Water table management for organic soil conservation and crop production in the Florida Everglades

Material Information

Water table management for organic soil conservation and crop production in the Florida Everglades
Series Title:
Bulletin - University of Florida Agricultural Experiment Station ; 801
Burdine, H. W.
Crockett, J. R.
Gascho, G. J.
Harrison, D. S.
Kidder, G.
Mishoe, J. W.
Myhre, D. L.
Pate, F. M.
Shih, S. F.
Place of Publication:
Gainesville, Fla.
Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida,
Publication Date:


Subjects / Keywords:
The Everglades ( local )
City of Pahokee ( local )
Soil science ( jstor )
Water tables ( jstor )
Agriculture ( jstor )

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.


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George H. Snyder, H. W. Burdine, J. R. Crockett, G. J. Gascho, D. S. Harrison,
G. Kidder, J. W. Mishoe, D. L. Myhre, F. M. Pate and S. F. Shih

Agricultural Experiment Stations Institute of Food and Agricultural Sciences
University of Florida, Gainesville F. A. Wood, Dean for Research

Bulletin 8C

Cover.-Organic soil subsidence affects sugarcane, cattle, vegetables, and
wildlife in the Everglades Agricultural Area. See Figure 6.

Water Table Management
For Organic Soil Conservation
And Crop Production
In the Florida Everglades

George H. Snyder
Chairman, Soil Subsidence Committee

H. W. Burdine, J. R. Crockett, G. J. Gascho, D. S. Harrison,
G Kidder, J. W. Mishoe, D. L. Myhre, F. M. Pate, and S. F. Shih


Dr Snyder is an Associate Professor of Soil Science, Dr. Burdine is
a Professor Emeritus of Plant Physiology, Dr. Crockett is an Associate
Professor of Animal Genetics, and Dr. Gascho is an Associate Professor
of Agronomy, all at the Agricultural Research and Education Center,
Belle Glade. Mr. Harrison is a Professor of Agricultural Engineering,
Agricultural Engineering Department, University of Florida, Gainesville.
Dr. Kidder is an Assistant Professor of Agronomy, Dr. Mishoe is an As-
sistant Professor of Agricultural Engineering, Dr. Myrhe is a Professor of
Soil Science and Center Director, Dr. Pate is an Associate Professor of
Animal Nutrition, and Dr. Shih is an Associate Professor of Agricultural
Engineering, all at the Agricultural Research and Education Center,
Belle Glade.

This public document was promulgated at an annual cost
of $1,150.00 or a cost of 234 per copy to provide the latest
IFAS recommendations for water table management in the
Everglades Agricultural Area.



Organic soil in the Everglades Agricultural Area is subsiding
at the rate of about 1 inch per year. By the year 2000, it has been
estimated that about 500 thousand acres (or 87% of the total) of
organic soil will be 3 feet or less in thickness, and over 250,000
acres will be less than 1 foot. The fate of agriculture on this soil
is uncertain. Large tracts of land that now are agriculturally
productive may be abandoned. Some soil may be suitable for
pasture. Perhaps some soil will be used for production of aquatic
and semi-aquatic crops. Such a usage could extend the agricul-
tural productivity of this area far into the future. However, if
agriculture is maintained at the present level of activity, a fea-
sible technique to reduce the subsidence rate is to maintain
water tables at the maximum possible height compatible with
crop production. The rate of subsidence is directly proportional
to the depth of water table. Thus if the water table depth is
halved, subsidence is halved. For sugarcane and pasture, water
tables of 20 and 12 inches, respectively, may be acceptable.
Minimum depths to water table for vegetables will vary with
the specific crop, ranging from 14 inches for radishes and pars-
ley to 30 inches for lettuce. When not in production, organic
soils should be kept flooded to prevent loss. This bulletin pre-
sents some concepts of how the water table relates to organic
soil conservation and crop production, and how these water
tables can be measured and maintained at a desirable level.


I. The Everglades Agricultural Area ...................... 1
A Soils ............................................. 1

B. Crop production ................................... 5
C. Water management .................. ............. 6
II. Organic Soil Subsidence ............................... 7
III. Water Table Management .............................. 11
A. Effect on subsidence ............................... 11
B. Effect on crop production .......................... 12
1. Vegetables .................................... 13
2. Sugarcane ..................................... 14
3. Pasture and sod ............................... 15
C. Measuring and maintaining water tables ............ 17
IV. The Future of the Everglades Agricultural Area ......... 19
V. Acknowledgement ..................................... 20
VI. Literature Cited ...................................... 21


Hurricane-induced flooding has threatened property and hu-
man life in south Florida ever since settlers moved into the area.
Over the years various local projects were undertaken to reduce
this threat. At other times droughts have resulted in uncontrolled
fires, water shortages and salt water intrusion. After torrential
rains left most of south Florida flooded for several months in
1947, the U. S. Congress passed the Flood Control Act of June
30, 1948, authorizing the Army Corps of Engineers to plan, de-
sign and construct a comprehensive project to solve water prob-
lems in all or parts of 18 counties in central and south Florida.
The State of Florida created the Central and Southern Florida
Flood Control District in 1949 to represent State and local in-
terests and to maintain most of the water control works after
construction by the federal engineers.
Protecting human life and property along the lower east
coast was a major consideration in this plan, and the first phase
of the project involved construction of a levee from Lake Okee-
chobee to near Homestead to keep flood water from sweeping
out of the Everglades into populated areas along the east coast
(Figure 1). The project was also designed to provide water con-
trol in the Everglades for soil and water conservation and for
farming. Studies made by the U. S. Department of Agriculture
and the University of Florida showed that only in the upper
Everglades were organic soils of sufficient depth and type to
support agriculture for a sufficient length of time to justify de-
velopment. This region was designated the "Everglades Agri-
cultural Area" (Figure 2). Three water conservation areas were
created on the south and east borders.
The Everglades Agricultural Area comprises only about one-
fourth of the original Everglades. It was recognized at the out-
set that the drained organic soils would subside and that the
region could not support conventional agriculture indefinitely.
Improved water control appeared to provide the means for re-
ducing the loss of this precious resource.

I-A. Soils
The Everglades extends from Lake Okeechobee south to
Florida Bay (Figure 1). The soils are predominantly composed
of organic matter residues from swamp vegetation that once
covered this area. The organic matter layer is 2 to 10 feet deep.
It generally is thickest near the lake and is thinnest near the

0 10 20 30 40Miles

Figure 1.-The Everglades and surrounding areas.

southern edges of the Agricultural Area. There are some very
deep deposits in an old slough that extends 20 miles southeast of
the southeast border of the lake.
Most of the soil is underlain by a very dense and hard rock
formation (Ft. Thompson limestone). Near the southern border
of the Agricultural Area this rock formation grades into another
formation of softer and more porous rock (Miami oolite). Along
the western edge of the Agricultural Area the organic soil is un-
derlain by sand.
McCullom et al. (13) have recently discussed classification
of the soils of the Everglades. The three predominant soil




Figure 2.-Florida Everglades Agricultural Area.

series in the Agricultural Area are identified by their profile
characteristics, i.e., by various physical and chemical properties
observed with depth (summarized in Table 1).
1) Torry series very poorly drained organic soils with
black organic layers more than 51 inches
thick. Portions of this soil are high in
fine-textured, inorganic material. Lime-
stone occurs at depths of 52 to more than
80 inches.
This soil, locally known as custard apple muck, may contain
between 35 and 70%5 mineral matter, most of which is sepiolite

Table 1.-Summary of profile characteristics of organic soils of the Everglades Agricultural Area.

Mineral Content

Thickness of
Organic Layer


Proportion of
Agricultural Area

(%) (inches) (%)

Terra Ceia

Soil Series

> 35
< 35
< 35
< 35
< 35
< 35
< 35

> 51
> 51
< 20
> 51


and montmorillonite clay. It accounts for about 7% of the or-
ganic soil area in the Agricultural Area. It is more highly pro-
ductive than other mucks in Florida and is much less subject to
subsidence. It is found within 2 to 5 miles of the lake. Most
urban development in the upper Everglades has occurred on or
near this soil type.
2) Terra Ceia very poorly drained organic soils with dark
organic layers more than 51 inches thick
over limestone.
3) Pahokee poorly drained organic soils with dark or-
ganic layers from 36 to 51 inches thick
over limestone.
The Terra Ceia and Pahokee soils are similar, differing only
in thickness. They both are comprised of muck (well decom-
posed organic matter) throughout the profile. They contain less
than 35% mineral matter by weight, and average 5 to 15%.
Together they constitute about 82% of the entire Agricultural
Area. Two other soil series closely related to the Terra Ceia and
Pahokee are the Lauderhill with 20 to 36 inches of muck over
limestone rock, and the Dania with 8 to 20 inches of muck over
limestone rock.
The Okeechobee soil (only about 2.6% of the total) has a
surface layer of muck over an underlying horizon of peat (less
well decomposed organic matter) and is at least 51 inches to
rock. The Okeelanta soil has muck over sand. The sand is en-
countered at 16 to 40 inches and may extend to considerable
depths, though rock may be found below 51 inches. Only about
6.2% of the soils in the Agricultural Area are of these two series.
The organic soils are decreasing in thickness, as is discussed
in the next section. Because of this phenomenon, soils now classi-
fied as Terra Ceia will be classified as Pahokee, Lauderhill, and
Dania, in that order, with the passage of time (Figure 3).

1-B. Crop Production
The traditional crops of the Florida Everglades are winter
vegetables, sugarcane, pasture for beef cow-calf operations, and
sod for lawns. In recent years the sugarcane acreage has in-
creased to over 300,000 acres, and sugarcane now is the domi-
nant crop in the area. In 1977-1978 total cash receipts for sugar-
cane were about $215 million, second only to oranges in Florida.
Expansion of sugarcane in recent years has been accomplished
by bringing previously idle land into production, and by con-

- Ceia
x 50-
< Pahokee
2 40-
30- Lauderhill

0o -
tJ< o ^ -- ^ ,u,.- -- El,';!, / ..- ,- ...:- - -

Passage of Time

Figure 3.-Classification of muck soils relative to thickness over
limestone rock. Upon drainage, the thickness and hence the soil type
changes with time.

verting other agricultural lands to sugarcane. Vegetable acreage
has been least affected by sugarcane expansion, and winter
vegetables remain an important crop in the Everglades. During
the 1977-1978 season about 60,000 acres of vegetables valued at
$103 million were grown in the organic soil portion of Palm
Beach County (in which most of the Agricultural Area is lo-
cated). Pasture acreage has declined but still amounts to 50
thousand acres.
Land holdings are usually large. Farming is intensive and
requires machinery specially designed to suit the soil and pro-
duction conditions of the area. The labor force and activity in-
creases significantly in the winter when sugarcane is harvested
and processed in the mills and vegetables are grown for the
northern U. S. markets.

I-C. Water Management
The South Florida Water Management District (WMD)'
maintains a network of canals that permeate the Agricultural
Area (Figure 2). A major function of the WMD is to establish a
permit system for water use from surface and groundwater in

'Formerly Central and Southern Florida Flood Control District.

the area. Thus, the District must be in a position to intelligently
evaluate applications for water use permits, whether they be
municipal, industrial, or agricultural. Upon receipt of proper per-
mits, growers may withdraw water from these canals for irriga-
tion and release drainage water into them. The WMD is respon-
sible for controlling the water level in their canals and for their
maintenance. Agricultural needs are only one of several consid-
erations that determine this level. Individual growers must de-
sign, construct and maintain the canal and ditch network and
pumping facilities on their own property.
This system of private and public water control facilities
provides storage of water in Lake Okeechobee and the conser-
vation areas during periods of excess rainfall, usually June
through October (16). However, at times excess water may be
released into the ocean by way of the canal systems. During the
winter dry season, Lake Okeechobee serves as the primary
source of irrigation water, which is moved through the same
canal system used for drainage. Most growers have the facilities
for fairly precise water control. Almost all irrigation is by seep-
age from field ditches, i.e., by regulation of the water table
within fields at a sufficiently high level to provide adequate but
not excessive moisture in the root zone.

Subsidence refers to a lowering of soil elevation. Evidence of
subsidence abounds in the Everglades Agricultural Area. Build-
ings once constructed at ground level upon pilings resting on
the underlying bedrock stand well above the soil surface within
a few years, unless receding soil is replenished periodically
(Figure 4). Sidewalks and driveways built on the soil surface
without pilings soon fall well below the intended elevation rela-
tive to the adjacent buildings (Figure 5). Subsidence posts and
other benchmarks placed throughout the agricultural area have
made it possible to continually document subsidence over the
years (Figure 6). The subsidence rate has averaged about 1 inch
per year (17, 18, 21). The fact that subsidence has occurred in
the past, is occurring today, and will continue in the future
throughout the entire Everglades Agricultural Area as long as
present conditions persist, cannot be denied or ignored by any-
one who has spent time in this region or who is concerned about
its future.
Subsidence of the organic soils of this region occurs as a re-
sult of a number of processes which have been discussed in de-

Figure 4.-Top: Buildings are constructed on pilings resting on
bedrock. As the soil subsides, the buildings stand well above the soil
surface. Bottom: To maintain grade, soil must be added periodically
to yards.


Figure 5.-Top: The house, steps, and sidewalks were constructed
on pilings but the subsiding soil was not replaced. Bottom: the house
and steps were constructed on pilings, but the sidewalk was built di-
rectly on the soil. With time the sidewalk falls below the steps.


Figure 6.-In 1924 this 9-foot concrete post was driven to bedrock
at the present location of the University of Florida Agricultural Re-
search and Education Center in Belle Glade. This picture, taken in
1977, shows that about 58 inches of soil subsidence has occurred at
this location in the past 54 years.

tail elsewhere (19). Major causes are shrinkage, compaction,
and oxidation. Shrinkage and compaction mainly occur soon
after the soil is drained and do not involve a loss of soil material.
Oxidation refers to microbial decomposition of the soil material,
ultimately converting it to carbon dioxide and water. This pro-
cess continues as long as the soil is drained, and will eventually


result in total destruction of all or most of the organic matter.
Most of the organic soil in the Everglades Agricultural Area is
underlain by a very hard and dense rock formation which is
probably not suitable for agriculture. The Terra Ceia, Pahokee,
Lauderhill, and Pania soils, which comprise about 87% of the
total organic soil acreage, contain 85 to 90% organic material
by weight, or more than 97% by volume. Thus, when the or-
ganic matter in a soil deposit as deep as 10 feet is destroyed by
biological oxidation, only about 3 to 4 inches of mineral matter
will remain over bedrock. Clearly, this is insufficient soil to sup-
port productive cultivation of crops now grown in this region.
Some have suggested that increased incorporation of crop
residues could offset subsidence. Few crops, if any, produce more
top growth annually than sugarcane. An average cane crop (30
tons/acre) contains about 8 tons of dry matter. If the entire
crop were incorporated into the soil, and about 50% were
rapidly lost during decomposition, about 4 tons of organic matter
would be returned to the soil. Since 1 acre-inch of dry organic
soil (top-soil) weighs about 50 tons, only about one-twelfth as
much organic matter as was lost during the year could be added
to the soil. Of course, only a relatively small portion of the cane
crop is actually returned to the soil. Total root growth during
the year is probably less than that of top growth, since root/
shoot ratios are usually low under nitrogen-rich conditions such
as occur in this region. So it appears that conventional crop
residues cannot be counted upon to "build" an organic soil, or
even to materially decrease its rate of loss.
Conservation of organic soil is very important. Assuming
present average rates of subsidence, projections (19) show that
by the year 2000, only 13%' of the soil in the Everglades Agricul-
tural Area will be greater than 3 feet deep, and 45% of the
total will be less than 1 foot deep. Individual landowners can
alter these averages and extend the life of their soil through
strict adherence to sound conservation practices, or they can
decrease the life of their soil through neglect.

IIf-A. Effect on Subsidence
The organic and mineral particles of a soil are arranged in
such a way that voids or pores of various sizes and shapes exist
among them. These voids are filled with either water or air. As
water enters a pore, it displaces the air; and when it drains
from a pore, or is taken up by a plant, it is replaced by air.

In organic soils there is free exchange of air between the soil
and the atmosphere. Sufficient oxygen is present throughout the
aerated portion of the soil profile to allow microorganisms to
actively decompose the organic soil. Microorganisms that oxidize
soil organic matter and cause the most serious form of subsi-
dence in the Everglades require oxygen from the soil air. How-
ever, the soil profile below the water table contains essentially
no air or dissolved oxygen, so the microorganisms are unable to
function, and the soil is protected from this type of subsidence.
Except for narrow transition zones near the water table and at
times at the soil surface, the soil profile is subject to one of two
conditions: (a) it is below the water table and is therefore pro-
tected from oxidation, or (b) it is above the water table and is
therefore subject to oxidation. Soil below the water table can be
thought of as soil "in the water bank". It is held for later use.
Soil above the water table is always oxidizing. From a soil con-
servation standpoint, the portion of the profile above the water
table should be kept to a minimum.
The relationship between water table and the rate of subsi-
dence in the Everglades Agricultural Area has been scientifically
documented (10, 21). Studies conducted on a soil typical of the
Agricultural Area have shown that water tables of 1, 2, and 3
feet resulted in subsidence rates of 0.65, 1.4, and 2.3 inches per
year, respectively. Thus if the depth of soil above water table
is doubled, the rate of subsidence is doubled, and the life of the
soil is cut in half. These studies were conducted under three
types of agriculture: sugarcane, vegetables, and pasture. It was
concluded that for a given water table, there was no difference
in the rate of subsidence among the three crops. However, a re-
cent re-examination of this and other data indicated that for a
given water table, the annual subsidence rate in sugarcane is
about 30% less than in fields of pasture or truck crops (17).
Nevertheless, oxidation occurs regardless of the crop use, and
even occurs when no crop is grown. The implication is clear.
For best conservation, organic soils should be kept flooded when-
ever not in use. When soils are used, the water table should be
maintained as high as is possible for that use.

III-B. Effect on Crop Production
Experience in crop production in the Everglades Agricultural
Area has shown that an excessively low water table is far less
damaging to the crop, except in cases of severe drought, than one
excessively high. Growers frequently maintain water tables lower

than that which could be used because they want to allow a
margin of safety in case of excessive rains. During rainy peri-
iods, at or near harvest, and between crops, some growers cease
to maintain the water table. Field ditches may be empty or the
water level may be below the rock surface when ditches have
been dug into the rock. While these practices may not hurt crop
production, they do expose more of the soil profile to biological
oxidation, thereby shortening the life of the soil. Any grower
concerned with future agricultural production on organic soils
must balance his immediate concern for crop production with
the necessity for maintaining water tables as high as possible
to extend the life of the soil. The optimum water table, and the
extent to which excessively high water tables affect production,
vary with the crop.


Vegetables representing many different families of plants
with varying growth habits and differing fertility and water
table requirements are grown in the Everglades. A number of
studies in the U.S. and England have been conducted to deter-
mine the response of various vegetables to water table in or-
ganic soils (2, 3, 4, 5, 6, 7, 9, 11, 14, 15, 23). Because of the diffi-
culty of maintaining differing water tables on adjacent small
plots, some of these studies did not utilize the randomization
and replication techniques that are necessary for drawing statis-
tically verifiable conclusions. Therefore, the data must be eval-
uated with care and caution. The studies conducted in the Ever-
glades, however, were replicated. In spite of the limitations in
some of these experiments, for many crops the data generally
agree as to a range of water tables over which high yields of
quality produce can be obtained. Table 2 presents the minimum
depth to water table found in these studies for maximum yield
and quality of a number of vegetable crops. A 24-inch water
table was found to result in high yields of most crops. Several
studies indicated that somewhat shallower water tables could be
used for some crops, such as celery, whereas others (sweet corn,
lettuce) appeared to require a lower water table. For lettuce the
main effect of lower water table may be reduction of certain
disease problems (23).
During extended dry periods somewhat higher water tables
than those in Table 2 may be beneficial. Also, higher water
tables were found to reduce frost incidence and damage in sev-
eral studies. As rains start, water tables probably cannot be

Table 2.-Minimum depth to water table found for maximum yields
and quality of several vegetable crops grown on organic soils.
Everglades Indiana3 England4 Minn.5
Crop (2,3,4,5,6)"(9,23) (7,11) (14) (15)
Beans, snap 18"-24" 18"
Beets (red) 27" -
Cabbage 18"-24" 26" 24"
Carrots 26" 24"
Cauliflower 24" 12"
Celery 18" 26" 18"-22" 18"
Corn, sweet 24"-30" 30" 24"
Kale 24" or more -
Lettuce 30"-36" 30"
Onions 18"-24" 30" 36"
Peas 18"-24" -
Potatoes 18"-24" 26" 16"-20" 24"
Spinach 26" --
Tomatoes 18"-24" 24"
Escarole 24"-30"'
Endive 24"-30"1
Radishes 14"-16"1 18"
Parsley 14"-16"1
1No data have been found on these crops, and depths given are estimates
under average Everglades conditions.
'Eight water table treatments: 30" with overhead spray, 12", 21", 30", 39",
48", fluctuating, 48" with overhead spray (the experiment was replicated).
3Three water table levels, two replications. 16", 27", 38".
4Water tables ranged from 10" to 38" (unreplicated).
5Five water table depth treatments: 12", 24", 36", 48", 60" (unreplicated).

safely maintained appreciably higher than those given in Table
Bedding, originally started to produce disease-free leafy
plants, has been found to greatly increase plant uniformity and
reduce the proportion of cull plants. Although there are no data
to support it, bedding may offer a means of reducing subsidence
by making it possible to place more soil in the "water bank",
assuming that the water table is raised so as to maintain the
desired level as measured from the bed top, rather than from
the former soil surface (Figure 7).

Water tables deeper than 24 inches below the soil surface are
usually maintained for sugarcane in the Everglades, although
they vary with the grower and location. In some locations
growers have been faced with a comparatively raw, fibrous peat
soil which holds excessive water against normal drainage prac-

tices. In these locations lowering water tables to 30 to 36 inches
greatly improved sugarcane growth and quality. However,
limited research on well-decomposed muck soils suggests that at
least some varieties can be satisfactorily grown at water tables
substantially higher than those currently being used.
In a 7-year study conducted at the AREC-Belle Glade
(formerly Everglades Experiment Station), a water table of
approximately 30 inches resulted in the best sugar tonnage per
acre for four varieties, but production was only reduced by 5%
with a 15-inch water table. The best yield for one variety,
F31-962 was at 15 inches (12, 17). In a recent study conducted
by the U.S. Sugar Corporation, no significant differences in the
quantity of sugar/acre were found over a 4-year period for the
two varieties tested (C1 54-378 and Cl 54-336) when grown at
20- and 36-inch water tables (1). However, soil subsidence at
the 20-inch water table was less than half that measured in the
36-inch water table fields. Thus it appears that some varieties
of sugarcane can produce good yields at water tables of 18 to
24 inches. Such production will require precise water table man-
agement, i.e., level land, adequate ditching and pumping, and
careful monitoring. Water tables will have to be lowered tem-
porarily during harvest to accommodate the heavy equipment used
for harvest operations.

Pasture and Sod
Water tables that would be considered high for most crops
are now used or can be used in cattle and sod production. In St.
Augustinegrass pastures, a 12-inch water table, considered high
by today's standards, might be acceptable. During the rainy sea-
son, water tables of 6 inches or less sometimes occur for several
weeks at a time. However, shallow water tables appear to reduce
St. Augustinegrass production by about 20%.
A few pasture grasses will grow at water tables higher than
are acceptable for St. Augustinegrass; e.g., paragrass will toler-
ate standing water. With very high water tables, the physical
damage inflicted upon the sod by grazing cattle would probably
be a serious problem. This would be especially true in areas
where the cattle concentrate, such as around water troughs. It
has been observed that mowing with large rotary mowers for
weed control during summer months inflicts more damage on
grass when the water table is extremely high. These types of
physical damage might be alleviated by rotational grazing (or
mowing), with a somewhat lower water table during the time

NON BEDDED New Soil Surface
Soil Surface Surface

Soil Exposed to Oxidation
Water Table

Additional soil protected from oxidation

Soil Protected from Oxidation
Soil Protected from Oxidation

Figure 7.-Influence of bedding which would allow a higher water table to reduce oxidation of organic soils.

cattle are grazing (or when a field is mowed). For acceptable
grass quality, a field probably should be grazed at least 2 weeks
out of each 6 to 8 week period, depending on the grass species.
High water tables might cause other problems. Where there
is standing water, sun scalding of the grass sometimes occurs.
More pumping may be required during the dry season to main-
tain the water table, and water removal during the wet season
may be more critical, since the high water table would not allow
room within the soil profile to accept rain water. It may be nec-
essary to use some nitrogen during very cool or cool-wet periods,
since nitrogen mineralization will be reduced. However, nitrogen
cannot be used too liberally, or nitrate toxicity problems can
arise with some forage species (particularly annual grasses).
St. Augustinegrass, once it is established, will grow well at
water tables of 2 to 3 feet, and at these depths there is reduced
threat of many of the previously mentioned problems. However,
with this water table subsidence will be quite high. With pasture,
subsidence can be minimized to a greater degree than with al-
most any other crop now grown in the Everglades, and produc-
tion can be sustained far into the future. Such sustained pro-
duction can only come about if conscientious, concerned cattle-
men make every effort to maintain water tables at depths of 12
inches or higher.

Ill-C. Measuring and Maintaining Water Tables

Rainfall in the Everglades area fluctuates significantly in wet
and dry seasons of the year and ranges between 34 and 85
inches annually. Seventy-five percent of the yearly total gen-
erally falls between May and October. Thus, provision must be
made for both irrigation and drainage (16).
Irrigation and drainage should be controlled so as to main-
tain a desired minimum depth to water table. Water table meas-
urement, the first step needed to control the water table, can be
gauged in several ways:
1. Stage posts within field ditches are commonly used in the
Everglades to roughly gauge the water table within the ad-
joining fields. This estimate will be in serious error during times
of rapid water movement, such as after rainfalls, or after sig-
nificant changes in the field canal levels.
2. A temporary hole (about 6" diameter) can be dug suffi-
ciently deep so that a measurement can be taken of the depth
to free water.

3. Permanent observation wells can be located within fields
centrally between ditches for making manual observations and
4. Recording devices are available for making continuous
measurements of water levels within field wells.2
Water table management requires consideration of both
topographic features and soil characteristics. Since surface ele-
vation varies only slightly in the Everglades, there is little sur-
face runoff. Water movement through the soil is rather slow
because of low hydraulic conductivity and small elevation dif-
ference. Hydraulic conductivity decreases as a result of tillage
operations, which tend to destroy the natural fibrous soil struc-
ture. Also, in some locations the relative content of mineral
matter increases sufficiently as the organic material is lost by
subsidence, and non-capillary pore space is decreased. A period
of flooded fallow, or flooded cover crop, may prove useful for
increasing water movement within the soil.
A system of large farm canals, lateral canals, and field
ditches is required for water table maintenance. Fields are gen-
erally 660 x 2640 ft, bordered by either a lateral canal or a field
ditch. Laterals are about 6 ft wide and field ditches 3 ft wide.
Water table levels are adjusted by pumping into farm canals for
irrigation and out of the farm canals for drainage. Water moves
laterally through the soil from the ditches into the fields during
irrigation and laterally from the field into the ditches during
drainage. Also, water moves up and down through the porous
rock. During periods of heavy rainfall, there is some surface
runoff into the field ditches.
Lateral movement of water during irrigation and drainage is
often aided by mole drains spaced 5 to 20 feet apart. Ten-foot
spacing is commonly used. Mole drains are formed by pulling a
6-inch diameter, bullet-shaped instrument through the muck soil
at a depth of 30 to 46 inches. These drains empty into the
lateral field ditches. At least 30 inches of soil are needed above
the mole drain to prevent it from collapsing under the weight
of the farm machinery used in the fields (8). Thus mole drains
may no longer be feasible in the year 2000 because of the shallow
soil. A new field ditch spacing system 330 feet apart has been
initiated in some fields with shallow muck for maintaining a
high water table. If the water table is maintained higher than

2Examples: Weather Measure Corp., Box 41257, Sacramento, Calif.
95841; Stevens, Inc., Box 688, Beaverton, Oregon

present, field-ditch spacing could be reduced to 165 feet apart to
provide more responsive water control.
The capacity, power requirements, and efficiency of pumps
vary widely -with their speed, lift, and design. Most farm pumps
in the Everglades are types commonly used for low head, high
volume water control, i.e., modified-centrifugal, propeller, and
helical pumps (20). Many of the pumps now used in this area
are axial flow propeller pumps, manufactured locally.
Due to the effect of subsidence, the pump head for drainage
water will be significantly increased, because the current aver-
age elevation of the main drainage canal will be maintained by
South Florida Water Management District. Thus, the elevation
between canal and field surface will increase. The seepage of
canal water to fields will be also increased, and the desired water
table level will be more difficult to control. The pumpage require-
ment also increases when the water table is maintained at a
higher level. A smaller unsaturated zone of soil for absorbing
rainfall exists and more runoff will be generated from the field
during heavy rainfall periods. Therefore, both the volume and
the lift head of farm pumps will be increased due to the effect
of subsidence and maintenance of a high water table.

Predictions of future social, political, and economic conditions
are always made with great reservation and a recognition that
many unforeseen technological advances can radically change
man's environment, capabilities, and expectations. Natural phe-
nomena, however, are much easier to predict since they are
often governed by comprehendable forces. Tides, planet move-
ments, comet reappearances, and the consequences of many bio-
logical phenomena can be predicted with great confidence and
accuracy. Soil organic matter decomposition, being a biological
phenomena, is highly predictable for a given set of conditions.
In 1951, Stephens (19) made estimates of soil depth through-
out the Everglades Agricultural Area through the year 2000.
His predictions, shown by decades in Table 3, appear to be on
target (22).
Subsidence, of course, will not stop in the year 2000 but will
continue as long as organic soil remains and the soil is not
Stephens' predictions assume an organic soil of low mineral
content and a substance rate of 1 foot per 10 years. The Torry
muck soils, which have a very high mineral content, will subside
at a much slower rate. and will be productive for more years.

Table 3.-Measured or predicted percentage of total organic soils of
various depths.
Year 0 to 1 ft 1 to 3 ft 3 to 5 ft over 5 ft
1912 0 1 3 95
1925 1 3 8 89
1940 1 7 7 85
1950 2 7 14 78
1960 4 12 28 55
1970 11 16 28 45
1980 17 28 41 14
1990 27 28 39 7
2000 45 42 9 4

But they occupy 7% or less of the total acreage. The subsidence
rate of 1 foot per 10 years corresponds to an average 20-inch
water table for soils typical of most of the Agricultural Area.
Those who maintain higher than average water tables can expect
lower than average subsidence rate and longer soil life. With
lower water tables, the subsidence will, of course, be accelerated.
The long term outlook is clear. By the year 2000 there will
be only about 80,000 acres of soil 3 feet or deeper, i.e., typical of
the soil depths to which growers have adapted their crop man-
agement systems. It is likely that sugarcane acreage on organic
soils will decline. Pasture acreage will probably increase signifi-
cantly, if cow-calf operations are profitable. Vegetable acreage
will remain almost unchanged if economically feasible.
By the year 2000, there probably will be over 500,000 acres
of organic soil 3 feet or less in thickness, and half of this will
be less than a foot in depth. The agricultural fate of this soil is
uncertain. Some may be suitable for pasture. Perhaps it will
simply be abandoned for agricultural purposes. Or perhaps the
remaining soil, in combination with the area's ability to control
large quantities of water, can be used for the production of
aquatic and semi-acquatic crops. Such a usage could extend the
agricultural productivity of this area far into the future.


Special thanks are expressed to other faculty members of
the Agricultural Research and Education Center at Belle Glade
for their assistance and helpful suggestions which enhanced the
value of this publication.
We also recognize the officials and technologists who had a
responsible part in planning and conducting the investigations,

analyzing the data, and formulating the conclusions presented
in "Soils, Geology, and Water Control in the Everglades Region",
Bulletin No. 442, University of Florida, Agricultural Extension
Station, in cooperation with United States Department of Agri-
culture and Soil Conservation Service. Help given by Mr. S. H.
McCollum on the classification of the organic soils of the Ever-
glades is gratefully acknowledged.


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