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PILOT EVAPOTRANSPIRATION STUDY:
Lysimeter Design
By
Paul C. Ekern
Technical Report .No. 130l-
August 1967
Project Completion Report
fur
PILOT EVAPOTRANSPIRATION STUDY
OWRR Project No. A-010-HI, Grant Agreement No. 14-01-0001-905
Principal Investigators: Paul C. Ekern and Jen-Hu Chang
Project Period: July 1, 1966 to June 30, 1967
The work upon which t his pUbl i cat i on is based was supported in partby funds provided by the United St at es Department of the Interioras author i zed under the Water Resources Act of 1964, Public Law 88-379 .
ABSTRACT.
The mari ne sub-tropic climate of Hawaii is particularly suited. to t he
use of semi-contained hydraulic l ysimeters. Field experiences in the use
of these l ys i met ers reveal a number of problems among which wer e f actors
r elat ed t o t he unusual tropical crops of pineapple and sugarcane. This
project inve s t igated the modification of the lysimeters to mi nimize some
of t hese probl ems .
Modular plant ing schemes in 1.52 meter rows or beds and tillage
depths of 0.3 to 0.6 meters dictated minimallysimeter size. The great
height and lodging of the cane required a large lysimeter area t o help in
the def i nit i on of the effective transpiring area. Polyester resin fiber
glas s reinfo rced tanks.• 3 x 3 x: 1.52 m deep with paper honeycomb strength
ened bot t oms were designed to meet the need for a large and r elati vely
deep container of minimal weight. The prevalence of high r elati ve humidi
ties nece ssitat ed the use of engi neer i ng graph paper to reduce di s t ortion
of r ecording traces from shrinkage and swelling of the paper. Des pite the
l imited diurnal and annual temperature variations, careful i nsulation of
the expos ed portions of the manometer was necessary. The regular diurna l
changes i n wind velocity impose d fluctuations on t he open-end manometer
used for r ecording the pressure changes i n the hydraulic load cells that
were off set by venting near ground level. Nylon reinforced buty l rubber
i r r igati on hose with the ends clamped was used to form the bolsters fo r
the l oad ce l l s . A silicone rubber sealant was used to ensure water t i ght. .
f ittings with standard copper tubing connectors to the bolsters. Stabi-
lity against rolling was achieved by placing some of the bolsters at right
angles to the ot her s . Large tensiometers of perforated polyvi nyl pipe
covered with porous Porvic membrane were designed to induce suction at the
base of the soil column. The water release curves for the Lat osols sug
gested a 0.1 bar suction for an approximation of field capacity.
iii
CONTENTS
FIGURES ' " v
INTRODUCTION: LYSIMETER DESIGN REQUIREMENTS 1
OBJECTIVES AND SCOPE 2
INSTRUMENTATION 2
Extant Lys imeter Des igns ; 2Principles of the Hawaiian Design 3Specifications of the Standardized Hawaiian Design forPineapp1e Lys imeters .........•.................................... 8
Problems in the Lysimeter Operation 9Modifications of the Original Design 14
SUMMARY 16
REFERENCES 17
APPENDIX ; " " 21
FIGURES
Figure
1 Diagram of Hydraulic Lysimeter 4
2 Hydraulic Lysimeter Record, Low Humic Latosol, 0.36m. Layer .. 6
3 Loading and Unloading Response of Lysimeter Number 3 7
4 Wind Effect Upon Hydraulic Lysimeters 13
5 Water Release Curve - Waimea Soil (Site 1,0-15 cm) 23
6 Water Release Curves - Waimea Soil (Site 1,7-15 cm) 24
7 Water Release Curves - Waimea Soil (Site 1,15-20 cm) 25
8 Water Release Curves - Waimea Soil (Site 1, 23-30 cm) 26
v
INTRODUCTION: LYSIMETER DESIGN REQUIREMENTS
Hydraulic lysimeters were designed originally for the measurement of
water use by pineapple in Hawaii. Stringent limitations are imposed on
field lysimeters by the peculiar nature of pineapple physiology and the
agronomic practices in Hawaii. The consumptive use of water reported for
pineapple plantings was 0.75 to 1.25 rom per day, an amount little more than
that of dew (Krauss, 1930; Leopold, 1952; Monteith, 1957; Stone, 1963 and
Ekern, 1965). This is in striking contrast to the evapotranspiration of
more conventional plants such as sugarcane and Bermudagrass since their
water use is ten-fold that of dew (Campbell, et a~. 1959; Ekern, 1966a
and Campbell, 1967) . Meaningful measure of water use by pineapple requires
an instrument not only of great sensitivity, but one which records the
diurnal pattern as well as the amount of such use.
The extreme height of the cane crop (4.3 m) and the lodging during
its 24-month cycle impose equally stringent requirements on the lysimeter
design. For use with sugarcane, large lysimeters are required to minimize
the problem of defining the effective lysimeter boundary. The mi ni mum di
mensions of the lysimeter are determined by the 1.52 m spacing of pineapple
beds and sugarcane furrow. Fortunately, the shallow rooting zone of the
pineapple makes a soil depth of 0.3 m acceptable (Bowers, 1929; Gwynne,
1962). However, the rooting depth of the cane is normally much greater,
and depends in large part on the depth of tillage (Trouse and Humbert, 1961).
The Latosols (oxisols) in which pineapple and cane are normally grown
in Hawaii have extremely high infiltration rates, release small amounts
of readily available water, and have unique thermal properties, thus, add
ing further criteria to the lysimeter design (Ekern, 1966) .
The climatic provinces where pineapple and sugarcane are grown in
the islands and the microclimates produced by such agronomic practices
as mulching with polyethylene arid irrigation make a large number of such
instruments necessary for use at different sites; hence, low cost per
l ysimeter is imperative.
The remarkable seasonal uniformity of the sub-tropic marine climate
with temperatures always above freezing makes the Hawaiian Islands ideally
suited for water-filled load cells (Blumenstock, 1961). However, the fre
quency of intense r ai nf a l l requires provision for the disposal of large
amounts of percolate through the lysimeters (Schwartz, 1963).
2
Because of these unique qualifications, an inexpensive, extremely
sensitive, recording instrument was needed with a modular width of 1.52 m
and a depth ranging from 0.3 to 1.5 m.
OBJECTIVES AND SCOPE
It was proposed in this project to initiate an investigation of the
effect of water on crop yield and quality of sugarcane, pineapples, and
tropical truck crops, extending earlier research on the magnitude of con
sumptive use in sugarcane and pineapple. Specifically in this pilot phase,
it was proposed to investigate necessary modifications of semi-contained
hydraulic lysimeters to make such lysimeters suitable for use with crops
in Hawaii, taking into account, for example, the great height of sugarcane
and the low level of transpiration in pineapple.
It was further proposed to review the currently available information
on the components of the hydrologic budget of suggested study sites since
the values reported for such meteorological variables as solar radiation,
wind velocity, and rainfall impose severe restrictions on the lysimeter
design. Among the variables rev iewed must also be the moisture storage
capacity of the Latosols and the effective rootipg depths of the crops
for these, too, are important determinants in the lysimeter design.*
INSTRUMENTATION
Extant Lysimeter Designs
The cost of extant continuously recording lysimeters presents a for
midable barrier to their wide spread use in the field. Such major instal
lations as the 6.1 m diameter lysimeter at Davis, California (Pruitt . and
Angus, 1960), the several lysimeters at Coshocton, Ohio, (Harrold and Drei
belbis, 1945, 1967), the English installations (Morris, 1959), and their
counterparts in Australia (McIlroy and Sumner, 1961) were all elaborate
and expensive instruments based on mechanical scales.
Small mechanically weighted lysimeters are less expensive, but the
degree of sensitivity demanded (detection of changes of 0.02% of the total
*Comprehensive review of the extant literature on these subjects is included in Climat e and agriculture: an ecological survey by Dr. Jen -Hu Chang,who is a project manager of this study. The book is in press.
3
mass) was difficult to obtain (England and Lesesne,1962).
The suggested use 6f electrical strain gages with a counterbalance
for increase sensitivity was limited by the expense of instrumentation
for continuous recording whether for the simple instruments at Tucson,
Arizona (Frost, 1962) or the elaborate installations at Tempe, 'Arizona
(Van Bave1 and Meyers, 1962) and in California (Libby and Nixon, 1963).
Floating 1ysimeters with buoyant air chambers are inexpensive, but
distort the root zones (King, et al.~ 1960 and Fulton and Findlay, 1966).
The use of zinc chloride solutions with specific gravities of 1.9 instead
of water eliminate the need for air chambers in these instruments (Mc
Millan and Paul, 1961), but the solution's must be treated gingerly. The
modified floating instruments are still temperature sensitive (King, et
al. 1965). The underground moat in the lysimeter of Russian design is
a massive and costly installation (Popov, 1959). A Danish instrument
with a mechanical counterbalance of the major portion of the lysimeter
weight and a floating technique for measurement of the remnant weight re
quires a precision beyond the intent of the 1ysimeters proposed for field
use (Aslyng, 1959).
Principles of the Hawaiian Design
The basic principles of the inexpensive instrument designed for
Hawaii have since been reported for instruments from Kenya (Forsgate,et
al.~ 1965 and Glover and F~rsgate, 1962), Canada (Holmes, 1963 and Natal,
Thompson and Boyce, 1967), Australia (Rose, et .al., 1966), the Netherlands
(Visser, 1965) and the United States (Hanks and Shawcroft, 1965; Middle
ton, 1965; Tanner, 1967 and Tanner, et al., 1967). The weight of the
so i I-Ei.Lled lysimeter box rests on water-filled rubber tubes which act
as hydraulic load cells. The pressure generated by the weight on the
tubes was measured by a water-filled open-end manometer (Fig. 1), and
traced by a float-activated water stage recorder. The recorder was
first installed on this newly designed hydraulic lysimeter at the Pine
apple Research Institute Experiment Station, Wahiawa, on August 20, 1958.
This initial instrument held soil in a square wooden box 25.4 ern deep
with a rigid yet permeable bottom through which excess percolate might
drain. The hydraulic cells were made from two water-filled automobile
inner tubes, and interconnected with rubber hose. A transparent riser
RECORDER
FIGURE I: DIAGRAM OF HYDRAULIC LYSIMETER (SCALE I CENTIMETER = 0 .3 METER).
.j::. •
5
from the tubes formed an open-end manometer. The two interconnected tubes
were laid flat on one side of the bottom of a 30.5-cm deep pit in the
coil. The walls on the pit were lined with: aluminum sheet to prevent col
lapse. There was a 2.54-cm clearance between the exterior of the lysi
meter box and the outer guard frame holding back the soil at the edges
of the pit. A 1.22 m long piece of 10 cm x 10 cm angle iron was laid
along the extreme outer edge of the opposite side of the bottom of the
pit with the corner edge of the iron faced upward. When the lysimeter
box was placed in the pit, the edge of the angle iron formed a fulcrum
and the inner tubes supported the remaining weight.
Later models of the lysimeter omitted the leverage system of the an
gle iron and rested the entire weight directly upon four tubes equispaced
on the bottom so that steady balance of the box was obtained. The hydrau
lic head developed by the pressure of the weight upon the water in the
tubes was counterbalanced by the expansion of the tubes and the static
head formed in the manometer. The upper end of the manometer was trans
formed into a 20 cmdiameter reservoir for automatic recording of the
water level. A simple float recorder made a continuous trace of the water
height in the reservoir and a levered linkage to the float magnified the.
level changes (Fig. 2).
Trial installations of lysimeter models with depths to as much as
1.5 m have been made. The greater pressures of the deeper lysimeters
caused the rubber tubes to stretch and greatly reduced the sensitivity
of the response. Later, non-stretching nylon reinforced irrigation hose
was used to form load cells which maintained sensitivity at these greater
pressures.
In another set of lysimeters, the percolate was contained in a sump
on the lysimeter box. The sump was pumped periodically so that the amount
of percolate could be measured. This design was not pursued because rain
fall amounts as great as 30.5 cm per day have been recorded for Wahiawa
and amounts of 7.5 to 15 cm per day are common. Such massive additions
of water area hundred times the expected evapotranspiration rate and it
was not feasible to design a recorder for such scale changes. The lysi
meter bottom was left open· to vent the percolate as quickly as possible.
The extremely high infiltration rates and peculiar moisture properties
of the Low Humic Latosol used for most pineapple culture in Hawaii made
this soil. i dea l l y suited for such a procedure (Ekern, 1966b). The
6
3
E2E
2.25
-
0.500 .25
6T
8A.M. 8A.M. 8A.M. 8A.M.
'E5o-...J4w>w 3...J
ffi 2J- () NOON
~I • MIDNIGHT
00 2 3 4TIME IN DAYS
FIGURE 2: HYDRAULIC LYSIMETER RECORD, LOW HUMIC LATOSOL,O.36m. LAYER.
70
60
50-. til,:,e.-I-
~ 40lJJ3:
w>I- 30~....J:::>~:::>u 20
10
o
1117
1101
IOS7
10471042
IOU, 1000,0lMl4POLYETHYLENEEDt! REMOVED
7
o 10 20 30 40 50 60MANOMETER LEVEL (mm FROM INITIAL DATUM)
FIGURE 3: LOADING AND UNLOADING RESPONSE OF LYSIMETERNUMBER 3 WITH 4mm I.D. GLASS MANOMETERAND INITIAL STATIC HEAD IOOcm. ABOVEGROUND SURFACE. l
j
I· 1iI.1
~
8
thorough aggregation of this Latosol results in a water release curve
similar to that of gravel (Fig. 3). Generally twenty-four hours suf
ficed to complete percolation from the shallow lysimeters.
Specifications of the Standardized Hawaiian Design
for Pineapple Lysimeters
Standard construction was used for eight lysimeters placed i n dif
ferent locations on the islands of Oahu, Molokai, and Lanai. An outer
guard shell of 16~auge galvanized iron formed a I.S2-m square opening
with walls 0.78 m high. The upper and lower edges of the shell had a
2.S-cm section turned to form a right angle that reinforced these edges.
The inner box which contained the soil was made from 14-gauge galvanized
sheet. The box opening was 14.7 m square and 0.45 m deep. Again a rein
forcing band was turned at the upper and lower edges. These particular
dimensions were imposed by the economical use of 1.2 x 3 m modular galvan
ized sheets. The bottom of the box was made of 1.25 cm expanded steel
mesh supported by two cross pieces of channel iron. Since the bottom was
not rigid, the box was set on a platform of 2 x 12 planks that rested
directly on the tubes. A 5-cm layer of coarse gravel was placed directly
over t he mesh and soil filled to within 5 cm of the top of the lysimeter
box. This gave a 0.355-m depth of soil for plant roots.
The double-walled reservoir which formed the upper end of the mano
meter had a 20-cm square inner and 25-cm square outer dimension. Panels
of styrofoam, 2.5-cm thick, were used as insulation between the walls.
The reservoir was 0.5 m deep and usually contained 0.38 m of water. In
the field, the reservoir was further insulated by a 15-cm jacket of dry
soil. The soil packed about the reservoir also served to stabilized the
system against wind vibrations.
The hydraulic cells were formed by four 750 x 16 heavy duty truck
i nner tubes. The inner tubes were interconnected by 6.34-mm polyethylene
tubing . The polyethylene tubing, which was connected to the reservoir
approximately 5 m from the lysimeter at the field edge, was buried 0.45 m
within the soil to minimize temperature changes .
Static hydraulic heads 0.6 to 0.9 m above the ground surface were
used i n most of the lysimeters. Since the depth of the pit for the stan
dard lysimeter was 0.45 m, the usual water pressure was 0.155 bar.
9
Despite the potential friction losses in the plastic tubing and fit
tings, operations at such low pressure heads gave a surprisingly rapid
response. When the response of the lysimeter was measured by manometers
3.95 to 6.3 mm in diameter, an approximate two-fold hydraulic magnifica
tion was observed. Moreover, a satisfactory degree of linearity was pre
sent over the range of change normally encountered (Fig. 3) in a week of
moisture used by the pineapple. A water stage recorder with a 10-cm dia
meter Leopold Stevens float was mounted directly on top of the reservoir.
Change in water level was given an additional lever magnification and
traced on a chart renewed weekly.
When the reservoir with a 100-fold greater cross section was coupled
to the end of the manometer, the increased volume of water which had to
be displaced to change the pressure head reduced the hydraulic magnifica
tion and introduced a time lag in the response of the instruments. The
advantage gained from the continuous trace of water level changes by a
float recorder more than offset the reduction in magnification and speed
of response. Even the~ 90 percent of the change in level produced by
the addit10n of a 11.32-kg weight was completed within 15 minutes.
The magnification of the standardized lysimeters installed ih 1959
was equivalent to a 3.08-fold magnification. The levers for these record
ers had a 2.75 multiplication, hence, the hydraulic magnification must
have been 1.12-fold for the static hydraulic head used. Several of the
lysimeters at PRI Wahiawa had a more sensitive recording lever with a 5.9
fold magnification. The total magnification of these more sensitive sys
tems was 1 mm chart travel per 0.15 mm of water use of a 6.65-fold magni
fication. This was again equivalent to a 1.12-fold hydraulic magnification,
though the static hydraulic head was slightly greater with a value of
1.52 m.
Problems in the Lysimeter Operation
Paper charts. One of the more exasperating problems arose from the shrink
age and swelling of the chart paper on the recorders . The sensitivity
demanded from the record was such that 1 mm of chart travel represented
from 20 to 50 percent of the total day's water use for pineapple plants.
When the water use of grass sod or pan evaporation was measured, changes
in the paper size were insignificant in comparison to the much greater
10
evaporation trace change . . When the 1ysimeters were planted to pineapple,
a diurnal pattern was imposed on the trace as a result of the 2 percent
shrinkage of ·t he paper upon drying by day and the swelling upon wetting
in the evening. A dry 202-W Bendix Friez Thermograph chart expands 1.5
scale units (1.78 mm) when moistened by a damp sponge. The pattern of
shrinkage is centered on the midline of the chart so that the trace of a
fixed pen on the upper edge of the chart has an apparent rise as the pa
per dries, while one in the center remains unchanged in position and one
near the bottom edge registers an apparent fall. This problem was parti
cularly acute for Wahiawa as a result of the regularity of the humidity
pattern of saturation by night and 50 percent by midday since the major
gain in paper size occurred when the relative humidity changed from 80
percent to 85 percent.
Charts made of Keuffel and Esser Co. tracing paper 359-14elimina
ted this problem of chart size and relative humidity . .
CabZe for fZoat connections. Bronze radio cable was first used for sus
pension of the floats from the recording lever. The linear coefficient
of thermal expansion of the bronze introduced only minor error. Strands
of saran were later used, since its expansion coefficient is fortuitously
almost identical with the volumetric thermal coefficient of water. A
braided nylon cable was briefly used to replace a bronze cable. The ny
lon responded to humidity much like hair and made an excellent hygrometer
but was useless as a recorder cable.
Reservoi r evaporation. Maximum daily evaporation rates from rain gages
and other small orifice devices have been reported to be 1.0 mm per day
(Gomm, 1941; Hamilton and Andrews, 1953, and Gill, 1961). Here too, be-.fore oil was added to the water surface, a deadweighted above-ground lysi-
meter installation had a daily loss of 0.5 mm. The oil layer eliminated
this net loss by direct evaporation from the reservoir.
Temperatupe changes. The changes in volume with change in temperature of
the several materials at critical points in the hydraulic system suggested
that only the expansion with temperature increase of the water in the re
servoir would be important. If the entire installation were set above
ground for the maximum effect of temperature change with the rubber tubes
exposed directly to sunlight and the circulation of warm air, the apparent
- ,I
11
rise and fall of the reservoir level would correspond closely to the
changes in air temperature,as reported for Kenya by Wangati (196S). When
the tubes were installed in a soil pit 4S-cm deep, they were shielded
from sunlight and rested in a zone where the diurnal soil temperature
°range was less than 1/2 C.
The styrofoam insulation about the reservoir reduced the diurnal
water temperature range to SoC, a SO% reduction from the daily air tem
perature range. An apparent 0.38-mm rise and fall of the water level
would be caused by this SoC temperature change . Addition of dry soil for
further insulation about the reservoir reduced the water temperature
change to less than 2.SoC, which would induce an apparent gain and loss
of only 0.19mm/day. When the daily rate of water use of transpiring
vegetation was measured, the near constancy of the average daily tem
peraturesin Hawaii made the change in reservoir level from temperature
negligible. The slight rise of the water level by expansion during the
day was overwhelmed by the fall from the actual water use rate of rap
idly evaporating soil or transpiring grass.
Although seasonal and diurnal flux of temperatures is a problem
in other geographical regions, the variation within Hawaiian Latosols is
so small that no attempt has been made to control temperatures within
the lysimeter. The buoyancy effect noted by Morris (19S9) in an above
ground lysimeter in a glass house would be equivalent to only 0.02S mm
of water for a 10°C rise in air temperature, and would be negligible
for the near constant temperatures within the soil pit in the field.
Temperature gradients within the lysimeter can cause rapid soil moisture
transfer in Latosols (Ekern, 1966). However, even with the very great
seasonal temperature changes reported at Davis, California and Tempe,
Arizona, only minor differences in soil temperatures within the lysi
meters have been reported (Pruitt &McMillan, 1961, 1962; Van Savel &Reginato, 1962). The large air space beneath the Davis lysimeter forms
an insulative barrier and subsoil temperatures have risen as much as
3.SoC above the undisturbed soil nearby. The seasonal and diurnal flux
of temperatures within Latosols in Hawaii is so small that no attempt
will be made to control temperatures within the lysimeter unless mea
sured temperature show marked departures from those in the undisturbed
surroundings.
12
The annular gap about the edge of the lysimeter and the outer re
taining wall has produced peculiar imbalances of temperature and moisture
transfer in several lysimeters. A vapor barrier across this gap pro
duced an apparent diurnal cycle of distillation and condensation in
Australian lysimeters which was reduced to a tolerable level if the gap
was left open (McIlroy &Sumner, 1961). The most spectacular resultant
of closure of the gap was found in the Coshocton lysimeters where expan~
sion and shrinkage of the grease seal caused an apparent diurnal rise
and fall of the lysimeter long interpreted as dewfall. Removal of the
grease seal stopped this distortion (Harrold, 1962; Harrold &Dreibelbis,
1967). The annular gap of the Hawaiian lysimeters was partially closed
with polyethylene film to prevent soil and other debris from washing into
the pit. No diurnal pattern was found on these lysimeters with the
partial closure of the annular gap.
Wind ef fe ct s . The strong diurnal wind pattern at Wahiawa (Leopold, 1948)
from nightime calm to coupling of the trades and 4.5 m/s wind at the
1.8-m level by day during the summer introduces an effect on the open-end
manometer.
The suction would be 1.25 mm of water for a 4.5-m/s wind across the
manometer calculated after Dines' suggestion (Middleton, 1942). The
actual change would depend upon the exact geometery of the openings. The
measured effect over the Hawaiian lysimeters was equivalent to 1.0 mm,
but was quite noticeable (Fig. 4). An apparent change of 0.75 to 1.25 mm
has been reported from the floating lysimeters at Davis (Pruitt &McMillan, 1961). When the California lysimeter was vented at ground
height considerable reduction in this wind-induced pressure drop occurred.
The flow of wind past the recorder housing produce complex pressure
pumping as well as a net pressure differential. Barography and open-end
sYmmetry has recorded these pumping effects as great as 32 mm of water
for a 22.35-m/s wind (Middleton, 1942). The size, shape, and location of
openings in any building can have a marked effect upon the pressure pat
tern produced (Theakston, 1962). This effect was noted to be marked on
the housing for the recorders for the lysimeters at Copenhagen (Ekern,
personal observation, Oct. 1960). Opening the access hatch to the area
beneath the 6.l-m diameter lysimeter at Davis, California, created an
open-end manometer and the pressure drop caused was recorded as an ap-
13
NOTE APPARENT GAIN IN MOISTUREIN MORNING AND lOSS IN EVENIN~, BUT NET LOSS DURING THEOAT.
/----I "f \\ I\ I
'- /-- .-'
..--, ./ \I I\ I
'--"---LNOTE APPARENT GAIN IN MOISTURE,
MORNING, AND EQUIVALENT LOSSIN EVENING.
/'/I\\ /
'-.: ./........ -
LEGEND
• POLYETHYLENEMULCH
() POLYETHYLENEPLUS TRASH MULCH
08 12 24 8 12 24 8 12 24
8 .... z ....~
....0:I: 0 :I: :I:
Z (!) Z (!) !:2z z zc c c~ ~ ~
-8/6/62-1-8/7/62-1-8/8/62 .1DATE AND TIME
FIGURE 4 : WIND EFFECT UPON HYDRAULIC LYSIMETERS.
3.125
3.750
0.625
eneno....J
~ 1.250zwa::~a..<{
~ 1.875=>~eno::E
-E~ 2.500
14
parent gain in the weight of the lysimeter. The pumping effect of wind
across the lysimeters at Tempe has been reported to limit their sensi
tivity and imposed a need for smoothing of the record on windy days
(Van Bavel and Meyers, 1962).
Durat ion of tubes. The rubber tubes in the underground installations
were protected from sunlight and were at a nearly constant temperature
of 24°C. Deterioration of the material was not a problem, for several
of the lysimeters remained operative over a 4-year period. In dry
locations on Molokai, rats, apparently in search of water, destroyed
both the polyethylene tubing and the rubber automobile inner tubes in
the underground installations.
I nstrument calibration. Periodic addition of known weights was used
to calibrate the instruments. The time of response with the reservoir
was greater than that for the manometer alone, but even then an hour
sufficed to complete the response. Attempts to calibrate the 1ysimeters
in the field from rainfall was limited by the precision of the rainfall
measurements. The outer rim of the 1ysimeter enclosed an area of 2.32 m2
and a weight change of 4.47 kg was considered to be equivalent to 1.94 mm
of evaporation.
Modifications of the Original Design
Use of nylon reinforced, butyl i rrigation hose. The rubber inner tubes
stretched under the weight of soil depths greater than 0.75 m, and a more
substantial hydraulic load cell was designed with nylon reinforced
20.3-cm butyl rubber irrigation hose . Bolsters were constructed from
the tubing by sealing the ends. The original scheme of vulcanization
proved too expensive, and strap iron clamps, 5 em wide, were bolted di-
. rectly through the hose with 3 bolts to ensure closure. A length of
1.59-mm welding rod caught between two iron straps close the tube end.
The bolts on one end could readily be loosened to allow air escape
when the tubes were filled with water .
Tube interconnections. Standard bulkhead connectors for copper tubing
had to be modified to ensure a water tight seal to the hose. Brass
washers and nuts were devised to make the seal and silicone rubber was
15
added prior to tightening to further secure the waterproof seal. Copper
tubing interconnections were felt necessary to preclude rat attack.
Bolster pat t ern . Two long bolsters were placed parallel the outer edges
of the lysimeter box, and a series of shorter bolsters placed between
them, but at right angle to the longer bolsters. This pattern gave sta
bility against rolling of the cells with side pressures on the lysimeter
box.
Lysimeter box desi gn. Fiberglass reinforced polyester boxes, 3.05 m2 x
1.52 m were designed for sugarcane lysimeters. The walls were 4 mID
thick, with 4 parallel reinforcing ribs of wooden 2 x 4's encased in the
plastic for flexural strength of each wall. The lysimeter bottom was
a sandwich of two 4 mID fiberglass polyester sheets enclosing a resin
impregnated paper honeycomb 12 mm thick. This gave a box of great
strength, but one which only weighed approximately 447 kg.
Drainage t ensiometers. Larger tensiometers were made from 5 cm dia
meter polyvinyl pipe, perforated, with an intervening layer of nylon
screen, and an outer Porvic membrane (Sedgley &Millington, 1957). Re
moval of soil percolate for the analysis of leachates and the establish
ment of soil drainage to suctions near field capacity at the lysimeter
base were sought. The M grade Porvic is purported to have a bubbling
pressure of 0.57 bar and the S grade pressure of 0.24 bar. Prelimi
nary trials indicate soil moisture suctions as great as these cannot
be developed with the membranes, but that drainage to suctions of 0.1
bar can be made. This approaches the 0.1 to 0.15 bar suction desired
for Latosols (Ekern, 1966b).
Soi l moi s ture release values. Soil moisture variables were determined
for the soils at Kamuela, Hawaii, proposed site for lysimeters. This
is an ash derived soil and differs from the moisture release charac
teristics of the Low Humic Latosols (Figs . 5 to 8 and Table 1 in Appen
dix).
16
SUMMARY
Review of extant lysimeter designs and field experiments suggested
that some form of the semi-contained hydraulic lysimeter based on a water
fill,ed load cell was best suited to evapotranspiration measurements un
der Hawaiian conditions. The extremely low water use by non-transpiring
pineapple plants required the development of a recording lysimeter of
great sensitivity, achieved by direct measurement of load cell pressures
with an open-end water manometer with a float recorder. The great
height, lodging, and potentially deep-rooting habit of sugarcane required
a large, deep lysimeter, but one of less sensitivity since the water
use rate was ten-fold that of pineapple. The large, deep lysimeter was
constructed of polyester resin fiber-glass reinforced for durability
and light weight. Reinforcing wooden ribs supplied flexural strength
to the sides against the later pressures of the Latosol. Paper honey
comb strengthened the bottom of the lysimeter but little additional
we ight was added.
Large drainage tensiometers of Porvic were designed to develop
suction at the base of the soil column and allow the removal of percolate
waters for analysis. The sub-tropic marine climate of the Hawaiian Is
lands eliminated the hazards of freezing, and reduced the problems from
temperature changes within the hydraulic system. Diurnal wind varia
tion posed a distinct problem in measurement with an open-end manometer,
solved in part by venting the housing near the surface. Even then, the
total weight of the large lysimeters was great. It was offset by using
nylon-reinforced irrigation hose for the bolsters which form the load
cells. Arrangement of the bolsters in a geometric pattern with several
of the bolsters at right angles to the others minimized the tendency of
the lysimeter to shift in place under the burden of the very tall cane.
The water release properties of the well aggregated Latosols were mea
sured, s ince they produce drainage, evaporation, and thermal properties
strikingly different from those of temperate latitude soils.
17
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Gill, H. E. 1961. Evaporative losses from smaZl orifiae rain gages.J. of Geophys. Res. 65(9):2877-2881.
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1962. Measurement of evapotranspirationNature. 195(4848):1330.
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18
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Ki ng, K. M., C. B. Tanner , and V. E. Suomi . 1956 . A floating lysimeterand i t s evaporation recorder . Trans. Amer. Geophys. Union 37: 738743 .
Krauss, B. H. 1930.Un i v. of Hawaii.
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M. S. Thes is,
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1965. HydrauLic weighing Lysimeters.Personal communication.
Wash. State Univ .
19
Middleton, W. E. K. 1942. Met eoroLogi caL instruments. Univ. of TorontoPress. pp. 13-14, 134-139.
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Ii
20
Thompson, C;. D. and ,J . P. Boyce. 1967. Dai l y measur ements of potent ia Levapo t ransp i rat i on from f ully canopied sugarcane . Agr. Meteor . 4(4) :267-279 .
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pp.1- 15.
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APPENDIX
21
TABLE 1. WATER RELEASE VALUES FOR WAIMEA SOIL SAMPLESvolumetric water content
Ntv
SUCTl~ ! SITE I SITE II SITE II I SI TE IV SI TE v SITE VIem HQH o - 15 em 7.5 - 15 em 15 - 23 c. 23 - 30 ClI o - 15 ClI 30 - ~5 em o - 15 em 15 - 23 ClI 15 - l O em o - 15 COl 16 ca sc C:I
10 61. 70 6l. 90 6l .0" 55 . 0" 6l .2" 6~.8:: 6~.20 6l . 0" 66.2" 7l .I " 62 .9" 7~ . I ~. 7" 58.9" 50.i" 59. 70 7~ .1 0 83. lIO 62.20 61. 0" 65.0" 57. 0" 6l . ~0 - 98.6"" 70 .2=
eo . 70 . 77 . 71 . 7~ .83 . 77 . 67 . 72 . 70 .6 7 . 90 .80 . 95 .8 9 1.02 .92 . 67 .66 . 81 . 86 . 92 . 95 .71 - . 71 . 73
13 - - - - - - - - - - - - - - - - - - - - - - - - - 60. 00
eo - - - - - - - - - - - - - - - - - - - - - - - - - -~7 . l - - 5~ . 1 50.0 56.2 57 .~ 51.00 55 . 00 58. 5 67 .6 56.9 57 .0 ~ . 60 50 . ~ ..... 50 - - - - 57. 00 63 .00 52.00 - - - . 78
50 57.10 56 .20 - - - - - - - - - - - _. - ~7 . 60 66 . 20 69. 00 50.5 0 - - - 58.80 55 . 60 77. 60 65 .7 0
75 5 0 .~0 52.20 - - - - - - - - - - - - - - - - 57 .5 0 - - - - - 62. l0 -9l - - 50 . 1 ~~ .O 53.2 5 3 . ~ ~5 .20 50.00 53.0 61.9 51.9 - - - - - - - - 53. 00 60 .00 "9.00 - - - -
100 ~~ .90 '+8. 60 - - - - '+2.80 - - - - '+8 .~ ..... 00 '+7.3 0 '+2. 30 ~.80 ~ . 90 - 5 5 .~ - - - - '10.9 0 - -105 - - - - - - - - - - - - - - - - - - - - - - ~.9O - - 59. 10
115 - - - - - - - - - - - - - - - - - 58.2 0 - - - - - - - -l l 5 - - - - - - - - - - - - - - - - - - - - - - .....~ - - 56 .7 0
136 '+0.80 '+~ .80 - - - - - - - - - - - - - - - - - - - - - - - -1'+6 - - '+7.2 '+1. 0 51.5 50. 8 37 . 90 ~ .OO 50.l 58.6 50 .6 - - - - - - - - ~9. 00 56 .00 ~7 . 00 - - - -1'+8 - - - - - - - - - - - - - - - - - 50 .90 - - - - - - 55.90 -150 - - - - - - - - - - - -r.e '+1.90 ~5. 00 ~ .~ 37.10 ~.OO - - - - - - 39 .9 0 . -200 30 .10 ll.80 - - - - l1. 30 - - - - - - - - 32.60 29 .8 0 - l O.3 0 - - - 30. l0 28 . 50 - 35. 30
eo . 56 . 59 - - - - . 56 - - - - - - - - . 71 ..... - .6 0 - - - . 51 .58 - . ~ 7
500 25 .80 28.90 - - - - 28 .8 0 - - - - - - - - 27 .2 0 25. 70 - 26. 30 - - - 30. 70 23.70 - 37. 90
eo . 55 . 6l - - - - . 56 - - - - - - - - .6 7 . ~ - . 59 - - - . 52 . 59 - . 52
1, 000 25 .20 26 .10 37.5 2~.'+ l~ .l - 28.0 0 23 .20 2'+ .~ 23 .1 26 .6 - 26 . '+0 25 . 90 lO.IO 28 .1 0 23 . 60 - 22 . 50 27.~ 32.20 30 .80 32.20 2~ . 60 - 29.2 0
eo - - - - - - - - - - - - .95 . 8~ 1.09 - - - - - - - - - - -~.OOO 20 . 80 21. 6 l2 .'+ 23 .2 31.3 - 2'+.9 0 21.20 22. 1 20.8 25.2 - 2~.20 23.2 0 26. ~ 25 .1 0 19.90 - 21. 30 23.00 27.20 25. " 29. 00 19.80 - 23 .~
8,000 17.90 19 . '+0 ll.8 22 .9 l l. l - 25.2 0 21.30 21. l 20 .1 2'+.3 - 23.20 22.10 25.00 23.60 17. 90 - 18.80 22.00 27.10 25.20 23. 10 18.60 - 20.80
15,000 17.60 17. 90 - - 29 . 1 - 22 .8 0 - - - - - - - - 20 .5 0 1~.70 - 16 .20 - - - 19.70 - - 17 . 10
eo = BULK DENS ITYx = CORE So'I'f'LES
:= = ASH POCKETS
0.100.08
0.06
0 .04
0.02
0.000 10 50
10.08.0
6.0
4.0
2.0
1.0~ 0.8
~ 0.6
Iz 0.4o~U::l(f) 0.2
20 30 40
VOLUMETRIC WATER- PERCENT
FIGUR E 5: WATER RELEASE CURVE - WAIMEA SOIL.SITE I, 0-15 em.
23
70
24
100.00
0.10 () CORE SAMPLES
• BULK SAMPLES
L-- l- ..L- -'-- --I..- --L -.L.._ (Jr.-----l
700.01
o 1020 30 40 50 60VOLUMETRIC WATER - PERCENT
FIGURE 6 : WATER RELEASE CURVES- WAIMEA SOIL.SITE I, 7-15 em.
10.00
CJ)0::<{(II
Iz 100O 'l-t)
:::lCJ)
25
100.00
() CORE SAMPLES
• SULI< SAMPLES
10 20 30 ~O 50
VOLUMETRIC WATER - PERCENT
FIGURE 7 : WATER RELEASE CURVES -WAIMEA SOIL.SITE I, 15-20 em .
0.01 L- L..- L..- L..- L..-__---'L..-__---'~CI
o
0.10
10.00
(f)
~mI
~ 1.00r-o:::>(f)
26
loono .
1000
ena::«enIz:o 100t-U:J(f)
010
() CORE SAMPLES
• BULK SAMPLES
001 '--- --'-- --L. ----' J-- {
o 10 20 30 40 50 60VOLUMETRIC WATER- PERCENT
FIGURE 8 : WATER RELEASE CURVES- WAIMEA SOIL.SITE I, 23- 30 em