Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Soil moisture relations in the coastal citrus areas of Florida
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Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026432/00001
 Material Information
Title: Soil moisture relations in the coastal citrus areas of Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 38, 10 p. of plates : ill. ; 23 cm.
Language: English
Creator: Young, T. W ( Thomas Wilbur ), 1905-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1953
Copyright Date: 1953
 Subjects
Subject: Soil moisture -- Florida   ( lcsh )
Citrus fruits -- Moisture -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 37-38).
Statement of Responsibility: T.W. Young.
General Note: Cover title.
General Note: "A contribution from the Citrus Experiment Station."
 Record Information
Bibliographic ID: UF00026432
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - AEN6703
oclc - 18270676
alephbibnum - 000926044

Full Text





HISTORIC NOTE



The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida







Bulletin 526 September 1953



UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
WILLARD M. FIFIELD, Director
GAINESVILLE, FLORIDA

(A Contribution from the Citrus Experiment Station)









Soil Moisture Relations in the

Coastal Citrus Areas of Florida


T. W. YOUNG
Formerly Associate Horticulturist, Citrus Experiment Station







TECHNICAL BULLETIN








Single copies free to Florida residents on request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE. FLORIDA











BOARD OF CONTROL EDITORIAL
J. Francis Cooper, M.S.A., Editor
Hollis Rinehart, Chairman, Miami Clyde Beale, A.B.J., Associate Editor
J. Lee Ballard, St. Petersburg J. N. Joiner, B.S.A., Assistant Editor
Fred H. Kent, Jacksonville William G. Mitchell, A.B.J., Assistant Editor
Wm. H. Dial, Orlando Samuel L. Burgess, A.B.J., Assistant Editor 3
Mrs. Alfred I. duPont, Jacksonville
George W. English, Jr., Ft. Lauderdale ENTOMOLOGY
W. Glenn Miller, Monticello
W. F. Powers, Secretary, Tallahassee A. N. Tissot, Ph.D., Entomologist
L. C. Kuitert, Ph.D., Associate
EXECUTIVE STAFF H. E. Bratley, M.S.A., Assistant
F. A. Robinson, M.S., Asst. Apiculturist
J. Hillis Miller, Ph.D., President" R. E. Waites, Ph.D., Asst. Entomologist
J. Wayne Reitz, Ph.D., Provost for Agr.3
Willard M. Fifield, M.S., Director HOME ECONOMICS
J. R. Beckenbach, Ph.D., Asso. Director Ouda Abbott, Ph.D., Home Econ.
L. Gratz, Ph.D., Assistant Director Ouida D. Abbott, Ph.D., Home con.
Rogers L. Bartley, B.S., Admin. Mgr.3 R. B French, Ph.D., Biochemist
Geo. R. Freeman, B.S., Farm Superintendent HORTICULTURE

G. H. Blackmon, M.S.A., Horticulturist
MAIN STATION, GAINESVILLE F. S. Jamison, Ph.D., Horticulturist 3
Albert P. Lorz, Ph.D., Horticulturist
R. K. Showalter, M.S., Asso. Hort.
AGRICULTURAL ECONOMICS R. A. Dennison, Ph.D., Asso. Hort.
IH G. Hamilton, Ph.D., Agr. Economist' R. H. Sharpe, M.S., Asso. Horticulturist
R.. Grilton, Ph.D., Agr. Economist3 V.F. Nettles, Ph.D., Asso. Horticulturist
E. Greene, Ph.D., Agr. Economist F. S. Lagasse, Ph.D., Horticulturist2
M. A. Brooker, Ph.D., Agr. Economists R. D. Dickey, M.S.A., Asso. fort.
Zach Savage, M.S.A., Associate L. H. Halsey, M.S.A., Asst. Hort.
A. H. Spurlock, M.S.A., Agr. Economist C. B. Hall, Ph.D., Asst. Horticulturist
D. E. Alleer, M.S., AssociateAustin Griffiths, Jr., B.S., Asst. Hort.
D. L. Brooke, M.S.A., Associate S. E. McFadden, Jr., Ph.D., Asst. Hort.
M. R. Godwin, Ph.D., Associate dde Ph.D. Asst
W. K. McPherson, M.S., Economists C. H. VanMiddelem, Ph.D., Asst. Biochemist
s A3 Buford D. Thompson, M.S.A., Asst. Hort.
Eric Thor, M.S., Asso. Agr. Economist Buford D. Thompson, M.v.A., Asst. t ort.
Cecil N. Smith, M.A., Asso. Agr. Economist M. W Hoover, M.S.A., Asst. Short.
Levi A. Powell, Sr., M.S.A., Assistant LIBRARY
Orlando, Florida (Cooperative USDA)
G. Norman Rose, B.S., Asso. Agri. Economist Ida Keeling Cresap, Librarian
J. C. Townsend, Jr., B.S.A., Agricultural
Statistician PLANT PATHOLOGY
J. B. Owens, B.S.A., Agr. Statistician 2 W. B. Tisdale, Ph.D., Plant Pathologist 1
AGRICULTURAL ENGINEERING Phares Decker, Ph.D., Plant Pathologist
Erdman West, M.S., Botanist & Mycologist
Frazier Rogers, M.S.A., Agr. Engineer Robert W. Earhart, Ph.D., Plant Path.2
J. M. Myers, M.S.A., Asso. Agr. Engineer Howard N. Miller, Ph.D., Asso. Plant Path.
J. S. Norton, M.S., Asst. Agr. Engineer Lillian E. Arnold, M.S., Asso. Botanist
C. W. Anderson, Ph.D., Asst. Plant Path.
AGRONOMY
POULTRY HUSBANDRY
Fred H. Hull, Ph.D., Agronomist 1 -
G. B. Killinger, Ph.D., Agronomist N. R. Mehrhof, M.Agr., Poultry Hush. 3
H. C. Harris, Ph.D., Agronomist J. C. Driggers, Ph.D., Asso. Poultry Husb.3
R. W. Bledsoe, Ph.D., Agronomist
W. A. Carver, Ph.D., Agronomist SOILS
Fred A. Clark, M.S., Associate F. B. Smith, Ph.D., Microbiologist 3
A. T. Wallace, Ph.D., Assistant Gaylord M. Volk, Ph.D., Soils Chemist
A1. E. McCloud, Ph.D., Assistant S J. R. Neller, Ph.D., Soils Chemist
G. C. Nutter, Ph.D., Asst. Agronomist Nathan Gammon, Jr., Ph.D., Soils Chemist
G. C. Nutter, Ph.., Asst. Agronomist Ralph G. Leighty, B.S., Asst. Soil Surveyor 2
ANIMAL HUSBANDRY AND NUTRITION G. D. Thornton, Ph.D., Microbiologists
G. F. Eno, Ph.D., Asst. Soils Microbiologist
T. J. Cunha, Ph.D., Animal Husbandman ts H. W. Winsor, B.S.A., Assistant Chemist
G. K. Davis, Ph.D., Animal Nutritionist 3 R. E. Caldwell, M.S.A., Asst. Chemist '
I. L. Shirley, Ph.D., Biochemist V. W. Carlisle, B.S., Asst. Soil Surveyor
A. M. Pearson, Ph.D., Asso. An. Husb.3 J. H. Walker, M.S.A., Asst. Soil Surveyor'
John P. Feaster, Ph.D., Asst. An. Nutri. William K. Robertson, Ph.D., Asst. Chemist
H. D. Wallace, Ph.D., Asst. An. Husb.3 O. E. Cruz, B.S.A., Asst. Soil Surveyor
M. Koger, Ph.D., An. Husbandman 3 W. G. Blue, Ph.D., Asst. Biochemist
J. F. Hentges, Jr., Ph.D., Asst. An. Husb. 8 J. G. A. Fiskel, Ph.D., Asst. Biochemist s
L. R. Arrington, Ph.D., Asst. An. Hush. L. C. Hammond, Ph.D., Asst. Soil Physicist 3
H. L. Breland, Ph.D., Asst. Soils Chem.
DAIRY SCIENCE
VETERINARY SCIENCE
E. L. Fouts, Ph.D., Dairy Technologist's
R. B. Becker, Ph.D., Dairy Husbandman 3 D. A. Sanders, D.V.M., Veterinarian 1'
S. P. Marshall, Ph.D., Asso. Dairy Husb.3 M. W. Emmel, D.V.M., Veterinarian 3
W. A. Krienke, M.S., Asso. Dairy Tech.3 C. F. Simpson, D.V.M., Asso. Veterinarian
P. T. Dix Arnold, M.S.A., Asso. Dairy HIusb. 3 L. E. Swanson, D.V.M., Parasitologist
Leon Mull, Ph.D., Asso. Dairy Tech.3 W. R. Dennis, D.V.M., Asst. Parasitologist
H. H. Wilkowske, Ph.D., Asst. Dairy Tech.3 E. W. Swarthout, D.V.M., Asso. Poultry
James M. Wing, Ph.D., Asst. Dairy Hush. Pathologist (Dade City)











BRANCH STATIONS F. T. Boyd, Ph.D., Asso. Agronomist
M. G. Hamilton, Ph.D., Asst. Horticulturist
NORTH FLORIDA STATION, QUINCY J. N. Simons, Ph.D., Asst. Virologist
D. N. Beardsley, M.S., Asst. Animal Husb.
W. C. Rhoades, Jr., M.S., Entomologist in
Charge SUB-TROPICAL STATION, HOMESTEAD
R. R. Kincaid, Ph.D., Plant Pathologist
L. G. Thompson, Jr., Ph.D., Soils Chemist Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
W. H. Chapman, M.S., Agronomist D. O. Wolfenbarger, Ph.D., Entomologist
Frank S. Baker, Jr., B.S., Asst. An. Husb. Francis B. Lincoln, Ph.D., Horticulturist
Frank E. Guthrie, Ph.D., Asst. Entomologist Robert A. Conover, Ph.D., Plant Path.
John L. Malcolm, Ph.D., Asso. Soils Chemist
Mobile Unit, Monticello R. W. Harkness, Ph.D., Asst. Chemist
R. W. Wallace, B.S., Associate Agronomist R. Bruce Ledin, Ph.D., Asst. Hort.
J. C. Noonan, M.S., Asst. Hort.
Mobile Unit, Marianna M. H. Gallatin, B.S., Soil Conservationist2
R. W. Lipscomb, M.S., Associate Agronomist WEST CENTRAL FLORIDA STATION,
Mobile Unit, Pensacola BROOKSVILLE
R. L. Smith, M.S., Associate Agronomist Marian W. Hazen, M.S., Animal Husband-
Mobile Unit, Chipley man in Charge2
J. B. White, B.S.A., Associate Agronomist RANGE CATTLE STATION, ONA
CITRUS STATION, LAKE ALFRED W. G. Kirk, Ph.D., Vice-Director in Charge
E. M. Hodges, Ph.D., Agronomist
A. F. Camp, Ph.D., Vice-Director in Charge D. W. Jones, M.S., Asst. Soil Technologist
W. L. Thompson, B.S., Entomologist
. F. Suit, Ph.D., Plant Pathologist CENTRAL FLORIDA STATION, SANFORD
E. P. Ducharme, Ph.D., Asso. Plant Path.
C. R. Stearns, Jr., B.S.A., Asso. Chemist R. W. Ruprecht, Ph.D., Vice-Dir. in Charge
J. W. Sites, Ph.D., Horticulturist J. W. Wilson, ScD., Entomologist
H. 0. Sterling, B.S., Asst. Horticulturist P. J. Westgate, Ph.D., Asso. Hort.
H. J. Reitz, Ph.D., Horticulturist Ben F. Whitner, Jr., B.S.A., Asst. Hort.
Francine Fisher, M.S., Asst. Plant Path. Geo. Swank, Jr., Ph.D., Asst. Plant Path.
I. W. Wander, Ph.D., Soils Chemist
J. W. Kesterson, M.S., Asso. Chemist WEST FLORIDA STATION, JAY
R. Hendrickson, B.S., Asst. Chemist
Ivan Stewart, Ph.D., Asst. Biochemist C. E. Hutton, Ph.D., Vice-Director in Charge
I. S. Prosser, Jr., B.S., Asst. Engineer H. W. Lundy, B.S.A., Associate Agronomist
R. W. Olsen, B.S., Biochemist
F. W .Wenzel, Jr., Ph.D., Chemist SUWANNEE VALLEY STATION,
Alvin H. Rouse, M.S., Asso. Chemist LIVE OAK
H. W. Ford, Ph.D., Asst. Horticulturist
L. C. Knorr, Ph.D., Asso. Histologist4 G. E. Ritchey, M.S., Agronomist in Charge
R. M. Pratt, Ph.D., Asso. Ent.-Pathologist
W. A. Simanton, Ph.D., Entomologist GULF COAST STATION, BRADENTON
E. J. Deszyck, Ph.D., Asso. Horticulturist L Spencer, Ph.D., Soils Chemist in Charge
C. IY. Leonard, Ph.D., Asso. Horticulturist E. G. Kelsheimer, Ph.D., Entomologist
W. T. Long, M.S., Asst. Horticulturist David G. A. Kelbert, Asso. Horticulturist
M. H. Muma, Ph.D Asso. Entomologist Robert 0. Magie, Ph.D., Plant Pathologist
F. J. Reynolds, Ph.D., Asso. Hort. J. M. Walter, Ph.D., Plant Pathologist
W. F. Spencer, Ph.D., Asst. Chem. S. S. Woltz, Ph.D., Asst. Horticulturist
R. B. Johnson, Ph.D., Asst. Entomologist Donald S. Burgis, M.S.A., Asst. Hort.
W. F. Newhall, Ph.D., Asst. Entomologist C. M. Geraldson, Ph.D., Asst. Horticulturist
W. F. Grierson-Jackson, Ph.D., Asst. Chem.
Roger Patrick, Ph.D., Bacteriologist
Marion F. Oberbacher, Ph.D., Asst. Plant FIELD LABORATORIES
Physiologist
Evert J. Elvin, B.S., Asst. Horticulturist Watermelon, Grape, Pasture-Leesburg
R. C. J. Koo, Ph.D., Asst. Biochemist
J. R. Kuykendall, Ph.D., Asst. Horticulturist J. M. Crall, Ph.D., Associate Plant Path-
ologist Acting in Charge
EVERGLADES STATION, BELLE GLADE C. C.'Helms, Jr., B.S., Asst. Agronomist
L. H. Stover, Assistant in Horticulture
W. T. Forsee, Jr., Ph.D., Chemist in Charge,
R. V. Allison, Ph.D., Fiber Technologist Strawberry-Plant City
Thomas Bregger, Ph.D., Physiologist A. N. Brooks, Ph.D., Plant Pathologist
J. W. Randolph, M.S., Agricultural Engr.
R. W. Kidder, M.S., Asso. Animal Husb. Vegetables-Hastings
C. C. Seale, Associate Agronomist A. H. Eddins, Ph.D., Plant Path. in Charge
N. C. Hayslip, B.S.A. Asso. Entomologist E. N. McCubbin, Ph.D., Horticulturist
E. A. Wolf, M.S., Asst. Horticulturist T. M. Dobrovsky, Ph.D., Asst. Entomologist
W. H. Thames, M.S., Asst. Entomologist Pan
W. G. Genung, M.S., Asst. Entomologist Pecans-Monticello
Frank V. Stevenson, M.S., Asso. Plant Path. A. M. Phillips, B.S., Asso. Entomologist2
Robert J. Allen, Ph.D., Asst. Agronomist John R. Large, M.S., Asso. Plant Path.
V. E. Green, Ph.D., Asst. Agronomist
J. F. Darby, Ph.D., Asst. Plant Path. Frost Forecasting-Lakeland
V. L. Guzman, Ph.D., Asst. Hort. Warren O. Johnson, B.S., Meteorologist in
J. C. Stephens, B.S., Drainage Engineer 2 Charge 2
A. E. Kretschmer, Jr., Ph.D., Asst. Soils
Chem. 1 Head of Department
Charles T. Ozaki, Ph.D., Asst. Chemist 2 In cooperation with U. S.
Thomas L. Meade, Ph.D., Asst. An. Nutri. Cooperative, other divisions, U. of F.
I. S. Harrison, M.S., Asst. Agri. Engr. 4 On leave
















CONTENTS


PAGE


THE SOILS STUDIED .......- ...... .........----------. ------------ ....-........... 5

SAMPLING OF THE SOIL .. --..---- -........... --------------..... ...----- ........... 8


M ETHODS OF STUDY ................................ ......... ------ ----------........... 9


PRESENTATION OF RESULTS ...........-----......- ....... ........- ..---- ......-- 14


D ISCUSSION ................... ...........- .. ... .... ....... ..---- ....... ....... .... 14


Permeability ....................... ........ -- -- ---- -............ 14


Non-capillary Porosity and Air Capacity .................. ....---........... 20


Available M oisture .................-- ..- .-- .... .........---....... 21


Effect of Drainage on Available Moisture ........................ ................ 25


FIELD OBSERVATIONS AND PRACTICAL CONSIDERATIONS ........ ..........-........ -28


SUMMARY .....-................ -..---. ..-..-.. .....--..... ......-- .. ......--- ..... 35


ACKNOWLEDGMENTS ...------.........---- .... -------.....-- ......... -.....-....-.........-- .......--. 37


LITERATURE CITED ................... ...... --................... ... --......-- .- ..-- .. ......-- -- ... 37


A PPENDIX ................- -- -------... .................. -----.. -............... 39


Tension-moisture Curves for 20 Soils .............................. ......... 39-48









Soil Moisture Relations in the Coastal

Citrus Areas of Florida

T. W. YOUNG

Citrus is planted in the coastal areas on a relatively large
number of soil series. These range in texture from very light
sands through loamy sands, sandy loams, sandy clay loams,
mucks and peats. For the most part these soils are inherently
poorly drained. On these soils citrus is occasionally planted on
mounds, but more generally on beds from one to three feet high
which provide broad furrows between the tree rows. These
furrows lead into ditches and canals for drainage.
Although it is generally conceded among growers that arti-
ficial drainage is usually necessary for successful citrus culture
on these soils, there is a wide variation of opinion as to how
intensive the drainage should be. The high incidence of un-
thrifty trees in these groves because of water damage is a strong
argument for more intensive drainage. There has been however,
no systematic information available on the moisture character-
istics of these various soils on which to base the degree of drain-
age that would be desirable and practical.
A knowledge of these moisture characteristics should enable
the individual grower to drain and irrigate his grove more effec-
tively. Such information would be valuable for those concerned
with the proper handling of the numerous drainage districts,
particularly in those districts where a water-control or conserva-
tion program is in effect or is being considered. An intelligent
interpretation of the results of any irrigation, drainage or water-
control program cannot be secured without the basic information
on the moisture characteristics of the soils concerned.
The principal purpose of this publication is to present the re-
sults of soil-moisture retension studies made in the laboratory
on representative coastal citrus grove soils and, in a general way,
to evaluate the moisture characteristics thus obtained with re-
spect to the drainage and irrigation requirements of the various
soils.
THE SOILS STUDIED
Although the soils included in these studies were collected from
citrus groves on the East Coast, they are equally representative
1Soil classification by J. R. Henderson, Extension Agronomist, Uni-
versity of Florida, and Ralph J. Leighty, Soil Scientist, USDA, in coopera-
tion with the Florida Agricultural Experiment Stations.









6 Florida Agricultural Experiment Stations

of the citrus grove soils found on the West Coast. Nine soil
series were selected to secure a wide range in textures. Profile
descriptions of the soils from which the 20 individual sets of
samples were taken for examination are based on the horizons
found near the bed crown and are as follows:

1. Lakeland fine sand.
0 7" Gray fine sand.
7 42"+ Yellow fine sand.
2. Leon fine sand, heavy substratum phase.
0 12" Gray to light gray or brownish gray fine sand-oc-
curring in no regular order.
12 34" Light brown to white sand.
34 40" Sand cemented with dark brown organic hardpan.
40 42"+ Gray sandy clay.
3. Delray loamy fine sand, shallow phase.
0 16" Dark gray loamy fine sand.
16 30" Light gray sandy loam-grading into lower horizon.
30 36" Light gray sandy clay to clay.
4. Felda fine sand.
0 6" Light gray fine sand.
6 12" Light gray fine sand to loamy sand.
12 24" Gray sandy loam to sandy clay-grading into lower
horizon.
5. Felda fine sandy loam.
0 15" Dark gray fine sandy loam.
15 40" Gray sandy loam to yellow mottled sandy clay.
40"+ Gray and yellow mottled sandy clay with occasional
pockets of calcareous materials-marl and shell.
6. Felda loamy fine sand.
0 12" Gray loamy fine sand.
12 16" Gray fine sandy loam-grading into lower horizon.
16 36"+ Gray sandy clay.
7. Felda loamy fine sand.
0 12" Gray loamy fine sand.
12 16" Gray fine sandy loam-grading into lower horizon.
16 36"+ Gray sandy clay.
8. Felda fine sandy loam.
0 9" Gray fine sandy loam.
9 14" Light gray fine sandy loam.
14 30" Gray sandy clay-grading into lower horizon.
30 40" Gray sandy clay-slightly calcareous.
40 48" Gray calcareous clay.
48"+ Mixture of sand, clay, marl and shell.
9. Sunniland fine sandy loam.
0 10" Dark gray fine sandy loam.
10 18" Gray sandy loam.
18 36"+ Gray-yellow mottled calcareous sandy clay.
10. Sunniland fine sandy loam.
0 8" Gray fine sandy loam.
8 20" Gray to dark gray sandy loam.
20 36" Gray, slightly yellow mottled calcareous sandy clay.
11. Sunniland fine sandy loam.
0 9" Light gray fine sandy loam.
9 16"Gray fine sandy loam.
16 24" Gray, slightly yellow mottled sandy clay-grading into
lower horizon.
24 36"+ Gray, yellow mottled calcareous sandy clay.








Soil Moisture Relations in the Coastal Citrus Areas 7

12. Sunniland fine sandy loam.
0 12" Gray fine sandy loam.
12 18" Light gray fine sandy loam.
18 36"+ Gray, yellow mottled sandy clay.
13. Parkwood loamy fine sand, shallow phase.
0 12" Dark gray calcareous loamy fine sand.
12 26" Gray sandy marl.
26 36"+ Gray, yellow mottled marl.
14. Parkwood fine sandy loam, very shallow phase.
0 6" Gray calcareous fine sandy loam.
6 36" Light gray marl.
36"+ Gray sandy marl.
15.. Parkwood fine sandy loam, shallow phase.
0 -12" Dark gray calcareous fine sandy loam.
12 36" Gray marl.
36"+ Gray, yellow mottled sandy marl.
16. Manatee fine sandy loam.
0 7" Dark gray fine sandy loam.
7- 16" Gray sandy marl.
16 26" Gray, yellow mottled calcareous sandy clay--grading
into lower horizon.
26 38" Gray sandy marl-grading into lower horizon.
38 48" Gray calcareous sand.
48"+ Gray sand and shell mixture.
17. Manatee fine sandy clay loam.
0 36" Black fine sandy clay loam.
36"+ Dark brown to black sandy clay-slightly calcareous.
18. Davie mucky fine sand (10% organic matter).
0 12" Gray sand and dark brown peaty-muck mixture.
12 26" Light gray fine sand.
26"+ Limerock.
19. Davie peaty muck (48% organic matter).
0 12" Dark brown peaty-muck and gray sand mixture.
12 30" Light gray fine sand.
30"+ Limerock.
20. Everglades peat (88% organic matter).
0 36"+ Dark brown to black organic matter, partially de-
composed and mixed with some light gray sand.

To a great extent the surface layers of these soils, and in some
the subsoils, are of simple structure without distinct cleavage
planes, several of them being single-grained sands and loamy
sands. In the process of working these soils into beds, a con-
siderable amount of mixing of the surface layers with the gen-
erally heavier subsoil layers has occurred, with the result that
both structure and texture usually vary widely within the grove.
Thus, the profiles have been altered from the original and de-
scriptions given here do not conform entirely with descriptions
found elsewhere which are based on undisturbed virgin soils.
Some profile descriptions are identical or very similar for two
soils of the same series; for example, Felda soils Nos. 6 and 7
and Sunniland soils Nos. 11 and 12. Although these cannot be







8 Florida Agricultural Experiment Stations

segregated readily by inspection, it is of interest to include them
here to show the variation in soil moisture characteristics which
may exist in soils that appear similar.

SAMPLING OF THE SOIL
For the particular type of physical assay employed in this
investigation it would normally be desirable to work with un-
disturbed soil samples, so as not to alter the structure and thus
obtain results different from those characteristic of the soil in
place. With soils as variable as these, in which the surface
layers had been disturbed more or less, it was considered ex-
peditious to make the samples composites of a large number of
borings to offset the heterogeneity of these soils.
Twenty-five borings were made at as many adjacent trees for
each soil. Borings were made on the side of the bed about four
feet from the tree row, where preliminary borings indicated
average profile conditions were most prevalent. A ll-inch
diameter soil auger was employed. From a previous investiga-
tion (18)2 on the rooting habits of citrus growing in the coastal
citrus areas, it had been found that the zone of principal rooting
was in the top foot of soil. Few roots were found below 18
inches and only rarely below 2 feet. For this reason, as well
as a matter of expedience, sampling was to 36 inches except
when rock or hardpan was encountered at shallower depths.
For the purpose of this particular investigation, the cores were
divided according to definite and uniform depths rather than
according to soil horizons. The 0-18 inch depth was divided into
its component 6-inch layers because of textural variations with
depth. The texture of the 18-36 inch depth was relatively uni-
form in the individual soils and no division was considered neces-
sary. The 0-6, 6-12, 12-18 and 18-36 inch soil layers were
separated as taken, and the 25 cores for each of these were com-
posited in the field. After compositing, a portion of each of
these was brought to the laboratory in soil cans where it was
air-dried, screened through a 5 mm. sieve and thoroughly mixed.
The expression of moisture on a volume basis gives a clearer
picture of soil moisture conditions than does the percent by
weight. A great variation in the volume weight of soils studied
has been found (12). In order to present the data obtained from
these studies on a volume basis, undisturbed volume-weight

Italic figures refer to Literature cited, in back of this publication.








Soil Moisture Relations in the Coastal Citrus Areas 9

samples were taken from the center of each of the four arbitrary
layers into which each soil was divided. These samples were
taken by means of a thin-walled steel clyinder about 31/2 inches
in diameter and having a volume capacity of one two-millionth
of an acre-six-inches. These weights are shown in Table 1.

TABLE 1.-WEIGHT PER UNIT VOLUME OF 20 SoILS FROM CITRUS GROVES
IN THE COASTAL AREAS OF FLORIDA.

oilgms. per 1/2,000,000 Ac. 6" of Soil
No. Soil Type Soil Layer_
S__ _0-6" 16-12" 112-18"l 18- 36"
II
1 Lakeland fine sand ..................... 460 474 474 474
2 Leon fine sand, heavy
substratum phase ............... 409 430 397 *409
3 Delray loamy fine sand,
shallow phase ................-....... 395 435 408 408
4 Felda fine sand ..............-.......... 460 463 465 463
5 Felda fine sandy loam .............. 463 40 4 3 I 4 1
6 Felda loamy fine sand ............. 420 445 420 1 422
7 Felda loamy fine sand .......... 454 476 422 431
8 Felda fine sandy loam .............. 415 414 416 477
9 Sunniland fine sandy loam .... 411 434 354 386
10 Sunniland fine sandy loam .... 414 405 439 409
11 Sunniland fine sandy loam ...... 421 458 446 443
12 Sunniland fine sandy loam ...... 429 468 458 454
13 Parkwood loamy fine sand,
shallow phase ....-........-......... 454 440 447 449
14 Parkwood fine sandy loam,
very shallow phase .-........- 422 404 436 436
15 Parkwood fine sandy loam,
shallow phase ....................... 360 396 390 393
16 Manatee fine sandy loam ....... 374 350 374 386
17 Manatee fine sandy clay loam 408 410 446 446
18 Davie mucky fine sand ....-...-..... 340 340 431 1 **452
19 Davie peaty muck ................... 182 183 477 f477
20 Everglades peat ................. ... 182 182 182 182

*18 34 ** 18 26"
t 18 30"

METHODS OF STUDY

The physical methods used in the soil moisture retention
studies were based on the energy concept of soil moisture intro-
duced by Buckingham (3). He suggested the term "capillary
potential" to express the value which measures the attraction
of the soil at any given point for water. Gardner and others (6)
suggested that the capillary potential be defined as the work re-
quired to move a unit mass of water from a point where the
potential is zero (saturation) to the point in question. An ex-
cellent discussion is given by Russell (14) on the energy concept







10 Florida Agricultural Experiment Stations

of soil moisture. The expression of the energy with which water
is held by soils was simplified by Schofield (15), who first used
the logarithm of the capillary potential, pF. Schofield proposed
the term pF in anology to the pH scale, and defined it as the
common logarithm of the soil moisture tension expressed in centi-
meters of water. If pF is to be accepted as a free-energy scale it
should be distinguished from moisture tension. Richards and
Weaver (13) have called attention to the effect of soluble salts on
pF and point out that in some soils dissolved materials may
account for a major part of the free energy of the soil water.
However, the humid region soils reported on here are leached and
are substantially salt free; thus one is justified in ignoring the
osmotic component of the pF.
To study the moisture retention of the various soils when
subjected to tensions effective from saturation to 316 cm. above
the water-table (pF 0 to 2.5) the method described by Jamison
(9) was followed. The apparatus consisted essentially of several
20 mm. diameter Buchner fritted funnels to which were attached
capalliary glass stems fitted with stop-cocks. The lower com-
partment and stem of each funnel was filled with water and the
absorbed air removed from the porous disc by applying suction to
the outlet while the funnel was inverted in water. The stop-
cock was then closed until the funnel was connected through
rubber tubing filled with water to a vessel of water that could be
adjusted to the desired level. Caution was necessary to avoid
introduction of air bubbles into the system when attaching the
rubber tubing initially and after weighing. Closing the stop-
cock before detaching the tubing and keeping it closed until
again connected lessened this trouble. Weighing was done by
suspending the funnel on an.analytical balance with a wire sling.
Mineral soil samples were moistened several days in advance of
using to aid in packing in the funnels and to expedite wetting.
Organic soils (peats and mucks), which are difficult to saturate
after being stored air-dry, were wetted rather thoroughly a
month or more before using to insure complete saturation and to
eliminate swelling after the sample was placed in the funnel. A
4 mm. layer of soil from each sample was placed on the porous
disc in individual funnels and packed firmly to the degree of
compaction approximating that found in the field. The use of
thin soil layers was essential here, as in the subsequent work
with a centrifuge, in order to attain equilibrium more precisely
at the specified pF throughout the entire volume of the sample.








Soil Moisture Relations in the Coastal Citrus Areas 11

Glass covers were placed on each funnel to prevent evaporation.
Soils were brought to saturation and carried through a series
of six or seven equilibrations at different tensions ranging from
pF 0 to pF 2.5, each followed by weighing, as outlined by Jamison
(8, 9). After the last equilibration and weighing, a moisture
sample was taken and determined by oven-drying. From this
the moisture content by weight at each of the equilibration
points was determined. These were converted to percent mois-
ture by volume by calculation with the volume weight data for
the respective soil sample. Triplicate determinations were made
on separate samples at each equilibration point for the four soil
layers from each soil and the results averaged.
Centrifugation was used to study moisture relations at pF 3.1,
where capillary movement of water practically ceases, and at pF
4.2, the wilting percentage, (15). A centrifuge apparatus (Fig.
1) was prepared in a manner similar to that described by Gard-
ner (5), but incorporating the modification of Jamison (7), who
used asbestos fiber conducting columns. In the centrifuge used
the distance from the axis of rotation to the free water surface
was 19.9 cm. (ri) and the distance from the axis to the center of
the sample 9.2 cm. (r2). Under these conditions, in a salt free
soil, the centrifuge equation at equilibrium (Jamison 7, 8) re-
duces to:
log S = 1/2pF + 1.3785

where S is the centrifuge speed in r.p.m. and pF is the base 10
logarithm of the moisture tension in centimeters. The latter
author's technique with respect to setting up the apparatus,
using salt free soil samples 4 mm. thick, bringing the centrifuge
up to speed, duration of centrifugation and methods of calcula-
tion were duplicated as nearly as possible. As in the determina-
tions in the lower pF range, mineral soils were slightly mois-
tened several days in advance and organic soils maintained near
saturation for several weeks before centrifugation.
The centrifuge used was not equipped with a constant speed
regulator and occasionally some difficulty was experienced in
maintaining the desired speed. Tachometer readings were made
at intervals of several minutes throughout centrifugation and
where speed could not be maintained to within T 10 r.p.m. the
samples were discarded. By maintaining the speed of the centri-
fuge within these limits, the maximum error in tension at pF 4.2
was 0.7 percent, with a difference of 0.95 percent between mini-












Rubber Gasket
One I mm Hole Drilled 8-1 mm Holes Drilled In Side
Blotting Paper In Triunnion Cup 2
Pod -
Center Of
Centrifuge .
"Asbestos Fiberr l>^ \T \ \ ^




Of Soil
9.2 cm(r2)-
13-1 mm Holes Drilled
19.9cm(r ) n Botto

Coarse Sand

Fig. 1.-Detail of centrifuge apparatus. Four such tubes in balanced pairs were used.







Soil Moisture Relations in the Coastal Citrus Areas 13

mum and maximum. At pF 3.1 the maximum error in tension was
2.4 percent, with a difference of slightly less than 4.5 percent
between minimum and maximum tensions. This degree of error
is probably not significant in comparison to the sampling error.
A minimum of three satisfactory runs was obtained for each
sample. After the moisture content was determined by oven
drying, the results were averaged. As at the lower tensions,
percent moisture by weight was converted to percent by volume
for presentation.
The wilting percentage on a volume basis was also determined
biologically for each of the soil samples, using sunflower as the
indicator plant, in order to check the centrifuge results. There
was a trend toward slightly lower values for the biological
method, which averaged 0.6 percent below the centrifuge values.
Values obtained by the two methods were in fair agreement, how-
ever, when one considers that the average of wilting percent-
ages for all these samples was approximately 10 percent.
It is pertinent at this point to emphasize that the error of
sampling probably had resulted in as much variation, or more,
in moisture characteristic values obtained for the same soils as
imperfections of laboratory methods of analyses used here. In
"a preliminary investigation moisture data had been obtained on
"a large number of samples of soils Nos. 3, 8, 10 and 11 direct from
the field. These field moisture studies were made by intensive
sampling at periods when soil moisture ranged from near the
wilting point to saturation and at the field capacity of the re-
spective soils with water tables at varying depths to about six
feet, as determined by water table wells. Fifteen borings were
made for each composite sample and the cores where divided into
the 0-6, 6-12, and 12-18 inch depths.
The moisture contents of these field samples at approximately
the same given tensions were much less consistent than those
of the so-called laboratory samples, and in general were only
in fair agreement with the latter. This wide variation can logi-
cally be accounted for by the heterogeneity of the soil texture
resulting from bedding. Rate of drainage will be influenced by
the permeability of underlying layers of soil. In view of the
nature of these soils, it appears that a clearer concept of their
true moisture relations can be secured from laboratory examina-
tions than from studies of moisture conditions in the field. Al-
though these laboratory data are not absolute, they are reason-
ably accurate approximations. They have a practical value for








14 Florida Agricultural Experiment Stations

application in the field, since these data are comparable for all
soils handled in the same manner.8

PRESENTATION OF RESULTS
The moisture percentage of the individual soil samples at the
equilibrations at various tensions by the two physical techniques
were combined and plotted against the corresponding pF values.
The tension-moisture curves for each of the arbitrary layers into
which the 20 soils examined were divided are found in the Appen-
dix. For economy of space in presenting these curves in this
bulletin, the four curves for each soil are superimposed one upon
the other, using the same coordinate axes.

DISCUSSION
Permeability.-Under natural conditions total soil pore space
is partly filled with water and partly with air in a reciprocal re-
lationship. When a soil is saturated and allowed to drain, the
larger pores empty rapidly at relatively low tensions and fill with
air. While the greater portion of the rapid entrance and exit
of water is through the large pores, a considerable amount moves
into the soil through the fine pores and is held there with suffi-
cient force to prevent easy drainage. Thus, in an adequately
drained soil the finer pores act as a reservoir for the bulk of the
water (water capacity) used by plants, while the pores of larger
diameter function in aeration (air capacity).
These larger pores are generally referred to in the literature
on soil permeability as "non-capillary" pores, while the smaller
ones that drain only at relatively high tensions are called "capil-
lary" pores. As pointed out by Baver (1), the amount of pore
space drained and filled with air (non-capillary) is dependent
upon the tension under which the soil is drained. The greater the
drainage tension the less the amount of water that will be held
by capillarity. In other words, with increasing drainage the
non-capillary pore space increases, with a proportional decrease
in the capillary pore space. Thus, this terminology may be mis-
leading if one attempts to define non-capillary and capillary pores

SA pressure-membrane apparatus is now favored for soil moisture re-
tention studies. Although the results obtained by this other method are
not more valid than those reported here, the pressure-membrane offers
certain advantages in simplicity and adaptability over a wide pF range.
See Reitemeier, R. F., and L. A. Richards. Reliability of the pressure-
membrane method for extraction of soil solution. Soil Sci. 57: 119-135.
1944.







Soil Moisture Relations in the Coastal Citrus Areas 15

altogether in terms of pore size and neglects to consider the ten-
sion at which they are drained.
The point at which a tension-moisture curve breaks more or
less sharply upward (flex point) represents the transition point
in that particular soil between a pore size distribution which
drains with relative ease (non-capillary pores) and a pore size
distribution which holds water by capillarity against a consid-
erable force (capillary pores). The flex point and its relation-
ship to the non-capillary and capillary porosity of a soil is indi-
cated on the pF curve for the 0-6 inch soil layer of soil No. 1
in the Appendix. Although the flex point is considered to be
the tension at which the soil will drain, as explained by Nelson
and Baver (11), a large volume of pores may actually have
drained at much lower tensions.
The smallest effective pore size drained at a given tension can
be calculated approximately (Bradfield and Jamison, 2) by the
equation:
.30
d=--
h

where d is pore diameter and h is tension in cm. of water. Since
the amount of water withdrawn from zero tension (saturation)
to the flex point is considered to represent the pores that have
drained and filled with air-i.e., the non-capillary pores-it is
interesting to apply this equation, using the pF of the flex point,
to calculate the effective pore size of the non-capillary pores in
the several soils examined here. The pF of the flex point, deter-
mined as suggested by Nelson and Baver (11)4, for each soil
sample is listed in Table 2. From these data it is found that
the smallest effective diameters of the non-capillary pores varied
from more than 23 microns in the 6-12 inch layer of Sunniland
soil No. 9 to more than 292 microns in the 18-36 inch layer of
Felda soil No. 4.
The relationship of the pF of the flex point and the shape of
the tension-moisture curve below that point to soil permeability
has been discussed by Baver (1). Certain soil characteristics
that affect the percolation rate are depicted by the pF curves.
The percolation rate is approximately proportional to the amount
of water withdrawn from zero tension to that of the flex point.

"Briefly, the method used is as follows: The lower and the upper limits
of the flatter portion of the curve are found with a straight-edge. The pF
value for each of these points is converted to centimeters of water tension
and the average tension obtained. Because of the logarithmic nature of pF
curves this average is the true water tension at the flex point.








16 Florida Agricultural Experiment Stations


TABLE 2.-PF OF FLEX POINT, NON-CAPILLARY POROSITY AND POROSITY
FACTOR FOR 20 REPRESENTATIVE SOILS FROM CITRUS GROVES IN THE
COASTAL AREAS OF FLORIDA.
Non-Capil- Porosity
Soil Soil pF of laryPorosity Factor
No. Soil Type Layer Flex at Flex, % (NCP/pF
Point I by Vol. I Flex)

1 Lakeland fine sand 0- 6" 1.57 21.3 13.6
6-12" 1.50 21.2 14.1
12-18" 1.38 19.0 13.8
18-36" 1.46 17.8 12.2

2 Leon fine sand, 0- 6" 1.56 19.3 12.4
heavy substratum 6-12" 1.50 17.9 11.9
phase 12-18" 1.60 22.7 14.2
18-34" 1.53 18.8 12.3

3 Delray loamy 0- 6" 1.71 15.0 8.8
fine sand, shallow 6-12" 1.57 14.4 9.2
phase 12-18" 1.33 12.9 9.7
18-36" 1.43 12.5 8.7

4 Felda fine sand 0- 6" 1.59 18.4 11.6
6-12" 1.50 16.0 11.7
12-18" 1.05 12.2 11.6
18-36" 1.01 10.7 10.6

5 Felda fine sandy O- 6" 1.52 18.3 12.0
loam 6-12" 1.49 17.6 11.8
12-18" 1.57 18.2 11.6
18-36" 1.19 12.2 10.2

6 Felda loamy fine 0- 6" 1.26 12.3 9.8
sand 6-12" 1.35 16.4 12.1
12-18" 1.43 13.2 9.3
18-36" 2.04 20.8 10.2

7 Felda loamy fine 0- 6" 1.54 17.3 11.2
sand 6-12" 1.60 22.6 14.1
12-18" 1.22 15.5 12.7
18-36" 1.86 18.1 9.7

8 Felda fine sandy 0- 6" 1.52 25.0 16.4
loam 6-12" 1.59 19.3 12.1
12-18" 1.58 15.0 9.5
18-36" 1.65 15.2 9.2

9 Sunniland fine 0- 6" 1.81 15.5 8.6
sandy loam 6-12" 2.11 17.0 8.0
12-18" 1.97 10.4 5.3
18-36" 1.82 16.3 9.0

10 Sunniland fine 0- 6" 1.45 12.9 8.9
sandy loam 6-12" 1.72 15.7 9.1
12-18" 1.27 12.5 9.8
18-36" 1.69 14.7 8.7









Soil Moisture Relations in the Coastal Citrus Areas 17


TABLE 2.-pF OF FLEX POINT, NON-CAPILLARY POROSITY AND POROSITY
FACTOR FOR 20 REPRESENTATIVE SOILS FROM CITRUS GROVES IN THE
COASTAL AREAS OF FLORIDA. (Continued).

Non-Capil- Porosity
Soil Soil pF of laryPorosity Factor
No. Soil Type Layer Flex at Flex, % (NCP/pF
Point by Vol. I Flex)

11 Sunniland fine 0- 6" 1.78 14.5 8.2
sandy loam 6-12" 1.84 11.4 6.2
12-18" 1.84 13.8 7.5
18-36" 1.86 17.2 9.2
12 Sunniland fine 0- 6" 1.32 11.7 8.9
sandy loam 6-12" 2.01 16.1 8.0
12-18" 1.75 9.6 5.5
18-36" 1.75 16.2 9.3

13 Parkwood loamy 0- 6" 1.32 19.5 14.8
fine sand, shallow 6-12" 1.37 14.6 10.6
phase 12-18" 1.27 11.0 8.7
18-36" 1.02 10.1 9.9
14 Parkwood fine 0- 6" 1.55 17.1 11.0
sandy loam, very 6-12" 1.60 9.0 5.6
shallow phase 12-18" 1.54 11.8 7.7
18-36" 1.54 12.6 8.2
15 Parkwood fine 0- 6" 1.41 19.2 13.6
sandy loam, 6-12" 1.47 13.1 8.9
shallow phase 12-18" 1.53 14.6 9.5
18-36" 1.77 20.3 11.5

16 Manatee fine 0- 6" 1.56 22.1 14.2
sandy loam 6-12" 1.56 10.8 6.9
12-18" 1.41 9.7 6.9
18-36" 1.59 11.9 11.9
17 Manatee fine 0- 6" 1.30 11.6 8.9
sandy clay loam 6-12" 1.33 18.0 13.5
12-18" 1.48 17.0 11.5
18-36" 1.06 12.7 12.0

18 Davie mucky 0- 6"' 1.35 23.4 17.3
fine sand 6-12")
12-26" 1.63 25.3 15.5
26"+ (ROCK)

19 Davie peaty 0- 6"- 1.28 28.0 21.9
muck i-12"
12-30" 1.85 26.5 14.3
30"+ (ROCK)
20 Everglades peat 0- 6"]
6-12" 1.30 21.5 16.5
12-18"
_____.S-3" ___________








18 Florida Agricultural Experiment Stations

Percolation is inversely proportional to the tension of the flex
point. Permeability tends to increase, usually with a decrease
in the slope of the curve, from saturation to the flex point.
Therefore, Baver points out that the permeability and percola-
tion rate will vary directly with the non-capillary porosity, but
inversely with the tension required to drain these pores-the pF
of the flex. It follows that the ratio, non-capillary porosity to
pF of flex point, of a soil characterizes it with respect to its rela-
tive permeability and percolation rate. The value of this ratio,
which Nelson and Baver (11) termed the porosity factor, is given
in Table 2, together with the non-capillary porosity and the pF of
the flex point for each soil examined.
Sandy soils such as Lakeland (soil No. 1) and the surface lay-
ers of Leon (soil No. 2), down to the hardpan, are known to be
extremely permeable. It is interesting to note that the porosity
factor of the several layers into which these were divided for
study ranged from approximately 12 to 14. Permeability studies
by Baver (1) on a number of soils indicate that soils with por-
osity factors in this range would have an infiltration and perco-
lation rate of around two feet of water an hour. Generally
speaking, the Sunniland series (soils Nos. 9 through 12) had low-
er porosity factors than any of the other soils examined-the
lowest value found being 5.3 for the 12-18 inch layer of soil No.
9. According to Baver's data, a factor of 5.3 would indicate an
infiltration and percolation rate of between three and four inches
an hour, which is adequate. The organic surface layers of the
peat and muck soils Nos. 18 through 20 had the highest porosity
factors found, ranging from 16.5 to 21.9. Percolation in these
would appear to be excessive when computed on the basis of
Baver's data. The sandy subsoils of these series were also quite
permeable. The loamy sands and the sandy loams usually had
porosity factors intermediate between these extremes.
In several cases with loams a relatively permeable layer of
soil would be immediately underlain with a layer of considerably
less permeability. This is illustrated by Manatee soil No. 16. In
other instances, Manatee soil No. 17 for example, the converse
was true. Interspersion of layers of greater or of lesser permea-
bility than the overlying layers in the soil profile will, of course,
speed or slow the movement of water downward through a given
depth of soil according to the permeability of the lower layers.
Nelson and Baver (11) demonstrated that the small pores at the
bottom of a column of soil limit the percolation rate, even though








Soil Moisture Relations in the Coastal Citrus Areas 19

the large pores are drained at low tensions. In general there was
no definite trend in permeability with depth.
Since these data indicate that water should move rather read-
ily through all these soils, the question naturally follows as to
why such unsatisfactory results are obtained from the flooding-
type irrigation (17) commonly practiced on these soils. The
poor irrigation results can be accounted for, at least in part, by
the very fact that these soils are generally quite permeable. The
trees are usually planted on beds, which raises the principal root
zone a foot or so above the bottom of the water furrow. Often
the water supply is not sufficient to raise it to the level of the
root zone. Because the soils are quite permeable, to a depth of
at least three feet, the principal portion of the water moves
downward into the even more permeable layers of sand and
shell with which most of these soils are underlain at depths
varying from about three feet to perhaps six feet. Little water
percolates laterally into the beds and even less moves upward
by capillarity into the principal root zone.
Excellent results are obtained by flood irrigation where the
water supply is sufficient to allow the middles to be flooded rapidly
to a level above the root zone-which will permit percolation in
a downward direction to the roots-and then the water released
before the roots in the lower portion of the root zone are dam-
aged. Soils with an impermeable layer a few feet below the
surface, such as Leon soil No. 2, are also irrigated rather readily
by flooding the middles, although the porosity factor for such
soils may be no greater than that for some of the so-called heavy
soils which do not irrigate so readily. This is because the im-
permeable layer retards the loss of water below and a relatively
large portion of the pore space is made up of large non-capillary
pores through which water percolates with ease.
Another factor probably involved in the inability to satisfac-
torily irrigate cirtus by flooding on many of these soils is that
heavy equipment passing along the furrows and bed sides may
compress the surface layers sufficiently to greatly reduce the non-
capillary porosity. Baver (1) has shown that compression of
loam soils results in a substantial lowering of non-capillary por-
osity and an increase in the pF of the flex point, which is indica-
tive of reduced permeability and percolation. It has been ob-
served that disking or plowing sometimes improves these loamy
soils, which, no doubt, is accounted for by an increase in the non-
capillary porosity as a result of stirring of the soil.








20 Florida Agricultural Experiment Stations

Non-capillary Porosity and Air-capacity.-Permeability of a
soil to air is equally as important for plant growth as is permea-
bility to water. Adequate soil aeration is probably more closely
related to non-capillary porosity than is favorable soil moisture.
For practical purposes the air-capacity of a soil is the same as the
non-capillary pore space. In spite of the importance of adequate
aeration to plant growth, little is known about the actual air
requirements of plants. Some crop plants will grow in soils
having an air-capacity of less than 10 percent by volume of the
soil, but Kopecky (10) recommended that all soils not having
an air-capacity greater than this should have increased drainage.
An inspection of the air-capacity (non-capillary porosity) data
in Table 2 shows that in soils Nos. 12, 14 and 16 one of the four
layers, into which the 0-36 inch depth of soil of each was ar-
bitrarily divided, had an air-capacity of less than 10 percent
when drained at tensions up to the flex point. None of these
layers, however, were at the lowest depths studied. In each case
the added tension that would be applied to the moisture in the
shallower layer to drain the deepest layer of the soil column at
the tension of its flex point would empty sufficiently more pores
in the shallower layer to increase its air-capacity to somewhat
over 10 percent.
This can perhaps be better understood by taking a specific
example such as the Sunniland soil No. 12 in situ. The 12-18
inch layer has an air-capacity of 9.6 percent when drainage is in
equilibrium with its flex point at pF 1.75 (56 cm.). In draining
the underlying 36-inch depth of soil to equilibrium with its flex
point, which in this case also happens to be pF 1.75, the tension
exerted on the moisture in the 12-18 inch layer will be increased to
a tension equal to the height of the 18-36 inch soil layer plus the
tension of pF 1.75. This is a total tension of approximately 102
cm. of water, or pF 2.01. By reference to the pF curve for this
particular soil sample, it is found that at a tension of pF 2.01 the
pore space drained is about 12 percent of the soil volume. A con-
stant water table at a depth of around five feet below the soil sur-
face would be required to maintain a tension of pF 1.75 at the
36-inch level of this soil. Calculations show similar conditions to
prevail in the other two soils. The air-capacity of all the other
soils was above 10 percent and ranged up to 28 percent in the
surface 12 inches of the Davie soil No. 19.
The depth to which each of these soils would have to be drained
(permanent water table) to maintain the air-capacity throughout







Soil Moisture Relations in the Coastal Citrus Areas 21

the entire 36-inch depth of soil equal to, or slightly above, the
non-capillary porosity can readily be determined. It has already
been established in the discussion that with these soils, if the pF
of the soil moisture at the 36-inch level is at the flex point for
that particular soil layer, then the entire soil column above it
will be drained sufficiently to empty at least the entire non-capil-
lary pore space. Therefore, in this consideration the critical
point is the tension to which the soil moisture at the 36-inch level
would have to be subjected to acquire the desired degree of drain-
age; that is, the distance below 36 inches to the water table. The
pF at the flex point is given in Table 2 for each.
For example, the Felda soil No. 6 has a pF 2.04 at the flex
point of the 18-36 inch layer. This is a tension of about 43
inches of water which, added to 36 inches, the distance to the
soil surface, means the water table would be at 6 feet 7 inches
below the surface when the 0-36 inch soil layer had an air-
capacity equal to or slightly greater than its non-capillary
porosity. All the other soils would require somewhat less
tension to drain; ranging down to the Felda soil No. 4, in
which all the non-capillary pores would be drained with a water
table at 3 feet 4 inches below the surface.
The wide difference in tension required to drain and aerate
these various soils, even between those of the same classification,
is significant. In the field, trees are often observed in an un-
thrifty condition, although growing on the same sort of soil with
apparently the same degree of drainage as nearby thrifty trees.
The explanation, in some cases at least, no doubt is that soils of
the same series and textural designation do not always drain with
the same ease. In these coastal areas where the degree of drain-
age is often near the minimum requirements for successful citrus
culture, lowering the water table a few feet would be advan-
tageous in a substantial portion of the groves.
Available Moisture.-In view of the importance of a knowledge
of wilting points and field capacities 5 of soils to efficient irriga-
tion, it is desirable to point out something of the magnitude of
the variations in these characteristics within and between the
several soil series examined in this investigation. For example,
assume that Parkwood soils Nos. 14 and 15 are both sufficiently

6 As used here, field capacity is the amount of water in a given soil layer
when the capillary and gravitational forces tending to drain it are in equi-
librium with the water table. When this equilibrium is reached, the rate
of drainage is greatly reduced.








22 Florida Agricultural Experiment Stations

well drained to empty the non-capillary pore spaces to a depth
of 36 inches, and thus insure rooting to this depth. From the
curves in Appendix Fig. 14 the amount of water at the wilting
point (pF 4.2) in any portion of the 0-36 inches of soil No. 14 can
be calculated in acre-inches. The total acre-inches of water in
the entire 36 inches is most readily calculated by obtaining the
percent moisture by volume at pF 4.2 in each of the six 6-inch
depths into which it can be divided, totaling these and multiply-
ing by 6. Following this procedure, it is found that Parkwood
soil No. 14 would contain 7.54 acre-inches of water in the 0-36
inches of soil at the wilting point.
In Table 2 it is found that the flex point of the moisture
in this soil at the 36-inch depth is pF 1.54. Therefore, to in-
sure drainage of the non-capillary pores and rooting to 36
inches the water table must be 35 cm. below the 36-inch level,
or approximately 50 inches from the surface. The tension on
the moisture at the center of each six-inch soil layer, when in
equilibrium (field capacity) with a water table at this depth, is
represented in order from the surface to 36 inches by pF 2.075,
2.017, 1.949, 1.869, 1.763 and 1.633. In this and similar subse-
quent examinations of the pF curves, the values are taken for
each of the component six-inch layers of the soil depth under
consideration rather than a single value for the entire depth,
although a single curve represents the 18-36 inch depth. Since
the pF scale is logarithmic, the accuracy of the readings is higher
when the narrower limits of the pF value are used.
Referring to the curves in Appendix Fig. 14 for this soil, the
volume percent moisture for each of these pF values is obtained
from the curve for the corresponding depth. Totaling these per-
centages and converting, as in the wilting point calculation, at
field capacity it is found that this soil would contain 12.18 acre-
inches of water in the 0-36 inch soil layer. The available mois-
ture (field capacity minus wilting point) would be 4.64 acre-
inches.
A similar inspection of the data for soil No. 15 (Appendix Fig.
15) shows that the 36 inches of soil would contain 4.31 acre-
inches at the wilting point. The flex point at the 36-inch level
is pF 1.77, which would fix the water table at 59 inches below
the surface to insure non-capillary drainage and rooting to 36
inches. The resulting tensions in the several soil layers with
moisture at field capacity would be, from the surface to 36 inches,
as follows: pF 2.152, 2.104, 2.049, 1.982, 1.908 and 1.819. The








Soil Moisture Relations in the Coastal Citrus Areas 23

moisture at field capacity represented by these pF values would
be a total of 7.37 acre-inches in the 36 inches of soil with 3.06
acre-inches as available moisture.
Note the difference of 4.81 acre-inches in the field capacity,
3.23 acre-inches in the wilting point, and 1.58 acre-inches in the
available moisture between these soils of the same series and
texture. But especially note that the wilting point of soil No.
14 is slightly greater than the field capacity of soil No. 15. The
water in the surface 36 inches at the wilting point of the soils
examined ranged from 0.58 acre-inches in Lakeland soil No. 1 to
13.98 acre-inches in Everglades peat No. 20. Over a water table
at 76 inches below the surface, which insured ample drainage
for all the soils to the 36-inch depth, the field capacities ranged
from 1.50 acre-inches in the Leon soil (0-34 inches) No. 2 to 20.15
acre-inches in the Everglades soil No. 20. The minimum avail-
able moisture under these conditions was 0.91 acre-inches in the
Leon soil (0-34 inches) No. 2 and the maximum 6.17 acre-inches
in the Everglades soil No. 20. These data are summarized in
Table 3.
While in a general way these data indicate that the available
moisture is somewhat proportional to the field capacity of the
soil, there are some notable exceptions. For instance, Felda soil
No. 6, with a field capacity of 5.97 acre-inches, ranked in the low-
er half of these soils with respect to moisture-holding capacity;
but because of its relatively low wilting point of 2.35 acre-inches
this soil ranked relatively high in available moisture at 3.62 acre-
inches. On the other hand, Parkwood soil No. 14 had a high
field capacity at 11.19 acre-inches with a high wilting point at
7.54 acre-inches, which left only 3.65 acre-inches of available
moisture. The available moisture of Everglades peat No. 20 was
slightly less than one-third of its field capacity, but about 63
percent of the moisture at field capacity of Felda soil No. 4 would
be available to plants. Obviously, a given unit of rainfall or
irrigation would be much more effective on some soils than on
others.
This may explain (19), at least in part, the small fruit sizes
often obtained on heavy soils as compared to the sizes grown
on the lighter series. Although the field capacity of heavy soils is
generally high, they also frequently have a high wilting point,
resulting in a relatively small amount of available water. In irri-
gating, the grower may fail to take this into account and apply
little more water on these heavy soils than on those where a









24 Florida Agricultural Experiment Stations


TABLE 3.-MOISTURE CHARACTERISTICS OF 20 REPRESENTATIVE SOILS
FROM CITRUS GROVES IN THE COASTAL AREAS OF FLORIDA.

Acre-Inches in *0-36" of soil with
Soil Soil Type water table @ 76" below surface
No. Field Wilting Available
_Capacity Point Moisture

1 Lakeland fine sand ............ 1.60 0.58 1.02

2 Leon fine sand, heavy
substratum phase *(to,
34 inches) .....................-- ... 1.50 0.59 0.91

3 Delray loamy fine sand,
shallow phase .................... 6.21 2.60 3.61

4 Felda fine sand .--..-........... 4.62 1.73 2.89

5 Felda fine sandy loam .... 6.12 2.97 3.15

6 Felda loamy fine sand ...... 5.97 2.35 3.62
7 Felda loamy fine sand ...... 6.16 2.62 3.54

8 Felda fine sandy loam ........ 6.20 2.91 3.29
9 Sunniland fine sandy loam 6.44 2.76 3.68

10 Sunniland fine sandy loam 6.19 3.64 2.55
11 Sunniland fine sandy loam 6.15 3.04 3.11
12 Sunniland fine sandy loam 6.30 2.91 3.39

13 Parkwood loamy fine sand,
shallow phase .................... 6.92 3.83 3.09

14 Parkwood fine sandy loam,
very shallow phase .......... 11.19 7.54 3.65

15 Parkwood fine sandy loam,
shallow phase .----.................. 6.73 4.31 2.42

16 Manatee fine sandy loam .. 7.45 3.93 3.52
17 Manatee fine sandy clay
loam ...................................... 9.37 5.14 4.23

18 Davie mucky fine sand
*(to 26 inches) .................... 2.91 1.64 1.27

19 Davie peaty muck
"*(to 30 inches) ........... 5.27 3.20 2.07

20 Everglades peat ................ 20.15 13.98 6.17

"*Except in 2, 18 and 19.








Soil Moisture Relations in the Coastal Citrus Areas 25

larger portion would be available. Moreover, a given unit of
water will percolate deeper in a light than in a heavy soil if the
two are initially at the same relative stages of dryness. This
difference in depth of wetting is especially pronounced if the soils
have dried somewhat below their wilting points.
To illustrate, take light Felda sandy loam soil No. 5 and heavy
Manatee sandy clay loam No. 17. Assume the six-inch surface
layer of each has dried by evaporation and root absorption to a
point below their respective wilting points about midway toward
air-dryness, and that the remainder of the soil in the root zone
of each is near the wilting point. Such conditions are not un-
common. Under them, a light irrigation or rain of one inch would
wet the Felda soil to field capacity to a depth of about 14 inches.
This would be of considerable benefit to trees growing here. The
same amount of water on the Manatee soil would wet to field ca-
pacity to a depth of only about five inches. Since evaporation
losses are great from this zone, trees would likely benefit little.
Fruit growth is dependent upon the turgor pressure exerted
on the cell walls by water in the fruit cells. Trees growing in
soils at or near the wilting point suffer a moisture deficit and
cannot supply the necessary water to the fruit cells for this pres-
sure. This may be the case even though the leaves show no
pronounced signs of wilt, since the leaves compete successfully
with the fruit for moisture.
Effect of Drainage on Available Moisture.-The amount of
water a soil will retain is of much importance to the grower. Such
fundamental information is essential to intelligent and economi-
cal irrigation and drainage. The pF curves presented in the
Appendix show, theoretically at least, the amount of water the
various soils examined in this study would retain at different
heights above a permanent water table, once it was supplied
through rainfall or irrigation and the soils had drained to equi-
librium (field capacity) with the water table. A clearer concep-
tion of the data contained in the curves can be secured by an
illustrative calculation of the gain or loss in available water
by a change of one foot in the water table level.
For the purpose of this example the pF curves in Appendix
Fig. 10 for a Sunniland fine sandy loam (Soil 10) can be used.
This is a palmetto flatwoods soil which in recent years has been
extensively planted to citrus after having been farmed to toma-
toes and other truck crops. The more pertinent moisture char-
acteristics of this soil, when drained to a water table at three







26 Florida Agricultural Experiment Stations

feet and at four feet, as obtained from the pF curves, are listed
in Table 4. It will be observed in both sections of this table that
only the soil layers to within one foot of the designated water
table are considered. Because of the normal seasonal fluctua-
tions in the water table, plus the fact that the soil layer im-
mediately over the water table for a distance of about seven or
eight inches would be near saturation, practically no roots would
be founded nearer the water table than one foot. This is borne
out by numerous observations in the field.
The tension in force at the center of each six-inch soil layer,
when drained to equilibrium with the water table, is given both
as the pF value and in cm. of water for the two different drainage
conditions. The moisture content (field capacity) at these ten-
sions for each soil layer is listed as percent by volume as well as
in acre-inches. The total field capacity of the several layers is
shown in acre-inches for both degrees of drainage. The wilting
points as percent by volume and in acre-inches, together with
the totals in acre-inches, are shown for each. The available
moisture is the difference between the field capacity and the
wilting point values. This is shown for each soil layer, together
with the totals, for both water table depths in acre-inches. Note
that while the field capacities of the 0-24 inch layers over the
four-foot water table are less than those over the three-foot water
table because of the greater drainage tensions, the addition of
the moisture in the 24-36 inch layers of soil in which trees can
root with the deeper drainage more than compensates for the loss
in upper layers.
The available moisture is 2.63 and 4.07 acre-inches for the
water table at three and four feet, respectively, a gain of 1.44
acre-inches or roughly 80 percent in favorof the deeper drain-
age. One can only speculate on what this would mean in terms
of days water supply to an acre of citrus trees. There is little
factual information on the water requirements of citrus under
Florida conditions. To speculate, however, it is known that
evaporation from the soil is effective to a depth of only a few
inches. This would take a larger portion of the total available
water from the shallower than from the deeper rooted trees.
A loss by evaporation of 50 percent of the available moisture
from the 0-6 inch soil layer can be assumed, regardless of the
depth of rooting.
It is not probable that trees extract all the available water
from the soil volume in which they are rooted before they wilt








TABLE 4.-MOISTURE CHARACTERISTICS OF SUNNILAND FINE SANDY LOAM (SOIL No. 10).

Water table @ 3' allowing rooting to 2' Water table @ 4' allowing rooting to 3'
pF curve reference 10-A 10-B 10-C 10-D Total | 10-A 10-B 10-C 10-D 10-D 10-D Total
Depth of soil layer 1 0-6" 6-12" 12-18" 18-24" 0-24" 0-6" 6-12" 12-18" 1 18-24" 24-30" 30-36" 0-36"

pF from center of
6" soil layer to
water table ......---...-. 1.923 1.836 1.727 1.581 2.058 1.996 1.923 1.836 1.727 1.581
Distance from center
of 6" soil layer to
water table-in cm. ....... 83.8 68.5 53.3 38.1 114.4 99.1 83.8 68.5 53.3 38.1
% moisture by vol.
(field capacity) .............. 20.3 21.3 17.8 27.2 19.1 19.0 15.7 22.6 24.6 27.2
Field capacity in
acre-inches .................. 1.22 1.28 1.07 1.63 5.20 1.15 1.14 0.94 1.36 1.48 1.63 7.70

Wilting point
% moisture by vol.
@ pF 4.2 .................---- 11.8 11.4 10.9 8.9 11.8 11.4 10.9 8.9 8.9 8.9
Wilting point in
acre-inches ..................... 0.71 0.68 0.65 0.53 2.57 0.71 0.68 0.65 0.53 0.53 0.53 3.63
Available moisture
(F.C. W.P. = A.M.)
in acre-inches ........ ---.. 0.51 0.60 0.42 1.10 2.63 0.44 0.46 0.29 0.83 0.95 1.10 4.07







28 Florida Agricultural Experiment Stations

because of incomplete root distribution. For this hypothesis it
can be assumed that 75 percent is extracted. Taking into ac-
count evaporation and incomplete rooting factors, and assuming
that an acre of trees under average conditions would require
1/10 acre-inch of water a day, then the trees over the four-foot
water table would have about 1.11 acre-inches additional, or an
extra 11-days' supply. This would likely eliminate the need
for irrigation except during extremely long dry periods.
The available water under the two conditions was computed
for all the soils in a similar manner. There was a gain because
of deeper drainage in all cases except with the organic soils
Nos. 18 and 19, where rock was encountered at the 24- and 30-
inch levels. In these a loss of 0.94 and 1.05 acre-inches, re-
spectively, was figured because trees would not likely root suffi-
ciently deep in the rock to compensate for the reduced moisture
in the upper layers resulting from greater drainage. A gain of
0.48 acre-inches was recorded for Leon soil No. 2, but it is
doubtful if this would be valid since hardpan was encountered
at 34 inches in this soil. Drainage would probably be poor even
if trees would root to the hardpan. The range with the other
17 soils was 0.69 to 2.70 acre-inches, an average gain of 1.70
acre-inches or 69 percent in favor of the higher degree of drain-
age.
FIELD OBSERVATIONS AND PRACTICAL
CONSIDERATIONS
During this discussion it has been pointed out that permea-
bility of these soils was satisfactory for citrus root growth to a
depth of at least 36 inches. In most cases the indications were
that it would be satisfactory to a somewhat lower depth. The
location at which the flex point fell on the pF curves disclosed
that aeration would be ample for good root growth to the 36-inch
depth with a permanent water table at a maximum depth of
about six feet, or in most cases at somewhat less. The advan-
tages of this degree of drainage-to secure deeper rooting and
thus a substantial increase in the potential available moisture-
have been explained.
Rooting habit studies on citrus in several of these groves (18)
had shown that only rarely did rooting occur below the two-
foot level. Water table well data from four of these soils
(Nos. 3, 8, 10, 11) which represented about average conditions
showed the normal weather water table to be at three to five
feet below the bed crowns. During drought it dropped to seven







Soil Moisture Relations in the Coastal Citrus Areas 29

feet in some. Excessively heavy rains or prolonged rainy pe-
riods, which are not uncommon in these areas, cause the water
to rise and remain in the root zone sufficiently long to damage
citrus in at least three of these soils. In these, as well as in
others from which soil was obtained for this study, but where
water table wells had not been installed, there was subsequent
evidence of water damage to trees. On the other hand, trees
growing on these soils and similar soils where drainage was
better than the average because of some natural advantage in
elevation or a nearby drainage ditch were usually thriftier, and
larger and bore better crops.
Observations of this sort are commonplace and emphatically
support the case for sufficient drainage to allow citrus to root
to its "normal" depth if the soil texture is suitable and if a rea-
sonably stable water table can be maintained. Obviously, there
is no advantage to extremely deep drainage where roots will en-
counter rock or other impermeable layers, as in soils Nos. 2, 18
and 19, through which they cannot penetrate. Here drainage
to permit permanent rooting to the impermeable layer is all that
one can feasibly accomplish.
Furthermore, there is no advantage to draining deeper than
the water table can be maintained except for fluctuations of
short duration. Deep drainage through relatively long periods of
favorable weather in groves where provisions are not made to
maintain a reasonably stable water table may result in the trees
rooting deeper, only to have a large portion of the added roots
killed in subsequent flooding. During the period of favorable
soil moisture conditions the chances are that top growth was
proportionately larger than root growth. Subsequent flooding
causes an ever larger ratio of top to roots and during drought
the trees suffer severely because of the reduced root system.
There may be a loss of foliage, fruit and shoots. A few cycles of
this sort and the trees will be found wilting during periods of
favorable soil moisture. Later, especially where the weakened
roots become diseased, tree decline and death result.
Maintaining a reasonably stable water table throughout any
sizable acreage at some desirable depth between four and six feet
presents so many difficulties as perhaps to be impractical in
some cases. There are few tracts of grove of over a few acres
that do not have a difference in elevation of a foot or more.
Where considerable differences in elevation exist, it would be
necessary to maintain water tables at various elevations to have








30 Florida Agricultural Experiment Stations

the water at the same soil depth throughout the grove. This
would probably entail diversion ditches around each block of a
given elevation and perhaps rather frequent pumping either in
or out of the various blocks as the occasion might demand.
In addition to the complications caused by differences in eleva-
tion is the factor of the uneven rainfall distribution. The in-
fluence of rainfall on the water table, even at relatively shallow
depths, is brought out by some water-stage recorder data
obtained from Sunniland soil No. 10. This soil had average
drainage with respect to ditches, which were considered to be
satisfactorily spaced and were about four to five feet deep. The
pumping equipment provided was adequate to remove the run-
off collecting in the main ditches within 24 hours and maintain
the ditch level at least four feet below the bed crowns. A re-
capitulation made from average daily water table levels (distance
below bed crown) from August 1, 1947, through July 17, 1948,
is given in Table 5.

TABLE 5.-MINIMUM, MAXIMUM, DIFFERENCE AND MONTHLY AVERAGE'
WATER TABLE LEVELS FOUND IN A SUNNILAND GROVE SOIL NEAR VERO
BEACH FROM AUGUST 1, 1947, THROUGH JULY 22, 1948. FIGURES
INDICATE DEPTH IN FEET FROM SOIL SURFACE.

Month Minimum Maximum Difference Average
Aug. ...... ...... ............. 1.05 3.50 2.45 2.47
Sept. ........................... 0.48 3.52 3.04 2.29
Oct. ............................ 1.21 2.55 1.34 1.97
Nov .............. ........ 1.84 3.04 2.20 2.67
Dec. ........................... 2.30 3.38 1.08 3.11
Jan .............................. 1.66 3.46 1.80 2.80
Feb. ............ .......... .. 2.56 3.28 0.72 2.98
M ar. ........... ................ 1.50 3.31 1.81 2.59
Apr. .......................... 2.45 3.47 1.02 3.13
May .. .............. 2.28 3.70 1.42 3.21
June ............. ......... 1.61 3.45 1.84 2.59
July .................... .. 1.62 3.48 1.86 2.94


Wide fluctuation was observed in water table depth, especially
in September when excessively heavy rainfall occurred. The
detailed data taken showed that the water level in the soil was
not below two feet for 16 days from September 17 through Oc-
tober 2. This was followed, after an interval of one day at 2.16
feet, by another period of several days of high water. Other
long periods when the ground water was not below two feet
occurred from August 17 through August 24 and June 12 through
June 17. It is possible that sour orange roots would not have








Soil Moisture Relations in the Coastal Citrus Areas 31

been damaged by the shorter periods of flooding, but they almost
certainly were by the 16-day period. The amount of damage
would be dependent in part on the soil type, whether heavy or
light. The soil was fine sandy loam and consequently the damage
was not likely as great as it would have been on a lighter soil
such as sand.
Somewhat comparable data were obtained from periodic read-
ings of the water table wells in the three other groves men-
tioned previously. In none of these, however, was so wide a
fluctuation recorded, nor did the water remain so near the sur-
face for such prolonged periods. In one grove (Delray soil No.
3) the highest water level noted was about two feet below the
bed crown for nearly three days during the storm period in Sep-
tember. Drainage here was much better than in most coastal
groves.
The grove where the water-stage recorder was set was irri-
gated when needed by sprinkler irrigation. This, no doubt,
tended to keep differences between minimum and maximum
water table depths from being even wider. It seems apparent
from these data that any attempts at maintaining a stable water
table should strive for somewhat greater depths than these, so
as to allow for relatively wide fluctuations below the desired
root zone.
When to irrigate and how much water to apply are practical
questions, but present problems for which there are no rule-of-
thumb formulae. Each grove, and sometimes individual por-
tions of the grove, must be considered separately because of
variations in such factors as soil moisture characteristics, in-
terrelation of depth of rooting to depth of water table and
amount of moisture present in the soil when irrigation is begun.
The wilting point and field capacity of a soil are the moisture
characteristics with which one is primarily concerned in evaluat-
ing irrigation needs.
For practical purposes, the wilting point of a soil in which
citrus is growing is reached when the trees remain wilted over-
night. Irrigation should start before this point is reached. Labo-
ratory methods permit the determination of this point with
relative accuracy. Unfortunately, no method has been devised
as yet that is applicable in the field. The grower, however, can
acquaint himself with the "feel" of the soil at various depths
around well-rooted trees that have an incipient or mid-day wilt








32 Florida A, ;,,,rf, i1 Experiment Stations

and by practice learn to judge with fair accuracy when the wilt-
ing point of the soil is approached. Furr (4) makes some prac-
tical suggestions in this connection.
It is both economically and biologically unsound to apply irri-
gation water in excess of the field capacity of the soil to full root
zone depth. Any excess water either passes through the soil
rapidly, carrying soluble fertilizer salts with it into the sub-
drainage, or runs off the surface, washing fertilizers into the fur-
rows and out of the grove in surface drainage. Where sprinkler
irrigation is practiced there is the extra loss for power. More-
over, when water is applied in amounts larger than field ca-
pacity, particularly over a shallow water table or on a soil with
a shallow impermeable layer like hardpan, there is always the
possibility that excess water will accumulate beneath the sur-
face in low areas in the grove in sufficient quantities to water-
damage roots.
As with the wilting point, there is no simple method available
to the grower for determining the field capacity quickly and
accurately. It can be approximated by acquaintance with the
feel of soil samples from various depths of a soil that has been
thoroughly wetted and allowed to drain for about three days
over a water table at a depth of several feet below the lowest
depth of sampling. Having acquired this working knowledge
of moisture characteristics of his various soils, the grower can
then, through further experience, learn how much irrigation
water will be required to bring a particular soil from an ap-
proximate degree of dryness to a point approaching field ca-
pacity to the depth of rooting.
Obviously the amount required will be less the higher above
wilting point the soil moisture is when irrigation is started. In
general it will be found more economical to bring the moisture to
full field capacity and irrigate less frequently than to apply less
at more frequent intervals. Where "furrow" irrigation (flood-
ing) is practiced, little control can be exercised over the amount
of water applied, especially on the lower portions of the beds.
The greatest concern here is in getting some water into the
soil of the upper portion of the root zone. This method is or-
dinarily extremely wasteful of water, and no doubt results in
considerable leaching of nutrients. Extensive damage has been
done in many groves by leaving the water in middles unduly long
in an effort to get it to a desired level.







Soil Moisture Relations in the Coastal Citrus Areas 33

In the culture of fruit trees it is axiomatic that they be
grown on deep, adequately drained, yet moist soil where they
can root deeply if they are to attain and remain at their maxi-
mum productive capacity for the largest number of years. These
investigations indicate that with better drainage citrus could be
rooted at least a foot or so deeper than is commonly found in
most of these soils. The advantage of deeper rooting with re-
spect to the larger supply of water thus available to the trees
has been demonstrated. With rooting to a depth of three or four
feet, they would suffer less from drought and it is doubtful that
expensive irrigation equipment would be economically feasible.
There are several additional distinct advantages associated
with adequate drainage. Fertilization would be more eco-
nomical because of the better utilization of the fertilizer ap-
plied with deeper rooting. Deep-rooted trees are more wind-
firm and the grower would be put to less expense resetting
and replacing uprooted trees after wind storms. It is be-
coming an advantage to have soils well enough drained to
use rootstocks other than sour orange in order to avoid tris-
teza or other diseases that affect certain rootstock-scion com-
binations.
Within the past decade more trees have been killed or ren-
dered unprofitable in coastal groves through water damage (in-
adequate drainage) alone than by all other causes combined. The
advantages and economy of adequate drainage extends through
all phases of citrus grove operation from planting to picking.
Because of the ever-increasing labor, materials and equipment
costs, there is little opportunity to reduce or even maintain the
present cost of producing a box of fruit other than through in-
creased production. In coastal groves as a whole, the most
essential step toward this economy in production is through
improved drainage. To attempt it without adequate drainage
is false economy.
The responsibility of improving drainage on a grove must
rest with the individual grower. It is neither practical nor de-
sirable to lower the water table throughout the entire coastal
areas. Pastures and truck farming require a relatively high
water table. If the drainage set-up on the individual grove is
as it should be, there is nothing incompatible with placing water
control structures in many drainage canals of the various drain-
age districts to hold back large volumes of water for use in
times of drought. It is assumed, of course, that these will be







34 Florida Agricultural Experiment Stations

handled properly, and in times of flood the water released to
take care of the discharge from groves and other agricultural
lands. If properly handled they will be a great asset to the areas
served. The flow from artesian wells, upon which many of the
citrus growers and farmers depend for irrigation, in some cases
becomes so weak that irrigation cannot be carried out rapidly
enough. Some wells have already become too salty for irriga-
tion (Wander and Reitz (16)). There is the possibility that
this trouble will increase.
On the other hand, growers who have been accustomed to
turning their wells on and letting them keep their ditches full
for long periods of time in an effort toward sub-irrigation will
need to be more cautious if the main drainage canals are filled.
As long as the main drainage canals in an area are at a low
level, most of the water going into grove ditches moves down
and out into the main canals through the relatively permeable
layer of sand and shell that underlies most of these areas. Little
of it moves laterally into the root zone, although occasionally
on light soils there is considerable lateral movement. Sometimes
low areas in groves show the results of too much water. With
the canals in the immediate vicinity at a high level, subdrainage
from the grove would be reduced. Water turned into grove
ditches could easily build up to a level where extensive damage
could be done to the lower roots before it is noticed.
It was not within the scope of this investigation to determine
the ways and means of maintaining a relatively permanent water
table at somewhat lower depths than are found in the coastal
areas in general. Briefly, however, water furrows should be
graded so water will not accumulate in them. They do not neces-
sarily need to be excessively deep and thus hard to maintain.
Ditches should be sufficiently deep, and spaced so as to allow
furrows to drain completely within a period of at least several
hours after heavy rains. The main drainage ditches within a
grove should usually be cut to a depth of about five or six feet
to take advantage of the subdrainage offered by the relatively
permeable layers of shell and sand underlying most of these soils.
In this connection it must be remembered, however, that
where cut to this depth water could also enter the grove readily
through the same permeable layer when the water in the main
canal was higher than in the grove ditches. Excessive pumping
in some instances might be necessary unless the water level in
the main canals in the area was carefully controlled. Unless







Soil Moisture Relations in the Coastal Citrus Areas 35

rapid gravity drainage from the grove is assured, pumping
equipment sufficient to take off three or four acre-inches from
the entire grove in 24 hours should be installed. This does not
take into account any seepage effects as just discussed. Where
seepage from outside is a factor, the pumping capacity should
be increased proportionately. Tight gates should be placed on
all pump outlets and ditches from the grove and dykes built
where it is possible for outside flood waters to enter. The proper
drainage, as with irrigation, of each grove is an individual
problem.
SUMMARY
Soil moisture retention studies were made on 20 representative
soils, which included nine series, collected from citrus groves
on the East Coast, and covering a wide range of soil types. These
soil types are equally typical of the citrus grove soils of the
Florida West Coast. Moisture retention determinations at the
lower tensions (pF 0 to 2.5) were made with a sintered glass
funnel connected to an adjustable water column to secure the
desired tensions. A centrifuge method was used for the higher
tensions of pF 3.1 and 4.2. The basic data are presented as
tension-moisture (pF) curves. Relative permeabilities, air-ca-
pacities, field capacities, wilting points and available moisture
percentages of the different soils at various soil moisture ten-
sions (theoretical height above permanent water table) are ob-
tainable from these curves. The variations in soil moisture
characteristics between soil types and within soil types and some
of the implications are briefly summarized below.
The porosity factor or relative permeability (non-capillary
porosity/pF of flex point) of the various soils ranged from 5.3
to 21.9. The permeability of these soils to water is satisfactory
for growth of citrus roots to a depth of at least three feet. This
is somewhat deeper than citrus is now generally rooted in these
soils. Compaction by heavy grove equipment may render the
permeability of the loams unsatisfactory in some cases. The
air-capacity (non-capillary porosity at flex point) in the dif-
ferent soils ranged from 9.0 to 28.0 percent by volume. In
most instances the air-capacity was well above 10 percent by
volume, which is thought to be adequate for citrus. In the few
cases where it was less than this, increasing the degree of drain-
age slightly so as to empty the non-capillary pores of the soil
to the 36-inch depth would aerate at least 10 percent by volume
of the pores in these particular soils to 36 inches. There are







36 Florida Agricultural Experiment Stations

groves in the coastal areas that no doubt would benefit greatly
through soil aeration alone by lowering the water table a few
feet.
With deeper drainage, soil conditions are made suitable for
deeper rooting. This results in a larger potential moisture sup-
ply to the tree. Although the layers near the surface may hold
slightly less water with deeper drainage, this is more than com-
pensated for by the additional water available to the trees in the
deeper layers. In these coastal soils citrus was rarely found to
root deeper than two feet with the prevailing drainage. In 17
of the soils examined, where impervious rock or hardpan was
not encountered, the texture would have permitted rooting to at
least 36 inches. Calculations made with data from the pF curves
for these soils indicated that deeper drainage so as to increase
depth of rooting a foot (from 24 inches to 36 inches) would result
in an increase of available moisture ranging from 0.69 to 2.70
acre-inches, with an average of 1.70 acre-inches, or 69 percent
gain because of improved drainage. This would lengthen con-
siderably the period of drought trees could endure without
irrigation to prevent wilting.
The wilting point of a soil and its field capacity are the mois-
ture characteristics a grower should take into consideration in
determining when to irrigate and how much water to apply.
Irrigation should be applied when the wilting point is approached.
Sufficient water should be applied to bring the soil to full
field capacity through the entire depth of the root zone, but
it should not be applied in excess of this because of losses through
drainage. The water in the 0-36 inches at the wilting point of
the soils examined ranged from 0.58 to 13.98 acre-inches. The
field capacity of the 36-inch soil layer ranged from 1.60 to 20.15
acre-inches with the water table held at 76 inches below the
surface. Obviously there are wide variations in these moisture
characteristics between soils of different series. Even within
a series the variations are sometimes wide.
For example, the wilting point of the surface 36 inches of
Parkwood soil No. 14 was 7.54 acre-inches, which was higher
than the field capacity of 6.73 acre-inches in this same depth of
soil of Parkwood soil No. 15 with the water table at 76 inches.
In a general way available moisture was roughly proportional
to the field capacity, but there were some notable exceptions.
Over a water table at 76 inches, the available moisture ranged
from 1.02 to 6.17 acre-inches in the surface 36 inches of soil.








Soil Moisture Relations in the Coastal Citrus Areas 37

Some soils having relatively high field capacities have propor-
tionately higher wilting points. Consequently, a given unit of
water applied through rainfall or irrigation on such soils may
not furnish as much available water as on soils with a more favor-
able ratio of the field capacity to the wilting point.
Observations in the field give substantial support to the argu-
ment for deeper drainage in most of these areas so as to allow
citrus to root deeper. In numerous groves where there is a dif-
ference in elevation of a foot or more, the best and highest
yielding trees will be found on the higher situations. Where soil
texture is suitable, better results could be obtained with citrus
in the coastal areas of Florida if a reasonably stable water table
was maintained at a sufficient depth to permit rooting to a depth
of four or five feet or slightly more.

ACKNOWLEDGMENTS
The author is indebted to Dr. A. F. Camp for directing attention to the
basic problems of soil moisture relations covered in this bulletin. Ac-
knowledgment is especially due Dr. V. C. Jamison, formerly Soils Chemist
at the Citrus Experiment Station, for his valuable assistance in setting
up the apparatus and for helpful suggestions during the course of the
study. Drs. H. J. Reitz and J. W. Sites are gratefully credited for assistance
in the manuscript arrangement and constructive criticism of its contents.
The author expresses his gratitude to Mr. J. R. Henderson and Mr. Ralph
J. Leighty for the classification of soils.
To all these and to others assisting in the laboratory studies, but not
mentioned here by name, the author extends his thanks and appreciation.

LITERATURE CITED
1. BAVER, L. D. Soil permeability in relation to non-capillary porosity.
Soil Sci. Soc. Am. Proc. 3: 52-56. 1938.
2. BRADFIELD, RICHARD, and V. C. JAMISON. Soil structure-attempts at
its quantitative characterization. Soil Sci. Soc. Am. Proc. 3: 70-76.
1938.
3. BUCKINGHAM, EDGAR. Studies on the movement of soil moisture.
USDA Bur. Soils Bul. 38. 1907.
4. FURR, J. R. Soil mositure factors of importance in citrus and avocado
grove management. Proc. Fla. State Hort. Soc. 58: 16-25. 1945.
5. GARDNER, ROBERT A. A method of measuring the capillary tension
of soil moisture over a wide moisture range. Soil Sci. 43: 277-283.
1937.
6. GARDNER, WILLARD, O. W. ISRAELSEN, N. E. EDLEFSEN and H. CONRAD.
The capillary potential function and its relation to irrigation prac-
tice. Phys. Rev. Ser. 2, 20: 196. 1922.








38 Florida Agricultural Experiment Stations

7. JAMISON, VERNON C. A study of the structure of Dunkirk silty clay
loam and some organic soils by means of pF moisture relations.
Thesis, Cornell Univ. Library. 1941.
8. -. Structure of a Dunkirk silty clay loam in relation to
pF moisture measurements. Jour. Amer. Soc. Agron. 34: 307-321.
1942.
9. Structure of some organic soils and soil mixtures as
shown by means of pF moisture studies. Jour Amer. Soc. Agron.
34: 393-404. 1942.

10. KOPECKY, J. Cited by Baver, "Soil Physics," p. 272. 1948.
11. NELSON, W. R., and L. D. BAVER. Movement of water through soils
in relation to the nature of the pores. Soil Sci. Soc. Am. Proc.
5: 69-76. 1940.
12. PEECH, MICHAEL, and T. W. YOUNG. Chemical studies on soils from
Florida citrus groves. Fla. Agr. Exp. Sta. Bul. 448. 1948.
13. RICHARDS, L. A., and L. R. WEAVER. Moisture retention by some
irrigated soils as related to soil-moisture tension. Jour. Agr. Res.
69: 215-235. 1944.
14. RUSSELL, M. B. The utility of the energy concept of soil moisture.
Soil Sci. Soc. Am. Proc. 7: 90-94. 1942.
15. SCHOFIELD, R. K. The pF of the water in soils. Trans. 3rd Int. Congr.
Soc. Soil Sci. 2: 37-48. 1935.
16. WANDER, I. W, and H. J. REITZ. The chemical composition of irriga-
tion water used in Florida citrus groves. Fla. Agr. Exp. Sta. Bul.
480. 1951.
17. YOUNG, T. W. A study of the irrigation of citrus groves in the Vero
Beach section of Florida. Proc. Fla. State Hort. Soc. 56: 8-22.
1943.

18. --- Citrus research on the East Coast of Florida. Proc. Fla.
State Hort. Soc. 59: 52-59. 1946.
19. The economy of adequate drainage for citrus in Florida
coastal areas. Proc. Fla. State Hort. Soc. 64. 1951.







APPENDIX

4.5 Soil I Lakeland fine sand

40 0-6" ---
S6-12 --'
3.5 12-18 .---
1 18-36*----.
3.0 -

2.5-

C.2.0-

1.5 --- .- Flex point (0-') pF 1.57

1.0

0.5- *
171 % C.P 21.3% N-C. 1P

0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 1.-Tension-moisture curves for Lakeland fine sand
(Soil 1) at four depths. This graph has been marked to illustrate flex
point, capillary porosity and non-capillary porosity.
4.5 Soil 2 Leon fine sand

4.0 V 0 6"
6 -12--
3.5 12-18 +-----
1[ \J 18-34'---
3.0 6

2.5 \-

o. 2.0o



1.0-

0.5


0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 2.-Tension-moisture curves for Leon fine sand (Soil 2)
at four depths.







4.5- Soil 3 Delray loamy fine sand

4.0- 0-6" -
6 -12-
3.5- \ 12-18 ---
18-36'---'
3.0

2.5

". 2.0-

1.5-

1.0-

0.5- ,*\*,\

0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 3.-Tension-moisture curves for Delray loamy fine sand
(Soil 3) at four depths.

4.5- Soil 4 Felda fine- sand

4.0 \ 0-6" ,----*
6 -12 --
3.5 \ 12-18 ----
i i 18-36---
3.0 -

2.5 \

0 2.0-

1.5-



0.5

10 20 30 40 50
Percent Water by Volume
Appendix Fig. 4.-Tension-moisture curves for Felda fine sand
(Soil 4) at four depths.








4.5r Soil 5 Felda fine sandy loam

4.0- 0-6".---
6 12 ---
3.5 \- \12-18 i----4
18-36*---*
3.0-

2.5- \ \
U-\
CL 2.0 *

1.5-

1.0

0.5-


0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 5.-Tension-moisture curves for Felda fine sandy
loam (Soil 5) at four depths.

4.5r Soil 6 Felda fine sandy loam

4.0 \ 0- 6"--
\ 6 -12 ---
3.5 12-18 *----
18-36o---
3.0

2.5 "\
LLA
" 2.0 "-

1.5 -

1.0 -

0.5- \
\ I
0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 6.-Tension-moisture curves for Felda fine sandy
loam (Soil 6) at four depths.









4.5- Soil 7 Felda fine sandy loam

4.0- 0- 6"'----
S6-12 "--
3.5- 12-18 4---4
18-36"---"
3.0-

2.5- .

a. 2.0- "-.

1.5 -

I.0- +

0.5- +


0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 7.-Tension-moisture curves for Felda fine sandy
loam (Soil 7) at four depths.

4.5- Soil 8 Felda fine sandy loam

4.0 0-6"----
\6-12'---
3.5 \ 12-18 -----
3. 18-36*----
3.0 -

2.5

" 2.0-

1.5

1.0

0.5

0 10 20 30 40 50 60
Percent Water by Volume
Appendix Fig. 8.-Tension-moisture curves for Felda fine sandy
loam (Soil 8) at four depths.








4.5- Soil 9 Sunniland fine sandy loam

4.0 06"---
\\ 6-12 A--*
3.5- \\ 12-18 ----+
3.0\ \ 18-36*---*


2.5
LL \+
"C. 2.0 _

1.0 \

1.0- +\ *^\

0.5 \

I I I
0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 9.-Tension-moisture curves for Sunniland fine
sandy loam (Soil 9) at four depths.

4.5- Soil 10 Sunniland fine sandy loam
*
4.0 0-6"---
I\\ 6 -12 --
3.5- ,\ 12-18 +---
i: 18-36---.
3.0-

2.5 '

" 2.0- +

1.5 -

1.0 -

0.5 -\ A\to


0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 10.-Tension-moisture curves for Sunniland fine
sandy loam (Soil 10) at four depths.






4.5 Soil II Sunniland fine sandy loam

4.0 0-6"----
S6-12 &---
3.5- 12-18 +-----
S\ 18-36 *----
3.0-

2.5

"- y n + A'^ ^
l. 2.0- -.

1.5 '

1.0 \

0.5


0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 11.-Tension-moisture curves for Sunniland fine
sandy loam (Soil 11) at four depths.

4.5- Soil 12 Sunniland fine sandy loam

4.0- 0 -6"---
\6 12-.- --a
3.5- \ 12-18 +-----
\\ 18-36 ---
3.0 V

2.5-

"a 2.0
1.5 ,
I.O


1.0

0.5 A


0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 12.-Tension-moisture curves for Sunniland fine
sandy loam (Soil 12) at four depths.









4.5 Soil 13 Parkwood loamy fine sand

4.0- \ 0-6"----
\ \ 6-12 h--
3.5 12-18 4---+
V \ \ 18-36 -----
3.0- +

2.5- \
u-
. 2.0 -

1.5- 44

1.05

0.5- + ',
\ \

0 10 20 30 40 50
Percent Water by Volume
Appendix Fig. 13.-Tension-moisture curves for Parkwood loamy
fine sand (Soil 13) at four depths.

4.5- Soil 14 Parkwood fine sandy loam
S (Shallow phase)
4.0 0\- 6" ---
6-12 a---
3.5 12-18 +----
\ Y 18-36*----



9.5-




1.0- *+

0.5

0 10 20 30 40 50 60
Percent Water by Volume
Appendix Fig. 14.-Tension-moisture curves for Parkwood fine
sandy loam (Soil 14) at four depths.









4.5 Soil 15 Parkwood fine sandy loam

4.0 0-6"----6
6 12--
3.5 12-18 *---
18-36*---"
3.0

2.5
U-
C. 2.0

1.5-

1.0 -

0.5- A


0 10 20 30 40 50 AO
Percent Water by Volume

Appendix Fig. 15.-Tension-moisture curves for Parkwood fine
sandy loam (Soil 15) at four depths.





4.5- Soil 16 Manatee fine sandy loam

4.0- 0-6"--*
6 12 ,--
3.5 12-18 --+
"5.0 \ 18-36*--"


2.5 \

" 2.0- V

1.5

1.0

0.5 -

o 10 20 30 40 50 60 70
Percent Water by Volume

Appendix Fig. 16.-Tension-moisture curves for Manatee fine
sandy loam (Soil 16) at four depths.









4.5r Soil 17 Manatee fine sandy clay loam
\ (Deep phase)
4.0- \\ 0- 6"
",\\ 6 -12 ---
3.5- \\ 12-18 ----+
\\ 18-36 ---.
3.0

2.5 -
U-\

"0 2.0

1.5 -

1.0

0.5

0 10 20 30 40 50 60
Percent Water by Volume
Appendix Fig. 17.-Tension-moisture curves for Manatee fine
sandy clay loam (Soil 17) at four depths.


4.5- Soil 18 Davie mucky fine sand
(10%0rganic Matter)
4.0 1 2-,2

3.5 12-26--

3.0 1-

2.5 \

"CL 2.0-

1.5-

1.0-

0.5- A

0 10 20 30 40 50 60
Percent Water by Volume

Appendix Fig. 18.-Tension-moisture curves for Davie mucky
fine sand (Soil 18) at two depths.

















4.5 Soil 19 Davie peaty muck (48% Organic Matter)

4.0

3.5 I \-l2--
S-12-30*---
3.0 |

2.5 -

S2.0 -

1.5-

1.0 -

0.5 A

S10 20 30 40 50 60 70 80 90 00
Percent Water by Volume

Appendix Fig. 19.-Tension-moisture curves for Davie peaty muck
(Soil 19) at two depths.









4.5 Soil 20 Everglades Peat (88%Organic Matter)

4.0

3.5

3.0-

2.5 0 36'"------

"2.0-

1.5-

1.0-

0.5-

0 10 20 30 40 50 60 70 80 90 100
Percent Water by Volume

Appendix Fig. 20.-Tension-moisture curves for Everglades peat
(Soil 20) at one depth.





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