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 Title Page
 Table of Contents
 Summary
 Introduction
 Materials and methods
 Results
 Discussion
 Literature cited














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 747
Title: Soil temperature in Florida citrus groves
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Permanent Link: http://ufdc.ufl.edu/UF00027190/00001
 Material Information
Title: Soil temperature in Florida citrus groves
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 15 p. b charts : ; 23 cm.
Language: English
Creator: DuCharme, E. P ( Ernest Peter )
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1971
 Subjects
Subject: Soil temperature -- Florida   ( lcsh )
Citrus fruits -- Soils -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 15.
Statement of Responsibility: E.P. DuCharme.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027190
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000929616
oclc - 18422704
notis - AEP0408

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
    Summary
        Page 3
    Introduction
        Page 3
    Materials and methods
        Page 4
    Results
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
    Discussion
        Page 13
        Page 14
    Literature cited
        Page 15
Full Text

Bulletin 747 (technical)


December 1971


SOIL TEMPERATURE IN FLORIDA


CITRUS GROVES



















Contents

Page
Summary ..............------ ---- 3

Introduction 3

Materials and Methods ........... ......----------- 4

Results 5......------------------- 5

Vertical ........... .........--.. ...------------. 6

Temperature Oscillations .......-...... 11

Discussion ..........--- ----. 13

Literature Cited .-~. .. --~. -.......... ..--------- 15







Soil Temperature in Florida Citrus Groves


E. P. DuCharme'

Summary
Soil temperature data was recorded from depths of 6,
18, 72, and 120 inches in shaded and unshaded Lakeland
fine sand in the citrus grove of the University of Florida,
Agricultural Research and Education Center, Lake Alfred,
Florida, and 6 and 24 inches deep in shaded and unshaded
Parkwood soil, Fort Pierce, Florida. The shaded soil under
citrus trees at both locations was somewhat cooler than the
unshaded soil. Annual mean soil temperatures ranged from
70.2 F at 6 inches deep to 71.9' F at 120 inches deep in
the shaded soil and from 73.3' F at 6 inches deep to 70.2 F
at 120 inches deep in unshaded Lakeland fine sand at Lake
Alfred. Annual mean soil temperatures in Parkwood soil
at Fort Pierce ranged from 68.6' to 69.8' F at 6 and 24
inches deep in the shaded soil and from 74.8- to 73.4 F at
6 and 24 inches deep in unshaded soil.
Diurnal temperature oscillations were not detected at
depths below 36 inches and were greater in unshaded than
shaded soil. Temperature fluctuations 72 inches deep were
associated with seasonal weather cycles of either increas-
ing or decreasing temperatures. At 120 inches, there was
only one annual cycle between the annual monthly maxi-
mum and minimum temperatures. Annual high and low
monthly mean temperatures 120 inches deep occurred 2 to
3 months later than at 6 inches.

Introduction
The transfer of heat into and out of soil occurs continuously
with diurnal and seasonal regularity. Heat transfer at the soil
surface and flow of heat within the soil are major factors in
soil climate and soil ecology. In nature, soil temperature has
direct influence on root growth, root functions, and soil organ-
isms that make up the biotic community associated with roots
and root diseases.
Citrus tree roots are known to have penetrated Lakeland
fine sand to 18 feet (2)' and burrowing nematodes, Radopholus

'Plant Pathologist, University of Florida, IFAS, Agricultural Research
and Education Center, Lake Alfred, Florida 33850.
2Numbers in parentheses refer to Literature Cited.







Soil Temperature in Florida Citrus Groves


E. P. DuCharme'

Summary
Soil temperature data was recorded from depths of 6,
18, 72, and 120 inches in shaded and unshaded Lakeland
fine sand in the citrus grove of the University of Florida,
Agricultural Research and Education Center, Lake Alfred,
Florida, and 6 and 24 inches deep in shaded and unshaded
Parkwood soil, Fort Pierce, Florida. The shaded soil under
citrus trees at both locations was somewhat cooler than the
unshaded soil. Annual mean soil temperatures ranged from
70.2 F at 6 inches deep to 71.9' F at 120 inches deep in
the shaded soil and from 73.3' F at 6 inches deep to 70.2 F
at 120 inches deep in unshaded Lakeland fine sand at Lake
Alfred. Annual mean soil temperatures in Parkwood soil
at Fort Pierce ranged from 68.6' to 69.8' F at 6 and 24
inches deep in the shaded soil and from 74.8- to 73.4 F at
6 and 24 inches deep in unshaded soil.
Diurnal temperature oscillations were not detected at
depths below 36 inches and were greater in unshaded than
shaded soil. Temperature fluctuations 72 inches deep were
associated with seasonal weather cycles of either increas-
ing or decreasing temperatures. At 120 inches, there was
only one annual cycle between the annual monthly maxi-
mum and minimum temperatures. Annual high and low
monthly mean temperatures 120 inches deep occurred 2 to
3 months later than at 6 inches.

Introduction
The transfer of heat into and out of soil occurs continuously
with diurnal and seasonal regularity. Heat transfer at the soil
surface and flow of heat within the soil are major factors in
soil climate and soil ecology. In nature, soil temperature has
direct influence on root growth, root functions, and soil organ-
isms that make up the biotic community associated with roots
and root diseases.
Citrus tree roots are known to have penetrated Lakeland
fine sand to 18 feet (2)' and burrowing nematodes, Radopholus

'Plant Pathologist, University of Florida, IFAS, Agricultural Research
and Education Center, Lake Alfred, Florida 33850.
2Numbers in parentheses refer to Literature Cited.







similis (Cobb) Thorne 1949, have been extracted from citrus
roots 12 feet deep (6). It also has been demonstrated that the
minimum and maximum temperature limits within which R.
similis could complete its life cycle were 55 to 90 F (1). The
effects of temperature on the interaction of soil organisms and
citrus root diseases have not been determined, since no data are
available regarding temperature, temperature gradients, and
heat flow in the deep-sand citrus groves of central Florida. A
direct relationship has been found between low soil temperature
and twig dieback of citrus trees in California (3). In the pres-
ent study, soil temperatures were measured at different depths
for 6 years to obtain basic information for further studies on
soil organisms and citrus root diseases.

Materials and Methods

The soil temperatures were taken with 4-probe recording
thermographs. The instruments were calibrated and adjusted
against a thermometer certified by the U. S. National Bureau
of Standards before placement in the soil and at the termination
of the study in order to correct for instrument drift. Thermo-
couples were placed horizontally at depths of 12, 36, 72, and 120
inches in Lakeland fine sand in May 1961. One set of probes
was placed 3 feet inside the periphery of the foliar canopy
under a citrus tree in a block of trees 35 years old. A second set
of probes was located in unshaded soil 100 feet away from citrus
trees. The surface above the probes in unshaded soil was kept
free of all vegetation. These thermographs were located in a
citrus grove that was not irrigated, but was subjected to com-
monly practiced cultivation procedures at the University of
Florida, Agricultural Research and Education Center, Lake
Alfred. In 1962, the probes 12 and 36 inches deep were re-
located to record temperature from depths of 6 and 18 inches.
All temperature readings were recorded as degrees Fahrenheit.
Temperatures were also taken in Parkwood soil at the Uni-
versity of Florida, Agricultural Research Center, Fort Pierce,
Florida. In the shallow soil profile of citrus groves in that area,
the probes were placed horizontally at 6 and 24 inch depths.
One set of probes was located in the shade 2 feet inside the
foliar canopy of a citrus tree 25 years old on the west side of a
grove, and the other set was placed in the open 6 feet from the
foliar canopy of the same tree. The surface in a 3-foot square
area above the probes in unshaded soil was usually, but not
always, kept free of vegetation by removing plants as they grew.








Results


In Lakeland fine sand, at Lake Alfred, the annual mean tem-
perature at depths for which data were accumulated ranged
from 70.4' F at 6 inches to 71.9- F at 120 inches in soil under
trees, and from 73.2- F at 6 inches to 69.9' F at 120 inches in
unshaded soil (Table 1). The lowest annual mean temperature
occurred at 6 inches in-shaded soil and 120 inches in unshaded
soil. The highest mean temperature occurred at 6 inches in un-
shaded soil and 120 inches in shaded soil. In the Parkwood soil
at Fort Pierce, the annual mean temperature at 6 inches both
in the shade and in the open were comparable to those in the
Lakeland fine sand at Lake Alfred (Table 2).

Table 1.-Annual mean temperatures at six depths in unshaded and shaded
Lakeland fine sand at the Agricultural Research and Education
Center, Lake Alfred, Florida, from 1962-67.
6 in. 12 in. 18 in. 36 in. 72 in. 120 in.
Year Unshaded soil
1962 72.5 72.3 71.3 68.6
1963 71.8 71.1 70.0 67.5
1964 72.5 71.5 70.9 67.9
1965 74.4 72.8 75.0 71.0
1966 74.1 74.0 74.7 74.3
Mean 73.2 72.5 72.4 72.3 72.4 69.9

Shaded soil
1962 70.2 70.9 70.6 71.6
1963 70.6 70.6 71.5 72.0
1964 70.7 71.1 71.5 71.3
1965 70.6 71.4 72.2 72.5
1966 69.6 69.0 71.9 72.1
Mean 70.4 70.2 70.5 70.9 71.5 71.9


Table 2.-Annual mean temperatures at two depths in unshaded and shaded
Parkwood soil at the Agricultural Research Center, Fort Pierce,
Florida, from 1962-64.
Year
Depth 1962 1963 1964 Mean
6"-shaded 68.7 68.5 68.6 68.6
6"-unshaded 73.2 73.1 75.1 74.8
24"-shaded 70.2 69.7 69.4 69.8
24"-unshaded 73.4 73.4 73.2 73.4


The greatest annual and diurnal temperature fluctuations
occurred down to 18 inches in both unshaded and shaded soil
(Figures 1 and 2). Below 18 inches, the mean minimum and













"70
60 J n.
C3
S50

1963 1964 1965 1966 1967

Figure 1.-Mean monthly temperatures, degrees F, 6, 72, and 120 inches
deep in Lakeland fine sand in the shade of a citrus tree, July 1962 to July
1967, University of Florida, Agricultural Research and Education Center, Lake
Alfred, Florida.


maximum temperatures were more uniform and virtually identi-
cal at 72 and 120 inches (Figure 3). Temperature extremes
were greater in unshaded than in shaded soil; therefore, the
temperature was more constant in shaded soil at all depths.

Vertical
Net transfer of heat into soil and heat accumulation con-
tinued from March through August, and heat loss occurred from
September through February. The annual low of monthly means
occurred in either December or January and the annual high in
either July or August, except in 1963 when the high occurred
in June. The annual lows and highs occurred during the same
months in shaded and unshaded soil at Lake Alfred and Fort
Pierce.
The month of the mean annual low varied with depth, and
there was as much as 2 to 3 months lag between the time when
the low occurred 6 inches and 120 inches deep (Figures 4 and
5). If the low at 6 inches was reached in January, the low at
120 inches was not reached until March. There was also a cor-
responding lag in time when the mean monthly annual high
was reached between 6 inches and 120 inches deep. At 6 inches,
the high was usually reached during July and occurred pro-
gressively later with depth until at 120 inches the high was not
reached until September or October (Figures 1, 4, and 5).
The occurrence and duration of the period of lowest tem-
peratures varied for each depth, but was about the same in
shaded and unshaded soil. From 6 inches to 36 inches, the period
of lowest temperatures extended from December to February,











SHADED


80


70


60


80
ELA

.70


660

80


70


60


SHADED


18 in.
I
M A


I I I I I I I


M J J
MONTH


AS ON D


Figure 2.-Comparison of the range between the mean minimum and
maximum temperatures 6, 12, and 18 inches deep in unshaded and shaded
Lakeland fine sand, 1962-1967, Agricultural Research and Education Center,
Lake Alfred, Florida.


SHADED


J F







80-


UNSHADED


70 SHADED


60o 36 in.

80-
UNSHADED






L"J
70 SHAEDHAED



70


UNSHADEDD

120 in.
60
I I I I I I I I I I I I
J F M A M J A S O N
MONTH
Figure 3.-Comparison of range between the mean minimum and maxi-
mum temperatures 36, 72, and 120 inches deep in unshaded and shaded
Lakeland fine sand, 1962-67, Agricultural Research and Education Center,
Lake Alfred, Florida.

at 72 inches from January through February, and 120 inches
from February through March (Figures 1, 4, and 5). The period
of lowest temperatures tended to be shorter than the periods
of highest temperatures in both shaded and unshaded soil. For
3 out of 5 years, the mean temperature in shaded and unshaded
soil was lower in December and February than in January
(Figure 1).



















J F M A M J J A
MONTH


S 0 N 0


Figure 4.-Mean monthly temperatures, degrees F, at four depths in
Lakeland fine sand in the shade of a citrus tree from 1962-67, University of
Florida, Agricultural Research and Education Center, Lake Alfred, Florida.


80-


C-,
770


6 60


120 in.
72 In.
18 In.
6 In.


J F M A M J J
MONTH


A S 0 N D


Figure 5.-Mean monthly temperatures, degrees F, at four depths in
unshaded Lakeland fine sand, 1962-67, University of Florida, Agricultural
Research and Education Center, Lake Alfred, Florida.

The duration of the period of highest temperature tended to
be longer in shaded than in unshaded soil especially at 72 and
120 inches deep (Figures 2 and 3). At 6 and 18 inches, the high
period extended from May to September in both the shaded
and unshaded soil. In the shade, the high at 72 inches lasted
from July to October and at 120 inches from July to November.


"70
60
`60


72 In.

- ... \ 18 n.
6 In.


IIIIIII


I I






In unshaded soil at 72 inches, the high period started in July
and ended in September; and at 120 inches, it extended from
August through October (Figures 4 and 5).
The rate and depth of vertical heat flow in the soil was de.
pendent on the duration and intensity of heat at the soil surface.
Periods of heat transfer and accumulation ranged from 4 to 20
days. During such periods of heat accumulation, the rise in
temperature 6 inches deep in unshaded soil at Lake Alfred varied
from 40 to 100. The increase in temperature at 18 inches during
periods of heat accumulation averaged 2.50 F, and the high for
the period usually followed by one day the high at 6 inches.
If the increase in air and soil surface temperature was intense,
the rise at 18 inches was measurable the same day as at 6 inches.
At 72 inches, the rise in temperature amounted to 0.50 to
1 and occurred 5 to 6 days later than at 6 inches. The heat
accumulation period at 72 inches lasted approximately 3 days
and then decreased slightly for a few days before the start of
the next heat accumulation period.
At 120 inches, heat accumulation and temperature increase
were very gradual, but continued for 6 months. The effect of
a short-term heat accumulation period became evident 6 to 8
days after the cycle started and amounted to 0.50 or less de-
pending on the intensity and duration of the atmospheric heat
cycle.
In Parkwood soil, the pattern and timing of temperature
increases were virtually the same as in Lakeland fine sand, but
the increases were less and more gradual.
During periods of net heat loss, there was a lag of 5 to 6
days in the progression of a heat-loss wave from 6 inches to
120 inches in the Lakeland soil. A typical day to day heat loss
cycle and progressive wave of decreasing temperature through
the soil is illustrated in Figure 6. At 6 inches, the heat loss
began the same day of low atmospheric temperature. Depend-
ing on the duration of low temperature periods and rate of heat
loss, the temperature at 6 inches decreased as much as 13 F
during a heat loss period. At 18 inches, heat loss could amount
to 70, and the temperature decrease started one day later than
at 6 inches. At 72 inches, the loss was less than 2 and occurred
3 to 4 days later than at 6 inches; and at 120 inches the heat
loss of 0.50 to 1 became evident 6 to 7 days after the start of
the decreasing heat cycle. The heat loss at 120 inches was
gradual and continuous, and did not oscillate either diurnally
or as a result of weather frontal systems (Figure 3).
The progressive changes in heat accumulation and heat loss










_70- 120 in
72 in.
18 in.
S60 6 In.


50


16 17 18 19 20 21 22 23 24 25 26
JANUARY
Figure 6.-Progression of a heat loss wave in Lakeland fine sand, in the
shade of a citrus tree, January 1965, University of Florida, Agricultural Re-
search and Education Center, Lake Alfred, Florida.

occurred at the same time and rate in bare and shaded soil.
Shaded soil was consistently cooler than unshaded soil down
to 72 inches; but at 120 inches, unshaded soil was somewhat
cooler than shaded soil. The largest mean temperature differ-
ential between shaded and unshaded soil occurred at 6 inches
and gradually decreased with depth down to 6 feet. From April
through September, unshaded soil at 6 inches was 40 to 5
warmer than shaded soil, and the difference at 72 inches
amounted to 3 from July through September. During the
winter, there was not much difference between the temperature
of shaded and unshaded soil at all depths, except at 120 inches
where the temperature was 3' higher in shaded than in un-
shaded soil.

Temperature Oscillations
Fluctuations due to diurnal oscillations were detected in the
Lakeland and Parkwood soils and in shaded and unshaded soil
(Figures 2, 3, and 7). The greatest oscillation between daily
highs and lows occurred at 6 inches and progressively decreased
with depth (Figures 2 and 3). The diurnal amplitude between
maxima and minima was greater in unshaded than in shaded
soil. Diurnal fluctuations were measured down to 36 inches in
Lakeland fine sand at Lake Alfred (Figures 2 and 3) and 24
inches in the Parkwood soil at Fort Pierce (Figure 7). The








80[ UNSHADED


70 SHADE


60 61 n.


S-80
UNSHADED

w70


60- 24 in.

I I I I I t I I I I I
J F M A M J J A S O N D
MONTH
Figure 7.-Comparison of the range between the mean minimum and
maximum temperatures 6 and 24 inches deep in unshaded and shaded Park-
wood soil, 1961-65, Fort Pierce, Florida.
amplitude of diurnal temperature fluctuations in Parkwood soil
was not as great as in Lakeland soil (Figures 2 and 7). Below
36 inches, no diurnal temperature oscillation was noted in either
unshaded or shaded soil (Figure 3).
At 72 inches, temperature oscillations were detected only
after several days of heat accumulation followed by a period of
heat loss or vice versa. Temperature oscillations below 36 inches
reflected changes in air mass thermal properties due to frontal
systems that normally follow one another at 7 to 10-day inter-
vals excluding the summer. The duration and amplitude of
oscillations due to weather cycle fluctuations were also dependent
on the heat content of the air mass.







Neither diurnal oscillation nor oscillations due to frontal
systems were detected 120 inches deep. At this depth, there was
only a measurable annual oscillation between the annual maxi-
mum and minimum (Figure 3).
The amplitude of the oscillation between annual maximum
and annual minimum mean monthly temperatures varied from
year to year, was greater in unshaded than shaded soil at all
depths, and progressively decreased with depth (Figures 4
and 5).

Discussion

Heat transfer into and out of Lakeland fine sand and Park-
wood soil is one of the most variable factors governing soil
climate in citrus groves. Temperature changes in regard to
heat accumulation and heat loss in soils are proportional to the
duration and intensity of solar radiation and atmospheric heat.
Other factors such as soil water, ground cover, proportion
of shaded and unshaded soil, and cultural practices also have
an effect on the amount and rate of heat transfer. Heat is either
absorbed or given off more rapidly by wet soil than dry soil, and
there is deeper diurnal penetration of heat in wet sand than in
dry sand (4). The water table is usually quite deep in the
Lakeland soil type and relatively shallow in Parkwood soil.
Soil under citrus trees was cooler and had a more uniform
temperature than unshaded soil in both Lakeland fine sand and
Parkwood soil. A difference between the soil temperature under
citrus trees and in open areas was also reported from southern
Russia (5). Interception of incident heat rays by foliage prob-
ably interferes with heat accumulation until the ambient atmos-
pheric temperature under the tree becomes greater than at the
soil surface. The root system under trees also periodically de-
pletes the water content of the soil, and the soil then becomes
a poor heat conductor until the soil water is recharged.
Lakeland fine sand in the area studied was subject to rapid
and, at times, extreme temperature fluctuations. The upper 6
inches of the soil were exposed to large diurnal temperature os-
cillations and short-term weather cycles. At depths below 18
inches in shaded and unshaded soil, the temperature was similar
and there was very little or no effect from diurnal atmospheric
temperature oscillations. Temperature fluctuations associated
with frontal systems resulted in either a gradual increase or
decrease in soil temperature at depths below 18 inches depend-
ing on the time of the year.







Generalizations regarding soil temperature in citrus groves
should not be made yet, because data from other areas are not
available except for southern Russia, where grove soil tem-
peratures are similar to those reported in this study (5). The
influence of cultivation and irrigation practices on soil tem-
perature in citrus groves has not yet been studied.
No data were obtained on horizontal or lateral flow of heat
in either the Lakeland or Parkwood soils. In the Parkwood soil,
the thermograph probes in the shaded and unshaded soil were
8 feet apart. At the 6-inch depth, there was a lag of 2 to 3
hours from the time either a diurnal high or low was reached
in unshaded soil to the time the high or low was reached at the
same depth under the tree. A sudden drop in soil temperature
due to the cooling effect of rain was followed after 1 to 2 hours
by a corresponding, but smaller soil temperature decrease under
the tree. This lag in soil temperature change under the tree
could be due to the shading effect of the tree as well as to hori-
zontal heat flow in the soil.
The data obtained in this study have been helpful in obtain-
ing a better understanding of the spreading decline problem in
Florida citrus groves (1). It is anticipated that this information
will also be useful in efforts to obtain a more complete knowledge
and better understanding of other citrus problems such as:
winter chlorosis, predisposition to root rot, water logged soil
coupled with anaerobic reducing processes, ability of roots to
absorb nutrients and efficient use of fertilizers, and timing of
soil fumigation for control of root diseases.








Literature Cited


1. DuCharme, E. P. 1969. Temperature in relation to Radopholus similis
(Nematoda) spreading decline of citrus. Proc. 1st Int. Citrus Symp.
2: 979-984.

2. Ford, H. W. 1954. The influence of rootstock and tree age on root
distribution of citrus. Proc. Amer. Hort. Soc. 63: 137-142.

3. Klotz, L. J., T. A. DeWolfe, L. C. Erickson, L. B. Brannaman, and
M. J. Garber. 1962. Twig dieback of citrus trees. Calif. Citrog. 47:
74, 86, 88-91.
4. Priestly, C. H. B. 1959. Heat conduction and temperature profiles in
air and soil. J. Australian Inst. Agr. Sci. 25: 94-107.
5. Shulgin, A. M. 1965. The temperature regime of soils. Translated
from the Russian by A. Gourevitch. Sivan Press, Jerusalem. 218 pp.

6. Suit, R. F., and E. P. DuCharme. 1953. The burrowing nematode and
other parasitic nematodes in relation to spreading decline of citrus.
Plant Dis. Reporter. 37: 379-383.




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