PRODUCTION OF HIGH-VALUE CASH CROPS
ON MIXTURES OF SAND TAILINGS AND
WASTE PHOSPHATIC CLAYS
Final Report
FIPR Project #86-03-075
December 20, 1986 to February 20, 1989
Prepared for:
FLORIDA INSTITUTE OF PHOSPHATE RESEARCH
Bartow, Florida
Prepared by:
BROMWELL & CARRIER, INC.
Lakeland, Florida
April, 1989
DISCLAIMER
The contents of this report are reproduced herein as received
from the contractor.
The opinions, findings and conclusions expressed herein are not
necessarily those of the Florida Institute of Phosphate Research
nor does mention of company names or products constitute endorsement by the Florida Institute of Phosphate Research.
ii
ACKNOWLEDGEMENTS
We gratefully acknowledge the continuing support of the
Florida Institute of Phosphate Research which has taken on the
task of addressing agricultural reclamation problems for the
industry. Also, we thank CF Industries of Hardee County and its
reclamation engineer, Mr. Jim Sampson, for permission to utilize
their land for our field studies. Their pioneer use of sand/clay
mix technology is a credit to the industry.
The following persons and organizations have been involved
in this study:
Bromwell & Carrier, Inc.
W.D. Carrier, III
Principal Investigator
J.B. Million
Co-project Manager
University of Florida
(Department of Environmental Engineering Sciences)
R.X. Gonzalez
Graduate Research Assistant
Consultants
J.B. Sartain
W.L. Miller
Prof. Soil Science Dept.
University of Florida
Prof. Environmental Engineering Science
University of Florida
Other persons who have contributed include: Al Adams and
Mike Grzelka, field work: Donny Waters and Pat Carlton, land
preparation; Harris Martin and Amir Varshovi, chemical analyses;
Cathy Manuel, report preparation: Dr. Emmett Bolch and Dave
Demorest, Ra226 analyses; Ken Pollard of Ft. Meade Sewage
Treatment Plant, Bill Farrell of Broward County Street and
Highways Division, Hugh Ettinger of Bioconversion Corp., and
Denny Reese of Union Camp Corp. for organic materials.
iii
EXECUTIVE SUMMARY
Mandatory reclamation has placed increased pressure on the
phosphate mining industry to utilize mined lands for agriculture.
Due to the unique physical and chemical properties of phosphatic
clays, farming pure clay settling areas has been limited
primarily to pasture systems. Recent research efforts have been
orientated towards devising new, sometimes unconventional
technologies, which will allow production of more diverse
agricultural commodities including vegetables, row crops,
turfgrass, and high-value forages.
Sand/clay mix technology, whereby sand tailings are mixed
with thickened clays prior to deposition into settling areas, is
an alternative disposal technology which has been successfully
adopted by CF Industries in Hardee County. The research
presented herein describes an attempt to evaluate the effect of
adding sand to phosphatic clay on the production and quality of
vegetables and high-quality forages.
The research was divided into three different phases. The
sand:clay ratio (SCR) phase evaluated the production and quality
of vegetables grown in varying SCR. The SP-1 alfalfa phase was
conducted to evaluate the production and quality of alfalfa grown
on sand/clay mix amended with several different organic
materials. A third phase was conducted to investigate the
capacity of phosphatic clay to reduce Cd uptake by plants grown
in sludge-amended soils.
For the SCR experimental phase, three seasons of vegetable
production research were conducted on four different sand/clay
mixes with sand:clay ratios (SCR) of 2, 4, 6, and 8. Vegetables
grown included turnip, cabbage, banana pepper, yellow squash and
mustard. Peat and phosphogypsum were evaluated as soil
amendments; peat to "lighten" the soil and provide a source of
organic matter, and phosphogypsum to increase soil Ca and thereby
competitively inhibit plant uptake of 226Ra. In addition to
yield, soil and plant nutrient levels were monitored as well as
Cd and Ra226 contaminants.
We found that yields were often l0-30% higher in the SCR = 2
mix than in the higher SCR mixes. However, from a production
perspective, yield increases in the SCR = 2 mix were offset by
the considerable increase in difficulty required to carry out
conventional farming operations in this mix versus the SCR = 4
and higher sand/clay mixes. Soil chemical properties remained
dominated by the phosphatic clay component so that variations in
226
soil and plant nutrient (also Cd and
Ra) levels due to varying
SCR were minor and not agronomically significant. Boron and Mn
deficiencies were identified for several crops for all SCR.
Peat had little effect on production and quality (including
226
Ra) of vegetables. Phosphogypsum had no effect on vegetable
yield, quality, and 226Ra concentration at both the 22 Mg/ha rate
(10 ton/acre) and the very high application rate of 134 Mg/ha (60
ton/acre).
Plant uptake of 226Ra was more affected by vegetable tissues
than by soil parameters and soil amendments. Results of over 600
226
Ra analyses revealed that tissue 226Ra was positively
correlated with tissue Ca. Maximum ratios between 226Ra and Ca
in tissues indicated that 226Ra did not excessively accumulate in
vegetable tissues due to indiscriminate uptake.
Alfalfa was grown on CF Industries' sand/clay mix
reclamation area, SP-1, to evaluate alfalfa yield and quality as
affected by several organic amendments. The organic materials
'investigated included sawdust, humate, composted garbage, peat,
sewage sludge, and composted sewage sludge. Due to the
sensitivity of alfalfa to waterlogged soil conditions, these
materials were added at two rates, 22 and 45 Mg/ha (10 and 20
ton/acre) in order to lower soil bulk density and improve
internal surface drainage.
Alfalfa yields were increased by the application of sewage
sludge but not sawdust, humate, peat, sludge compost and garbage
compost.
Annual dry-weight yields (7 cuttings) were 11.0 and
13.6 Mg/ha (4.9 and 6.1 ton/acre) for control and sludge-amended
plots, respectively. The benefit of sewage sludge additions
appeared to be due to micronutrient contributions, especially Mn.
vi
Organic materials had little effect on alfalfa nutrient
226
composition,
Ra conc., and in-vitro-organic-matterdigestibility.
At the University of Florida, glasshouse experiments were
conducted in which sand tailings and 4:l sand:clay mix were
amended with several different waste organic materials in order
to determine the influence of phosphatic clay on the growth and
Cd uptake by legume forages. Materials evaluated included
sawdust, peat, raw shredded garbage, garbage compost, and a highCd sewage sludge.
Dry-matter yields of Alyce clover and alfalfa were greater
in sand than in sand/clay mix and, with the exception of high
sludge rates which decreased or killed plants, were generally
unaffected by organic amendments. Increasing application rates
of high-Cd sludge to sand and sand/clay mix resulted in
increasing extractable Cd levels in both soils. However,
increases in extractable soil Cd for a particular application
rate of the high-Cd sludge were greater for sand than for
sand/clay mix.
vii
xii
xiv
1.0
INTRODUCTION
Eighty percent of U.S. phosphate ore production occurs in
Florida. The phosphate ore mining process involves the removal
of a matrix material which typically contains equal proportions
of sand, clay and phosphate rock pebbles. During the
benefication process, sand and clay are separated from the
phosphate pebbles and returned to the mined-out site. Because of
the large quantities of water used in the beneficiating process
and the physical properties of the clay, the clay-water fraction,
often called slimes, occupies a larger volume than the void from
which the matrix was originally removed. Therefore, large
impoundments typically covering 70% of the mined area are
constructed to retain these semi-solid slimes. Due to the
hydrophilic nature of the phosphatic clays, water is released
very slowly from the slimes. Many years of consolidation are
often required before the slime ponds can support traffic. After
40 years some slime ponds are no more than 35% solids.
Mandatory reclamation has placed increased pressure on the
phosphate industry to utilize mined lands for agriculture.
Florida produces a large share of the nation's vegetables. At
present, most of the vegetables are produced on the organic soils
south of Lake Okeechobee. These organic soils are subsiding at
the rate of approximately one inch per year due to oxidation so
that in the near future these organic soils, as we know them
today, will not exist. Furthermore, many of these areas in South
Florida are being converted to non-agricultural uses. Vegetable
production will have to shift to other areas of the state such as
Polk, Hillsborough, Manatee and Hardee counties which already
produce large quantities of vegetables on sandy soils. Vegetable
production could be expanded in these counties where a strong
market system already exists.
Numerous problems have been encountered in trying to utilize
slime ponds for agricultural production. These problems center
around the unique physical characteristics of the extremely
1
Poor water drainage and limited ability to
plastic clays.
conduct mechanized farm operations pose major constraints to
production of high-value, high-maintenance crops. A cooperative
effort between the Florida Institute of Phosphate Research, Polk
County, and the University of Florida is currently investigating
methodologies for production of a wide range of agricultural
commodities on phosphatic slime ponds. Their initial experience
has revealed that conventional tillage and crop management
practices will have to be modified to utilize successfully waste
phosphatic clay for anything other than pastureland.
A successful alternative for phosphatic clay disposal is
sand-clay mix technology whereby dewatered sand tailings are
mixed with thickened clays (15-18% solids) prior to deposition
Besides enhancing clay consolidation and
into impoundments.
dewatering rates and tying up less storage volume, sand-clay
mixes are compromises between the plastic but fertile clays and
the less fertile but well-drained sands for agricultural
reclamation. The use of sand-clay mix technology for disposal of
phosphate mining by-products has been successfully adopted by CF
Industries, Inc. of Hardee County. Using the dredge-mix system,
CF Ind. currently deposits a 2:1 sand:clay ratio (SCR) mix. The
first sand-clay mix disposal area, SP-1, underwent reclamation
(reforestation and pasture) within 4 yr from the last sand-clay
discharge in September 1983.
Beneficiation plants generally produce sand and clay byTechnological
products in ratios ranging from 1:l to 3:l.
capabilities currently exist to pump mixtures with SCR up to 4:l
However, if proven economically and
with well-thickened clays.
agronomically advantageous, shallow surface mixtures or caps with
SCR greater than 4:l might be achieved by mechanical mixing of
additional sand tailings. By evaluating the effect of increasing
SCR on crop productivity and land reclamation potential, one
could more confidently make sound decisions relative to the safe
use of various SCR mixes in agricultural reclamation schemes.
2
Although addition of sand tailings improves the physical
properties of phosphatic clays, the extremely plastic nature of
the clays is such that sand/clay mixes remain sensitive to soil
In order to improve the tilth of sand/clay mixes, the
moisture.
Organic matter
addition of organic materials may be important.
binds to clay particle edges and forms stable complexes which
result in separation of individual clay particles. The formation
of organo-clay complexes can result in lower soil bulk density
and greater soil porosity necessary for better drainage and
Since phosphatic clays and sand tailings have
improved tilth.
naturally low organic-matter contents, addition of organic
materials should be a quick method for improving soil structure.
Various organic materials are available for use in landreclamation projects. Peat is a standard material widely used in
experiments involving organic materials because it is relatively
uniform, decomposes relatively slowly, has a moderate N content,
and contains low levels of contaminating metals that might
otherwise confound the effects of certain waste organic
Sawdust is a bulking agent which is relatively
materials.
resistant to microbial decomposition.
Sawdust, however, lacks
properties that are
the chemically active colloidal
characteristic of peat and other materials.
Sawdust should,
therefore, give some indication of the importance of the charge
and surface area characteristics of other materials.
Municipal waste products are potential sources of organic
Land application of sewage sludges has gained
material.
widespread popularity in agricultural and reclamation projects.
The usefulness of sewage sludge as a source of organic matter may
be limited by land-application guidelines established by the
Department of Environmental Regulation.
Maximum application
rates which are based on N content may be too low to have a major
effect on soil organic matter levels.
Composted sewage sludge,
composted garbage, and composted sludge-garbage mixtures are
organic materials which may improve the productivity of
sand/clay mixes.
These municipal waste products are becoming
3
increasingly available as landfill costs have pressured many
Twentycommunities to reduce the volume stream to landfills.
three cornposting facilities are operational, under construction,
or are being planned in Florida itself (Goldstein, 1987).
Important benefits of composted materials include relatively high
solids content and less stringent land application rules and
regulations.
Health-safety concerns have been voiced relative to the
Radionuclides,
quality of crops grown in sand/clay mixes.
including Ra226, which is present in both the phosphatic clay
Initial
and tailings sand, are important health concerns.
studies have shown increased levels of tissue Ra226 in leafy
vegetables and certain root crops grown on reclaimed phosphate
The effect of increasing SCR on Ra226 uptake by
mined land.
vegetables needs to be studied.
Another health concern is enhanced heavy metal uptake by
plants grown on phosphatic clay soils. Relatively high levels of
many heavy metals not commonly found in natural surface soils are
associated with the apatite fraction of phosphatic clays and sand
tailings. Fortunately, sand/clay mixes are highly buffered at pH
High soil pH depresses the dissolution/
values higher than 7.
solubility of most contaminating metals in the soil thereby
Nonetheless,
limiting potentially high rates of plant uptake.
levels of selected metals such as Cd and how these levels are
affected by increasing SCR, need to be monitored in plants grown
on sand/clay mixes.
Soil amendments may have an effect on the uptake of metals
Peat and
and radionuclides by plants grown in sand/clay mixes.
other organic materials have many reactive sites which can
complex certain contaminating metals. Therefore, the application
of organic materials may decrease plant uptake of potentially
harmful heavy metals. On the other hand, certain waste products
The
are additional sources of heavy metal contamination.
chemical activity of the clays and the high pH of the sand/clay
mixes may render these metal contaminates unavailable to plants.
4
If this proves to be the case, sand/clay mixes may become a
viable site for safe utilization of sewage sludge-based
materials.
Phosphogypsum, a calcium sulfate by-product of phosphate
fertilizer manufacturing, may improve the productivity of
sand/clay mixes and decrease Ra226 uptake. Researchers have
The
suggested that Ca2+ inhibits Ra2262+ uptake by plants.
addition of Ca in the form of phosphogypsum may decrease plant
Potentially negative effects from
concentrations of Ra226.
phosphogypsum addition must also be investigated due to its Ra226
content (similar to phosphatic clay) and its acidifying effect on
The acidifying effect of unreacted acid in
the soil.
phosphogypsum may increase the solubility of micronutrients,
These important unknowns relative to
heavy metals and Ra226.
phosphogypsum and its effect on sand/clay mixes were
investigated.
5
2.0 LITERATURE REVIEW
2.1 Physical and Chemical Properties of Phosphatic Clays and
Sand/Clay
Mixtures
The use of waste phosphatic clays and/or mixtures of
phosphatic clays and sand tailings as media for growing crops
presents special problems due to the unique physical and
chemical properties of the waste clay fraction. Much information
and mechanicalregarding chemical composition, mineralogy,
physical properties of waste phosphatic clays and tailings sand
has been reported (Garlanger, 1982; Barwood, 1982; Bromwell,
1982). The nature of these characterizations is largely oriented
towards understanding clay consolidation (dewatering) principles
necessary to develop disposal schemes and towards elemental
Unfortunately, their use for predicting the
resource recovery.
capacity of these media to support plant growth is limited. For
example, a typical chemical analysis is a total elemental
analysis which gives limited information relative to plant
Some important characteristics of
nutrient availability.
phosphatic clays and sand/clay mixtures follows.
2.1.1
Mineralogy
Both physical and chemical properties of phosphatic clay are
The dominant clay minerals in
governed by their mineralogy.
phosphatic clay are smectites and apatites with minor components
of attapulgite, mica, kaolinite, wavellite, crandallite, quartz,
dolomite, and K-feldspar (Barwood, 1982). The smectite clays are
dominant in the <0.0002 mm fraction while apatite minerals are
primarily found in the coarser clay (0.0002-0.002 mm) and silt
(0.002-0.05 mm) fractions (Hawkins, 1973).
2.1.2
Physical
properties
The particle-size distribution (hydrometer) in phosphatic
clays and sand/clay mixtures formulated from clay slimes and sand
tailings obtained from CF Industries, Hardee Co., is provided in
6
The classification is based upon the U.S.D.A. system
Fig. 2.1.
according to which the clay fraction is less than 0.002 mm, silt
between 0.002 and 0.05 mm, and sand between 0.05 and 2.0 mm.
Several observations are noteworthy. Phosphatic clay consists of
Sand tailings consist of 99%
slightly greater than 25% silt.
sand. The addition of two, four, and six parts of sand tailings
to phosphatic clay changed the textural class from a clay to a
sandy clay loam, sandy loam, and loamy sand, respectively.
Most investigations of the physical properties of
phosphatic clays include mechanical properties which aid in the
Atterberg limits for
designing and planning of settling ponds.
phosphatic clays typically range from 75-240 (Barwood, 1982) and
The high plasticity
are among the most plastic found on earth.
values are indicative of the smectite and attapulgite minerals
and the high surface area (850-1000 m2/g) (Hawkins, 1973) of the
Major problems of phosphatic clay usage include
clay fraction.
permeability and compressibility. The addition of two parts sand
to one part phosphatic clay increased soil permeability and
decreased soil compressibility which accounts for the enhanced
consolidation rates observed for sand/clay mixtures over pure
phosphatic clay (Bromwell and Carrier, 1983; Garlanger, 1982).
Field moisture content (FMC) (weight basis) measured at
0.033 MPa (1/3 bar) is a measure of a soil's capacity to hold and
In Fig. 2.2 it can be seen that FMC decreases
retain moisture.
with an increase in sand content. Sand/clay mixtures have higher
Sand
FMC than do sandy soils typically found in the region.
tailings exhibit almost no moisture-holding capacity having a
This inability to
water content of only 0.4% at 0.033 MPa.
retain moisture is a major reason why attempts to reclaim pure
sand tailings have proven difficult at best.
7
2.1.3
Chemical
properties
The chemical properties of phosphatic clay have been
described (Barwood, 1982; Hawkins, 1973; Bromwell, 1982).
Typical chemical analyses for phosphatic clays are given by
Barwood (1982):
The amount of nutrients available or potentially available
to plants is usually less than the total amount present in the
Plant availability of nutrients is commonly measured by
soil.
extracting the soil with solutions that have been found to cause
selective dissolution of nutrients in amounts related to plant
Hawkins reported the following ammonium acetate (pH 7)
uptake.
extraction from five phosphatic clay samples:
average (mg/kg)
range
cmol(+)/kg
Ca
515
289-606
2.6
Mg
203
139-242
1.7
K
41
20-86
0.1
Na
49
34-80
2.1
These values were considerably lower than those reported by
Bromwell (1982) who used a sodium acetate extraction, also on
five phosphatic clay samples:
average (mg/kg)
range
cmol(+)/kg
Ca
3300
1620-5780
16.5
Mg
1480
1280-1570
12.3
K
60
51-78
1.5
Of importance is the fact that the cation exchange complex of
The high base
phosphatic clays is dominated by Ca2+ and Mg2+.
10
saturation is reflected in the observation that phosphatic clay
and mixtures thereof generally give a water pH between 7 and 8
(Gonzalez and Sartain, 1986; Barwood, 1982).
Cation exchange capacity is a measure of a soil's ability to
retain nutrient cations. Cation exchange capacity ranged from 17
to 43 cmol(+)/kg for the 0.002-0.0002 mm clay fraction and from
61 to 88 cmol(+)/kg for the <0.0002 mm clay fraction (Hawkins,
1973). Bromwell (1982) reported CEC values ranging from 37 to 46
Addition of sand to phosphatic clay decreases CEC
cmol(+)/kg.
It is important to note that the CEC of both
(Fig. 2.3).
phosphatic clay and sand/clay mixes is much greater than that
typically found in sandy soils in the region. Sand tailings have
an extremely low CEC of only 1.1 cmol(+)/kg (Fig. 2.3).
Gonzalez and Sartain (1986) extracted phosphatic clay and
sand/clay mixtures with Mehlich I (double acid) solution (Table
2.1). Mehlich I extractable Ca, Mg, and P were very high in all
Extractable P increased while K decreased with
sand/clay mixes.
increasing sand content. Phosphatic clay tested medium in K for
vegetable production while sand/clay mixtures tested low.
High
Mehlich I extractable levels of Cu, Zn, and Mn were low.
total levels of micronutrients are present in the apatite
However, since
minerals in phosphatic clays (Barwood, 1982).
apatite is relatively insoluble at a neutral pH and is more
coarser-sized fraction of
abundant in the less-reactive,
phosphatic clays, high extractable levels of micronutrients,
It follows that
including Zn, Cu, and Mn, were not found.
corrective applications of micronutrients may be required for
growing crops in soils derived from phosphatic clay.
11
2.2 Agricultural Reclamation Research on Phosphate Mined Lands
2.2.1
General
topics
Very little agricultural research on phosphate mined lands
has been documented, particularly on phosphatic clays in settling
Traditional agricultural reclamation of clay settling
ponds.
Most
ponds has been limited to pasture lands (Marion, 1986).
reported research had evaluated phosphatic clay as an amendment
for improving sandy soils (Mislevy and Blue, 1981; Hortenstine
and Rothwell, 1972; Diamond and Fiskell, 1965). The Polk County
Mined Lands Agricultural Research and Demonstration Project
(1986) has recently initiated a wide scope of experimental and
demonstration projects aimed at successfully farming pure
phosphatic clay settling ponds. Initial results of their pioneer
projects should provide much needed information relative to
technical aspects of agricultural reclamation of these areas.
At this time it appears that the major limiting factor to
successful farming in existing settling areas has been surface
13
water management and the timing of tillage operations with
cropping systems.
Blue and Mislevy (1982) reported success with introduced
tropical grasses and N fertilization on a phosphatic clay slime
Mislevy has continued to have excellent results with
pond.
tropical grasses and biomass crops on a clay settling pond at
Citrus plantings have been limited to
IMC's Phosphoria Mine.
overburden and sand tailings with a few attempts on sand/clay
mixes (Robertson, 1987). Plantings of certain tree species have
been successful on both phosphatic clay and sand/clay mixes
(Harrell, 1987) but these have been for meeting mandatory
reclamation guidelines and not for timber production.
Mislevy et al. (1989) reported excellent yields of biomass
crops on phosphatic clays over a 4-yr period with only N
fertilizers applied. The addition of a 5-cm layer of sand on the
Nutrient
surface had no observable effects on crop yields.
concentrations in crop tissues were generally adequate although
there were some questions regarding micronutrient sufficiency.
No correlations were reported between nutrient concentrations and
yield.
2.2.2
Previous research with sand/clay mixtures
Foundation studies related to the present research were
completed in a project funded by the Florida Institute of
Phosphate Research entitled "Vegetable Production Potential of
Selected Mixtures of Sand Tailings and Waste Phosphatic Clay"
(FIPR Project #83-03-050). Some published results of that study
For
include Gonzalez et al. (1986) and Million et al. (1987).
this pioneer project, four l-acre test pits of varying SCR mixes
(8:1, 6:1, 4:1, 2:l) were developed and evaluated over two
In the first spring 1986
seasons of vegetable production.
five vegetables were grown on raised beds either
season,
unamended, amended with peat at 100 Mg/ha (45 tons/acre) or
In the second season (fall 1986),
mulched with plastic film.
three vegetables (turnip, cabbage, and banana peppers) were grown
14
in the same plots but with a phosphogypsum amendment variable
added. All SCR mixes produced excellent crops with the exception
Difficulties encountered with tractor work
of snap beans.
(rotovation, bed-pulling and plastic mulching), planting, and
weeding in the 2:l SCR mix were dramatically reduced in the 4:l
and higher SCR mixes.
The practice of mulching the beds with plastic increased
production primarily by restricting weed growth. The benefits of
plastic-mulching were found to be greater in the fall than in the
Peat and phosphogypsum had variable effects:
spring seasons.
peat generally enhanced growth and improved soil structure while
phosphogypsum had little observable effects on either soil or
Phosphogypsum was applied to
crop growth and crop composition.
evaluate the potential for limiting plant uptake of Ra226 by
increasing soil Ca activity; however, no Ra226 data were
obtained from the study.
2.3 Amendments to Improve Phosphatic Clays Soils
2.3.1
Organic
materials
The addition of organic materials has long been known to
impart favorable chemical and physical characteristics to soils.
Lucas et al. (1970) listed eight desirable improvements that can
result from the use of peat:
1.
2.
3.
4.
5.
6.
Increase the moisture-holding capacity of sandy soils
Increase the rate of water infiltration of fine-textured
soils
Make soils more friable and better aerated
Decrease soil volume weight and thereby ease root
penetration
Increase the buffering effect of the soil which make
acidity and soluble salt levels more difficult to change
Increase microbial activity in the soil which may help
produce desirable plant growth regulators and antibiotic
substances
15
7.
8.
Serve as a source of slow-releasing forms of nitrogen
Make certain elements, such as iron and phosphorus, more
available to plants.
Improvements in soil physical characteristics from organic
matter additions have generally been attributed to an increase in
porosity for fine-textured soils. Organic-inorganic complexes of
varying stability will form, often with the inclusion of
multivalent cation "bridges" which join together negatively
charged functional groups on clay and organic matter surfaces
Mays et al. (1973) showed that compost from
(Allison, 1973).
municipal garbage increased water retention at field capacity and
reduced soil bulk density. Total soil porosity was increased by
the addition of sewage sludges and sewage sludge/garbage composts
(Pagliai et al., 1981). The application of increasing amounts of
cattle feedlot manure up to 90 Mg/ha decreased soil bulk density,
increased water retention at field capacity (20 kPa) and wilting
point (1500 kPa), but slightly decreased plant available water
content (water held between 20 and 1500 kPa); infiltration rates
and saturated conductivities of their clay loam soil were not
greatly affected.
Organic materials vary in their effect on soil aggregation.
Easily decomposable organic materials, e.g. legume hay or
sucrose, result in greater increases in water-stable aggregates
but the effects are short-lived compared to slowly decomposable
materials such as peat which tend to result in more resistant
humic products (Tisdall and Oades, 1982; Martin and Focht, 1977;
According to an excellent review by Allison
Brady, 1982).
(1973) , undecomposed materials such as peat, sawdust, well-rotted
manures, and composts which decompose slowly have little effect
on aggregate formation but do aid in aggregate stabilization. A
more important benefit of these materials, however, is an effect
These materials improve
in limiting large-sized aggregates.
fine-textured soils by a dilution effect.
16
Phosnhoovnsum
2.3.2
Phosphogypsum
production
(PG)
is
a
in which phosphate
by-product
of
phosphoric
rock is acidulated with
acid
sulfuric
acid according to the following reaction:
Ca3(PO4)2 + 3H2SO4 + 6H2O
3CaS04*2H20 + 2H3PO4.
--->
Phosphogypsum
is composed of 92% gypsum
contaminants
consisting
of
(CaS04'2H20) with major
insoluble
phosphate,
radium,
and
A typical chemical analysis is depicted in Table 2.2.
fluorine.
Typical chemical composition of phosphogypsum
(Palmer and Kouloheris, 1985).
Table 2.2.
Percent
composition@
Component
CaS04*2H20
SiO2
Fe203, Al203
Excess CaO
MgO
F
p2°5
Loss on ignition
92.4
2.8
0.9
0.6
0.1
0.3
0.3
3.2
(230-950°C)
@ Dry weight basis
Uses
in
approximately
1980).
50%
of
the
accounts
Phosphogypsum
Asriculture.
gypsum
used
in agriculture
for
(Borris,
The largest agricultural usage of phosphogypsum
is for
soils
U.S.,
reclamation
of
particularly
saline/sodic
in
in
the
arid
has
Phosphogypsum
California.
western
also
been
effectively used as a fertilizer source for Ca and S (Baird and
Kamprath,
kg/ha
1980).
(CaS04 basis)
Phosphogypsum
were
used.
17
application
Sumner
rates
et al.
of
250-907
(1986) studied
phosphogypsum as an ameliorant to subsoil acidity and poor
Rates of
surface-water penetration due to dispersive clays.
phosphogypsum up to 10 Mg/ha (4.5 ton/acre) were applied in their
The
field studies conducted at the University of Georgia.
beneficial effects of phosphogypsum in their studies were the
lowering of exchangeable and solution Al while increasing soil Ca
Since phosphatic
levels and increased flocculation of clays.
clays are Ca/Mg-saturated, it is doubtful whether further
additions of Ca in the form of gypsum will improve flocculation
of phosphatic clays.
Although calcium sulfate is a neutral salt, and as such
should have minimal effect on soil pH, residual acid from the
acidulation process results in a low pH phosphogypsum material.
Depending on the freshness of the material and its location in a
"stack", the water pH of phosphogypsum generally ranges from 3-6
(May and Sweeney, 1980). Since nutrient and contaminating metal
availability to plants is governed to a large extent by soil
reaction, pH reduction from heavy applications of relatively
fresh phosphogypsum to phosphatic clay soils may influence plant
nutrition beyond that expected by its own elemental composition.
More specifically, lowering of an alkaline pH could be beneficial
as far as increasing micronutrient uptake but detrimental as far
as increasing uptake of contaminating metals.
Selected micronutrient and heavy metal
analyses of phosphogypsum samples are provided in Table 2.3.
According to EPA toxicity tests, no element would be considered
Of interest is
to be at a toxic level (May and Sweeney, 1980).
the fact that levels of micronutrients, including B, Cu, Fe, Mn,
Fluorine levels are high but F
and Zn are relatively low.
toxicity should be limited by the relative insolubility of CaF2.
Contaminants.
18
2.4
Environmental Concerns
2.4.1 Plant uptake of contaminating metals
The uptake of contaminating metals by plants depends upon
Assuming the presence of
both plant and soil factors.
important soil factors
contaminating metals in the soil,
affecting plant uptake of these metals include soil pH, soil
organic matter content, mineralogy, CEC, soil moisture, and
19
concentrations of competing cations.
include plant type and plant tissue.
Important plant factors
The pH of the soil solution has a major
influence on plant uptake of metal contaminants by controlling
High (>7) soil
adsorption/precipitation reactions in the soil.
PH, either through liming or natural effects, has been found to
This reduction is attributed
decrease plant uptake of cadmium.
Soil
factors.
to precipitation of Cd in carbonates, sulfates, and phosphates,
depending upon the presence of these ions in the soil, and also
to the competitive ion effect of high Ca activity (Lagerwerff,
1977). Uptake of other contaminating metals such as lead, nickel
and chromium can also be limited by high pH and/or Ca (Chaney and
Therefore, the alkaline pH of phosphatic clays
Giordano, 1977).
should help to limit uptake of any hazardous metals present in
phosphatic clays.
Increased CEC is related to decreased plant uptake of Cd
although this factor appears to be less important for sludges
than for applied Cd salts (Hinesly et al., 1982).
Movement of elements within the plant can
Chaney and Giordano (1977) listed Cd, B, MO, Se, Mn, and
vary.
Zn as readily moveable; Ni, Co, and Cu as intermediate: and Cr,
Pb, and Hg not mobile, therefore, limiting their presence in
shoots and roots. Higher levels of Cd are found in leaf versus
grain and fruit tissues. For example, in a high Cd soil, tomato
fruit contained 2.4 mg Cd/kg while the leaves contained 71 mg
Cd/kg and cabbage wrapper leaves contained 39 mg Cd/kg while
cabbage head interiors contained 2 mg/kg (Bingham et al., 1975).
Plants differ in their uptake and sensitivity to metals.
Chaney and Giordano (1977) listed selected crops according to
their sensitivity to soil and tissue Cd. For a soil contaminated
with 10 mg Cd/kg, leaf Cd ranged from less than 1 mg/kg for rice
Soil Cd levels which
to over 160 mg/kg for turnip and spinach.
caused a 25% decrease in yield ranged from 4 mg/kg for dry beans
Plant factors.
20
to 170 mg/kg for cabbage: leaf tissue Cd for the same crops at
25% yield reduction ranged from 15 mg/kg for dry beans to 160
mg/kg for cabbage.
Whereas elements such as Cu, Zn, Hg, Pb, and Ni will become
phytotoxic before tissue concentrations become a concern to
human consumers, the reverse is true for Cd (Dowdy and Larson,
1975). While considerable research has investigated the effects
of Cd contamination from the use of sewage sludges, and to a
lesser degree phosphate fertilizers (Mortvedt, 1981), no
information is available on Cd uptake by plants grown on soils
Non-phosphatic soils commonly
derived from phosphatic clays.
Since
contain less than 1 mg Cd/kg soil (Baxter et al., 1983).
apatite generally comprises between 20 and 50% of phosphatic
clays and apatites may contain 18 mg Cd/kg (above), Cd levels in
crops grown on waste clays should be monitored.
2.4.2
Radium-226
During the formation of phosphate sediments, U4+ replaced
significant amounts of Ca2+ in the precipitation process (Osmond
21
The uranium contents of marine phosphorites
et al., 1984).
The most common
typically range between 100 and 200 mg/ kg.
uranium radioisotope, U238, and its more significant decay
are important
and Po210,
Pb210,
Ra226,
series members,
environmental concerns relative to the use of phosphate products
and waste by-products (Guidry et al., 1986; Lindeken, 1980).
Radium-226 is of special concern because of its long halflife of 1600 years and for its emission of biologically damaging
Ra226 exists as a divalent
alpha radiation (Roessler, 1985).
cation, and being chemically similar to the secondary plant
nutrient Ca, is taken up by plants. When consumed, Ra226 enters
the bloodstream where it is deposited in metabolically active
bone tissues (Guidry et al., 1986).
The distribution of Ra226 in mined
Radium-226 in Soils.
Compared to
and unmined phosphate lands is given in Table 2.4.
topsoil and overburden, which includes the topsoil down to the
phosphate matrix, clay settling areas contain high levels of
Sand tailings have slightly higher, but still relatively
Ra226.
low, Ra226 contents than do topsoil and overburden materials.
22
No data are available concerning Ra226 levels in sand/clay
Assuming Ra226 contents of 32 and 5 pCi/g
mix reclaimed sites.
for phosphatic clay and sand tailings, respectively, predicted
concentrations of Ra226 in SCR of l:l, 2:1, 4:1, 6:1, and 8:l
Since
would be 19, 14, 10, 9, and 8 pCi/g, respectively.
phosphatic clays have lower soil bulk densities than sand
3
tailings (0.86 vs 1.42 g/cm )(Roessler et al., 1978), the total
amount of Ra226 in a given soil volume, e.g. rooting depth, of
clay slimes or low SCR soil may be not as great as these numbers
Nonetheless, the addition of sand to
would initially indicate.
phosphatic clay should decrease the total Ra226 content of the
phosphatic clays.
The Ra226 content of a wide variety of
edible fruits and vegetables grown on unmined and reclaimed
phosphate mined lands was surveyed by Guidry et al. (1986).
Results from this study showed that, in general, leafy and cole
vegetables contained higher concentrations of Ra226 than fruits
and other common garden vegetables. Whereas the Ra226 content of
most surveyed vegetables grown on unmined lands ranged from 0 to
11 pCi/kg (fresh-wt. basis), leafy and cole vegetables ranged
For reclaimed lands, fruits and
from 0 to 103 pCi/kg.
Ra226 and plants.
vegetables ranged from 0 to 12 pCi/kg while leafy and cole
vegetables ranged from 3 to 221 pCi/kg. It should be noted that
only a few of the data from mined lands were actually from clay
The survey is
settling ponds where soil Ra226 levels are high.
currently expanding its data base in this area.
Mislevy et al. (1989) reported that Ra226 concentrations in
several biomass grasses and legumes averaged approximately six
times the levels found in the same species grown on unmined
The highest Ra226 concentration was 0.37 pCi/g found in
lands.
the legume Desmodium cinerascens A. Gray. Radium-226 values for
all the crops evaluated ranged from 0.09 to 0.37 pCi/g dry in
phosphatic clay and from 0.02 to 0.06 in unmined sandy soil.
23
Certain vegetables contained particularly high levels of
Ra226 including collards, turnip leaves, and carrots (Table 2.5).
Ra226 concentration of turnip leaves was greater than that of
Ra226 concentrations of turnip roots were not
turnip roots.
This was
dramatically increased when grown on reclaimed lands.
not the case for turnip leaves whose average Ra226 concentration
increased from 9 pCi/kg in unmined lands to 83 pCi/kg in
Carrots sampled from reclaimed lands gave the
reclaimed lands.
Other root crops analyzed,
highest Ra226 concentrations.
including onion, radish, and turnip root did not exhibit the same
high accumulation of Ra226 as was observed for carrots.
A factor of 0.01 has been given as the ratio of radium in
foods (dry weight) to the radium in the soil (Lindeken, 1980).
This factor agrees well with Ra226 data reported by Mislevy et
Although not calculated, their data indicate uptake
al. (1989).
factors ranging from 0.004 to 0.019 in biomass crops grown on
phosphatic clay containing 19.8 pCi/g soil. As observed for all
nutrients, the actual uptake ratio will depend on a wide variety
of soil and plant factors. It has already been shown above that
Ra226 at different
accumulate
vegetables
different
24
And, as described above for turnip leaves,
concentrations.
different parts of a plant may preferentially accumulate Ra226.
Soil factors may play an important role in the uptake of
Ra226 by plants. Table 2.6 has been presented by Lindeken (1980)
as evidence that increased levels of soil Ca may inhibit Ra226
However, these Ra226 concentrations were very low and
uptake.
the differences in tissue Ra226 were very small. No information
was provided relative to the characteristics of the soil or to
the experimental design used.
The idea that added Ca may decrease Ra226 uptake by plants
However, it is based on the wellhas not been investigated.
known phenomenon that alkaline earth metals such as Ca, Mg, and
Sr compete at root surfaces for active transport by selective
carriers across root boundaries into root tissue.
Thus, while
k + , Ce+, and Rb+ compete for binding sites on one particular
transport carrier, Ca2+, Mg2+, and Sr2+
+ compete for binding sites
on a different carrier (Tisdale and Nelson, 1975). Research with
gOSr and Ca indicated that the observed ratio between 90Sr:Ca in
the plant and 90Sr:Ca in the soil remained constant over a wide
25
range of soil Ca activities: i.e., only a slight discrimination
226
It follows that, by decreasing the
Ra.
between 90SR and
90Sr:Ca ratio in the soil through Ca additions, one may reduce
Menzel (1960) suggested that
the same ratio in plant tissues.
application of lime, gypsum, fertilizer, and organic matter may
reduce 90Sr uptake from soils especially in soils having low CEC
and low exchangeable Ca levels.
Soil samples taken during the food radioactivity survey by
Current follow-up
Guidry (1986) were not analyzed for Ca.
research by the same research team is designed to include Ca
analyses to investigate this potential effect.
Phosphogypsum
-
Potential
Effect
on
Ra226
Uptake.
Phosphogypsum, which contains 20% Ca, is a readily available
source of Ca. However, the application of phosphogypsum as a Ca
supplement is confounded by its own Ra226 content. As previously
mentioned, during the acidulation of rock phosphate, radium
coprecipitates with gypsum as the sulfate salt (RaSO4).
Phosphogypsum from Central Florida typically contains 20-30 pCi/g
of Ra226 (May and Sweeney, 1980; Roessler, 1985) although values
have been reported as high as 65 pCi/g (Roessler et al., 1977b).
The contribution of Ra226 from phosphogypsum should be minimized
due to the very low solubility of RaSO4 (Ksp of 10-10.4).
Additionally, one might suspect that large additions of sulfate
may decrease Ra226 solubility by causing a sulfate precipitation.
However, according to Osmond et al. (1984) , Ra226 solubility is
little affected by sulfate unless Ba is present as a coprecipitant.
Potential Ra226 contamination from phosphogypsum
additions was investigated by Mays and Mortvedt (1986) who
applied up to 112 Mg/ha (50 ton/acre) of phosphogypsum in a field
Corn yields were
experiment to corn, wheat, and soybeans.
reduced by the high application rate but the yields of wheat and
Grain levels of Ra226 were not increased by
soybeans were not.
the highest application rate of phosphogypsum.
26
3.0 PRIMARY OBJECTIVES
The primary objectives of this research were to evaluate the
growth and composition of selected vegetables and forages grown
on sand/clay mixes as affected by sand/clay ratio and soil
amendments. The research is divided into three phases:
I. Sand:Clay Ratio Phase
The objectives of this phase were to evaluate the effects of
sand:clay ratio,
peat, phosphogypsum, and micronutrient
Three
fertilizers on yield and composition of vegetables.
seasons of experimentation were conducted on four different
sand:clay ratio mixes.
II. SP-1 Alfalfa Phase
This phase was conducted to assess the influence of selected
organic soil amendments on yield and composition of alfalfa. The
study was carried out on sand/clay reclamation area SP-1 at CF
Industries' Fort Green mine.
III. Glasshouse Phase
The purpose of this experimentation was to look more closely
at the influence that phosphatic clay has on the growth and metal
(particularly Cd) content of forage legumes grown in sand/clay
This
mixes amended with several waste organic materials.
research was conducted at the University of Florida by Rick
Gonzalez as part of his Master of Science degree in the
Environmental Engineering Department.
27
4.0 SAND CLAY RATIO PHASE
4.1
Objectives
The objectives of the sand:clay ratio phase of the research
program were:
1)
2)
3)
4)
4.2
to evaluate the effect of sand:clay ratio on the yields and
compostion of selected vegetables grown on sand/clay mixes;
to evaluate the effect of peat on yields and composition of
selected vegetables grown on sand/clay mixes:
to evaluate the effect of phosphogypsum on yields and
composition of vegetables grown on sand/clay mixes; and
to evaluate the effect of micronutrient fertilizers on yield
and composition of selected vegetables grown on sand/clay
mixes.
Methodology
Three seasons of vegetable experimentation were conducted:
All
spring 1987 (S87), spring 1988 (S88), and fall 1988 (F88).
experimentation was carried out in research plots previously
established during a companion study also funded by the Florida
Institute of Phosphate Research (Final Report, FIPR No. 83-03050, Million et al., 1987).
In brief summary, sand/clay mixes with SCR of 2, 4, 6, and 8
were hydraulically deposited (3-5% solids) in February 1985 into
four adjacent l-acre impoundments constructed on the property of
Drying and consolidation
C.F. Industries in Hardee County.
Problems of sand-clay
resulted in a final depth of 2-3 feet.
separation in the SCR = 6 and SCR = 8 mixes were alleviated
fairly well with mechanical mixing by pulling a large disc plow
In order to
through the fluid sand/clay mix with a bulldozer.
assess field variation in SCR, SCR measurements were made for
each of the 270 individual plots.
By January 1986, the first raised beds were formed using
equipment
and
and bed-pulling
tillage
conventional
28
experimentation proceded with spring and fall crops in 1986.
Treatment factors evaluated in the first two seasons included
peat, plastic mulch, phosphogypsum, and vegetable crops.
A list of treatment variables evaluated in the three
experimental seasons in the present study is provided in Table
Some of the listed treatments represent residual effects.
4.1.
Residual effect treatments can be ascertained by reading the
footnotes at the bottom of the table to find when the
applications were originally made.
4.2.1
Spring
1987
The only modification over the previous fall 1986 (F86)
season's design was the application of 100 Mg peat/ha (45
ton/acre) to one of two peat-amended treatments from the previous
This modification allowed us to assess the residual
experiment.
effectiveness of the first peat addition made in spring 1986
Unlike the F86 season, plastic mulching was utilized on
(S86).
The
all beds thereby eliminating it as a treatment variable.
three vegetables crops were re-randomized over the SCR-peat
treatment combinations.
The raised beds from the previous F86 season were rotovated
on 15-16 Feb. 1987. Peat was incorporated into appropriate plots
On 17 Feb. 1987, fertilizer was broadcast over
at that time.
the rotovated beds at the rate of 108 kg N/ha as ammonium
nitrate and 150 kg K/ha as KCl. Twice the latter rate was applied
Broadcast fertilizer was incorporated by a second
to cabbage.
The beds were pulled using a 'superpress' followed
rotovation.
A fertilizer spreader attached to the
by a 'finishing press'.
'finishing press' was used to deliver a band application of 84 kg
N/ha as ammonium nitrate and 140 kg K/ha as KC1 down the center
of the bed at the rate of 560 kg/ha. This operation worked well
on SCR = 4, SCR = 6, and SCR = 4 mixes but some modifications
The 'finishing press' (and
were required on the SCR = 2 mix.
fertilizer spreader) could not be pulled through the more clayey
Because the fertilizer spreader was attached to
SCR = 2 site.
the 'finishing press', the center band application in the 2:1 SCR
Four passes of the 'superpress' were
mix was made by hand.
The
needed to form acceptable beds in the SCR = 2 mix.
resultant beds formed in the SCR = 2 mix were rough and cloddy.
Immediately after the band application of fertilizer, black
The soil sweeps
plastic mulch was laid down over all beds.
functioned poorly in the SCR = 2 mix and, therefore, much hand
labor was required to shovel the sand/clay mix onto the edges of
A similar but lesser
the plastic to hold the plastic down.
problem experienced in the SCR = 4 mix was remedied by following
30
the plastic laying machine with a small tractor with side disk
All tractor work was
sweeps to cover any missed areas.
contracted out to Waters Farms of Fort Green.
Vegetable seedlings were obtained from Carter's Nursery of
Turnips were transplanted on 21 and 22 Feb. 1987;
Lake Wales.
cabbage on 2 and 3 Mar. 1987; and banana peppers on 4 Mar. 1987.
Fireants were controlled by applying a diazinon soil drench 1 wk
after transplanting.
Overhead irrigation from a solid-set system was used. Weeds
were hand-pulled in the beds and herbicide-sprayed between beds.
Alternating insecticide sprayings of Diazinon and Orthene were
made on a weekly to biweekly schedule as needed.
Fresh weight
Turnips were harvested on 1 and 2 Apr. 1987.
yields of roots and leaves were measured. Roots and leaves were
The
sampled from every other plant for compositional analyses.
Turnip samples were transported to Gainesville where they were
sliced, dried, and ground. Out of 20 turnip roots sliced up, the
number with brown rot symptoms was recorded.
Marketable fresh-wt.
Cabbages were harvested on 6 May.
Cabbage heads over 10 cm (4
yields of cabbage were determined.
in) in diameter were considered of marketable size ('Golden
Cross' is an early-maturing cultivar with a small compact head).
Wedge-shaped slices from 10 cabbages per plot were saved for
compositional analyses. Turnip and cabbage samples from selected
SCR = 2 plots were given to Jerome Guidry of Post, Buckley,
Schuh, and Jernigan for additional Pb210 and Po210 analyses in
accordance with their on-going radioactivity study.
Banana peppers were picked on 29 April, 9, 15, 21 and 30
May, and 12 June. Fresh-wt. yields were recorded. Peppers were
collected from 15 and 21 May pickings for compositional
analyses. Samples were sliced in a food processor and kept in a
freezer until drying and grinding processes could be completed.
31
Approximately 100 grams of dry ground tissue from selected
plots were forwarded to Core Laboratories, Casper Wyoming for
Ra226 analyses. A total of 188 samples were analyzed:
60 root samples
turnip
60 leaf samples
60 leaf samples
cabbage
8 fruit samples
peppers
188 total samples
The 60 samples represent all 24 plots (3 peat trt. X 2
phosphygypsum trt. X 4 replications = 24) in each of the SCR = 2
and SCR = 4 mixes and only 6 (combined replications) in the SCR =
6 and SCR = 8 mixes.
Core laboratories utilized a procedure that is essentially
equivalent to method 903.1 in the Environmental Protection
Agency's "Prescribed procedure for measurement of radioactivity
in drinking water". According to Core Laboratories' abstract of
methodology (Dave Demorest, personnel communication),
sample pretreatment initially involved destroying the organic
material in a muffle furnace. The ash was digested in acid and a
sodium sulfate fusion to completely solubilize all material. A
BaSO4 procedure was used to co-precipitate Ra226. The supernate
is redissolved in a strong chelating agent (EDTA). This solution
is transferred to a radon bubbler, de-gassed and stored for over
At the end of the ingrowth period, radon gas is de8 days.
emanated into a radon flask, aged for 4 hrs and counted.
Air-dried soil samples were analyzed for Ra226 by the radonemanation method (Gonzalez, 1984) by Emmett Bolch at the
University of Florida.
Bulk density measurements were made in each turnip plot in
Bulk density was determined by driving a 200 cm3 core
August.
sampler into the raised bed and measuring the weight of dry soil.
Two measurements were made per plot.
On five additional beds formed in the SCR = 4 mix, a Bfertilizer experiment was conducted utilizing a randomized
The
complete-block design with five replications (5 beds).
treatments were a factorial arrangement of three B application
32
rates (0, 1, and 3 kg/ha) and two rates of peat (0 and 100
Boron, as sodium tetraborate (17%), was applied along
Mg/ha)
with banded fertilizer as described for the main experiment.
Turnip seedlings were transplanted on 23 Feb. 1987 and harvested
After root and leaf yields were measured, tissue
on 2 April.
samples were saved for chemical analyses.
Plant tissues were dried, ground, dry-ashed at 450°C, and
Air-dried soil samples
brought into solution with 0.1 M HCl.
taken from each turnip plot (5 cores per plot) were extracted
with 1:l0 (w/v) Mehlich III solution (0.2 M HoAc, 0.25 M NH4NO3,
0.015 M NH4F, 0.013 M HNO3, 0.001 M EDTA) shaken for 5 minutes
Solutions were analyzed for Ca,
and filtered (Mehlich, 1982).
l
Mg, K, P, Fe, Zn, Mn, Cu, B and Cd, by the Analytical Research
Laboratory at the University of Florida, Gainesville.
Additional analyses performed on soil samples included pH (1:2
water), electrical conductivity and organic carbon (Walkley-Black)
all according to Rhue and Kidder (1983).
4.2.2 Spring 1988
Plastic
Existing plots were utilized for S88 experiments.
mulch was removed and the beds tilled in September 1987 and again
on 5 Feb. 1988. Plots which had received 22 Mg phosphogypsum/ha
received an additional 112 Mg phosphogypsum/ha (50 tons/acre).
The phosphogypsum, which was obtained from an old stack at
Estech's Silver City Mine, was broadcast over the bed and
Base
rotovated into the soil along with base fertilizer.
fertilizer applied to all plots included 108 kg N/ha as ammonium
nitrate, 108 kg K/ha as K2SO4, 20 kg Zn/ha as zinc sulfate, 10 kg
Fe/ha as iron sulfate, and 5 kg Cu/ha as copper sulfate.
By reducing plot size from 6.1 to 3.05 m and cultivating
only two crops at one time, three micronutrient treatments were
evaluated:
2 kg B/ha and 50 kg Mn/ha
1.
2 kg B/ha and 0 kg Mn/ha
2.
0 kg B/ha and 50 kg Mn/ha.
3.
33
The B source was sodium tetraborate (17% B) and the Mn source was
Micronutrient treatments and basemanganese sulfate (27% Mn).
mix fertilizer were broadcast and preplant incorporated during
final tillage operations. No plastic mulch was used.
Turnip and cabbage seedlings were transplanted 23 Feb. 1988
Yellow squash was transplanted
and 1 Mar. 1988, respectively.
Turnips were harvested 5-7
behind the turnip crop on 13 April.
April, cabbage 24-25 April, and squash 16,21,25 and 31 May, and 3
Soil and tissue samples and subsequent chemical analyses
June.
226
Ra
For
were performed as described for the S87 season.
analyses, 80 samples (2 peat trt. X 2 phosphogypsum trt X 2
fertilizer trt. X 4 replications = 80) of each of the following
plant tissues were collected: turnip leaves, turnip roots, yellow
squash fruit, and cabbage heads.
4.2.3
Fall 1988
Weeds from summer fallow were killed with Gramaxone
One week later, the dead
(paraquat) herbicide on 19 August.
Preparatory tillage
vegetation (primarily grasses) was mowed.
The sequence of tillage was as follows:
began on 23 September.
one pass with the rotovator followed by two passes with a bed
This sequence was performed twice in the SCR = 8, SCR =
press.
The
6, and SCR = 4 mixes and three times in the SCR = 2 mix.
raised beds in the SCR = 2 mix were rough and cloddy while the
beds in the other mixes became smoother with increasing sand
content. The dramatic increase in ease of tillage in the SCR = 4
versus the SCR = 2 beds has been noted in each season of
expermentation.
On 29 September, 150 kg N/ha as ammonium nitrate and 150 kg
K/ha as K2SO4, 20 kg Mn/ha as manganese sulfate, and 1 kg B/ha
The fertilizer was incorportated in the
as sodium tetraborate.
bed with two passes of the rotovator; each pass of the rotovator
was followed by one pass of the bed press. No plastic mulch was
used.
34
Seedlings were transplanted 1 October 1 (squash), 2 October
(turnip) and 3 October (mustard) in double rows with a withinrow spacing of 30 cm for turnip and mustard and 45 cm for squash
Plots were
(the squash was a compact, early-maturing variety).
In order to avoid
6.1 m long containing 40 plants per plot.
interactions with micronutrient fertilizer treatments evaluated
in the spring season, squash were planted in +Mn-B plots, turnip
in the +Mn+B plots, and mustard in the -Mn+B plots.
Diazinon or Orthene insecticide/Bravo fungicide mixtures
were sprayed on squash on 6, 18, and 27 Oct. 1988; mustard and
turnip were sprayed with the same mixtures only on 6 October.
All plots were hoed on 21 October; squash were also hoed on 4
November. Irrigation was applied every other day from 12 through
Thereafter, plots were irrigated almost daily until
22 October.
21 November.
Squash were harvested 31 October and 2, 7, 10, 16 and 21
As with previous experiments, fresh-wt yields of each
November.
Select mustard and squash samples were
crop were recorded.
collected from the SCR = 2 mix by PBSJ's Radioactivity in Foods
survey team.
Soil and plant tissue collection and subsequent analyses
were conducted as described for the S87 season.
Statistical analyses were performed for each season and for
each vegetable. Analysis of Variance (ANOVA) procedures were run
using Statistical Analysis System (SAS) software on a personal
The ANOVA used for both the S87 and F88 seasons is
computer.
given in Table 4.2 and for the S88 season, in Table 4.3.
35
36
37
4.3
Results and Discussion
4.3.1 Sand:clay ratio effects
The effect of increasing SCR on the
Crop yields.
4.3.1.1
relative crop yield (percent of maximum) depended upon the crop
(Fig. 4.1). The yield levels plotted were averaged over several
seasons when more than one season was involved.
Higher yields of turnip, cabbage, and mustard were obtained
in the SCR = 2 mix. In contrast, higher yields of banana pepper
Cabbage
and yellow squash were obtained in the SCR = 8 mix.
yields dropped 30%, turnip yields l0-15%, and mustard yields 1227% when the SCR was increased above 2, while squash yields
dropped 19% and banana pepper yields 20% when going from a SCR =
4 to a SCR = 2 mix.
Sand:clay ratio effects were not always consistent from one
For example, higher turnip
season to another (Tables 4.4-4.6).
yields were observed in SCR = 2 mix in S87 but not in S88 and
One might expect that high clay content may physically
F88.
Although the 1eaf:root ratio
restrict turnip root growth.
decreased with increasing sand content in S88 and F88, the
increase in yield of turnips produced in the SCR = 2 mix
(observed in S87 only) was due to yield increases in both turnip
Average turnip root yields
tops and turnip roots (Table 4.4).
were lower in the fall than in the spring (4.3 vs. 10.3 Mg/ha)
but this may have been due to higher soluble salt levels in F88.
Higher yields of cabbage in the SCR = 2 mix in both seasons
of production may be due to the fact that cabbage places large
demands on the soil for water and nutrients both of which are
associated with higher clay content. The cabbage variety used in
this study, 'Golden Cross', is an early-maturing cultivar with a
small, compact head. Cabbage yields obtained in the two seasons
averaged 24 Mg/ha (428 50-lb bushel) for the SCR = 2 mix and 16
Mg/ha (285 50-lb bushel) for the SCR = 4 mix.
Yellow squash yields gave variable results during the two
Yields were lower in the SCR = 2 mix in S88 but not
seasons.
F88. The lower yields in SCR = 2 mix in S88 were due in part to
38
the shape of the raised bed.
= 2 mix were relatively low
needed to achieve high beds
movement which in turn
In the S88 season, beds in the SCR
because the degree of bed-pulling
would have caused excessive soil
would have resulted in cross
contamination of fertilizer and phosphogypsum treatments.
Although banana pepper yields were higher in the SCR = 8 mix
in 587, results in F86 (previous study) indicated no SCR effect
on banana pepper yields and results in F86 indicated higher
Clearly, further
yields of bell pepper in the SCR = 2 mix.
trials would need to be conducted to argue for a higher SCR mix
based on yield alone for any proposed crop.
The results above indicate that from a yield perspective,
there is no advantage in farming a high SCR mix for most of the
However, from a production perspective,
vegetables tested.
potential yield increases in the SCR = 2 mix are offset by the
considerable increase in difficulty needed to carry out normal
farm operations in the SCR = 2 mix versus the SCR = 4 and higher
SCR mixes.
4.3.1.2
Soil and plant nutrition. Soil and tissue chemical
analyses were made to identify any nutritional problems which
might exist for crop production in the various SCR mixes.
Soil-test results from S87 are presented in Table 4.7.
Highest soil test levels of all nutrients were found in the SCR =
2 mix except for K and Zn which were slightly higher in the SCR =
Of all these elements, only Mn tested low for crop
8 mix.
The critical range below which a soil would be
production.
considered deficient in Mn is 5-9 mg/kg (Cox and Kamprath, 1972).
Soil-test Mn, which averaged between 4-6 mg/kg in all SCR mixes,
It follows from
would thus be considered marginally deficient.
these soil-test results that application of Mn fertilizer would
be recommended for all SCR mixes. All other nutrients (except N)
tested high indicating no or minimal response to fertilizer
applications.
42
Soil-test results for S88 are presented in Table 4.8.
Mehlich III extractable P, Mg, and Fe were greater in the SCR = 2
mix than in the sandier mixes. These elements also tested higher
in the previous S87 season. Unlike the S87 season, soil-test Ca
This was due to the overriding effect
was not affected by SCR.
of treatment gypsum which raised average Ca levels from 2760
Due to the application of
mg/kg in S87 to 5750 mg/kg in S88.
micronutrient fertilizers in S88, micronutrients tested higher in
Of particular interest, average soil Mn was
S88 than S87.
increased from a possible deficiency level of 4.3 mg/kg in S87 to
a sufficiency level of 7.8 mg/kg in S88.
Soil pH did not change much during 3 yr of vegetable
production despite high rates of fertilizer, phosphogypsum and
peat applications (Table 4.9). Soil pH decreased several tenths
of a unit from S87 to F88 in the sandier SCR = 8 mix (7.45 to
7.14); little change was evident in the other mixes. Mislevy et
al. (1989) reported a pH reduction from 7.6 to 7.3 after 4 yr of
The lack of observed
crop production on pure phosphatic clays.
pH differences between the different SCR mixes is further
43
evidence that the highly buffered clay fraction dominates the
soil chemistry in sand/clay mixes.
Electrical conductivity results are presented in Table 4.9.
Conversion to ppm soluble salts is made by multipling EC values
by 1400. This enables comparison to established tolerance levels
for vegetable crops (Rhue and Kidder, 1983). For example in S87,
mean soluble salt levels ranged from 1120 ppm in the SCR = 2 mix
to 1960 ppm in the SCR = 8 mix. According to Rhue and Kidder,
the soil would be considered slightly saline in the SCR = 2 mix
Because most vegetables
and moderately saline in the others.
prefer a salt level below 700 ppm, the salt level was too high.
However, soil samples taken for soluble salt tests in S87 were
sampled from the center of the bed through the fertilizer band
thereby giving relatively high values in that season.
44
All fertilizer was broadcast-incorporated in S88, resulting
in lower soluble salt levels. The values were still unfavorably
However, soluble salt
high averaging 1650 ppm soluble salts.
levels in the plots which did not receive phosphogypsum were at
or below the 700 ppm critical level (see phosphogypsum section
Electrical conductivity increased from an
from more details).
average of 1.18 mmhos/cm (1650 ppm salts) in S88 to 1.53 mmhos/cm
In plots which did not receive
(2140 ppm salts) in F88.
phosphogypsum, EC increased from 0.5 mmhos/cm (700 ppm) in S88 to
1.2 mmhos/cm (1680 ppm) in F88. The increase was due in part to
cross contamination of phosphogypsum from phosphogypsum-treated
plots to untreated plots during land preparation.
can also be used to help identify
Plant analyses
Nutrient composition of
nutritional deficiencies or imbalances.
vegetables averaged over SCR is presented in Table 4.10; SCR
effects are presented in Table 4.11.
45
All macronutrient concentrations were normal and seasonal
differences were minimal. One exception was a higher turnip leaf
The
Mn concentration in S88 (59 mg/kg) than in S87 (16 mg/kg).
higher concentration in S88 was due to treatment Mn fertilizer.
Also noteworthy was an observed increased in Ca concentration in
This
turnip and squash leaves versus other vegetable tissues.
difference will be investigated further in the radionuclide
section.
Due to alkaline soil conditions, plant micronutrient
Iron concentrations for
concentrations deserve closer scrutiny.
all crops were higher than 50 mg/kg which is generally considered
Critical
to be a critical level in many crops (Jones, 1972).
For example, cabbage heads
levels do depend on the crop.
commonly contain 40-100 mg/kg Fe while tomato leaves usually
contain 100-300 mg/kg (Geraldson et al., 1973). Sand:clay ratio
had little effect on tissue Fe despite higher extractable Fe
levels in the SCR = 2 mix.
Tissue Zn
Zinc concentrations were normal in all tissues.
concentrations less than 20 mg/kg are considered deficient
(Jones, 1972). As with Fe, tissue Zn was not affected by SCR.
Manganese concentrations were low. The sufficiency range of
Mn in mature cabbage heads is 25-50 mg/kg (Jones, 1972). In S87,
cabbage heads averaged only 8 mg/kg Mn and cabbage Mn
concentration was correlated with cabbage yield (r=0.32). It was
found that cabbage yield averaged 18.5 Mg/ha when Mn
concentration was less than 10 mg/kg and 23.2 Mg/ha when Mn
concentration was greater than 10 mg/kg. No correlation between
cabbage Mn and yield was observed in S88 when cabbage Mn
concentration averaged 16 mg/kg.
Turnip leaves in S87 contained 15-17 mg Mn/kg which would
also be deficient. No correlation was found between turnip root
Mn or turnip leaf Mn and turnip yield in S87 or S88.
Banana pepper fruit Mn conc. was correlated with pepper
yield (r = 0.32). Mustard leaf Mn conc. was not correlated with
yield.
49
In S88, squash leaves contained between 60 and 70 mg Mn/kg,
Although no correlation between
a level considered sufficient.
squash leaf Mn concentration and yield was observed, squash fruit
Mn concentration was significantly correlated with squash yield
in S88 (r = 0.15) and F88 (r = 0.17).
As observed for Fe and Zn, Mn concentrations in plant
tissues were not greatly affected by SCR.
The correlations between tissue Mn and yield indicate that
The low correlation
Mn was deficient in the sand/clay mixes.
coefficients indicate that other factors played a greater role in
For more on Mn, see the micronutrient
yield determination.
section.
Copper concentrations less than 5 mg/kg in plant tissue are
No plant tissue had a Cu conc. less than
considered deficient.
this critical level. Sand:clay ratio had no observable effect on
tissue Cu conc.
Boron concentrations less than 15 mg/kg in diagnostic
Certain crops such
tissues are generally considered deficient.
as the crucifers and alfalfa can require higher levels.
Cabbage is known to be sensitive to B deficiency. Cabbage B
concentration ranged from a low 13 mg/kg in the SCR = 8 mix to an
average of 45 mg/kg in the SCR = 2 mix. Although yield was not
correlated with cabbage B conc. in S87, cabbage B was negatively
(see
correlated with brown rot symptoms (r = -0.64)
micronutrient section). In S88, cabbage B conc. averaged only 15
mg/kg and was correlated with cabbage yield (r = 0.43).
Turnip leaf B conc. also decreased with increasing sand
Turnip leaf B conc. in S87 was correlated with browncontent.
rot symptoms (r = -0.31) but not yield (r = 0.03). No
correlation was observed between turnip root B conc. and brownIn S88, turnip leaf B
rot or between root B conc. and yield.
conc. was correlated with turnip root yield (r = 0.24) but not
Low tissue B concentrations and
turnip leaf yield (r = 0.05).
positive correlations between tissue B and yields indicate B
deficiency in the sand/clay mixes (see micronutrient section).
50
Although Mehlich III
extractable soil Cd levels decreased with increasing sand
The
content, observed differences were minimal (Table 4.12).
Mehlich III extractant contains EDTA which extracts the less
soluble carbonate and sulfide Cd compounds (Lake et al., 1984).
From 40-70% of total soil Cd is typically extracted by EDTA
(Chang et al., 1984). With typical uncontaminated soils testing
0.1 mg/kg or less (Chang et al., 1984; Kelling et al., 1977;
Singh and Narwal, 1984), extractable Cd in the various SCR mixes
was six to ten times greater than in non-phosphatic soils.
Phosphatic clay slimes contain between 4-15 mg Cd/kg (total)
(Wakefield, 1980). The low extractable levels of Cd observed in
the sand/clay mixes indicate that plant available Cd is not as
great as total amounts would otherwise indicate.
Cadmium concentrations in plant tissue depended upon the
vegetable and vegetable part (Table 4.12). As has been
established for most crop species evaluated in Cd-contaminated
soils, higher Cd conc. were observed in leaf tissue than in fruit
For turnips, leaf Cd was double that found in
or root tissues.
the roots (7.9 vs. 3.7 mg/kg). Squash leaves were also found to
have over four times the Cd conc. of squash fruit (2.7 vs. <0.6
Vegetable tissues, when placed in decreasing order of
mg/kg) .
tissue Cd conc., were turnip leaves > turnip roots > squash
leaves > banana pepper fruit > squash fruit > cabbage = mustard
leaves.
Green, leafy vegetables do not necessarily have high Cd
concentrations as evidenced by the low leaf Cd conc. of 0.5 mg/kg
found in mustard leaves.
Sand:clay ratio affected tissue Cd conc. but differences
were insignificant compared to differences between vegetables or
between tissues within a vegetable (e.g. turnip root vs. turnip
It follows that higher sand:clay ratios would not be
leaves).
recommended in order to significantly decrease Cd
concentrations in vegetables.
In fact, higher Cd concentrations
were found in the SCR = 8 mix than in the SCR = 2 mix for turnip
leaves in S88 (7.7 vs 6.1 mg/kg), turnip roots in S87 (7.1 vs 3.1
mg/kg) , and in banana pepper fruit (1.8 vs 0.2 mg/kg).
4.3.1.3
Soil and tissue cadmium.
51
52
No permissible concentrations of Cd in foods have been
For reference, turnips grown in uncontaminated
established.
soils had a leaf Cd conc. of 1.8 mg/kg while root Cd conc. was
Cabbage heads grown in
0.1 mg/kg (Chaney and Giordano, 1977).
the same soil contained 0.2 mg Cd/kg. Reported concentrations of
Cd in others vegetables included 2.6 and <0.1 mg/kg in tomato
leaves and fruit, 3.9 and <0.1 mg/kg in corn leaves and grain,
and 3.6 mg/kg in spinach.
The concentrations of Cd in vegetables grown on the
sand/clay mixes were within the general concentrations ranges
Turnip leaves contained up to five times the
described above.
soil but these
found in uncontaminated
concentration
Average
concentrations should not be of any health concern.
daily human intake of Cd is 40-150 ug/day with average background
levels in foods of 0.05 to 0.40 mg/kg (Allaway, 1977). Assuming
6% dry matter and a maximum Cd concentration of 10 mg/kg in dry
leaves, fresh turnip leaves from sand/clay mixes contained 0.6
One
This is just outside normal background levels.
mg/kg Cd.
would have to eat over 0.25 kg of turnip leaves to exceed the
It follows that for
normal dietary intake of 150 ug Cd/day.
normal human diets, Cd levels in vegetables grown on sand/clay
mixes are not a health threat.
4.3.2
Peat
effects
Peat was initially applied as a
treatment to selected plots in S86 (previous study). During that
first season, peat increased squash but not tomato, cantaloupe,
The increase in squash yield from the
or bell pepper yields.
peat amendment over the unamended control in S86 was 38%. In the
following season, F86, peat had no effect on yield of turnip,
cabbage, or banana pepper. In the first year of this study, S87,
half the plots amended with peat in the previous study received
an additional application of peat. One objective was to compare
the difference between the residual and the direct effect of
The yield comparison between the 100 Mg/ha and
peat amendment.
4.3.2.1
Crop
yields.
53
l00+l00 Mg/ha rates in S87 assessed any benefits from direct peat
Residual effects were evaluated by the 100 Mg/ha
application.
rate in S87 and all rates in S88 and F88.
Two instances of yield gains from peat were noted in the
In both instances,
three seasons of experiments (Table 4.13).
the yield benefit of peat was observed only during the season in
A yield benefit from any
which the peat application was made.
residual effect of peat was never observed for any of the crops
In the first instance, the application of an additional
tested.
Total turnip
100 Mg peat/ha increased turnips yields in S87.
yield was increased 17% (20.5 vs. 17.5 Mg/ha) with a preplant
incorporated application of peat at 100 Mg/ha. The leaf to root
ratio was unchanged indicating that peat did not preferentially
No turnip yield response to the
affect root or shoot growth.
residual 100 Mg peat/ha application applied in S86 was observed
during the same season.
In the second instance, a yield benefit from peat was
observed for banana peppers. As reported earlier, banana pepper
54
For the SCR = 4 mix, the
yields increased with increasing SCR.
addition of peat improved yields to the level found in the SCR =
8 mix (Fig. 4.2). Pepper yields were increased in the middle two
of six pickings. As with turnip, the benefit of peat in the SCR
= 4 mix was observed for peat applied just prior to planting and
not for residual peat applied during a previous season. A
similar increase in pepper yield from peat was not observed in
the SCR = 2 mix.
Besides these two instances, peat had no effect (direct or
It follows from
residual) on yields of the other crops tested.
yield results of this study that peat amendment can not be
recommended as a general management practice to increase crop
However, for certain crops such
yields in the sand/clay mixes.
as banana pepper, which prove to yield better in sandier mixes,
the application of an organic amendment may be worthy of further
consideration.
55
Soil and tissue
Soil and plant nutrition.
4.3.2.2
chemical analyses were made to evaluate the effects of peat
application on soil-plant nutrition in sand/clay mixes.
Extractable nutrients in peat are given in Table 4.15.
Soil-test results indicate that peat had very little effect
on Mehlich III extractable macronutrients and micronutrients for
either the S87 (Table 4.16) or S88 season (Table 4.17). In both
seasons, soil P was decreased by peat application but the
In S87, the
differences were not agronomically important.
application of an additional 100 Mg peat/ha decreased Mehlich III
extractable Cu. No residual peat effect on soil Cu was noted the
Copper deficiency is common on muck
following S88 season.
farmland in Florida due to Cu complexation by soil organic matter
Despite the reduction in extractable
(Murphy and Walsh, 1972).
Cu due to peat application in S87, soil-test Cu levels were
higher than the critical level of 0.75 mg/kg (Cox and Kamprath,
1972).
57
Soil pH and electrical conductivity values as affected by
Despite the fact
peat application are presented in Table 4.18.
that the water pH of peat was 4.0 (4.5 in 1986), peat applied at
the high rate of 100 Mg/ha had no effect on soil pH, even for the
Peat
S87 season during which a preplant application was made.
amendment decreased soil pH from 7.8 to 7.3 during the spring
1986 season when peat was first applied (Million et al., 1987).
Soil EC for any of the sand/clay mixes was not affected by peat
amendment.
With a few exceptions, nutrient composition of vegetables
was not affected by peat application for either S87 (Table 4.19),
One noted exception was
S88 (Table 4.20), or F88 (Table 4.21).
that Mn concentrations in turnip leaves, turnip roots, and
cabbage heads in S87 were increased by the higher peat
Tissue Mn was not increased by residual peat
application rate.
in S87 or in subsequent seasons. Increases in tissue Mn from
59
peat application were agronomically insignificant as the
increased levels were still in the deficiency range as described
More useful is the conclusion that large
in the SCR section.
applications of peat did not adversely affect vegetable
nutrition.
Although Mehlich III
extractable Cd was not affected by peat amendment, Cd
concentrations in turnip leaves and roots were (Table 4.22).
Averaged over the three seasons, the high peat application rate
decreased turnip leaf Mn conc. from 8.6 to 7.0 mg/kg and turnip
Cadmium concentrations in
root Mn conc. from 4.0 to 3.5 mg/kg.
other vegetables were too small to notice any effects of peat on
In light of the previous discussion on tissue Cd
tissue Cd.
4.3.2.3
Soil and
tissue
Cd.
(page 51) the reductions in tissue Cd from peat were relatively
It follows that large applications of peat would not be
small.
recommended to significantly reduce Cd uptake in vegetables.
However, these results do indicate that management practices
which favor increased organic matter content will aid in limiting
plant uptake of Cd.
Peat, as
a standard organic material, was applied to improve the physical
characteristics of the sand/clay mixes by "lightening" the heavy
soils.
Assuming
Bulk density is a measure of soil compaction.
constant particle density, a soil with lower bulk density is less
4.3.2.4 Soil organic matter and bulk density.
compacted and has greater porosity than one of greater bulk
density:
Bulk density = weight of core
volume of core
x 100%
% Pore space = 100 - bulk density
particle density
Results of bulk density measurements taken at the end of S87
are provided in Fig. 4.3. These results indicate that each
63
addition of peat lowered bulk density in all but the SCR = 2
However, the decrease in bulk density from residual peat
mix.
applied in 1986 (100 Mg/ha treatment) was not statistically
Greater variability in bulk density measurements
significant.
was noted in the SCR = 2 mix than in the other mixes. This fact
was revealed by a three-fold higher coefficient of variation
(11.3% vs 3.7%) in the SCR = 2 versus the average of the other
The greater variability in the SCR = 2 was
three mixes.
apparently due to due to less uniform mixing of the peat.
Because the variability in SCR was lowest in the SCR = 2 plots,
greater variability in bulk density measurements was not
Lower reported bulk density
attributed to variability in SCR.
values for the SCR = 8 mix versus the SCR = 6 mix were due to a
slightly different sampling technique and should not be used to
Higher bulk density values would be
compare the two mixes.
expected in the SCR = 8 mix than in the SCR = 6 mix.
The effect of peat applications on soil organic matter (OM)
As expected, application of
levels is presented in Table 4.23.
peat increased soil organic matter levels. If all of the peat in
a 100 Mg/ha application was recovered by the Walkley-Black
then soil OM would have been increased by
procedure,
Because much of peat is large, undecomposed
approximately 5%.
and woody material, only a fraction (l0-30%) was actually
recovered. The increase in soil OM from peat was greater in the
SCR = 2 and SCR = 4 mixes than the others. This was especially
evident in subsequent seasons in which soil OM levels dropped
Apparently the
more rapidly in the SCR = 6 and SCR = 8 mixes.
higher clay content of the other mixes limited decomposition.
66
4.3.3
Phosphogypsum
effects
Phosphogypsum had no effect on yields
of any of the vegetables grown during the three seasons (Table
This finding held true for both the residual effect of
4.24).
the low application rate of 22 Mg/ha (10 ton/acre) applied in F86
and the very high application rate of 134 Mg/ha (60 ton/acre)
No yield response to the high application rate
applied in S88.
was noted for either the season in which the phosphogypsum was
applied (S88) or the subsequent season (F88).
One noted effect of the high rate of phosphogypsum was to
increase the leaf to root ratio of turnip from 0.74 to 0.84.
This means that added phosphogypsum decreased root growth while
increasing leaf growth; total yield remained unaffected. The
4.3.3.l
Crop
yields.
67
reduction in turnip root growth from the heavy application of
phosphogypsum may have been due to elevated soluble salt levels
No other root crops were grown
in phosphogypsum amended soil.
Turnip root yields were unaffected by
for comparison.
phosphogypsum in the subsequent F88 season.
The lack of yield response to phosphogypsum amendment does
not eliminate the potential usefulness of this material. In
226
Ra
fact, if phosphogypsum addition resultes in reduced
concentrations in plants, it may be important to know that very
high application rates of phosphogypsum do not decrease vegetable
yields.
4.3.3.2 Soil and plant nutrition. Mehlich III extractable
nutrients in phosphogypsum are given in Table 4.25. For purposes
of comparison, average values for sand/clay mixes are also
all extractable
With the exception of Ca,
included.
macronutrient and micronutrient levels were lower in
68
phosphogypsum than in the unamended sand/clay mixes. Mehlich III
extractable Ca was approximately five times greater for
No appreciable Mg was
phosphogypsum than in sand/clay mixes.
Although application of
extracted from phosphogypsum.
phosphogypsum should have no nutritional benefit based upon its
extractable nutrient composition, it may alter nutrient
availability in sand/clay mixes through indirect effects of its
acidic pH (5.1).
Soil-test results depicting the effect of phosphogypsum
applied to sand/clay mixes are given in Tables 4.26 (S87) and
Residual effects of phosphogypsum applied in S86
4.27 (588).
were evident in S87 by an increase in soil Ca from 2470 to 3010
Except for a small reduction in soil-test P, extractable
mg/kg.
levels of other nutrients were not affected. The small reduction
in soil P due to phosphogypsum can be attributed to precipitation
reactions resulting in the formation of calcium phosphates.
A higher rate of phosphogypsum was applied in S88 in order
to increase soil Ca levels substantially and to evaluate
226
Due to interactions
Ra concentrations in crops.
subsequent
between SCR and phosphogypsum, interaction means as well as main
As observed for S87,
effect means were presented in Table 4.27.
phosphogypsum increased soil-test Ca and decreased soil-test P in
69
S88. Due to the much higher phosphogypsum application rate, soil
Increases in
Ca was increased much more in S88 than in 587.
soil-test Ca due to phosphogypsum were greater in SCR = 8 plots
(9,830 vs 1,760 mg/kg) than in the SCR = 2 plots (8,430 vs 3,070
mg/kg).
Application of phosphogypsum decreased soil-test Mg in all
sand/clay mixes. Extractable levels of both Mg and K as well as
most of the micronutrients were' also reduced by phosphogypsum
Despite the reductions in soil-test levels, all
applications.
nutrients tested in the sufficiency range for crop production.
Phosphogypsum effects on soil pH and electrical conductivity
Phosphogypsum applied in S86
are summarized in Table 4.28.
decreased pH an average of 0.13 pH units in S87. A reduction of
0.33 pH units was observed in S88 following the high application
Phosphogypsum continued to cause a pH
rate of phosphogypsum.
reduction of 0.18 pH units in the following F88 season.
70
71
As expected, electrical conductivity (EC) was increased due
to phosphogypsum amendment (Table 4.28). The residual effect of
phosphogypsum applied in S86 was an almost doubling of EC in S87
(1.43 vs. 0.88 mmhos/cm).
The greatest increase in EC from the
addition of phosphogypsum was observed during the subsequent S88
season when an additional 112 Mg/ha phosphogypsum increased EC
from 0.5 to 1.85 mmhos/cm. According to Rhue and Kidder (1983),
yield reduction can begin to occur when EC values exceed 0.5
mmhos/cm.
Phosphogypsum-amended sand/clay mixes which had EC
values up to 2.0 mmhos/cm would normally be considered too saline
for optimum production of most vegetables. However, as noted in
the yield section above, phosphogypsum had no detrimental effect
on vegetable yields at low and at high application rates.
Residual effects of phosphogypsum applied in 1986 on
vegetable nutrient composition in S87 are presented in Table
Despite an increase in Mehlich III extractable Ca, no
4.29.
72
increase in plant tissue Ca was observed for turnip, cabbage or
banana pepper grown in phosphogypsum-amended sand/clay mixes.
Similarly, all other plant
This held true for all SCR mixes.
tissue nutrient concentrations were unaffected by phosphogypsum
The only exception for S87 was a decrease in root B
amendment.
for turnips grown in phosphogypsum-treated
concentration
(see the micronutrient section for more
sand/clay mixes
information on the inverse relationship between Ca and B).
In S88, an additional 112 Mg/ha phosphogypsum were applied
Although added phosphogypsum
to phosphogypsum-amended soils.
increased average tissue Ca concentrations in all vegetable
tissues, only in turnip leaves was the increase statistically
(see radionuclide section for the
significant (Table 4.30)
relationship between turnip leaf Ca and Ra226 concentration).
Phosphogypsum decreased Mg concentration in turnip leaves,
cabbage heads, and squash leaves, but not turnip roots and squash
fruit. Reduction in tissue Mg was attributed to the competitiveIn this case, high Ca levels competitively inhibited
ion effect.
Phosphogypsum increased tissue Zn and Mn in all
uptake of Mg.
Remember, increased
vegetable tissues except for squash fruit.
Zn and Mn uptake were not predicted from soil-test results. It
is possible that localized reductions in soil pH from
phosphogypsum may have resulted in increased Zn and Mn uptake.
Regardless, the decrease in levels of Mg and the increase in
levels of Zn and Mn due to phosphogypsum were minor and
agronomically insignificant.
Residual effects of the high rate of phosphogypsum on the
nutrient composition of vegetables grown in the subsequent F88
As in S88, phosphogypsum
season are presented in Table 4.31.
increased Ca and decreased Mg concentration of vegetable tissues.
Increased Mn concentrations were only observed for mustard leaves
and squash fruit. Tissue Zn concentrations were not affected by
residual phosphogypsum as they were in S88.
73
Soil and Tissue Cadmium.
Phosphogypsum had no
4.3.3.3
effect on the Cd concentration in vegetables grown in sand/clay
mixes (Table 4.32). One exception was an increase in turnip leaf
Cd conc. from 6.5 to 7.1 mg/kg when turnips were grown in
The difference, although
phosphogypsum-amended sand/clay mixes.
small, indicates that pH-lowering materials such as acidic
Cadmium
phosphogypsum may increase Cd uptake by vegetables.
uptake is highly correlated with pH as more insoluble carbonate
and sulfide compounds form at higher soil pH levels (see SCR
section for more on cadmium).
77
4.3.4
Micronutrient
effects
Previous observations and experimental results indicated
that Mn and B deficiencies may exist in crops grown on the
Boron deficiency was first suspected in S86
sand/clay mixes.
(previous study) when brown-rot symptoms appeared in turnip and
cabbage heads and when leaf B concentrations were found to be low
Through visual symptoms of interveinal chlorosis
(Fig. 4.4).
and plant tissue analysis, manganese deficiency had been
In order to gather
suspected in banana peppers grown in S87.
more evidence relative to these suspected micronutrient
deficiencies, fertilizer treatments lacking either Mn or B were
compared to plots receiving both Mn and B fertilizer. Fertilizer
In addition, an
treatments were evaluated in S88 only.
independent B fertilizer experiment was conducted in S87 with
turnip.
Boron deficiency is
evidenced by brown-rot symptoms. Brown-rot disease results in a
brown discoloration of internal tissues within the vegetable
Severe symptoms are accompanied by cracking and rotting
tissue.
(Hurst and Macleod, 1936). Visual B-deficiency symptoms observed
in affected cabbages and turnips in S87 are depicted in Fig. 4.5
and 4.6.
During the S87 experiment, cabbage head and turnip root
Turnip root brown-rot,
interiors were rated for brown-rot.
reported as the percentage of affected roots, was 34, 23, 19 and
0% in sand/clay mixes with SCR equal to 8, 6, 4, and 2,
Turnip leaf B conc. was a better indicator of
respectively.
brown-rot than turnip root B conc. as evidenced by the negative
correlation between leaf B and turnip brown-rot (r = -0.31).
Neither leaf B nor root B was not correlated with yield (Table
Turnip root yields were negatively correlated with
4.33).
increasing Ca:B ratio. Tissue Mn was not correlated with brownrot or yield of turnips.
4.3.4.1
Boron results in S87 season.
78
79
82
Boron fertilizer study in SCR = 4 mix. Results of
4.3.4.2
the independent B fertilizer study indicate that the application
of sodium borate (17% B) at the rate of 1 and 3 kg B/ha decreased
the incidence of brown-rot in turnip roots grown in SCR = 4 mix
(Fig. 4.7).
Brown-rot symptoms were observed in over 80% of
turnip roots not receiving fertilizer B.
Applied B reduced the
rate of incidence to less than 40% in soil without peat
amendment. Peat amendment reduced the effectiveness of applied B
so that brown-rot symptoms were greater in peat-amended versus
unamended soil.
Further evidence that B deficiency was causing brown-rot
symptoms in sand/clay mixes is provided by nutritional data (Fig.
4.8 and Table 4.35).
Brown-rot incidence decreased with
increasing root and leaf B concentrations. Leaf B conc. was 18,
24, and 36 mg/kg in turnip leaves receiving 0, 1, and 3 kg B/ha,
respectively.
Root B concentrations were not greatly increased
by B application.
83
85
The Ca:B ratio in plant tissue has been used to diagnose B
deficiency problems (Gupta and Cutliffe, 1972; Drake et al, 1941;
Reeve and Shive, 1944).
High Ca/B ratios are related to B
Simple correlation coefficients reveal that tissue
deficiency.
Ca/B ratio is more highly correlated with yield and brown-rot
incidence than tissue Ca or tissue B alone (Table 4.36).
Root
Ca/B ratio was very highly correlated (r = 0.65) with brown-rot
incidence; leaf Ca/B ratio was also highly correlated (r = 0.42)
with brown-rot incidence. Root B was negatively correlated (r =
-0.49) with brown-rot incidence.
While B deficiency increased brown-rot incidence, yields
were not greatly reduced (Fig. 4.9).
Peat increased turnip
yields, especially leaf yields, but yields were not correlated
with tissue B concentrations (Table 4.36) despite an increase in
leaf B from peat application.
Leaf yield was negatively
correlated (r = -0.44) with leaf Ca/B ratio, again indicating the
importance of this nutrient interrelationship.
87
88
4.3.4.3
Boron
fertilizer
effects
in
Spring
1988.
Fertilizer B increased yield of turnip but not yield of cabbage
and squash (Table 4.37). Turnip yields were reduced 8% without B
fertilizer. Yield reductions due to lack of B fertilizer were 4,
12, 10, and 8% in the SCR = 2, SCR = 4, SCR = 6, and SCR = 8
mixes, respectively.
Boron fertilizer increased both root and
leaf growth so that the 1eaf:root ratio was unaffected.
Boron
fertilizer had no effect on cabbage or squash yields. This lack
of yield response to B was consistent in all SCR mixes.
The effects of boron fertilization on soil and plant tissue
B are presented in Table 4.38.
Application of 2 kg B/ha
increased hot-water-soluble B (hwsB) from 0.6 to 1.0 mg/kg.
Critical hwsB levels depend upon the crop as some crops are more
sensitive to B-deficiency or B-toxicity than others.
A hwsB
level greater than 1.0 mg/kg is usually adequate for vegetables
although a level between 1.2 and 1.5 mg/kg is recommended (US
Borax, 1982).
89
Boron fertilization increased plant B concentration in each
vegetable tissue.
For turnip leaves,
normal leaf B
concentrations range from 25 to 60 mg/kg. Fertilizer B increased
turnip leaf B conc. from what would be considered a low
concentration of 19 mg/kg to a normal concentration of 28 mg/kg.
Squash leaf B was also greatly increased by fertilizer B (61 vs
However, unlike turnip, no yield response from B
31 mg/kg
fertilizer was noted for squash.
Increased tissue B without an
associated yield increase was also observed for cabbage.
l
4.3.4.4
Manganese effects in spring 1987 season.
Interveinal chlorosis of banana pepper leaves was observed in
Leaf samples taken from normal and chlorotic pepper plants
S87.
were analyzed for several nutrients (Table 4.39). Manganese was
very low considering that plant tissues containing less than 20
Calcium and Mg
mg/kg are considered deficient in Mn.
concentrations were higher in normal-looking pepper leaves than
in chlorotic leaves but this should not have caused the
interveinal chlorois.
Boron concentrations were in the
sufficiency range (>25 mg/kg).
90
Manganese was correlated with yield of banana pepper and cabbage:
a positive but statistically insignificant correlation was
observed between turnip leaf Mn and yield. In order to follow up
on the indications of Mn-deficiency, treatments of Mn fertilizer
were applied in S88.
4.3.4.5 Manganese effects in spring and fall 1988 seasons.
Yields of vegetables as affected by Mn fertilization in S88 are
presented in Table 4.40.
Manganese fertilizer increased turnip
yields an average of 6% (24.6 vs. 23.1 Mg/ha).
Fertilizer Mn
increased turnip root but not turnip leaf yield.
Although
91
fertilizer Mn was not evaluated in F88, turnip yield in F88 was
correlated with leaf Mn (r = 0.27) and with root Mn (r = 0.22).
The response to Mn was greater when the high rate of peat was
applied (14% increase) than when no peat was ever applied (4%
increase)(data not given).
Cabbage and squash yields were not affected by fertilizer
However, squash yield was correlated with fruit Mn (r =
Mn.
The low correlation indicates that factors other
0.18; p<.05).
than Mn were more important determinants of yield.
The effects of Mn fertilization on soil and plant tissue Mn
are presented in Table 4.41.
The application of 50 kg Mn/ha
doubled Mehlich III extractable Mn from 4.1 to 8.7 mg/kg. Plant
uptake of Mn was increased in each vegetable tissue with the
greatest increase observed for turnip leaves (64 vs. 28 mg/kg).
Although average squash leaf Mn and fruit Mn were not greatly
affected by fertilizer Mn, squash fruit Mn was correlated with
squash yield (r = 0.18); no correlation existed between leaf Mn
and squash yield (r = 0.04).
92
4.3.5 Radium-226
The influence of sand/clay ratio on
soil Ra226 content is depicted in Fig. 4.10.
Soil Ra226 ranged
from a high of 16.0 pCi/g in the SCR = 2 mix to a low of 7.8
pCi/g in the SCR = 8 mix (Table 4.42).
Average soil Ra226 was
13.4, 11.5, 10.7, and 8.2 for SCR = 2, SCR = 4, SCR = 6, and SCR
= 8 mixes, respectively.
Soil Ra226 values for undisturbed
surface soils in Florida average 0.5 pCi/g (0.2-3.8 pCi/g). It
follows that total Ra226 content was approximately 20 times
greater in the SCR = 2 mix than in undisturbed soils.
4.3.5.1
Soil
Ra226.
93
94
An ANOVA to test sand:clay
ratio,
and phosphogypsum effects on tissue Ra226
peat,
concentration was only conducted for Ra226 data obtained from
SCR = 2 and SCR = 4 mixes: values for the SCR = 6 and SCR = 8
mixes as given in Tables 4.43-4.45 were based on composites
samples from each of four replications.
These composites were
included in regression analyses but not in the ANOVA. Except for
the reduction in the number of sand/clay mixes evaluated, the
ANOVA used to evaluate treatment effects on Ra226 was identical
to that used on other parameters (page 36).
An exception to the above discussion was followed for the
F88 season.
No composites were taken in F88 and the ANOVA
included SCR = 6 and SCR = 8 data.
Ra226 concentrations in vegetable tissues as affected by SCR
are given in Tables 4.43-4.45.
Means for SCR = 2 and SCR = 4
mixes were extracted from these tables and summarized in Fig.
4.11 which also indicates statistically significant differences.
It should be noted that Ra226 values are given as pCi/g dry
tissue.
Conversions to pCi/kg fresh tissue are given as
footnotes to the tables.
No simple generalizations can be made concerning the effect
of SCR on plant Ra226 concentration. Comparing SCR = 2 and SCR =
4 mixes (Fig. 4.11), it was observed that the Ra226 concentration
in turnip roots (S88), cabbage heads (S87) and squash fruit (F88)
was greater in the SCR = 4 mix than in the SCR = 2 mix. Greater
Ra226 concentrations were also observed for turnip leaves (S88),
turnip roots (F88), cabbage head (S88), and squash fruit (F88)
grown in the SCR = 4 mix than in the SCR = 2 mix but the
increases were not statistically significant. The fact that this
trend was observed for several different crops over three
cropping seasons led us to the conclusion that plant Ra226
concentration was either unaffected or slightly increased when
increasing the SCR from 2 to 4. Clearly, selection of a SCR = 4
mix over a SCR = 2 mix can not be recommended on the basis of
reduced plant Ra226 uptake despite reduction in total soil Ra226.
4.3.5.2
Ra226
in
vegetables.
95
97
98
Why an increase in plant Ra226 concentration as SCR is
increased from 2 to 4 when the SCR = 4 mix had a lower soil Ra226
One reason might have been a dilution effect from
content?
greater yields obtained in the SCR = 2 mix. Cabbage yield in S87
was negatively correlated with Ra226 (r = -0.44); turnip leaf
yield in F88 was negatively correlated with leaf Ra226 (r =0.42). This was not the case for squash in S88 when yields were
greater in the SCR = 4 mix while fruit Ra226 concentrations were
greater in the SCR = 2 mix. Another possible explanation is the
lower soil bulk density of the SCR = 2 mix. The bulk density was
approximately 25% greater in the SCR = 4 mix.
This indicates
that a given root volume in the SCR = 4 mix would contain 25%
more dry soil. Because soil Ra226 was only 17% higher in the SCR
= 2 mix (13.4 vs. 11.5 pCi/g), it follows that total Ra226 was
greater in the SCR = 4 than the SCR = 2 mix on a volume basis.
Other chemical factors in the soil may have been important but
the limited effect of SCR on the nutrient composition of
vegetables places less importance on these factors.
Tissue Ra226 concentrations were not substantially decreased
in the more sandy SCR = 6 and SCR = 8 mixes.
In fact, average
Ra226 concentrations were higher in squash and cabbage grown in
SCR = 8 mix than in the same vegetables grown in the SCR = 2 mix.
Regression analyses between nutrient concentrations and
Ra226 were conducted for each vegetable in order to determine if
any nutrient element was correlated with Ra226 uptake (Table
4.46).
It should be noted that correlation does not indicate
cause or effect.
However, plant nutrient uptake of one element
is often correlated with other nutrient elements and, therefore,
the regression analyses may offer some clues as to nutritional
effects on Ra226 uptake.
No nutrient element was consistently correlated with Ra226.
Tissue K was positively correated with turnip leaf Ra226 in S88
and cabbage Ra226 in S87.
Increased K often is related to a
decrease in Ca uptake due to the competitive-ion effect. Reduced
Ca uptake as such may have in turn caused, also through the
100
competitive-ion effect, an increase in Ra226 concentration.
Although a negative correlation was obtained between cabbage
(S88) Ca and Ra226, the positive correlation between mustard leaf
Ca and Ra226 observed in F88 and the lack of correlation between
Ca and Ra226 for other vegetables sheds some doubt on the
hypothesis that increased tissue Ca is related to decreased Ra226
uptake in vegetable tissues.
When all the data from each vegetable are combined, some
interesting results are noted with respect to tissue Ca. It was
observed that Ra226 concentration in different vegetable tissues
was highly correlated with Ca concentration (Fig. 4.12).
Although this relationship has never been proposed as far as we
know, it makes sense. Ra226 behaves in a chemical manner similar
to the alkaline earth metals Ca and Mg. It follows that a tissue
which takes up higher amounts of Ca would also take up higher
amounts of Ra226.
Regression analyses of 595 observations
indicated that a quadratic equation based upon tissue Ca
predicted 55 percent of the variation in Ra226 content:
Y = 0.08 + 0.31x - 0.028x2
where y = plant Ra226 conc. in pCi/g dry and x = plant Ca conc.
in %.
This predictive equation is surprisingly good considering
the high variability in Ra226 measurements.
This information
should be quite useful if one wishes to predict the Ra226
concentration of a particular crop.
Because Ca is a structural
element in plant tissues, plant tissue Ca concentrations tend to
be more stable and fall within narrow concentration ranges.
Therefore, 226Ra predictions from Ca conc. in tissues should not
vary considerably depending upon soil conditions.
Note that
these results are based upon sand/clay mixes with soil Ra226
values ranging between 8 and 16 pCi/g. These findings should be
compared with results found in other phosphatic clay soils.
102
226
Ra and Ca in tissues was included in
The ratio between
Table 4.47 for a couple of reasons. One point to be made is that
226
tissues was
ratio in vegetable
Ra:Ca
the m a x i m u m
226
Therefore, we can not only
approximately 100 pCi
Ra/g Ca.
226
Ra value from the quadratic equation (Fig.
predict an average
226
Ra concentration
4.12), but we can also predict the maximum
that is likely to occur. Perhaps more importantly, these results
226
Ra did not excessively accumulate in plant
indicate that
tissues due to indiscriminate uptake.
226
Ra:Ca ratios is to
A second reason for presenting
According to results
compare average ratios among crops.
226
Ra:Ca ratio
presented in Fig. 4.12 and Table 4.47, the
decreased as tissue Ca increased. Therefore, a vegetable tissue
226
Ra:Ca ratio.
with a lower 226Ra conc. had a higher
This
observation may be more practical from a health perspective than
Upon ingestion by humans, gut
from an agronomic perspective.
226
Ra and subsequent deposition into bone tissues
absorption of
has been found to be inversely related to the amount of Ca in the
226
Ra and Ca
diet (Eisenbud, 1973). Therefore, the ratio between
226
in a diet may be more important than the actual
Ra conc. by
It follows that, when ingesting vegetables grown in
itself.
these sand/clay mixes, greater deposition of 226Ra in bone would
result from ingesting foods which contain relatively low levels
226
Ra:Ca) than foods which contain relatively
of 226Ra (higher
226
high levels of
Ra (lower 226Ra:Ca).
Radium-226 data were within reported ranges of 226Ra in
vegetables sampled by Guidry et al. (1986).
Results of their
which involved diet models and radiation dose
study,
226
Ra in foods
calculations, indicated that elevated levels of
from mined lands did not significantly effect human radiation
exposure.
Uptake ratios or concentration factors (ratio between Ra226
in the soil to Ra226 in the plant) can be useful when comparing
Ra226 uptake by different crops and under different soil
conditions. As noted in the literature review section, an uptake
105
ratio of 0.01 has been given as a general guideline for
Our
predicting uptake of Ra226 from Ra226-containing soils.
results indicate that the uptake ratio will be greater than 0.01
Uptake ratios were 0.067, 0.026, 0.018,
in sand/clay mixes.
0.025, and 0.056 for turnip leaves, turnip roots, cabbage, yellow
The overall uptake
squash, and mustard leaves, respectively.
ratio for all crops over all SCR's was 0.024.
Phosphogypsum had no observable effect on vegetable Ra226
concentration for several vegetables and for several seasons
(Tables 4.48-4.50). There was no effect for either the 22 Mg/ha
Phosphogypsum increased soil and tissue
or the 134 Mg/ha rate.
Ca for most vegetables but tissue Ca was not correlated with
tissue Ra226.
106
107
The question of the Ra226 concentration in the phosphogypsum
and its confounding effect on Ra226 uptake should be addressed.
The phosphogypsum used in this study contained 22.6 pCi/g. This
concentration was almost 1.7 times the level found in the SCR = 2
mix and almost 2.5 times the level found in the SCR = 8 mix.
These differences in Ra226 content are greatly diluted when one
considers that application of 134 Mg/ha of phosphogypsum only
represents a total Ra226 increase from 13.4 to 14.1 pCi/g in the
SCR = 2 mix and 8.2 to 9.3 pCi/g in the SCR = 8 mix:
Before phosphogypsum application
1800 Mg/ha soil
(bulk density = 1.2 g/cm3, 15 cm depth)
SCR = 2 mix contains 13.4 pCi/g
SCR = 8 mix contains 8.2 pCi/g
After phosphogypsum application
Phosphogypsum applied at 134 Mg/ha and contains 22.6 pCi/g Ra226
SCR = 2 mix:
SCR = 8 mix:
(134/1800 x 22.6) + (1666/1800 x 13.4) = 14.1 pCi/g
(134/2250 x 22.6) + (2116/2250 x 8.2) = 9.1 pCi/g
Furthermore, phosphogypsum-amended soils contained over four
times (9290 vs 2250 mg/kg) the extractable Ca levels of unamended
sand/clay mixes while increases in Ra226 would have been only 1.1
times greater.
Our hypothesis was that by increasing the soil Ca to soil
Results
Ra226 ratio one might decrease the uptake of Ra226.
indicate that phosphogypsum had no effect on Ra226 uptake by
vegetables despite its effect in increasing soil Ca and in some
One possibility is that the majority of
cases plant Ca levels.
feeder roots of vegetables were growing in the clay matrix and
not in the vicinity of PG particles. High localized salt levels
from PG might have caused this effect.
If this were the case,
increases in the soil Ca to Ra226 ratio from PG would not have
No direct evidence for this
been agronomically significant.
possible explanation was obtained.
108
109
5.0 SP-1 ALFALFA PHASE
5.1
Objectives
The objectives of the SP-1 Phase experimentation were:
1. to evaluate the yield and composition of alfalfa grown on a
2:l SCR mix;
2. to evaluate and compare the effects of selected organic
amendments on soil physical and chemical properties;
3. to evaluate and compare the effects of selected organic
amendments on the production and quality of alfalfa.
5.2
Methodology
A one-acre portion of CF Industries' sand-clay reclamation
area, SP-1, was chosen as the site for this experiment.
Naturally invading vegetation, composed primarily of willows,
grasses, and cattails, was mowed and disc-plowed in June 1987.
The site was tilled using a rotovator on 29 Sept. 1987. Once the
land had been rotovated a drainage system was formed using a
ditch-plow which created small lateral ditches on 5.5 m centers.
Individual plot dimensions were 9.1 m by 5.5 m with 1.8 m
separation strips dividing plots in the long dimension.
The following treatments were arranged in a randomized
complete block design with four replications:
1. Unamended control
2. Unamended control + 200 kg N/ha
3. Sawdust at 22 Mg/ha
4. Sawdust at 45 Mg/ha
5. UNICAM humate at 1.1 Mg/ha
6. UNICAM humate at 2.2 Mg/ha
7. Composted garbage/sludge at 22 Mg/ha
8. Composted garbage/sludge at 45 Mg/ha
9. Composted garbage/sludge at 67 Mg/ha
10. Peat at 22 Mg/ha
11. Peat at 45 Mg/ha
12. Sewage sludge at 22 Mg/ha
13. Sewage sludge at 45 Mg/ha
14. Composted sewage sludge at 22 Mg/ha
15. Composted sewage sludge at 45 Mg/ha
110
Composted sewage sludge and composted garbage are becoming
popular processed waste products around the country.
The
composted sewage sludge was obtained from Broward County Streets
and Highways Division in cooperation with Mr. Bill Farrell. The
sludge compost was made by combining sewage sludge with yard
waste and allowing composting to occur in windrow piles.
The
composted garbage material was produced in Gladewater, Texas by
Vital Earth Resources. Dr. Hugh Ettinger of Bioconversion Corp.
offered to ship the material from Texas to the site.
According
to Dr. Ettinger, a large cornposting facility is to be constructed
in Brooksville, Florida in the near future.
Sewage sludge from
Fort Meade's sewage treatment facility was used in this study.
The Grade I sewage sludge was collected after dewatering in
drying beds.
Peat and sawdust were obtained from Townson Peat
and Soil in Lakeland.
UNICAM humate is a granular (also
available in powder form) material which is an organic by-product
of the titanium mining industry. The material has been reported
to have several beneficial effects as a soil supplement including
increased nitrogen and micronutrient uptake efficiency, plant
growth regulator functions, and soil conditioning (Conover and
Poole, 1978; Stevenson, 1979; Burns et al., 1986).
The UNICAM
product has the following properties (Union Camp Corporation,
1987):
Bulk density 0.75-0.77 g/cm3 (48 lb/ft3)
Moisture 10%
Ash
30%
Organics 60%
Humic acid 48-53%
Fulvic acid 7-12%
On 11 Nov. 1987, organic materials and fertilizer were
broadcast and incorporated by rotovation to a l0-15 cm depth.
Base fertilizers, which included 200 kg K/ha as KCl, 25 kg N/ha
as urea, 3 kg B/ha, 3 kg Cu/ha, 9 kg Fe/ha, 7 kg Zn/ha, and 7.5kg
Mn/ha, were broadcast and incorporated along with the organic
materials.
111
Alfalfa 'Florida 77' seed were sown by broadcasting at the rate
Excellent emergence
of 22 kg/ha (20 lb/acre) on 16 Nov., 1987.
was obtained without incorporating the seed into the surface of
the soil. No irrigation was used.
Soil samples were collected from each plot in March after
the first harvest and in November after the seventh and last
Soil samples consisted of five cores per plot to a
harvest.
Sand:clay ratios were determined to assess any
depth of 15 cm.
textural variation throughout the site. Soils were analyzed for
Mehlich III extractable P, K, Ca, Mg, Fe, Zn, Mn, Cu, and Cd.
Soil pH and conductivity measurements were also made as described
Soil bulk density
for the SCR Phase experimentation.
measurements were made as described for the SCR Phase
Four cores were sampled per plot in March and
experimentation.
After determing soil bulk density, the four samples
November.
were cornposited into one sample per plot and analyzed for organic
carbon content using the Walkley-Black procedure.
Vane shear
tests were made in November after the final harvest.
The vane
shear instrument was manufactured by Pilcon Engineering of
Measurements were made with a 19 mm vane inserted to
England.
both 10 and 20 cm depths.
Seven alfalfa harvests were taken on a 6-wk schedule (see
Plots were mowed and fresh cut material weighed.
Table 5.5).
Moisture content was determined by taking grab samples and drying
in an oven overnight. Yields were recorded on a dry-wt. basis.
Alfalfa tissue samples from each plot of each harvest
(except harvest 6) were dried and saved until the end of the
season.
After the final November harvest, composites were made
for each plot by combining tissues from each harvest. In
addition, composites from control and sewage sludge amended plots
were made for each harvest date to evaluate seasonal changes in
nutrient content. The sewage sludge treatment was chosen because
it resulted in increased alfalfa yields.
All tissue composites
were dry-ashed and analyzed chemically as described for the SCR
Composites were also sent to Core Laboratories
experimentation.
112
for Ra226 analyses and to the Forage Evaluation Support
Laboratory at the University of Florida for in vitro organic
matter digestion (IVOMD).
5.3
Results
and
Discussion
5.3.1 Soil and plant nutrition
Nutrient analyses of the various organic materials are
The effects of these materials once
given in Table 5.1.
incorporated into the sand/clay mix are presented in Table 5.2.
All organic materials had pH values less than that found in
Peat had a relatively low pH of 4.0 and
the sand/clay mix.
caused a reduction in soil pH from 7.8 to 7.6 with the highest
application rate (Table 5.2). A similar decrease in pH from peat
application was also observed in the SCR Phase experimentation.
Sewage sludge had an even smaller effect decreasing soil pH from
7.8 to 7.7. Sawdust, both composts, and humate had no observable
effect on soil pH.
Nutrient contributions varied tremendously from one
When comparing the extractable levels of
material to another.
the organic materials to levels observed for the sand/clay,
material application rates of 22 and 45 Mg/ha are approximately
equivalent to a 1 and 2% application rate.
Therefore, for the
materials to make a significant nutrient contribution, they
would need nutrient levels over 100 times that found in the
Due to the high P content of the sand/clay mix,
sand/clay mix.
higher extractable P, Ca, and Mg values observed for sewage
sludge and the two composts should not be agronomically
The two composts had relatively high extractable K
important.
When applied at 22 and 45 Mg/ha rates, garbage/sludge
contents.
compost increased soil test K 65 and 100 mg/kg; sewage sludge
compost at the two rates increased soil test K 20 and 95 mg/kg
By the end of the season, soil test K had dropped
(Table 5.2).
dramatically and was unaffected by treatment (Table 5.3).
113
Micronutrient contributions of the organic materials were
Soil test Zn was increased in sand/clay mix
quite variable.
amended with either sewage sludge or the two compost materials.
Small increases in soil test Mn resulted from the highest
garbage/sludge compost rate (12 vs 9 mg/kg).
Sawdust contained
relatively high extractable Cu levels.
Both the low and high
application rates of sawdust resulted in increased soil test Cu
values.
Plant tissue analyses indicated that very little variation
existed in the nutrient composition of alfalfa tops due to
treatment effects (Table 5.4) or due to harvest date (Table 5.6).
This was contrary to observed variations in soil test K, Zn, Mn,
and Cu caused by organic amendments.
No correlations between
nutrient concentrations and yield were observed.
Normal nutrient concentration ranges for alfalfa can be
used to assess potential nutrient deficiencies:
By comparing values in Table 5.5 with normal ranges provided
above, it can be seen that macronutrient concentrations were
normal and that, except for Mn, micronutrient concentrations were
Manganese deficiency was also observed for vegetable
normal.
production in sand/clay mixes. Although soil-test Mn and tissue
Mn conc. were low, neither was correlated with alfalfa yield.
117
Because the treatment x harvest date interaction was not
significant, annual treatment totals were compared.
Yield
increases of 16% over the unamended control could be detected in
this experiment at the 5% confidence level. In this regard,
119
application of sewage sludge increased yield an average 24% (13.6
vs. 11.0 Mg/ha). There was no additional benefit of applying the
higher rate of sewage sludge.
The highest application rate of
the garbage compost increased annual yield 22% (13.4 vs. 11.0
Lesser yield increases were observed for the 22 and 45
Mg/ha).
Mg/ha application rates.
The other organic materials increased
yields from 3-14% but these increases were not statistically
significant.
According to the ANOVA, block effects were greater than
treatment effects.
We observed that the elevated side of the
site produced better in the summer while the lower side produced
better in the late spring when it was dry.
It follows that site
selection and drainage characteristics will be important yield
determinants.
For the first two cuttings, the sewage sludge plots were
easy to distinguish from the other plots as alfalfa in these
plots was lush and darker green than in other plots.
Areas of
leaf yellowing were evident in certain areas.
Yellowing tended
to disappear after a rainfall.
In an effort to identify the
"sludge factor" that was contributing to lusher alfalfa growth,
dark green alfalfa tops from sewage sludge plots were sampled on
February 20 (before the first harvest) along with leaves from
isolated chlorotic plants growing in control plots. Both grab
samples were chemically analyzed:
chlorotic
dark green
N
P
K
Ca
Mg
Fe
Zn
Mn
Cu
3.5
3.7
0.5
0.4
1.1
1.2
1.1
0.9
0.2
0.2
92
90
25
100
10
20
7
47
A comparison between these two analyses indicates that the
micronutrient elements Zn, Mn, and Cu may be important.
Of the
three, Mn levels appear more deficient.
Sufficiency
concentrations of Mn in alfalfa tops have been reported to be >20
The above results indicate that Mn was deficient in
mg/kg .
chlorotic plants and normal in dark green plants.
Manganese
122
deficiency is also consistent with findings in the SCR Phase
experimentation.
Treatment samples composited over all harvest dates failed
to show differences in micronutrient concentrations.
One
explanation is that micronutrient deficiencies were transient and
came and went with surface moisture levels.
The greening up of
alfalfa in the plots was quite dramatic after rains.
Nitrogen
release from sewage sludge was discounted as the "sludge factor"
because tissue N concentrations were not greatly different and
because N fertilizer had no effect on alfalfa yields.
It would
seem that the "sludge factor" may have been due to micronutrient
contributions (particularly Mn) of sewage sludge.
An increase in yield of 3.5 Mg/ha, which was observed for
the application of sewage sludge, is equivalent to 1.5 tons/acre.
Assuming 25% moisture in hay and a modest price of $125/ton of
hay, this increase would be worth a gross return of $250/acre.
Transportation and land application costs can be quite variable
depending upon the distance from the source and moisture content
of the material.
The sewage sludge used in this experiment had
been dried in drying beds.
This allowed for relatively high
application rates of solids to be made.
By pinpointing the particular quality of the sludge which
had the greatest influence on yield, the optimum rate of sewage
sludge needed to increase yields may turn out to be low enough to
consider lower solids content sludges and lower application
rates.
Alternatively, if the "sludge factor" is in fact due to
micronutrient relationships, efficient micronutrient fertilizer
programs could prove more economical.
5.3.3
Bulk density. organic carbon, and shear strength
Bulk density, soil organic carbon, and vane shear strength
results are presented in Table 5.7.
Soil bulk density was unaffected by treatment when measured
in March after the first harvest.
Field variability including
clay cracking and tractor compaction resulted in large
123
differences in measurements. When measured in November after the
final harvest, differences in bulk density due to treatments were
detected. Bulk density was decreased by the 45 Mg/ha application
rate of garbage compost, peat, sludge compost, and sewage sludge.
Similar effects were not observed for the lower 22 Mg/ha rates
for any of these materials.
124
The organic C content of sand/clay mix was increased by
organic amendments.
The greatest increase in organic C was
observed for the garbage compost treatments.
This was not
surprising considering that the garbage compost was a thoroughly
composted product that had been screened to remove coarse
As with soil bulk density, wide variability in
materials.
organic carbon measurements was noted.
Pockets of organic
materials were frequently encountered during sampling.
This was
most likely due to non-uniform incorporation of organic materials
into the clays.
Vane shear strength measurements were taken in the field to
assess any strength changes in sand/clay mix that might have
resulted from applications of organic materials.
As was noted
for bulk density and organic C measurements, wide variations in
vane shear tests were noted within the same plot. No differences
in vane shear strength due to treatment effects were noted at
either the 10 or 20 cm depths. Moisture content at the time of
sampling ranged from 26 to 33% on a dry wt. basis.
5.3.4 In vitro organic matter digestibility.
In vitro organic matter digestibility is a measure of forage
Increased IVODM is associated with increased nutritive
quality.
value due to greater absorption in the ruminant digestive system.
Grasses generally have lower IVODM values than those for highquality legume forages.
High IVODM of alfalfa is one factor
which makes alfalfa such a high-quality forage.
Organic amendments had no observable effects on IVODM of
alfalfa cornposited over six harvests. Values were all within a
narrow range of 67.2-70.1%.
In-vitro-organic-matter-digestibility varied among the
different harvests (Fig. 5.2).
After the first harvest, which
had the highest value, IVODM decreased with each of the next four
cuttings. For the last cutting in November, IVODM increased back
to spring levels.
125
.
5.3.5 Ra226 in alfalfa.
Radium-226 concentration in alfalfa was determined for
samples cornposited over all harvests.
Other than the control,
the high application rate of each organic amendment was analyzed
for Ra226.
In addition, composites for each harvest were made
for control and sewage sludge treatments to assess any changes in
Ra226 during the year.
The Ra226 concentration in alfalfa as affected by organic
amendments is presented in Table 5.8. Organic amendments had no
observable effect on alfalfa Ra226 concentration. Alfalfa 226Ra
conc. ranged from 0.251 to 0.678 pCi/g.
Radium-226 conc. was higher in alfalfa leaves than in stems:
alfalfa leaves
alfalfa stems
0.55 pCi/g dry
0.31 pCi/g dry.
Because leaf drop can be significant during harvesting and baling
operations,
actual concentration of Ra226 in alfalfa will
probably decrease somewhat during normal harvesting operations.
Samples from our study were taken before baling operations and,
therefore, reflect the maximum likely concentrations that would
be found.
Further evidence for our earlier conclusion that tissue Ca
can be used to predict tissue Ra226 concentration is provided by
the above results.
Calcium concentration is lower in alfalfa
stems than in alfalfa leaves.
Bickoff et al. (1972) reported
stem Ca conc. to be approximately half that of leaf Ca conc.
Regression analysis was conducted in order to correlate soil
and tissue nutrient levels with plant Ra226 conc. (Table 5.9).
Although no nutrient in alfalfa was correlated with Ra226, the
correlation with leaf N was noteably stronger than the rest of
the nutrients with an observed significance level just exceeding
the 5% confidence level (p<R = 0.055).
Mehlich III extractable Ca was inversely correlated with
plant Ra226.
The correlation was observed for both March and
November soil sampling dates. The negative coefficient indicates
that increased extractable Ca levels are associated with
decreased Ra226 levels.
This result was expected as wider
ranges in soil Ca were present in the vegetable experiments with
no effects on Ra226 uptake.
128
Sand:clay ratio was relatively uniform within the plots and
was not correlated with Ra226 in alfalfa tops.
Bulk density of
samples taken in November was negatively correlated with Ra226
(r = -0.46).
No correlation was observed for the March density
sampling date (r = 0.31).
One explanation of the negative
correlation between bulk density and Ra226 may be based on the
assumption that lower bulk density soil contains less dry soil on
a root-volume basis.
This hypothesis was suggested earlier in
the SCR section when it was observed that higher Ra226
concentrations were found in vegetables grown in the SCR = 4 mix
than in the SCR = 2 mix: the SCR = 4 mix had a 25% higher bulk
density.
The 226Ra:Ca ratio (pCi 226Ra/g Ca) averaged 30.3 and was,
therefore, similar to that found in vegetable tissues.
The
226
maximum
Ra:Ca ratio observed for the 28 observations was 83.3
226
pCi
Ra/g Ca.
This agree well with the conclusion presented
earlier that the maximum Ra226:Ca ratio in plant tissues grown on
these sand/clay mixes does not exceed 100 pCi 226Ra/g Ca.
129
6.0
6.1
GLASSHOUSE
PHASE
Introduction
The glasshouse phase of this research project was designed
to quantify the degree of heavy metal uptake by forages grown on
soils which had been amended with various organic amendments.
Soils used were tailings sand and a mixture of tailings sand and
waste phosphatic clay. The primary focus of the research was to
determine the influence of phosphatic clay on the plant uptake of
selected heavy metals.
The objectives of this phase of the
research were i) to determine waste phosphatic clay influence on
Cd availability to plants, and ii) to determine the influence of
organic waste materials on heavy metal uptake by plants.
6.2
Materials
and
Methods
Five 55-gallon barrels of waste phosphatic clay (clay) and
three barrels of waste tailings sand (sand) were collected at
Consolidated Farmers Industries' Hardee County phosphate mine at
Fort Green.
The clay had been allowed to settle in a primary
settling area for several months prior to being dredged and
hydraulically transferred to a batch mix station for mixing with
sand.
The clay was sampled at the mix station. During storage,
supernatant water was removed from the barrels of clay as the
clay continued to settle.
6.2.1 Experiment one
The objective of the first glasshouse experiment was to
determine the degree to which heavy metal uptake by plants is
influenced by the addition of organic amendments to tailings sand
and a sand/clay mix.
A SCR = 4 mix was formulated (dry wt. basis). Mixing of the
sand and clay was facilitated by use of a rotary mixer. Clay was
poured into the mixer and the appropriate amount of sand was
added.
After 10 min of mixing, the sand/clay mix was spread in
thin layers and allowed to air dry.
130
Pour soil amendments were utilized in this experiment,
namely Florida sedge peat, sawdust, shredded garbage, and sewage
The sedge peat was a commonly available commercial
sludge.
The sawdust was obtained from Goodwin Lumber Company,
product.
in Micanopy, and was a random mixture of pine and cypress. This
sawdust had been stored in an open pile for approximately 1 yr
prior to collection.
Sewage sludge was obtained from the Jacksonville Naval Air
This material was an activated sludge, taken from a
Station.
This sludge was reported by the Naval Public
sand drying bed.
Works Department to have had a very high concentration of heavy
metals such as Pb and Cd.
It was estimated that approximately
75% of the sludge was derived from domestic sources while 25% was
from industrial sources.
Industrial sources included aircraft
maintenance and repair facilities located at the station.
Shredded garbage was obtained from Lakeland's McIntosh Power
Plant.
This material was collected by garbage curbside
collection crews and delivered to the power plant in garbage
trucks.
Upon offloading, material unsuitable for shredding was
removed.
Material removed included white goods, automobile
tires, flammables, and any other material which would interfere
with the shredding process.
A sample of the light fraction
consisting mainly of cellulosic material,
plastics,
and
putrescible materials was collected for use in this study.
Four replications of the following soil/amendment
combinations were evaluated:
1.
2.
3.
4.
5.
6.
7.
8.
sand/clay
sand/clay
sand/clay
sand/clay
sand/clay
sand/clay
sand/clay
sand/clay
mix
mix
mix
mix
mix
mix
mix
mix
or
or
or
or
or
or
or
or
sand
sand
sand
sand
sand
sand
sand
sand
+
+
+
+
+
+
+
200
16
16
16
16
kg/ha N as NH4NO3
g/kg peat
g/kg sawdust
g/kg shredded garbage
g/kg sewage sludge
80 g/kg sewage sludge
160 g/kg sewage sludge
131
The amendments, with the exception of the shredded garbage,
were air-dried prior to being mixed with the soil. The shredded
garbage was applied at an average moisture content of 30%.
The
moisture of all other materials was determined according to the
method described for the clay samples.
All application rates
were on a dry-wt. basis.
Fifteen cm plastic pots were lined with cheesecloth and 2.5
cm of gravel were placed in the bottom of each pot. Two thousand
five hundred grams of each mixture were placed in one of four
pots. A fertilizer solution supplying 100, 25, 5, 5 and 1 mg/kg
of K, Fe, Mn, Zn, and B, respectively, was added to the surface
of each pot. After adding the fertilizer, the top 10 cm of each
soil mixture were removed, thoroughly mixed and placed back into
the pots.
Twenty five pregerminated seedlings of Alyce clover
(Alysicarpus vaginalis) were planted per pot along with a
Rhizobium (Rhizobium meliloti) culture which was sprinkled onto
each pregerminated seed prior to covering.
Plants were thinned
to 17 per pot after establishment.
Water was applied daily as
needed.
Plants were maintained in a glasshouse for 150 d. Tops
were harvested on day 75, 110, and 150.
Harvested plant
material was dried overnight in a 80°C oven and weighed.
After the final harvest, root material was removed from the
pots, dried, and weighed.
Soil samples collected from each pot prior to and after
plant growth were analyzed for the following:
pH (in H2O and KCl)
Electrical conductivity
DTPA extractable metals
Mehlich I extractable nutrients
Exchangeable bases by the summation method
Total Kjeldahl nitrogen
Plant tissue samples were ground in a Wiley mill fitted with
stainless steel blades and sieves.
Ground tissue samples were
132
ashed at 450°C, taken up in HCl and analyzed for selected plant
nutrients by atomic adsorption spectrophotometry.
Tissue N was
determined by micro Kjeldahl techniques.
Elemental soil analysis included Mehlich I extractable Cd,
Cu, Ca, Mg, Zn, and Mn; DTPA extractable Fe, Zn, Mn, Cu, Cd, Pb,
and Cr; and NH4OAc extractable Na, K, Ca, and Mg.
Plant tissue
extracts were analyzed for Cd, Cu, Zn, Fe, Ca, Mg, and Mn.
6.2.2 Experiment two
The objective of the second glasshouse study was to
determine the degree to which plant uptake of Cd is influenced by
the presence of waste phosphatic clay.
In addition to Cd, the
uptake of Cu, Zn, Mn, and Fe was evaluated.
Four organic amendments were utilized in this experimentshredded garbage, digested garbage, and two sewage sludges. The
sewage sludges were derived from two sources.
The first source
of sludge (JS) was taken from the Jacksonville Naval Air Station
as described for the first experiment.
The second source of
sludge (GS) was taken from the drying beds located at the
University of Florida's wastewater treatment facilities. The JS
had a Cd content of 550 mg/kg.
Six Cd-loading rates were
evaluated:
Sludge application rate
Cadmium loading rate
g/kg
5.7
11.4
22.7
45.4
68.1
90.9
mg Cd/kg
3.13
6.25
12.50
25.00
37.50
50.00
Shredded garbage (SG) was obtained from Lakeland's McIntosh
Power Plant.
It was ground and sieved prior to addition to the
pots.
133
Anaerobically digested garbage (DG) was obtained from Vital
Earth Resources in Gladewater, Texas.
This material was a
mixture of wet brewery sludge and household garbage collected
by garbage curbside collection crews.
The two materials were
composted for at least 72 hrs at 55°C. The screened compost was
subsequently windrowed in open fields for up to six months prior
to distribution.
Three application rates were utilized for the two garbage
sources (22.7, 45.4 and 68.1 g/kg). Gainesville sludge (GS) was
mixed 1:l with JS to from a "mixed sludge" (MS) and applied at
the same rates as the garbage-derived materials.
Soils utilized were tailings sand and a SCR = 4 mix. Three
replications of each soil/amendment combination were evaluated.
The following summarizes the setup utilized for the second
experiment.
1. sand/clay mix or sand
2. sand/clay mix or sand + 200 kg N/ha as NH4NO3
3. sand/clay mix or sand + JS at 5.7 g/kg
4. sand/clay mix or sand + JS at 11.4 g/kg
5. sand/clay mix or sand + JS at 22.7 g/kg
6. sand/clay mix or sand + JS at 45.4 g/kg
7. sand/clay mix or sand + JS at 68.1 g/kg
8. sand/clay mix or sand + JS at 90.9 g/kg
9. sand/clay mix or sand + DG at 22.7 g/kg
10. sand/clay mix or sand + DG at 45.4 g/kg
11. sand/clay mix or sand + DG at 68.1 g/kg
12. sand/clay mix or sand + SG at 22.7 g/kg
13. sand/clay mix or sand + SG at 45.4 g/kg
14. sand/clay mix or sand + SG at 68.1 g/kg
15. sand/clay mix or sand + MS at 22.7 g/kg
16. sand/clay mix or sand + MS at 45.4 g/kg
17. sand/clay mix or sand + MS at 68.1 g/kg
The setup of pots including amendment and fertilizer
additions was the same as described for the first experiment.
134
Pre-germinated alfalfa (Medicago sativa) seedlings were planted
Prior to covering with soil, each seedling was
in each pot.
sprinkled with a peat culture of (Rhizobium meliloti).
After
establishment, each pot was thinned to 17 plants per pot. Forty
nine days after planting, 40 mg Mn/kg, as a solution of manganese
sulfate, was added to the surface of each pot. The first harvest
On day 71, a fertilizer solution
was made 64 d after planting.
containing 50 mg/kg Fe, as iron sulfate, and 25 mg/kg Mg, as
sulfate of potash magnesium, was sprayed on the foliage.
This
fertilizer application was repeated on day 87 and day 113.
White flies were controlled as needed by spraying with either
Diazinon or Malathion.
Alfalfa was grown for 155 d. Alfalfa tops were harvested on
day 64, 100, and 155. Analytical procedures for plant tissue and
soil samples were the same as outlined above in the previous
experiment.
General Linear Models (GLM) procedures of SAS were utilized
to analyze all data statistically.
Orthogonal contrasts were
calculated to compare the effects of individual soil treatment
with their respective controls.
Linear regression analysis was
performed on data from the second experiment in order to relate
plant uptake of Cd to DTPA extractable soil Cd.
6.3
Results
6.3.1
and
Discussion
Experiment
one
The addition of shredded garbage, peat, or
sawdust (16 g/kg) did not increase soil total Kjeldahl N (TKN)
levels (Table 6.1). Sewage sludge addition increased TKN at all
application rates. Total Kjeldahl N levels measured in the sand
did not differ from sand/clay mix TKN levels. This was true for
soil samples taken at the beginning and at the end of the
experiment.
Sewage sludge typically contains from 20 to 40 g N/kg (2 to
Therefore, when sewage sludges are applied to soils, an
4%).
increase in soil N content is expected.
Such an increase was
6.3.1.1 Soil N.
135
noted here.
The other organic amendments contained no
appreciable amounts of N and, therefore, caused no observable
increase in soil TKN.
Soil samples taken prior to potting were
analyzed for pH in deionized water and in 1 M KCl. No
differences in pH by the two procedures were noted, thereby
indicating a low level of exchangeable acidity.
Subsequent pH
determinations were done in deionized water only.
Peat and sawdust caused pH changes in both sand and
sand/clay mix Table 6.1.
The pH of the sand/clay mix amended
with either peat or sawdust amendment was lower than the
unamended sand/clay mix.
The highest rate of sewage sludge
caused the pH of the sand/clay mix to decrease from 6.8 to 5.6.
6.3.1.2
Soil
PH.
At the 16 g/kg loading rate, the pH of sludge-amended sand did
not differ from the unamended sand. The two higher sludge rates
(80 and 160 g/kg), when applied to the sand, caused a pH
decrease from 7.2 to 6.7 and 5.9, respectively.
Initially, EB levels
were increased by the addition of all organic amendments on both
the sand and the sand/clay mix with the exception of the
Analysis of the soil cores taken
addition of sawdust on sand.
from the pot, after the last harvest, indicated that the 16 g/kg
application rate of materials had no lasting effect on the
exchangeable base level of any of the amended soils.
However,
the initial increase caused by the two highest sludge rates (80
and 160 g/kg) was still noted in the final soil cores.
6.3.1.3
Exchangeable
bases
(EB).
The 16 g/kg rate of
sewage sludge, shredded garbage, sawdust, and peat caused no
change in soil electrical conductivity (EC). The higher rates of
sewage sludge (80 and 160 g/kg) increased the EC of both the sand
and the sand/clay mix. The addition of clay to the tailings sand
caused a three-fold increase in EC (4.0 vs. 1.3 dS/m).
6.3.1.4
Electrical
conductivity.
With a few noted
exceptions, Mehlich I extractable Ca and Mg levels were not
affected by organic amendments (Table 6.2). One exception was an
increase in extractable Mg with increasing rates of SS
The increase in extractable Mg was greater for
applications.
the sand versus the sand/clay mix.
Another noted effect was a
reduction in extractable Ca in both sand and sand/clay mix from
peat addition. The sand/clay mix had higher Ca levels (7220 vs.
5620 mg/kg) and higher Mg levels (547 vs. 85 mg/kg) than the
sand. Both soils have more than adequate levels of Ca and Mg for
plant growth.
Extractable Zn, Mn, and Cu levels were not affected by
shredded garbage, peat, or sawdust in either sand or sand/clay
6.3.1.5
Mehlich
1
extractable
137
metals.
Increasing application rates of SS up to 160 g/kg
mix.
increased extractable Zn from 6 to 42 mg/kg in sand and from 8 to
36 mg/kg in sand/clay mix, increased extractable Mn from 7 to 19
mg/kg in sand and from 8 to 17 mg/kg in sand/clay mix, and
increased extractable Cd from 0.3 to 10 mg/kg in sand and 0.8 to
7 mg/kg in sand/clay mix.
Addition of peat, sawdust, and shredded garbage did not
effect Mehlich I extractable extractable Cd levels in either sand
or sand/clay mix. Addition of the three rates of sludge to the
sand caused 16-, 44-, and 62-fold increases in Mehlich I
extractable Cd levels, while similar additions to the sand/clay
mix caused increases of only 2.2, 5.6, and 9.5 times the level
found in the unamended sand/clay mix.
Comparing the sludge-amended sand to sludge-amended
sand/clay mix revealed that the addition of phosphatic clay
resulted in lower levels of Mehlich I extractable Cd. Thus, even
though unamended sand/clay mix had a greater soil Cd level than
the unamended sand (0.91 vs. 0.18 mg/kg), Mehlich I extractable
Cd levels were actually lower in the sand/clay mix for each of
the sewage sludge loading rates tested.
Yields of Alyce clover were
higher when grown in sand than when grown on sand/clay mix (Table
Poorer drainage in the pots containing sand/clay mix may
6.3).
have been a factor.
Addition of peat to both sand/clay mix and
sand resulted in increased yields. These increases were observed
in all harvests of clover grown on the sand/clay mix, but only in
the final harvest in sand.
Sludge applications to the sand
increased yield; sludge applications to sand/clay mix had no
observable effect on yield except at the highest rate.
The 160
g/kg application rate of sewage sludge to the sand/clay mix
caused plants in three out of four replications to die prior to
the final harvest.
Sewage sludge applied at 160 g/kg did not
kill plants grown on the sand. This difference may have been due
to the more favorable drainage properties of the sand and the
6.3.1.6
Alyce clover yield.
138
Addition of peat to the sand/clay
associated lower EC values.
mix improved drainage yet did not increase salt levels (Table
For sand, it appears that sewage sludge amendments
6.3).
increased the supply of plant available nutrients.
6.3.1.7
Alyce
clover
tissue
nutrient/metal
concentration.
Concentrations of Fe, Mn, Cu, Zn, and Cd in alyce clover tissue
are presented in Table 6.4.
Iron concentration was not affected by organic amendments
In sand/clay mix, the 80 and
except for SS in sand/clay mix.
160 g/kg application rates of SS increased tissue Fe from 264 to
445 and 377 mg/kg, respectively.
Manganese tissue conc. was affected by organic amendments.
Shredded garbage doubled Mn conc. in sand/clay mix but had no
Unlike SG, peat and SS (16 g/kg rate) had
effect in the sand.
no effect in the sand/clay mix but decreased Mn conc. in sandgrown clover. Sawdust had no effect in either sand or sand/clay
140
High application rates (80 and 160 g/kg) of sewage sludge
mix.
Sludge-Mn complexes may have formed
increased plant tissue Mn.
in the sand causing soil Mn to be less available for plant
uptake. Higher applications of sludge would have supplied enough
Manganese levels
Mn to overcome the effects of this reaction.
found in sand/clay mix-grown clover were considerably lower
compared to sand-grown clover.
Copper conc. in clover was not affected by organic
amendments although some trends were noted. A reduction in plant
tissue Cu levels was observed in Alyce clover grown on sand/clay
mix which had been amended with sawdust. The 16 g/kg application
rate of sewage sludge increased tissue Cu levels found in sand
grown clover but caused the opposite reaction when applied to
the sand/clay mix. This application rate caused extractable soil
Higher soil Zn
Zn levels to double that measured in the sand.
levels may have suppressed Cu uptake by sand/clay mix grown
clover.
Zinc conc. in clover tissue was also not greatly affected by
In both sand and sand/clay mix, addition of
organic amendments.
SS decreased tissue Zn at the low rate and increased tissue Zn at
the high rate.
Cadmium tissue levels were affected by organic amendments
Addition of shredded garbage, sawdust, and peat had
and soils.
no effect on Cd conc. of clover grown in sand or sand/clay mix.
Clover grown in sand receiving 16 g sewage sludge/kg contained
approximately five times more Cd than did unamended sand (14 vs.
Unlike that observed in sand, addition of 32 g
3 mg/kg).
sewage/kg to sand/clay mix had no effect on clover Cd conc. This
indicates that phosphatic clay converted added Cd into a form
unavailable for plant uptake.
6.3.2
Experiment
Two
For statistical purposes all data were broken down into two
The first subset included soils which had received
subsets.
organic amendments at the rates of 22.7 g/kg, 45.4 g/kg, and 68.1
142
The second subset included all soils which had been
g/kg
amended with Jacksonville sewage sludge.
l
Addition of organic materials had
variable effects on soil pH (Table 6.5). Increasing rates above
45.4 g/kg of SS decreased pH in both sand (6.2 vs. 6.7) and
sand/clay mix (7.1 vs. 7.5). Like SS, mixed sludge decreased pH
in sand and to a lesser degree in sand/clay mix.
Digested
garbage caused a slight pH increase in both sand and sand/clay
Shredded garbage increased pH in sand but slightly
mix.
decreased pH in sand/clay mix.
Reduction in pH from sludge additions has been attributed to
nitrification of mineralized N.
Digested garbage is a more
stable product which has a lower mineralizable N content and thus
a lower nitrification rate.
The low N content of shredded
garbage resulted in a low nitrification rate and, therefore, a
minimal effect in lowering the pH.
6.3.2.1
Soil
PH.
Increasing application
rates of organic materials increased soil EC values.
The
materials in decreasing order of magnitude of this effect were SG
> MS > SS > DG for sand/clay mix and SG > DG > SS > MS for sand.
Shredded garbage, which had not undergone any stabilization,
cornposting, digestion, etc., contained higher levels of salts
than the other materials.
Land application of large amounts of
shredded garbage may be limited by this salt effect. Alleviation
of this problem may require an initial pretreatment of the
garbage or some degree of composting to mellow the product before
land application.
6.3.2.2
Electrical
conductivity.
Increasing application rates of organic
materials increased organic C levels in both sand and sand/clay
mix.
The organic C content of the soils was increased by
addition of all amendments at all application rates (Table 6.5).
The organic C content of the organically amended soils is an
6.3.2.3
Organic
C.
143
indication of the amount of added material remaining in the soil.
Decomposition rates of SG ranged from 33 to 58% in the sand and
40 to 55% in the sand/clay mix, while decomposition rates of
sewage sludge ranged from 15 to 66% in the sand and 33 to 63% in
the sand/clay mix.
Decomposition rates of digested garbage
ranged from 0 to 20% in the sand and 18 to 43% in the sand/clay
mix. Digested garbage utilized in this experiment was subjected
144
to 55°C for 5 d in a rotating drum and then windrowed for
approximately 180 d. This treatment led to the decomposition of
a large proportion of the putrescible materials, leaving those
High decomposition rates of organic
which were more stable.
amendments might allow these materials to be applied on a
repeated basis with new applications being made once the
originally applied material has partially decomposed.
6.3.2.4 Soil nutrients/metals. Levels of DTPA extractable
Mn, Fe, Zn, Cu, and Cd are presented in Table 6.6.
Manganese was increased in both sand and sand/clay mix by
increasing rates of SS and MS. No change in soil Mn was observed
for sand or sand/clay mix amended with either DG or SG.
Iron levels in both sand and sand/clay mix were increased
due to organic amendments. Percentage increases were greater in
amended sand as compared to the sand/clay mix due to the
initially low levels of extractable Fe found in the sand.
Soil
amended with the mixture of JS and GS generally contained higher
levels of extractable Fe as compared to that due to similar rates
of JS alone.
Zinc levels in both sand and sand/clay mix were increased by
Extractable Zn levels were similar in both
organic amendments.
sand and sand/clay mix for each application rate of a particular
The organic materials in order of their effect on
amendment.
increasing Zn soil levels were:
SS > DG > MS > SG
sand
sand/clay mix
SG > SS > MS > DG.
Copper levels in both sand and sand/clay mix were increased
by each organic amendment at each rate. The organic materials in
order of their effect on increasing soil Cu levels were:
sand
SS > MS > DG > SG
SS > MS > DG > SG.
sand/clay mix
Extractable Cu levels in SS-amended sand/clay mix tended to
decrease as the growing period progressed.
No such pattern was
noted in similarly amended sands.
This suggests that added Cu
was complexed to some degree by the clay.
145
Cadmium levels in both sand and sand/clay mix were increased
due to SS and MS amendments but not DG and SG amendments. Sewage
sludge amendments increased soil Cd levels at all -application
rates on both soils.
Sewage sludge utilized in this experiment
contained approximately 550 mg Cd/kg. Extractable soil Cd levels
tended to decrease with time in sludge-amended sand/clay mix
indicating that a clay-Cd complex was formed during the 150 day
This decrease in extractable Cd with time was
growing period.
not as apparent in sand.
One to one mixtures of JS and GS (MS)
were made in order to determine if increasing levels of soil
organic matter decreased the plant availability of Cd, added as a
component of JS.
Analysis of soils amended with these mixtures
revealed no consistent trends with regard to Cd extractability.
As was observed with Alyce clover,
alfalfa yields were higher in sand than in SCM (Table 6.7). We
believe poorer drainage and aeration in the sand/clay mix
contributed to the lower dry matter yields in this soil.
Adequate nodulation was observed in both soils.
Shredded garbage decreased alfalfa yields in both sand and
sand/clay mix. The other organic amendments had little effect on
alfalfa yield even when applied at the high rate of 136 mt/ha.
6.3.2.5
6.3.2.6
Alfalfa
yields.
Alfalfa tissue metal composition.
Manganese conc.
in alfalfa tops was increased by addition of SS and MS; variable
effects were observed for DG and SG (Table 6.8).
Digested
garbage decreased tissue Mn at the higher rates in the sand/clay
mix but not in the sand. Shredded garbage decreased tissue Mn in
the sand/clay mix-grown alfalfa but increased tissue Mn in sandgrown alfalfa. All Mn conc. fell within the sufficiency range of
20-500 mg/kg (Jones, 1972).
Iron conc. in alfalfa tops was not greatly affected by
organic amendments.
Tissue Fe conc. was 2-3 times greater in
sand/clay mix-grown alfalfa than sand-grown alfalfa.
Iron
toxicity is not a problem in plants although it may cause
147
148
Iron conc. above 250 mg/kg
nutrient imbalances within a plant.
are generally considered excessive. Iron conc. in alfalfa grown
in sand/clay mix averaged over 300 mg/kg.
Zinc conc. in alfalfa tops was not greatly affected by
Shredded garbage had the greatest effect
organic amendments.
increasing tissue Zn from 73 to 129 mg/kg (high rate of SG) in
Unlike most of the other
sand and from 46 to 77 in SCM.
micronutrients, Zn conc. was higher in sand-grown alfalfa versus
Zinc conc. greater than 100 would be
alfalfa grown in SCM.
considered excessive or toxic (Jones, 1972).
Copper conc. in alfalfa tops was similar whether grown in
sand or sand/clay mix. In sand, all organic materials except DG
increased Cu conc. In sand/clay mix, both SS and MS increased Cu
The general guideline for Cu toxicity for alfalfa tops
levels.
Even the highest rate of SS and MS
is 30 mg/kg (Jones, 1972).
did not cause alfalfa tops to have a tissue concentration greater
than 30 mg/kg (23.5 and 20.2 mg/kg, respectively).
Cadmium conc. in alfalfa tissue was affected by both soil
and organic amendment. Without organic amendments, alfalfa grown
in sand/clay mix had twice the Cd conc. found in alfalfa grown in
sand (2.8 vs. 1.5 mg/kg).
Only the sludge sources increased the Cd content of alfalfa;
Municipal solid waste contains very
DG and SG had no effect.
little Cd and its application to soil should not cause an
increase in plant tissue Cd levels.
Increasing application rates of SS and MS increased Cd
Cadmium concentrations found in sand-grown
content of alfalfa.
alfalfa were increased with each increase in rate of SS and MS
Only the three highest application rates of JS and
application.
the two highest rates of MS caused an increase in the Cd
concentration of alfalfa grown in sand/clay mix.
Even though
alfalfa grown in unamended sand/clay mix had a higher level of Cd
as compared to that grown on unamended sand, the average plant
tissue Cd concentrations were higher in alfalfa grown on sludge
amended sand than that found in alfalfa grown on sand/clay mix
150
which had received similar amendments. Mixing of the JS and the
GS did not have a discernable effect on plant tissue Cd
concentrations.
Regression analysis was preformed comparing the average
alfalfa tissue Cd concentration to the level of DTPA extractable
Cd concentration found in soils which had received JS.
Figure
6.1 graphically depicts the results of this analysis. Equations
2
for the best fit line were Y = 3.0 + 0.49x (r = 0.81) for the
sand/clay mix-grown alfalfa and Y = 2.74 + 1.05x (r2 = 0.98) for
sand-grown alfalfa.
The respective slopes of these lines along
with Cd concentrations found in sand-grown alfalfa, as compared
to sand/clay mix grown alfalfa, demonstrate that the presence of
waste phosphatic clay reduced the uptake of Cd added as a
contaminant of sewage sludge.
6.4 Conclusions
Addition of organic waste products to tailings sand and/or
sand/clay mix did not influence the soil pH and salinity level
when applied at 16 g/kg.
Increasing the rate of application of
sewage sludge to 80 g/kg decreased sand and sand/clay mix pH by
0.5 and 0.9 units, respectively.
Application of 80 g/kg of sewage sludge increased the
soluble salts level of the sand and sand/clay mix by 1970 mg/kg
and 5680 mg/kg, respectively. One possible reason for the large
increase in soluble salts in the sand/clay mix was that water
movement through the sand/clay mix was insufficient to leach out
added salts.
Mehlich I extractable levels of Cd increased in response to
the addition of shredded garbage and sewage sludge on both the
sand/clay mix and sand.
Initially, the sand/clay mix contained
about five times more extractable Cd than did the sand.
The
addition of a 80 g/kg rate of sewage sludge to the sand
increased the extractable level of Cd 44-fold; whereas, the same
rate of sewage sludge resulted in only a 5.5-fold increase in
extractable Cd in the sand/clay mix.
151
Clover yields were not reduced by the high salt or
extractable Cd levels which resulted from the application of 80
g sewage sludge/kg, but Cd uptake by the clover increased
Clover yields were not reduced by the high salt or extractable Cd
levels which resulted from the application of 80 g sewage
sludge/kg, but Cd uptake by the clover increased ten-fold on the
Tissue Cd conc. in clover grown on the sand/clay mix
sand.
receiving 160 g sewage sludge/kg did not increase.
Tissue Cd conc. of sand/clay mix-grown Alyce clover was high
relative to other published findings (Chaney and Giordano, 1977).
Plants grown on unamended sand did not contain as much Cd, but
larger percentage increases in tissue Cd concentration were noted
when sewage sludge was added to sand than to sand/clay mix.
Soil chemical properties did not change as much in response
to the addition of the organic waste products following the
growth of alfalfa as were noted following clover.
This
observation may be associated more with the cultural practices
than with the crop species.
Mixing the two sludges (one
containing high amounts and the other low amounts of Cd) did not
improve the complexation of Cd.
The rate of increase in tissue Cd conc. in plants grown on
sand/clay mix in response to increasing soil extractable Cd
levels was about twice the rate of increase in tissue Cd conc. in
plants grown on sand. The addition of clay to the sand decreased
the rate of Cd uptake.
153
7.0 SUMMARY AND CONCLUSIONS
7.1
Sand:clay
Ratio
Phase
Three seasons of vegetable production research were
conducted on four different sand/clay mixes with sand:clay ratios
(SCR) of 2, 4, 6, and 8.
Vegetables grown included turnip,
cabbage, banana pepper, yellow squash and mustard.
Peat and
phosphogypsum were evaluated as soil amendments; peat to
"lighten" the soil and phosphogypsum to increase the soil Ca:soil
Ra226 ratio and decrease Ra226 uptake.
In addition to yield
yield, soil and plant nutrient levels were monitored as well as
Cd and Ra226 contaminants. Detailed results for these parameters
and how they were affected by SCR, peat, and phosphogypsum are
presented in the text.
Some important conclusions from these
results follow.
o
Yields of turnip, cabbage, and mustard were higher in the
SCR = 2 mix while yields of yellow squash and banana peppers
were higher in the SCR = 8 mix.
Yield differences were on
the order of l0-30%.
o
From a production perspective, yield increases in the
SCR = 2 mix were offset by the considerable increase in
difficulty required to carry out conventional farming
operations in this mix versus the SCR = 4 and higher
sand/clay mixes.
o
Despite increasing the SCR up to 8, soil chemical properties
remained dominated by the phosphatic clay component. Thus,
soil pH, conductivity, and extractable soil nutrients were
generally unaffected by SCR.
The few differences that
existed were not agronomically significant.
o
Nutrient concentrations in vegetables were not greatly
affected by SCR and, with the exception of boron and
manganese, were normal.
154
o
Boron was deficient or marginally deficient for vegetable
production.
Boron deficiency was evident in cabbage and
turnip roots as brown-rot symptoms.
Application of 2 kg
B/ha along with base fertilizer was recommended for Bsensitive crops.
o
Manganese was also deficient or marginally deficient for
vegetable production.
In banana peppers, Mn deficiency was
evident as an interveinal chlorosis; visual symptoms were
not evident in other crops. Plant tissue Mn was correlated
with yield for cabbage, squash, and banana pepper and was
probably masked by B deficiency in turnips.
o
Peat decreased soil bulk density of all but the SCR = 2 mix.
o
Peat had little effect (direct or residual) on vegetable
One exception was a pepper yield increase in the
yields.
SCR=4 mix to yield levels observed for the SCR=8 mix. It
was concluded that application of organic amendments can not
be recommended as a general management practice to increase
vegetable production on sand/clay mixes.
However, for
certain crops such as banana pepper, which yielded better in
sandier mixes,
organic amendments may deserve further
consideration.
o
Phosphogypsum had no effect on vegetable yields. This held
true for both the 22 Mg/ha rate (10 ton/acre) and the very
high application rate of 134 Mg/ha (60 ton/acre).
o
Phosphogypsum had little effect on plant nutrient
composition. Some exceptions included small increases in Ca
and Mg and small decreases in Zn and Mn for certain
vegetables and in certain seasons.
155
o
Although extractable soil Cd decreased with increasing sand
content, observed differences in plant Cd concentrations
were small or undetectable.
o
Vegetables when placed in increasing order of Cd
concentration (mg/kg dry) were - turnip leaves (7.9) >
turnip roots (3.7) > squash leaves (2.7) > banana pepper
fruit (1.1) > squash fruit = cabbage = mustard greens
(<0.5).
o
Except for turnip leaves, Cd concentrations in vegetables
were within reported normal Cd concentration ranges.
o
Turnip leaves contained over four times the Cd concentration
reported for turnips grown on non-contaminated soil (7.9 vs
1.8 mg/kg).
Calculations indicated that one would have to
eat over 0.25 kg of fresh turnips to exceeded the normal
dietary intake of 0.15 mg Cd/day.
o
Peat decreased tissue Cd concentration in turnip leaves and
roots.
Because relatively high rates of peat were applied
and relatively small reductions in tissue Cd were observed,
large applications of organic matter would not be
recommended for significant reduction in Cd uptake by
vegetables.
However, management practices which favor an
increase in organic matter content will aid in limiting
plant uptake of Cd from sand/clay mixes.
Phosphogypsum had no effect on tissue Cd concentrations in
vegetables.
Soil Ra226 ranged from a high of 16.0 pCi/g in the SCR = 2
mix to a low of 7.8 pCi/g in the SCR = 8 mix. Average soil
Ra226 was 13.4, 11.5, 10.7, and 8.2 pCi/g for the SCR = 2,
Soil Ra226 values in
4, 6, and 8 mixes, respectively.
156
sand/clay mixes were l0-20 times higher than levels found in
"normal" soils which average 0.5 pCi/g (0.1-3.8).
o
Although soil Ra226 decreased as the SCR increased,
vegetables had higher Ra226 concentrations when grown in the
SCR = 4 mix than in the SCR = 2 mix. However, compared to
SCR had
differences observed between vegetable crops,
minimal effect on tissue Ra226 concentrations.
o
Vegetables when placed in decreasing order of Ra226
concentration (pCi/g dry) were turnip leaves (0.80) >
mustard greens (0.62) > turnip roots (0.36) > yellow squash
(0.28) > cabbage (0.19) > banana pepper (0.09).
o
For a particular crop, tissue Ra226 concentrations were not
consistently correlated with tissue concentrations of other
nutrient elements.
o
Combining all crops together, tissue Ra226 was very highly
correlated with tissue Ca and could be predicted according
to the following quadratic equation.
2
Y = 0.08 + 0.31x - 0.02x
(r2 = 0.55)
where y = plant Ra226 in pCi/g dry and x = plant Ca in
In other words, plant tissues which had higher Ca
percent.
concentrations had higher concentrations of Ra226.
o
Results from over 600 Ra226 analyses revealed that the
maximum observed Ra226:Ca ratio in vegetables was 100 pCi
Ra226/g Ca.
Therefore, we were able to predict both the
average (from the quadratic equation) and the maximum likely
Ra226 concentration in vegetables knowing the Ca
concentration in the particular tissue.
These results
indicated that Ra226 did not excessively accumulate in
vegetables due to indiscriminant uptake.
157
o
Despite increasing
phosphogypsum had
concentrations.
o
Peat had no effect on the Ra226 concentration in vegetables.
o
Except for comments relative to the implications of Ra226:Ca
ratio in foods and foodchains, detailed health implications
of Ra226 results were not discussed. Data were provided to
Post, Buckley, Schuh, and Jernigan to add to their database.
Health perspectives will be addressed by their study group
(FIPR # 86-05-028).
7.2
SP-1 Alfalfa Phase
the
no
Ca:Ra226 ratio in the soil,
effect on vegetable Ra226
Alfalfa was grown on CF Industries*
sand/clay mix
reclamation area, SP-1, to evaluate alfalfa yield and quality as
affected by several organic amendments.
The organic materials
investigated included sawdust, humate, composted garbage, peat,
sewage sludge,
and composted sewage sludge.
Due to the
sensitivity of alfalfa to waterlogged soil conditions, these
materials were added at two rates, 22 and 45 Mg/ha (10 and 20
ton/acre) in order to lower soil bulk density and improve
internal surface drainage.
Detailed information regarding
alfalfa yields and soil and plant tissue nutrient analyses are
included in the text.
Some important conclusions from these
results are listed below.
158
o
Alfalfa yields were increased by the application of sewage
sludge. Annual dry-weight yields (7 cuttings) were 11.0 and
13.6 (4.9 and 6.1 ton/acre) for control and sludge-amended
plots, respectively.
The benefit of sludge additions
appeared to be due to micronutrient contributions,
especially Mn.
o
Application of sawdust, humate, peat, sludge compost, and
garbage compost had no effect on alfalfa yields at the 22
and 45 Mg/ha application rates.
o
As evidenced by highly significant block effects, the
elevated side of the site produced better during the wet
summer months while the lower side of the site produced
better in the late spring when the site was relatively dry.
o
Detectable decreases in soil bulk density due to organic
amendments were observed for the 45 Mg/ha but not the 22
Mg/ha application rate. Higher application rates of organic
materials may be needed to effect soil physical
characteristics significantly.
o
Organic materials had 'little effect on alfalfa nutrient
composition and in-vitro-organic-matter-digestibility.
o
Ra226 concentration of alfalfa averaged 0.42 pCi/g dry and
was unaffected by organic amendments.
Alfalfa leaves
contained a higher Ra226 concentration than stems (0.55 vs.
0.31 pCi/g dry).
o
Soil Ca, but not tissue Ca, was correlated (r = -0.46) with
Ra226 concentration in alfalfa tops. The Ra226:Ca ratio in
alfalfa tops agreed well with conclusions derived from
vegetable experimentation.
159
7.3
Glasshouse
Phase
At the University of Florida, glasshouse experiments. were
conducted in which sand tailings and 4:l sand:clay mix were
amended with several different waste organic materials in order
to determine the influence of phosphatic clay on the growth and
metal uptake by legume forages.
Materials evaluated included
sawdust, peat, raw shredded garbage, garbage compost, and a highCd sewage sludge. Of particular interest was the high-Cd sludge
which contained 550 mg Cd/kg and, as such, was classified as a
hazardous waste material.
Details of these experiments were
presented in this report as well as in Richard Gonzalez's
Master's thesis, a copy of which was presented to the Florida
Institute of Phosphate Research.
Important conclusions of this
research are listed below.
o
Due to increases in soluble salt levels, application rates
of "hot" materials such as sewage sludge and shredded
garbage should not exceed 50 g/kg.
For a given rate of
application, higher conductivity measurements were observed
for sand tailings than for sand/clay mix.
This difference
was attributed to decreased leaching of salts out of the
sand/clay mix during irrigation.
o
Dry-matter yields of Alyce clover and alfalfa were greater
in sand than in sand/clay mix and, with the exception of
high sludge rates which decreased or killed plants, were
generally unaffected by organic amendments.
o
Increasing application rates of high-Cd sludge to sand and
sand/clay mix resulted in increasing extractable Cd levels
in both soils.
However, increases in extractable soil Cd
for a particular application rate of the high-Cd sludge were
greater for sand than for sand/clay mix.
160
o
Linear equations, which described the relationship between
extractable soil Cd and Cd concentration in alfalfa tops,
were different for the two soils.
sand
Y = 2.74 + 1.05x
sand/clay mix Y = 3.00 + 0.49x
2
(r = 0.98)
2
(r = 0.81)
where y = plant Cd concentration in mg/kg and x = DTPA
extractable Cd in mg/kg. Thus, for a particular extractable
soil Cd level, alfalfa grown in sand tailings had twice the
Cd concentration than when grown in sand/clay mix.
This
indicates that phosphatic clay reduced the uptake of Cd
added as a contaminant of sewage sludge.
161
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9.0
APPENDIX
Note: Because SI Units are the accepted format for scientific
presentations, values in the text generally follow this format.
Below are c onversion factors which can be used to convert SI
units to the more common English units.
Mg/ha x .446 = tons/acre
Mg/ha x 893 = pounds/acre
ha x 2.47 = acre
m x 3.28 = ft
kg x 2.205 = pound
cmol/kg = meq/g
mg/kg = ppm
dS/cm x 10 = mmhos/cm
dS/m x 0.1 = mmhos/cm
169