consisted of 10 fruit/tree

(Wardowski et al., 1979) from three trees/bed and four beds/treatment. Fruit

were sectioned equatorially so that peel thickness could be measured with a

hand caliper and the juice extracted by hand with a Sunkist motor driven

extractor. TSS was determined with a temperature compensating refractometer

and TA by titration of a 25 ml aliquot of juice using 0.3125N NaOH to an end-

point with phenolphthalein as an indicator (Wardowski et al., 1979).

Levels of Cd, Pb and Ni were determined by taking 7 mm core samples

from the peel of 10 fruit/tree from three trees/bed and four beds/treatment on

15 Oct. 1991 and 6 Jan. 1993. The samples were then dried at 70C for 48 h

and then processed as previously described for leaf tissue.



Yield

Yield was determined from 1991-94 by counting the number of bins

harvested/bed and dividing the total by the number of healthy productive








46
trees/bed. Yield was then averaged for four beds (replicates)/treatment. In Mar.

1993, a severe storm caused a large number of fruit to drop prior to harvest of

some of the trees. An estimate of fruit drop, was made by counting fruit under

sample trees in each bed. Fruit drop averaged 20-25% of total yield. In

addition, each bed was evaluated yearly for missing or severely diseased trees.

The healthy tree count per bed was then revised prior to harvest.



Water quality analysis

Water quality was monitored monthly for both the canal water and

reclaimed wastewater by collecting samples at the water input source to the

irrigation system (Table 3.5). Three water samples from each source were

collected and analyzed for pH, electrical conductivity (EC), NH4*, NO;,

PO,, K, Ca, Mg, Zn, Cu, Cd, Ni, Pb, Na and B. The pH was determined using

a pH meter (Orion Research Inc. model 520A Boston, MA) and EC with a

conductance meter (YSI model 35 YellowSprings, OH). Nitrate-N was

determined on the rapid flow analyzer (Alpkem Corp. Clackamas, Ore.).

Ammonium-N and P04 were determined on an AutoAnalyzer II (Technicon

Instruments Corp. Tarrytown, N.Y.). All other nutrients were analyzed by the

Analytical Research Laboratory, Univ. of Florida, Gainesville on an Inductively

Coupled Argon Plasma Spectrometer (Thermo Jarrell Ash Corp., Boston, MA).

Analysis of influent and effluent water for enteroviruses was made

quarterly (Table 3.6). Samples consisted of three 1-liter influent samples

















o C
odd
+ 1 + 1 + 1 +
Z z












o o
C' 00 N





















Ed d
+o +1 +1 +1


























E Z


0 0 0 z 0
OO 0 JS


0
o o sc o









o o




0 C
+1 +1 +1 +1 +1





+ +I + +I



10 o
7-


0a
I-

5 a h
Z E-.Q=c


6O
0)


0
Z

4-.
C



0
E
0





8
E

E

V=


0,
0 -

E
0



)







0.o
- 0-












o
-az
>0


.i







C- w
.Q)

C
0
0










Table 3.6. Influent and effluent analyses of enterovirus levels, Vero Beach, Fla.
1990-93.z


Sample date


Nov. 19, 1990x
Feb. 12, 1991x
Apr. 29, 1991x
Sept. 11, 1991
Dec. 9, 1991
Mar. 17, 1992
June 11, 1992
Sept. 1, 1992
Jan. 11, 1993
Mar. 25, 1993
June 10, 1993
Sept. 23, 1993


Mean


Influent


79.2
1.6
0.7
380.0
28.7
21.3
166.7
466.7
188.3
62.5
325.0
625.0
195.5 290


Z Numbers represent the mean of three one liter samples taken from the
influent and three 387 liter samples from the effluent.
Y PFU/liter = plaque-forming units per liter.
x Analysis was conducted by the Florida Dept. of Health and Rehabilitative
Services. All other analyses were done be Dr. S. Farrah, Dept. of Microbiology
and Cell Science, Univ. of Fla.


Effluent


PFU/litery


< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003
< 0.003


Mean








49
collected at the inlet valve where the wastewater entered the treatment facility

and three 387-liter effluent samples collected at the efflux valve. Analysis

during 1990-91 was conducted by the State of Florida, Dept. of Health and

Rehabilitative Services (HRS). Subsequent analysis was performed by Dr. S.

Farrah at the Dept. of Microbiology and Cell Sciences, Univ. of Florida,

Gainesville. Procedures used for analysis of enteroviruses levels were modified

from those described in the USEPA Manual of Methods for Virology.

(Cincinnati, OH).

In addition, eight fruit from both the high-reclaimed wastewater and

control treatments were harvested in 17 Mar. 1992 and 18 Feb. 1993 and

analyzed for the presence of enteroviruses (Farrah, unpublished). One

grapefruit was placed in a sterile beaker with 200 ml of 0.05% beef extract at

pH 9. After mixing for 5 min, the solution was removed and concentrated by

adjustment to pH 3.5 and addition of 0.005M ferric chloride to enhance

flocculation. Samples were centrifuged at 14,500 x g for 10 min. The floc was

suspended in 10 ml of 0.15M sodium phosphate and again centrifuged. The

supernatant was adjusted to pH 7 and assayed as described in the USEPA

Manual of Methods for Virology. (Cincinnati, OH). Seeded studies with

poliovirus added to the surface of the grapefruit showed that 58% of the added

virus could be recovered in the final sample. Therefore, these techniques gave

an accurate representation of the presence of enteroviruses on grapefruit.









Weed intensity

Weed intensity within the tree rows was determined monthly by visual

evaluation beginning in Jan. 1992. Ratings ranged from 0 (no weed growth) to

5 (> 50% of ground surface covered with weeds). All beds had bahiagrass

ground cover between rows which was mowed as necessary. Pest, weed and

disease control treatments were applied as currently recommended for groves

receiving standard irrigation in the Vero Beach area. No adjustments in

herbicide or pest control practices were made initially for the reclaimed

wastewater treatments. However, after observing the influence of high rates of

reclaimed wastewater application on weed growth some changes in herbicide

practices were made which included use of less water soluble materials and

more frequent spot sprays.



Weather data

Weather data were collected using a Campbell Scientific, Inc. remote

weather station (Logan, UT). Temperature (average, maximum and minimum)

and rainfall data were collected daily (Figs. 3.1-3).



Statistical analysis

Experiments were analyzed using the SAS general linear model (GLM)

procedure and analysis of variance (ANOVA). Visual ratings and trunk diameter

values were analyzed using analysis of covariance to standardize differences in

















EE
E
E ,
Oc'J
cli

0


V 0
CD






00)
EE

0-0




LOLi
-0)




c

C.)


C'o,
~II
crc
0035
EE
C E
(. 0
co
~cdM
(D LL
C~C


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E

E~8
c' E


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CbS
i L 0











52



I














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o
































S i L.








: i -- (

.



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ZE

E
cv)u
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scu


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4)




*0 c
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75




.LCD
CTC








0).
E



N- II

CVcz
0 0)


a,
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mo


C6~C
CD -C 0






























/


0 0 00T0 m O
0 0 O 01 0 (0 0 0 0
(%) eJnls!olu I!os (LUL) IIeu!eyl














21



E
E
E ,
Cr)CUJ
06


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(UD
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OC
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:3
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E
I-C

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roE
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i z ~d











































0 0 0 0 0
(%) eJnis!ou I!OS


0 0 0
(UU) IIeUCeI








57
initial tree measurements. Repeated measures analysis was used in analyzing

fruit growth, fruit quality and weed intensity. Regression analysis and

orthogonal contrasts were used to determine trends in the data and to

separate means where appropriate.



Results and Discussion



Soil moisture content and rainfall

Soil moisture content and rainfall were monitored from 1991-93 (Figs.

3.1-3). In 1991, soil moisture content represented the combined readings from

two separate experiments, this experiment in the south part of the grove and

an other experiment in the north part of the grove. Although both experiments

were conducted on the same soil types differences in drainage patterns and

irrigation levels resulted in lower mean soil moisture content levels in 1991. Soil

moisture content averaged 12.4%, 12.5%, 11.6% and 17.4% for beds receiving

the canal water, low, moderate and high-reclaimed wastewater treatments,

respectively (Fig. 3.1). The low soil moisture content for all beds in Dec. 1991

resulted from discontinuation of treatments from 25 Nov. to 16 Dec. to clean

and repair the water furrows to improve drainage.

In 1992, soil moisture content data represent measurements from this

experiment only. Beds receiving the canal water, low, moderate and high-

reclaimed wastewater treatments averaged 13.9%, 21.5%, 19.5% and 33.3%








58
soil moisture content, respectively (Fig. 3.2). All reclaimed wastewater treated

beds had a lower soil moisture content until July and Aug. 1992 compared to

the rest of the year when soil moisture content began to increase. The increase

in soil moisture content coincided with an increase in weed growth which may

have impeded water furrow drainage.

Aluminum access tubes were added to the east and west ends of each

of the control beds and the average of the three lowest soil moisture content

measurements were used to more accurately control irrigation levels. Soil

moisture content averaged 10.9%, 29.8%, 29.8% and 38.5% for beds receiving

the canal water, low, moderate and high-reclaimed wastewater treatments,

respectively (Fig. 3.3).

Soil moisture contents were consistently higher for the reclaimed

wastewater treatments compared to the control. Beds receiving the low and

moderate-reclaimed wastewater treatments had similar soil moisture contents

which were lower than the high-reclaimed wastewater treated beds in 1992-93.

The difference between beds receiving the low and moderate-reclaimed

wastewater treatments and the high treatment resulted from more frequent

applications at the high rate. The low and moderate-reclaimed wastewater

treated beds were irrigated twice/wk, but the high-reclaimed wastewater beds

which had a higher soil moisture content were irrigated three times/wk. Soil

moisture content measurements were taken prior to irrigation so that the lowest

soil moisture depletion level was measured. The longer durations between








59
irrigations for the low and moderate-reclaimed wastewater treatments allowed

for greater soil moisture depletion. After periods of heavy rainfall, the control

beds periodically showed higher soil moisture content than beds receiving

reclaimed wastewater which was due to time measurements were taken after

rainfall occurred.



Tree growth

Trees receiving moderate-reclaimed wastewater were in general more

vigorous than those receiving the other treatments (Table 3.7); however, in

1992, all reclaimed wastewater treated trees were significantly more vigorous

than trees receiving canal water. Results are similar to those observed for

citrus growing on the Ridge area of Florida (Koo and Zekri, 1989; Wheaton

and Parsons, 1993; Zekri and Koo, 1990; Zekri and Koo, 1993). However, in

these studies no adjustment in fertilization rate was made to account for

nutrients in the reclaimed wastewater. Consequently, both fertilizer and water

levels were varied.

Trunk diameter also was similar in 1990, 91 and 92 for all treatments,

however; in 1993, trees receiving low and moderate-reclaimed wastewater

treatments had statistically greater trunk diameters than those receiving the

canal water or high-reclaimed wastewater treatments although the increase

was small (Table 3.8). Visual ratings and trunk diameter measurements

suggest that trees receiving reclaimed wastewater at high rates may have been









Table 3.7. Reclaimed wastewater and canal water effects on vegetative growth
and development of 'Redblush' grapefruit trees at Vero Beach, Fla., 1989-93.


Treatments


Visual rating
28 Nov. 13 Dec. 16 May 14 Sept. 23 Dec.
1989 1990 1991 1992 1993


Control


Canal water


Reclaimed wastewater
Low 23.1 mm-wk-1

Mod. 30.7 mm wk-'

High 38.6 mm wk-'


5.1x
(4.9)


5.1
(5.0)
5.1
(5.3)
5.1
(5.3)


5.1
(4.9)


5.1
(5.2)
5.5
(5.7)
5.3
(5.6)


5.2
(5.1)


5.3
(5.4)
5.8
(5.9)
5.4
(5.7)


Significance
Treatment NS *** *** *** ***


Contrasts
CW vs. Low
CW vs. Mod.
CW vs. High


Low vs. Mod. *** *** *** ***
Low vs. High
Mod. vs. High *** ** ***

2 Visual ratings ranged from 1 (a poorly growing, unhealthy) to 8 (a healthy,
vigorous).
x Numbers in parenthesis are actual means. Other numbers represent adjusted
means from the analysis of covariance. Each number represents the mean of
12 samples/bed with four replicates/treatment.
NS.',".* Nonsignificant or significant at P 0.05, 0.01, or 0.001, respectively.


5.3
(5.2)


5.6
(5.7)
6.1
(6.2)
5.7
(5.9)


5.5
(5.3)


5.7
(5.9)
6.4
(6.5)
5.6
(5.9)









Table 3.8. Reclaimed wastewater and canal water effects on trunk diameter of
'Redblush' grapefruit trees at Vero Beach, Fla., 1990-93.
Treatments Trunk diam (mm)z
Nov. 90 Sept. 91 Sept. 92 Nov. 93
Control
Canal water 223x 226 229 231
(206) (211) (213) (218)
Reclaimed wastewater
Low 23.1 mm wk-" 223 229 231 236
(221) (226) (229) (236)
Mod. 30.7 mm wk-' 223 226 229 236
(229) (231) (236) (241)
High 38.6 mm*wk"1 223 226 226 231
(234) (239) (241) (244)
Significance
Treatment NS NS NS *
Contrasts
CW vs. Low *
CW vs. Mod. *
Low vs. High *
Mod. vs. High *

z Trunk diameter measurements were taken approximately 20 cm above ground level.
Y Numbers in parenthesis are actual means. Other numbers represent adjusted
means from the analysis of covariance. Each number represents the mean of 12
samples/bed with four replicates/treatment.
NS*.* Nonsignificant or significant at P : 0.05, 0.01, or 0.001, respectively.








62

over-irrigated, although soil in the treated area was rarely anaerobic based on

soil redox potential measurements (data not shown). Soil moisture content

(Figs. 3.1-3), however, for the high-reclaimed wastewater treatment was

consistently higher than for the other treatments. In addition, soil moisture

content in the low and moderate-reclaimed wastewater treatments was typically

higher than for the areas receiving canal water. Trees receiving canal water

also had reduced growth compared to those in the low and moderate

treatments, which in this instance was more likely due to water stress rather

than to excess water.



Leaf nutrient concentrations

Macronutrients

Leaf tissue N was similar for all treatments in 1990 and 91 (Tables 3.9-

10); however, in 1990 the leaf N was in the optimum range (2.5-2.7%) (Koo et

al., 1984), whereas in 1991 leaf N was in the deficient range (<2.2%) (Koo et

al., 1984). These deficient N levels were attributable to the higher than normal

rainfall (Appendix A), which caused leaching of fertilizer from the root zone.

Additionally, the wet soil conditions prevented a second fertilizer application.

Boman (1993) observed a similar reduction of leaf N from excessive rainfall

and leaching at an experiment near Ft. Pierce, Fla. In 1992 and 93, leaf N

concentrations for trees receiving canal water were slightly but significantly

higher than those for the reclaimed wastewater treatments (Tables 3.11-12). In











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1993, leaf N concentration was greater for trees receiving the moderate and

high-reclaimed wastewater treatments than for those receiving the low levels.

The differences in leaf N levels, however, were small and are probably not

significant from a practical standpoint. In addition, lower than optimum leaf N

concentrations may be desirable for the production of fresh market grapefruit

in the Indian River area (Koo et al., 1984).

Leaf P concentrations were similar for all treatments in 1990, 91 and 92

(Tables 3.9-11). In 1990 and 92 leaf P concentrations were in the optimum

range (0.12-0.16%) (Koo et al.,1984), however, in 1991 leaf P was in the low

range (0.09-0.11%) (Koo et al.,1984), again due to excessive rainfall. Although

there were statistically significant differences in leaf P among treatments in

1993, levels were within the optimum range (Table 3.12). Increases in leaf P

are often associated with reclaimed wastewater irrigation as seen in citrus

(Zekri and Koo, 1993), peaches (Basiouny, 1984), cherries (Neilsen et al.,

1991), apples (Neilsen et al., 1989a) and grapes (Neilsen et al., 1989b). The

low levels of P in the reclaimed wastewater could account for a lack of

difference among treatments in this study.

Leaf K concentrations were similar for all treatments in 1990, 91 and 92

(Tables 3.9-11). In 1990 and 91, leaf K was in the deficient-low range (0.7-

1.1%) (Koo et al., 1984), but increased to the optimum range (1.2-1.7%) in

1992 (Koo et al., 1984). Leaf K concentration was significantly higher for all

reclaimed wastewater treatments than for the canal water treatment in 1993









(Table 3.12). Although the reclaimed wastewater contained about twice the

level of K as the canal water differences in leaf K concentrations were not

apparent until 1993.

Leaf Ca concentrations were similar for all treatments in 1990 and 91

(Tables 3.9-10). All leaf Ca concentrations were in the high range (5.0-6.9%)

(Koo et al., 1984). In 1992, leaf Ca levels in trees receiving the moderate levels

of reclaimed wastewater were significantly higher than for those receiving the

canal water or high-reclaimed wastewater treatments. Leaf Ca concentrations

were in the optimum range (3.0-4.9%) (Koo et al., 1984) (Table 3.11). In 1993,

trees receiving canal water were significantly higher in leaf Ca than trees

receiving moderate and high-reclaimed wastewater rates (Table 3.12);

however, all treatments were within the optimum range.

Leaf Mg concentrations were similar for all treatments in 1990, 91 and

92 (Tables 3.9-11), with all concentrations within the optimum range (0.30-

0.49%) (Koo et al., 1984). In 1993, trees receiving canal water had significantly

higher leaf Mg levels than those receiving reclaimed wastewater, with the low-

reclaimed wastewater treatment having significantly higher Mg levels than the

moderate and high-reclaimed wastewater treatments (Table 3.12). Although,

there were statistical differences, all leaf Mg levels were within the optimum

range.









Micronutrients

Leaf boron (B) concentrations were not analyzed in 1990 (Table 3.9),

but in 1991 all treatments produced similar leaf B concentrations (Table 3.10),

which were in the low end of the high range (101-200 ,g g-') (Koo et al.,

1984). Trees irrigated with reclaimed wastewater showed a 50% increase in

leaf B over the canal water treatments in 1992 (Table 3.11), but all leaf B levels

were in the high range. In 1993, trees receiving reclaimed wastewater had

twice the concentration of leaf B than those receiving canal water (Table 3.12).

Irrigation at the moderate-reclaimed wastewater rate increased leaf B

concentrations more than at the other two reclaimed wastewater rates.

However, leaf B levels for the reclaimed wastewater treatments were within the

high range. Reclaimed wastewater contained four times more B than the canal

water which accounts for increased leaf B concentrations. However, leaf B

concentrations were below toxic levels (> 250 ~g g') for citrus trees (Koo et

al., 1984). Increases in leaf B due to reclaimed wastewater treatment is

consistent with previous results on citrus (Zekri and Koo, 1993).

Leaf Na concentrations were similar for all treatments in all four years;

however, leaf Na levels were lowest in 1991 (Tables 3.9-12) due to leaching of

Na beyond the root zone by excessive rainfall. Leaf Cu concentrations were

also similar for all treatments (Tables 3.9-12), but varied greatly from year-to-

year due to the addition of Cu containing fungicide sprays applied for

melanose and greasy spot control. Similarly, leaf Fe concentrations were







70

similar for all treatments for all four years (Tables 3.9-12), however, in 1990, 91

and 93, leaf Fe concentrations were in the low range (36-59ug g-') (Koo et al.,

1984), while in 1992 they were in the optimum range (60-120 ug-g-') (Koo et

al., 1984). Leaf Mn concentrations were similar for all treatments in 1990, 91

and 92 (Tables 3.9-11). Levels were in the deficient range (>17 #g-g'') (Koo et

al., 1984) in 1990 and 91, and the low range (18-24 pg-g'1) (Koo et al., 1984)

in 1992. In 1993, trees receiving canal water and low-reclaimed wastewater

treatments had significantly higher leaf Mn than those in the other treatments

(Table 3.12), but all leaf Mn concentrations were in the deficient range. Leaf Zn

concentrations were similar for all treatments in each year with levels in the low

range (18-24 ug-g'') in 1990 and 91 (Tables 3.9-10) and in the optimum range

(25-100 #g-g') (Koo et al., 1984), in 1992 and 93 (Tables 3.11-12). The similar

leaf Fe, Mn and Zn levels for all treatments may have resulted from the low

levels of the elements in the reclaimed wastewater and canal water.

The accumulation of nutrients in leaf tissue in this experiment reflect the

levels received from the reclaimed wastewater, canal water or supplemental

fertilization. The results obtained here may not be comparable to other

experiments due to the variability in nutrient content of reclaimed wastewater.

In addition, the short duration of this experiment may not account for long-term

accumulation of nutrients with continued reclaimed wastewater use. Omran et

al. (1988) found that leaf nutrient levels tended to increase with increasing

duration of reclaimed wastewater use.









Fruit growth

Fruit growth patterns were similar for all treatments in 1990, 91 and 92,

(Figs. 3.4-5), for all treatments and followed a typical sigmoid growth pattern

for citrus fruit (Bain, 1958). In contrast, in 1993 trees receiving reclaimed

wastewater had significantly larger fruit than those receiving canal water (Fig.

3.5B). The lack of difference in fruit growth in 1991 may have been attributed

to above normal rainfall during the summer (Fig. 3.1).

Fruit weight for trees receiving reclaimed wastewater treatments was

significantly greater than for those receiving canal water in 1991-92 (Fig. 3.6A).

Fruit weight of trees receiving canal water was significantly less than for the

other treatments from Aug.-Nov., but was similar from Dec.-Feb. Similarly, in

1992-93 fruit weight was significantly greater for reclaimed wastewater

treatments compared to the canal water treatment (Fig. 3.7A). However, fruit

weight for the reclaimed wastewater treatments was significantly greater than

the canal water treatment for Oct. and Nov.; fruit weight was similar from Dec.-

Feb. In 1993-94, fruit weight for the reclaimed wastewater treatments was

significantly greater than for those in the canal water treatment (Fig. 3.8A).

Juice weight exhibited a similar trend to fruit weight. Fruit from trees

receiving reclaimed wastewater had significantly higher juice weight than those

receiving canal water in all three seasons (Figs. 3.6B-8B). In 1991-92, juice

weight decreased for trees receiving canal water until December, but juice

weight was similar for all treatments by Jan. and Feb. In 1992-93, fruit from



























Fig. 3.4. Reclaimed wastewater and canal water effects on fruit growth of
'Redblush' grapefruit at Vero Beach, Fla., 1990 (A) and 91 (B). Control = canal
water, and reclaimed wastewater at low = 23.1 mm-wk', mod. = 30.7 mm-wk'
Sand high = 38.6 mm-wk'. Means of eight fruit/tree for four trees/bed for four
beds/treatment. There were no significant differences among treatments in
both years. (A) Fruit growth 1990, y = 12.87 + 21.02x 1.35x2; R2 = 0.99 all
treatments pooled and (B) Fruit growth 1991, y = 40.65 + 16.36x 1.24x2; R2
= 0.97 all treatments pooled.










100
A


80 -......

E

60


(0









Mar.
E


LL
20 .



0
Mar.


100
B

90





E
) 70 -
a)
E
.0 60 -

4-
2 50 -


Apr. May June July Aug. Sept.


June July Aug.


Apr. May


Sept. Oct. Nov.


























Fig. 3.5. Reclaimed wastewater and canal water effects on fruit growth of
'Redblush' grapefruit at Vero Beach, Fla., 1992 (A) and 93 (B). Control = canal
water, and reclaimed wastewater at low = 23.1 mm-wk', mod. = 30.7 mm-wk
1 and high = 38.6 mm wk'. Means of eight fruit/tree for four trees/bed for four
beds/treatment. (A) There was no significant difference among treatments in
1992,. y = 38.38 + 19.95x 1.70x2; R2 = 0.97. (B) Pooled reclaimed
wastewater treatments were not significantly different but differed from canal
water, P = 0.06, reclaimed wastewater y = 38.18 + 19.01x 1.74x2; R2 = 0.99;
canal water y = 41.89 + 19.03x 1.72x2; R2 = 0.97.










120




100

E
E
L 80


E
c0
: 60


LL.
I-
40




20



100


90





L.-
0 70

E

o

L" 50
U-LL

40


May June July Aug. Sept. Oct. Nov. Dec.




B








-I

A*I








/ Control Low Mod. High
.. .. .. .. .. .. .. .. ..
Coto o o. Hg

.
.9jI


Oct.


Nov. Dec.


Control Low Mod. High


.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .


June


30


July


Aug.


Sept.






















Fig. 3.6. Reclaimed wastewater and canal water effects on fruit and juice
weight and peel thickness of 'Redblush' grapefruit at Vero Beach, Fla., 1991-
92. Control = canal water, and reclaimed wastewater at low = 23.1 mm wk'1,
mod. = 30.7 mm-wk'' and high = 38.6 mm-wk-'. Mean of 10 fruit/tree for four
trees/bed for four beds/treatment. (A) Fruit weight for low, mod. and high
reclaimed wastewater treatments differed significantly from canal water at P =
0.006, 0.019 and 0.078, respectively. Monthly analysis of variance were
nonsignificant from Dec.-Feb. y = 290.08 + 49.93x 3.49x2; R2 = 0.73 for the
canal water; y = 321.28 + 44.25x 3.12x2; R2 = 0.75 all reclaimed wastewater
treatments pooled. (B) Fruit juice weight for low, mod. and high reclaimed
wastewater treatments was significantly different from canal water at P = 0.003,
0.002 and 0.002, respectively. Monthly analysis of variance were nonsignificant
from Dec.-Feb. y = 138.38 + 44.97x 3.20x2; R2 = 0.84 for the canal water
treatment; y = 159.10 + 43.63x 3.19x2; R2 = 0.89 all reclaimed wastewater
treatments pooled. (C) Fruit peel thickness was not significantly different
among treatments. y = 5.99 0.77x + 0.07x2; R2 = 0.77 for all treatments
pooled.











500



450



-4O
400


- 350
I-

300



250



300



250

a)
0 200
'3
.-)

150



100



E 6
E
5.5


0
S5


U)
4m 4


4


3.5
P


A









-.
-A-





I B

B


--
I I I
















So
g.S.
. .............................................. ............... ....................................................... ..... ................... ... .. ........... ... ..... .. ....













....... ....................











_. ......................... .. .................. .. ... .
< \




.....----'.. .. N o D e Ja..... .
.........................


rug. Sept. Oct. Nov. Dec. Jan. Feb.


Control Low Mod. High


L I





















Fig. 3.7. Reclaimed wastewater and canal water effects on fruit and juice
weight and peel thickness of 'Redblush' grapefruit at Vero Beach, Fla., 1992-
93. Control = canal water, and reclaimed wastewater at low = 23.1 mm-wk'',
mod. = 30.7 mm-wk1' and high = 38.6 mm-wk'. Mean of 10 fruit/tree for four
trees/bed for four beds/treatment. (A) Fruit weight for trees receiving canal
water were significantly different from the low, mod. and high reclaimed
wastewater trees at P = 0.02, 0.03 and 0.09, respectively. Canal water trees
were significant from reclaimed wastewater trees in Nov. and Dec. in monthly
analysis of variation, y = 315.97 + 30.05x + 0.13x2; R2 = 0.65 for the canal
water treatment; y= 325.72 + 45.11x + 3.91x2; R2 = 0.68 for all treatments
pooled. (B) Fruit juice weight for the canal water trees was significant different
from the low, mod. and high reclaimed wastewater trees at P = 0.01, 0.06 and
0.07, respectively. Juice weight for canal water trees was significantly different
from reclaimed wastewater trees in Nov. and Dec. in monthly analysis of
variation. y = 148.89 + 32.36x 1.22x2; R2 = 0.86 for the canal water
treatment; y = 152.47 + 39.1 Ox 2.43x2; R2 = 0.88 for the reclaimed
wastewater treatments pooled. (C) Fruit peel thickness was not significantly
different among treatments. y = 5.29 0.65x + 0.08x2; R2 = 0.69 for all
treatments pooled.










500


4 5 0 ...........................................
450
0)


400 .



350 ..



300
B


2 5 0 ............ .............................
U)


2 0 0 ....................... .........
fr *

150-



6
C

E 5 .5 ....... ....................
E


C -
0 4.5 .....

-C


0)
0 ) 4 ....... ... ... .................
a0




3.5
Sept. Oct.


Nov. Dec.


Jan. Feb.
























Fig. 3.8. Reclaimed wastewater and canal water effects on fruit and juice
weight and peel thickness of 'Redblush' grapefruit at Vero Beach, Fla, 1993-
94. Control = canal water, and reclaimed wastewater at low = 23.1 mm-wk",
mod. = 30.7 mm-wk' and high = 38.6 mm*wk". Mean of 10 fruit/tree for four
trees/bed for four beds/treatment. (A) Fruit weight from trees receiving canal
water were significantly different from trees receiving reclaimed wastewater P _
0.001. y = 279.32 + 25.21x 0.41x2; R2 = 0.44 for the canal water treatment; y
= 325.31 + 37.86x 2.28x2; R2 = 0.49 for all reclaimed wastewater treatments
pooled. (B) Fruit juice weight for trees receiving canal water were significantly
different from trees receiving reclaimed wastewater P s 0.001. y = 99.37 +
35.64x 3.05x2; R2 = 0.82 for the canal water treatment; y = 116.38 + 46.79x -
5.38x2; R2 = 0.72 for all reclaimed wastewater treatments pooled. (C) Fruit peel
thickness was not significantly different among treatments. y= 6.31 1.38x +
0.35x2; R2 = 0.56 for all treatments pooled.










450


400



" 350


LL
300


220

200

-180

- 160

a 140

:5
3 120

100

7


6.5



0) 6
0 6
C
t-


5.5


0) 5
0.


4.5 '
Oct.


Nov. Dec.


Jan.









trees receiving canal water had significantly lower juice weight in Nov. and

Dec.; however, juice weight was similar for all other months. Juice weight of

trees receiving reclaimed wastewater was significantly greater for the entire

season in 1993-94.

Peel thickness was similar for all treatments in each of the three years

(Figs. 3.6C-8C) even though juice and fruit weight differed for some treatments.

This similarity may have been due to similar K levels for all treatments.

Potassium has a significant regulatory effect on peel thickness in citrus

(Embleton et al., 1973).



Fruit quality

Total soluble solids (TSS) were significantly lower for trees receiving

moderate-reclaimed wastewater compared with the other treatments in 1991-92

(Fig. 3.9A). However, from December until harvest all treatments had similar

fruit TSS. In 1992-93, fruit had similar TSS for all treatments (Fig. 3.10A). In

1993-94, again fruit from the moderate-reclaimed wastewater treatment were

significantly lower in TSS compared to fruit receiving canal water (Fig. 3.11A).

The variable effects of high irrigation levels on TSS are consistent with results

obtained in other studies (Boman, 1992; Zekri and Koo, 1993).

Juice titratable acidity (TA) levels were similar for all treatments in 1991-

92 (Fig. 3.9B) and 1993-94 (Fig. 3.11B), but in 1992-93 TA of trees receiving

the canal water was significantly higher than for those receiving the reclaimed
























Fig. 3.9. Reclaimed wastewater and canal water effects on fruit total soluble
solids (TSS), titratable acidity (TA) and TSS:TA ratio of 'Redblush' grapefruit at
Vero Beach, Fla, 1991-92. Control = canal water, and reclaimed wastewater at
low = 23.1 mm-wk'1, mod. = 30.7 mm-wk' and high = 38.6 mm-wk1'. Mean
of 10 fruit/tree for four trees/bed for four beds/treatment. (A) Fruit TSS for trees
receiving the mod. reclaimed wastewater was significantly different from other
treatments. Fruit TSS for trees receiving the mod. reclaimed wastewater were
similar to other treatments from Dec.-Feb. in monthly analysis of variation. y =
9.20 + 0.06x + 0.04x2; R2 = 0.79 for the mod. reclaimed wastewater
treatment; y = 9.39 + 0.06x + 0.04x2; R2 = 0.72 for all treatments pooled. (B)
Fruit TA was not significantly different among treatments. y = 1.67 0.28x +
0.03x2; R2 = 0.87 for all treatments pooled. (C) Fruit TSS:TA ratio was not
significantly different among treatments, y = 5.46 + 1.43x 0.11x2; R2 = 0.89
for all treatments pooled.









84

11.5
A Control Low Mod. High

11



1 0 .5 ................................ .. ... ................................................. ........... ....... .... .............. ... ...........................


9 .5 1 0 .... ........ .. :-. .. .' '.. ..... .................... ...................... ........ ........... ..............
10.5









1.8 i --------------------------
9.5 ...-.....*



1.8
B



1.6 .








.o
1 4 ................... ........ ..... ....... ........... ... ... .... ... ............ ............ ... .............. .. ...................... ......... .......





''"^:---"



C

10 ....


8 ................ ...... .. .. .. ... ... ...... ....... ...................... ... ..... .... .. ....... ...
9

8 .


7 ....... .... .... .... ....... ........................... ...... ........... .. ..... ................. ...............
7-


6I
6 . . .. . .. .. .. . . . . .. . . . . .. ..


5
Aua. Seot. Oct. Nov. Dec. Jan. Feb.


-I-





















Fig. 3.10. Reclaimed wastewater and canal water effects on fruit total soluble
solids (TSS), titratable acidity (TA) and TSS:TA ratio of 'Redblush' grapefruit at
Vero Beach, Fla, 1992-93. Control = canal water, and reclaimed wastewater at
low = 23.1 mm-wk-', mod. = 30.7 mm-wk' and high = 38.6 mm-wk''. Mean
of 10 fruit/tree for four trees/bed for four beds/treatment. (A) Fruit TSS was not
significantly different among treatment. y = 5.83 + 0.64x + 0.006x2; R2 = 0.89
for all treatments pooled. (B) Fruit TA for trees receiving canal water were
significantly different from trees receiving reclaimed wastewater. Fruit TA for
trees receiving canal water were significant from the reclaimed wastewater
trees from Nov. Feb. in monthly analysis of variation, y = 1.59 0.07x +
0.0008x2; R2 = 0.55 for the canal water treatment; y = 1.57 0.12x + 0.008x2;
R2 = 0.79 for all reclaimed wastewater treatments pooled. (C) Fruit TSS:TA
ratio for trees receiving canal water was significantly different from trees
receiving low and mod. reclaimed wastewater. Fruit TSS:TA ratio for trees
receiving canal water were significant from trees receiving reclaimed
wastewater from Dec.-Feb. in monthly analysis of variation. y = 3.83 + 0.42x
+ 0.06x2; R2 = 0.78 for the canal water treatment; y = 3.72 + 0.71x + 0.04x2;
R2 = 0.86 for all reclaimed wastewater treatments pooled.









86

10
A
A Control Low Mod. High

9-







7 ... ..-.... .......... ..................



6-






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1.7. .






1 1 ........................ .................. ......................................................................................... ... ........ .... .. ... .. .
1.6 -










9
C

8 ............................ .................................. ... .......... ...
8


7-





5
4 ......................... .... .......... ......... ............................................. ......... ........ ..... ......





4"


Sept. Oct. Nov. Dec. Jan. Feb.
Sept. Oct. Nov. Dec. Jan. Feb.
























Fig. 3.11. Reclaimed wastewater and canal water effects on fruit total soluble
solids (TSS), titratable acidity (TA) and TSS:TA ratio of 'Redblush' grapefruit at
Vero Beach, Fla., 1993-94. Control = canal water, and reclaimed wastewater at
low = 23.1 mm-wk1, mod. = 30.7 mm-wk'1 and high = 38.6 mm-wk'. Mean
of 10 fruit/tree for four trees/bed for four beds/treatment. (A) Fruit TSS for tree
receiving canal water were significantly different from trees receiving mod. and
high reclaimed wastewater. y = 10.39 + 0.29x 0.004x2; R2 = 0.39 for the
canal water treatment; y = 10.19 + 0.20x + 0.002x2; R2 = 0.21 for all
reclaimed wastewater treatments pooled. (B) Fruit TA was not significantly
different among treatments. y = 1.61 0.19x + 0.03x2; R2 = 0.53 for all
treatments pooled. (C) Fruit TSS:TA ratio was not significantly different among
treatments. y = 6.35 + 0.99x 0.14x2; R2 = 0.71 for all treatments pooled.