Tennessee
Valley
Authority
Office of Natural
Resources
Chattanooga TN 37401
TVA/ONR-79/10
United States
Environmental Protection
Agency
Office of Energy. Minerals, and
Industry
Washington DC 20460
EPA-600/7 79-109
April 1979
Research and Development
Accumulation of
Atmospheric
Sulfur by Plants and
Sulfur-Supplying
Capacity of Soil
Interagency
Energy/Environment
R&D Program
Report
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EPA-600/7-79-109
TVA/ONR-79/10
April 1979
ACCUMULATION OF ATMOSPHERIC SULFUR BY PLANTS
AND SULFUR-SUPPLYING CAPACITY OF SOILS
by
J C Noggle and Herbert C, Jones
Office of Natural Resources
Tennessee Valley Authority
Muscle Shoals, Alabama 35660
Interagency Agreement EPA-IAG-D8-E721-DO
Project No. E-AP 80 BDO
Program Element No. INE 625A
Project Officer
S. R. Reznek
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Prepared for
OFFICE OF ENERGY, MINERALS, AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
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DISCLAIMER
This report was prepared by the Tennessee Valley Authority and has
been reviewed by the Office of Energy, Minerals, and Industry, U.S.
Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and
policies of the Tennessee Valley Authority or the U.S. Environmental
Protection Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
11
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ABSTRACT
Sulfur (S) requirements to maintain high crop production range from
10 to 40 kg/ha*yr. A decline in the use of S-containing fertilizers in
recent years has placed a greater dependency on the atmosphere as a source
of supplemental S to meet the S needs of plants. The Tennessee Valley
Authority (TVA) and the U.S. Environmental Protection Agency (EPA)
initiated an investigation in 1976 to measure the amount of S that is
transferred from the atmosphere to agro-ecosystems and to determine the
S-supplying capacity of soils in the Tennessee Valley.
Because a plant can accumulate S from both the soil and the atmo-
sphere, three techniques were tested for determining the fractional
contribution of the soil and the atmosphere to the total S in field-
grown plants. Soybeans, cotton, and fescue were grown in equal quan-
tities of the same low-sulfur soil at three field locations and in a
greenhouse with charcoal-filtered air. The first technique assumed that
S uptake from the soil was the same at all locations and that increased
S accumulation by field-grown plants over plants grown in the greenhouse
was a measure of atmosphere-derived S. This technique proved unsatis-
factory because total S uptake was higher in the greenhouse than at a
field location. In technique II, an equal amount of fertilizer S,
labeled with 35S (a radioactive isotope of S), was applied to the soil
in each growth container. The S in each unit weight of plant tissue was
partitioned into two parts: (1) S derived from fertilizer and (2) S
derived from soil and the atmosphere. Although this technique was
useful in demonstrating a source of S other than the soil, the amount of
S accumulated from the atmosphere could not be calculated by this method.
Technique III provided a direct method for calculating the amount of plant
S that was derived from the soil at any location. Soil S was labeled
with 35S, and the specific activity (ratio of radioactive S to stable S)
was determined by measuring the specific activity of S in plants grown
in the absence of atmospheric S. The amount of S accumulated from the
atmosphere was obtained by subtracting soil-derived S from total plant S
at each field location. This technique proved to be satisfactory for
measuring the amount of atmospheric S accumulated by plants. Cotton
grown 4 and 3 km from coal-fired power plants accumulated 125 and 240
mg S per 100 g (dry wt), but fescue accumulated only 65 and 58 mg S per
100 g (dry wt) at the same two locations. The cotton grown near the
power plants produced significantly more biomass than that grown at a
location remote to industrial sources of S02, illustrating the importance
of atmospheric sulfur as a plant nutrient where the sulfur content of soils
may be inadequate to meet plant requirements.
The S-supplying capacity of selected soils was evaluated by measuring
the rate of S accumulation by fescue grown in a greenhouse with charcoal-
filtered air. The rate of S mineralization in soil collected from a depth
of 0 to 30 cm at five sites was about 1 mg/kg of soil during the 27 weeks
of plant growth.
iii
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This report was submitted by the Tennessee Valley Authority, Office
of Natural Resources, in partial fulfillment of Energy Accomplishment
Plan 80 EDO under terms of Interagency Agreement EPA-IAG-D8-E721-DO with
the Environmental Protection Agency. Work was completed as of December
31, 1977.
IV
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CONTENTS
Abstract „ iii
Figures vi
Tables vii
Acknowledgment viii
1. Introduction 1
2. Conclusions and Recommendations 3
3. Experimental Considerations and Procedures 5
General Considerations 5
Measurement of Sulfur Transfer from the
Atmosphere to Crops 5
Technique I 5
Technique II 8
Technique III 8
Measurement of Sulfur-Supplying Capacity of
Soils 9
Experimental Procedures 9
Field Study-1976 9
Soil Preparation and Treatment 10
Method I 10
Method II 10
Method III 10
Experiment Establishment 10
Field Study—1977 11
Growth Containers 11
Soil Preparation and Treatment 11
Sand Culture 13
Nutrient Solution 13
Site Location 13
Experiment Establishment and Data
Collection 13
Sulfur-Supplying Capacity of Soils 14
Soil Treatment 16
Experimental Procedure 16
4. Results and Discussion 17
Sulfur Transfer from Atmosphere to
Agro-Ecosystem 17
Field Study-1976 17
Technique I 17
Technique II 18
Field Study—1977 19
Cotton 19
Technique 1 19
Technique II 22
Technique III 24
Fescue 26
Techniques I and II 26
Technique III 26
General Discussion 30
Sulfur-Supplying Capacity of Soils 32
References 37
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FIGURES
Number Page
1 General relationship between sulfur supply and
crop yield 6
2 Diagram of experiment installation in the field . 12
3 Sulfur accumulation by fescue grown in soil
collected from the 0- to 30-cm depth 33
4 Sulfur accumulation by fescue grown in soil
collected from the 0- to 30-cm depth at site 4 . 34
5 Sulfur accumulation in fescue grown in soil
collected from the 30- to 60-cm depth at three
sites 35
6 Sulfur accumulation in fescue grown in soil
collected from the 30- to 60-cm depth at four
sites 36
VI
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TABLES
Number
1 Summary of the Techniques used to Measure the
Transfer of Sulfur from the Atmosphere to
Crops 7
2 Locations of Experimental Growth Containers ... 14
3 Summary of Experimental Protocols Used in 1976
and 1977 15
4 Collection Sites for Soil Used in Experiment
to Determine Sulfur-Supplying Capacity 16
5 Vegetative Production and Sulfur Content of
Soybeans Grown at Three Locations in Soil
Prepared by Three Methods 17
6 Sources of Sulfur in Soybeans Grown at Three
Locations 18
7 Vegetative Production and Sulfur Content of
Cotton Grown at Four Sites 21
8 Sources of Sulfur in Cotton Grown at Five Sites . 23
9 Determination of Specific Activity of Sulfur in
Cotton Grown at Crossville 25
10 Source of Sulfur in Cotton Grown at Three Sites . 25
11 Vegetative Production and Sulfur Content of
Fescue Grown at Four Sites 27
12 Sources of Sulfur in Fescue Grown at Five Sites . 28
13 Specific Activity of Plant Sulfur for Fescue
Grown at Crossville 29
14 Source of Sulfur in Cotton Grown at Three Sites . 29
15 Vegetative Production, Sulfur Content, and Source
of Plant Sulfur for Cotton and Fescue Grown at
Four Sites 31
VII
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ACKNOWLEDGMENT
This work was conducted as part of the Federal Interagency Energy/
Environment Research and Development Program with funds administered
through the Environmental Protection Agency (EPA Contract No.
EPA-IAG-D8-E721-DO, TVA Contract No. TV-41967A).
The EPA Project Officer for this project is S. R. Reznek,
401 M Street, SW, Washington, DC. His contribution to the direction
of the research and his constructive review of the reported results
are gratefully acknowledged. The TVA Project Director is Herbert C.
Jones, E and D Building, Muscle Shoals, Alabama.
Vlll
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SECTION 1
INTRODUCTION
Sulfur (S) is an essential plant nutrient needed for the synthesis
of proteins and other organic compounds within vegetative tissue. The
amount of S needed for medium to high crop yields ranges from about 10
to 40 kg/ha-yr.1 Crops such as corn (Zea mays L.) and wheat (Triticum
aestiuum L.) use the lowest amount of S, whereas crops such as cabbage
(Brassica oleracea), turnips (Brassica rapa), and alfalfa (Medicago
sativa L.) use the highest amount.
Three possible sources of S to meet crop requirements are the soil,
fertilizers, and atmosphere. In humid regions, most S in the soil is
present as proteinaceous compounds in the soil organic matter, with a
lesser amount in inorganic forms in the soil solution and adsorbed on
the clay fraction. The S in organic matter is in a chemical form that
cannot be used directly by plants. The gradual decomposition of organic
matter by soil microorganisms oxidizes proteinaceous S compounds to the
sulfate SOl2 form, which is readily absorbed by plant roots. Although
the release of S from soil organic matter has seldom been measured
directly, Bettany et al.2 found that, depending on the characteristics
of the organic matter, 30 to 70 percent of the S in alfalfa plants grown
in the greenhouse was derived from mineralized S. Because the soils used
in this study contained 2 to 6 percent organic matter, these data suggest
that only soils high in organic matter content can supply an appreciable
percentage of the crop's S needs from decomposition of organic matter.
Soil retention of sulfate S is limited to about one year because of
leaching and crop removal; consequently, S usually must be added annually
to prevent reductions in yield.
Fertilizer materials such as ammonium sulfate, potassium sulfate,
and ordinary superphosphate, when applied to soils, usually add adequate S
along with the other plant nutrients. However, the recent trend to apply
fertilizers with a relatively high N, P, and K content and essentially no
S should have resulted in increased occurrences of S deficiency, but this
has not been the case. According to Beaton et al.,3 the only crops that
show S deficiencies are usually found on highly leached soils at sites
remote from industrial areas. This indicates that the increase in com-
bustion of fossil fuels, which has occurred concurrently with the decrease
in application of fertilizer S, may have prevented a significant S shortage
by supplying S to plants and soils through the atmosphere.
Sulfur in the atmosphere exists as sulfur dioxide (S02) and hydrogen
sulfide (H2S) in a gaseous form and as sulfate in association with aerosols
and particulate matter. Sulfur is transferred from the atmosphere to agro-
ecosystems by direct sorption of S02 by plants and soil, dry particulate
deposition, and rainfall. Numerous investigators have reported that
atmospheric S02 is absorbed directly by plant foliage. Fried4 used 35S-
labeled S02 to demonstrate that alfalfa plants can absorb S02 through
the leaves and convert it into organic sulfur compounds. Cowling et al.5
found beneficial effects of S02, such as increases in yield and S content,
in perennial ryegrass that was grown with an inadequate supply of S to
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-2-
the roots. Olsen6 showed that cotton plants grown in an atmosphere
containing O.OL to 0.05 ppm S02, although supplied with adequate sulfate
in a nutrient solution, still absorbed about 30 percent of their S from
the atmosphere. Several investigators7"10 have reported direct adsorption
of S02 by soils. Jordan et al.,11 who extensively surveyed S in precipi-
tation and dry particulate deposition in southern states, reported values
of 10 to 30 kg/ha-yr; these values are similar in magnitude to crop
requirements.
A comprehensive evaluation of S02 control strategies at coal-fired
power plants should take into account the economic impact on agriculture
if sulfur is significantly reduced in the atmosphere.
To evaluate the economic significance of the atmosphere as a source
of S for crop production, the Tennessee Valley Authority (TVA) conducted
a study to measure the amount of S transferred from the atmosphere to
agro-ecosystems and to determine the S-supplying capacity of soils
representative of the Tennessee Valley.
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
At the beginning of this study, we found that a reliable technique
for measuring the amount of S accumulated by crops from the atmosphere
was not available. Crops were grown in equal quantities of the same
soil near coal-fired power plants, at a remote location, and in a
greenhouse equipped with charcoal-filtered air. We experimented with
three techniques for measuring the transfer of S from the atmosphere to
agro-ecosystems to select the most appropriate one for use in future
investigations.
The results of two years' study indicate that labeling the soil S
with radioactive 35S has definite advantages over the method of compar-
ing the total S content of plants grown in the presence and absence of
atmospheric S. Results from the 1976 study showed no apparent advantage
in using S-depleted soil rather than a low-S soil.
Cotton was more efficient than fescue in accumulating S from the
atmosphere, as shown by a higher concentration of atmospheric S in
cotton than in fescue grown near coal-fired power plants. The amount of
S accumulated from the atmosphere was apparently influenced by the level
of S supply in the soil relative to the S requirement of the plant. A
crop grown in an S-deficient soil will accumulate more S from the
atmosphere than the same crop grown in a soil that has an adequate
supply of S. Cotton grown in the vicinity of coal-fired power plants
accumulated significantly more atmospheric S than was transferred in
rainfall and dry deposition, which indicated that 75 to 90 percent of
the total S accumulated from the atmosphere was in the form of S02.
The cotton grown near the steam plants produced significantly more biomass
than that grown at a location remote to industrial sources of sulfur, which
illustrates the importance of atmospheric sulfur as a nutrient where soil
sulfur levels are inadequate to meet plant needs.
The use of sand cultures to measure accumulation of atmospheric S
by plants proved satisfactory. In the future, both soil and sand cultures
will be used to study the relationship between supply of soil S to the
roots and accumulation of atmospheric S by the leaves.
This study supports the use of S accumulation by plants to measure
the S-supplying capacity of soils. The S uptake pattern during the
27-week growth period showed a readily available sulfate pool in the
soil and a constant rate of S mineralization from the soil organic matter.
The size of the sulfate pool varied among soils and was larger in the
subsoil than in the topsoil. In the absence of fertilizer S or atmospheric
S, the sulfate pool can be replenished only by S that is mineralized from
soil organic matter. The rate of S mineralization, measured in the soils
of this study, was not great enough to promote maximum plant growth.
Because many field experiments have failed to show a growth response
to applied fertilizer S, one can only conclude that atmospheric S prevents
depletion of the available sulfate pool in the soil to a level that limits
plant growth. This result shows the importance of determining the S-supplying
capacity of soils under conditions that eliminate the atmosphere as a
source of S to soils and plants.
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The economic importance of atmospheric S can be assessed only
after the S-supplying capacity of soils and the amount of S transferred
from the atmosphere to the agro-ecosystem have been measured. The S
requirements of plants relative to the supply of soil S must also be
considered. Plants with a high S requirement, when grown on soil with
a low S supply, will soon become S-deficient if S is removed from the
atmosphere.
After consideration of all these parameters, the consequences of
removing a significant amount of sulfur from the atmosphere can be esti-
mated. For example, cotton grown in the containers at Crossville contained
152 mg S. About one-half, or 76 mg, of this S would be removed in the
harvested lint and seed. The soil mineralization rate of the soil used
in this study (same as soil No. 5 in the S-supplying capacity study) was
1 mg S per kilogram of soil per 27 weeks, or about 45 mg S during the
growing season for the 45 kg of soil used. At Crossville, 41 mg S was
added to each container as wet-dry deposition from the atmosphere. The
contribution of soil mineralization and atmospheric deposition to the
sulfate pool is equivalent and totals the estimated amount of S removal
in the harvested portion of the crop. Application of fertilizer S for
cotton grown on this soil is recommended by the State Agricultural Experi-
ment Station. Any reduction in deposition of atmospheric S must be
replaced by an equal amount of fertilizer S to maintain present yields.
The cost of removing S at the power plant and the cost of supplying
additional fertilizer to agricultural crops should be considered in estab-
lishing emission standards and control technology.
The findings in this study have implications other than that of
atmospheric S having an economic significance to crop production. Studies
that are designed to measure the effects on plants of chronic exposure to
S02 must include a consideration of S as a plant nutrient. The S level
in the soil in which the plants are grown would be especially critical to
the proper interpretation of the results. Additions of fertilizer S or
the use of high-S soil would eliminate the potential for observing a g'rowth
response to S and, therefore, would not provide an accurate evaluation of
the total effect of low-level exposure to S02.
Soil and plants provide a "sink" for atmospheric S. The rate of S
transfer from the atmosphere to the terrestrial ecosystem will influence
the distance that power plant emissions are transported in the atmosphere.
A method of measuring atmospheric SC>2 transfer to soils and plants is
essential for predicting long-range transport. Because the relationship
between soil S supply and crop requirement influences the rate of S accu-
mulation from the atmosphere, these studies should be expanded in this
area of investigation.
In this experiment, the sulfate pools in some of the soils were not
depleted during the 27 weeks of plant growth. Therefore, fescue has been
replanted to extend the growth period for a sufficient time to measure
the S-supplying capacities. Other soil types, representative of the
Tennessee Valley, will be collected to determine S-supplying capacities.
Accumulation of S from the atmosphere by plants will be measured at
several locations with technique III (use of 35S-labeled fertilizer
to measure the amount of S derived from the soil directly).
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SECTION 3
EXPERIMENTAL CONSIDERATIONS AND PROCEDURES
GENERAL CONSIDERATIONS
The approach taken in this investigation is based on the relation-
ship that exists between crop yield and S supply, as illustrated in
Figure 1. As the supply of S is increased, crop yield increases to some
constant level, at which another growth factor limits further increase
in yield. To obtain maximum yield under a given set of environmental
conditions, total S supply must at least equal the total S requirement
identified as point "A" on the S supply axis. The actual value for
point "A" will depend on crop species and yield level. Sulfur supplied
in excess of the S requirement cannot be used effectively by crops.
The total S supply, which is the amount of S in a form that is
readily available to plants during the growing season, consists of
native soil S and supplemental S. The amount of S supplied by the soil,
indicated by point "B" in Figure 1, depends on the rate at which S is
released during decomposition of soil organic matter and on the size of
the "pool" of soluble and adsorbed sulfate. The relative position of
point "B" could be at any point on the supply axis, depending on the
total S requirement value. For example, a given amount of soil S could
supply the total requirement for a relatively low crop yield, but only a
part of the requirement for a relatively high crop yield. When the
supply of native soil S is less than the total S requirement (A - B > 0),
thus requiring supplemental S for maximum crop yields, atmospheric S
becomes extremely important.
For atmospheric S to affect crop production significantly, supple-
mental S must be needed, and the S that is transferred from the atmos-
phere to agro-ecosystems must contribute a relatively large proportion
of these supplemental needs. This study (1) investigates three
techniques for determining the fractional contributions of the soil and
the atmosphere to the total S content of field-grown crops and (2)
evaluates a bioassay method for determining the S-supplying capacity of
soil from selected sites.
Measurement of Sulfur Transfer from the Atmosphere to Crops
At the beginning of this study, we found that a reliable technique
for measuring the amount of atmospheric S accumulated by crops was not
available. Three techniques were considered in this study to select the
most appropriate one for use in future work. These techniques are
summarized in Table 1.
Technique I--
This method of estimating the input of atmospheric S into the agro-
ecosystem consists of comparing the total S content of plants grown
in the presence and absence of atmospheric S. For this comparison to be
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Q
_J
j
Q_
O
cr
o
B
-Soil-S-
-*r* Supplemental-S
A
-Total S Requirement For
Maximum Yield
SULFUR SUPPLY
Figure 1. General relationship between sulfur supply and crop yield.
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TABLE 1. SUMMARY OF THE TECHNIQUES USED TO MEASURE THE TRANSFER OF SULFUR FROM THE ATMOSPHERE TO CROPS
I ten
Technique I
Technique II
Technique III
Basic equation ATM S = TOTAL PLANT S - SOIL S
Variables
[Plant S]_ ., = S concentration in plant = (mg/g)
BiomasSp G = g(dry wt)/plant
[SOIL S + ATM S]F G = [PLANT S]f g - [FERT S]f fi
fFert Si - total cpm 35S/gdw _ ,
Lrert &J_ - - ~, - img i
' cpm 03S/mg S in fertilizer
[Plant S]_ ., = S concentration in plant = mg/g
BiomasSp „ = g(dry wt)/plant
35C
Radioactivity in plant- „ = total cpm S
[Plant S]F G = [S] in plant = mg/g
Biomass- - = gCdry wt)/plant
Calculations Total plant SG = biomasSg X [plant S)G = Soil SG
Total plant Sj. = biomasSj. X [plant S]j.
If [atm SJG = 0, then [soil S + atm S]g = [soil S)G
Assume: [soil S]G = [soil S]f
Total plant S = [plant S] X biomass
Then: Ata S = total plant S_ - soil S
Then: [soil S * atn S]p - [soil S]G = [atm S]F
Total cpm S- specific activity of available
Plant S* = =—^ =——=- = S in soil _
(j lotal plant S (j,r
Total cpm 35Sj.
Soil SF * Plant S*
Requirements
2. No source of S in greenhouse other than
readily available soil S
4. Plants must be grown in containers
1. [Soil S]G = [soil S]F
2. The uptake of atmospheric S must not reduce the
[soil S]r
3. [Plant S]F = [plant S]G
S]p > [fert S]G
and overestimates {atm S]_
4. If [fert S]p > [fert S]G then [soil S]p > [soil S]G
5- Plants must be grown in containers
6. No source of S in greenhouse other than readily
available soil S
1. No source of S in greenhouse other than readily
available soil S
2. Plants must be grown in containers
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valid, the amount of S accumulated from the soil by plants grown in the
presence of atmospheric S must be the same as that accumulated by plants
grown in the absence of atmospheric S. To assure a constant supply of
soil S, both sets of plants must be planted in the same amount of
uniform soil.
A set of plants grown in a greenhouse equipped with filters to
remove all forms of atmospheric S is used to measure the amount of S
accumulated from the soil. This value is subtracted from the total S
content of plants grown in the field to determine the amount of S
accumulated from the atmosphere.
This technique is limited to conditions in which vegetative pro-
duction in the field is equal to that in the greenhouse.
Technique II—
To eliminate some of the effect of differences in plant size, the
source of S in each unit weight of plant material grown in the presence
of atmospheric S can be compared with that grown in the absence of
atmospheric S. The S per gram of plant material was derived from three
possible sources: fertilizer, soil, and atmospheric S. By labeling the
fertilizer S with 35S, one can determine the amount of plant S derived
from the fertilizer. This technique separates the plant S into two
sources--[fertilizer S] and [soil S plus atmospheric S]—and can be used
when the concentrations of S in the plants are equal, despite a differ-
ence in plant size. The concentration of [soil S plus atmospheric S] in
plants grown in the absence of atmospheric S was assumed to be the
amount of soil-derived S per unit weight of plant material. This value
was subtracted from the concentration of [soil S plus atmospheric S] in
plants grown in the field to obtain the amount of atmospheric S
accumulated per unit weight of plant material.
Technique III--
This technique provides a direct method for calculating the amount
of plant S derived from the soil. Basically, it consists of determining
the specific activity of available soil S in the absence of atmospheric
S and using this value to calculate soil-derived S in plants grown at
any location.
Before planting, a sufficient quantity of soil was thoroughly mixed
and divided equally into growth containers; consequently, available
native soil S was the same in all containers. An equal amount of
fertilizer S, labeled with 35S, was added to each growth container
thereby establishing an unknown specific activity of the combined
fertilizer S and sulfate pool in the soil. It is not necessary to know
the specific activity of the fertilizer S with this technique. Plants
accumulated S from these two sources in the same proportion as the
sources occurred in the soil; therefore, if the fertilizer and soil were
the only sources of S, the specific activities of plant S and soil S
were the same. Soil S, as used in this technique, included both
fertilizer S and soil S.
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The accumulation of atmospheric S is calculated by three steps:
(1) Divide the total radioactivity by total plant S in plants grown in
the absence of atmospheric S to obtain the specific activity of the soil
S; (2) divide the total radioactivity of plants grown in the field by
the specific activity of the soil S to obtain the amount of soil-derived
S in the field plants; (3) subtract soil-derived S from total S in the
field-grown plants to obtain the amount of S accumulated from the
atmosphere.
Measurement of Sulfur-Supplying Capacity of Soils
The S fractions in soil available for use by plants include (1) the
soluble inorganic sulfate, (2) the sulfate adsorbed on clay surfaces,
and (3) part of the organic S that is mineralized from the soil organic
matter during the growing season. In this study, a distinction is made
between S supply and the S-supplying capacity of a soil. The S supply
consists of a sulfate pool that includes the soluble and adsorbed sul-
fates in the soil. Beaton et al.12 reviewed the chemical extractions
that have been suggested for estimating the amount of soluble and
adsorbed sulfates in soil. The size of the sulfate pool is finite, and
in many soils the sulfate pool contains only one or two times the annual
S requirement of crops. Therefore, additions to the sulfate pool are
required to maintain maximum crop production for an extended time. The
S-supplying capacity of a soil is the rate at which S moves into the
sulfate pool by mineralization from the soil organic matter. Assessment
of S-supplying capacity of soils based on data from field experiments is
difficult because of the inability to evaluate the contribution of
atmospheric S to the sulfate pool.
The rate of S uptake by plants can be used to estimate the S-
supplying capacity of soils. Plants have been shown to deplete the
sulfate pool in a fixed amount of soil in greenhouse pots. Therefore,
the rate of uptake after depletion of the sulfate pool can be used as a
measure of the rate of S mineralization from soil organic matter. This
study was conducted in a greenhouse equipped with charcoal filters for
removing atmospheric S.
EXPERIMENTAL PROCEDURES
Field studies were conducted in 1976 and 1977 to evaluate the three
techniques for measuring the transfer of S from the atmosphere to crops.
The S-supplying capacity of selected soils was measured in a greenhouse
experiment.
Field Studv--1976
Growth containers were prepared by cutting 15-cm-diam, polyvinyl
chloride (PVC) pipe into 90-cm lengths and covering one end with a
standard PVC cap; 20 kg of soil was placed in each container to within
15 cm of the top.
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Soil Preparation and Treatment--
Method I--A quantity of Hartsells fine sandy loam (fine-loamy,
siliceous, thermic, Typic Hapludults) soil with a very low S content was
collected at the Auburn University Agriculture Experiment Station in De
Kalb County, Alabama. This facility is located about 70 km SSW of the
TVA Widows Creek coal-fired power plant. The soil was mixed thoroughly
and placed in nine PVC growth containers; 5 g of concentrated superphos-
phate (CSP) and 2 g of potassium chloride (KC1) were mixed into the top
30 cm of soil. This soil is referred to as "low-S soil."
Method II--Because the source of S in plants was to be determined
by a difference in the total S content, a reduction in soil S before
growing the experimental plants might make the measurements more pre-
cise. A quantity of Hartsells fine sandy loam was collected from a site
in Colbert County, Alabama, limed to pH 6.5, and placed in greenhouse
pots. All nutrients needed for maximum growth, except S, were added and
all pots were seeded to corn. After seven weeks of growth, the plants
were harvested at the soil surface and discarded. The pots were again
seeded to corn. This procedure was repeated until the corn showed
visual symptoms of extreme S deficiency, indicating depletion of the
readily available soil S. The soil was removed from the pots, separated
from the plant roots, thoroughly mixed, and placed in 18 PVC growth
containers; 5 g of CSP and 2 g of KC1 were mixed into the top 30 cm of
soil in each container. This soil is referred to as "S-depleted soil."
Method III—One gram of normal superphosphate containing 127 mg S,
labeled with 1.5 mCi ^5S per milligram of sulfur, was mixed into the top
30 cm of soil in nine of the growth containers prepared by method II.
Experiment Establishment--
Three replicates of each method of soil preparation were installed
at three locations. The first site, located 4 km from the TVA Widows
Creek coal-fired power plant, is frequently exposed to relatively high
levels of S02. The second site was at the Auburn University Agriculture
Experiment Station, 70 km SSW of Widows Creek Power Plant, where only
background levels (<0.05 ppm) have been recorded, and the third location
was in a greenhouse equipped with charcoal-filtered air supply at Muscle
Shoals, Alabama.
At the field locations, the growth containers were inserted vertically
in the soil, with the tops of the cylinders 15 cm above the soil sur-
face. In the greenhouse, the growth containers were supported vertically
in a rack and exposed to the greenhouse air. Eight soybean seeds were
planted in each growth container on June 15, 1976, and thinned to two
per container after a stand was established. Field-grown soybeans were
exposed to natural precipitation, but supplemental deionized water was
added as needed to maintain soil moisture above the wilting point.
Deionized water was added to greenhouse-grown soybeans as needed to
maintain a moisture content of the soil approximating field capacity.
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-11-
A collector, with the same area as a growth container, was installed
at each field location to measure the amount of S deposited in rainfall
and as dry particulate into each container.
The entire portion of the soybean plants above ground was harvested
on September 15, 1976, dried at 70°C in a forced-air oven, and ground to
pass a 20-mesh screen. The concentration of plant S was measured with
the Leco furnace method.13 In method III, the radioactivity, as counts
per minute, was determined simultaneously in the plant material and in a
sample of the 35S-labeled, normal superphosphate. The specific activity
of the fertilizer was calculated as counts per minute per milligram of
S, and the amount of fertilizer-derived S in the plant tissue was calcu-
lated by dividing the total radioactivity in the plant by the radio-
activity per milligram of S in the fertilizer.
Field Study--1977
The results of the 1976 study were used to modify the technique in
1977.
Growth Containers—
Results of the 1976 study showed that a drainage system in the
growth containers was essential to prevent the soil from remaining
water-saturated for an extended time after a heavy rain. Because sulfate
is water-soluble and will readily leach from soil, a system was devised
by which the leachate was collected and returned to the soil after the
moisture content had been reduced below field capacity. Plastic pots,
30 cm in diameter and 60 cm high, were prepared by sealing a hose con-
nector near the bottom of the sidewall. The growth containers were
placed in the field as shown in Figure 2. A 50-gallon garbage can was
placed in the soil, with the top about 10 cm above the soil line. Four
growth containers were placed symmetrically around the garbage can at a
distance of 50 cm. Tygon tubing, 10-mm inside diameter, was fastened to
the hose connector on each growth container and passed through a hole in
the wall of the garbage can to one of four polyethylene bottles inside.
The tygon tube passed through a rigid 1-in. PVC pipe, extending from the
growth container to the garbage can, to prevent collapse of the tygon
tube due to compression of the soil. The garbage cans were covered with
lids, except during transfer of the leachate back to the growth containers.
Soil Preparation and Treatment--
A sufficient quantity of low-S soil to fill 32 of the growth con-
tainers was collected from the site described in method I of the 1976
study and mixed thoroughly. A 5-cm layer of gravel was placed in the
bottom of each growth container, and 45 kg of soil was added to within
10 cm of the top.
-------
GROWTH
CONTAINER
^^//ss
LOW-S
^.SOIL
-GRAVEL
SOIL LINE
PVC
PIPE
GARBAGE
CAN
COLLECTING
BOTTLES
N>
I
Figure 2. Diagram of experiment installation in the field.
-------
-13-
The top 15 cm of soil was removed and mixed with four fertilizer
materials: 3.50 g nitrogen (N) as ammonium nitrate; 2.38 g phosphorus (P)
and 3.00 g potassium (K) as KH2P04; 1.00 g magnesium (Mg) as magnesium
chloride: and 100 mg S as potassium sulfate in solution, labeled with
3.2 mCi "S per gram of S. The treated soil was returned to the growth
container.
Sand Culture—
Although the soil used in this study was low in soluble S, an
unknown amount of S was mineralized from soil organic matter during the
growing season. A sand culture was included at one field site to test
the feasibility of using a growth medium in which the S supply could be
better controlled. Soil has a higher moisture-holding capacity than
sand, and the frequency of supplemental irrigation required for optimum
growth was a major concern. Eight growth containers were prepared as
described above, except that sand was used instead of soil.
Nutrient Solution--Deioni2ed water was used to prepare 1 L of each
stock salt solution, which was then stored in polyethylene bottles. The
salts used and the amounts (in grams per liter) of each were NH4N03,
60.4; Ca(N03)2, 131.2; KH2P04, 334.8; MgCl2, 75.2; H3B03, 2.86; MnCl2-4H20,
1.81; ZnS04-5H20, 0.22; CuS04-5H20, 0.08; H2Mo04-H20, 0.02; FeS04, 5.00.
The nutrient solution was prepared by transferring 100 ml of each
stock salt solution to a polyethylene container and diluting to a final
volume of 20 L with deionized water. Each sand culture received 2.5 L
of the nutrient solution just before planting and every 7 to 10 days
thereafter until eight applications were received. Also, 100 mg S, as
potassium sulfate in solution and labeled with 3.2 mCi 35S per gram of
S, was applied just before planting.
Site Location—
Eight growth containers with soil were installed at each location
used in 1976. Eight soil containers and eight sand cultures were also
installed near TVA's coal-fired Colbert power plant. This site was
selected because its location, about 20 km from Muscle Shoals, would
allow supplemental irrigation of the sand cultures. Site designations
and locations are shown in Table 2.
Experiment Establishment and Data Collection--
Four replicates each of cotton (Gossypium hirsutum L.) and tall
fescue (Festuca arundinaces Schreb.) were planted in the growth con-
tainers on May 17, 1977. Cotton was thinned to four plants per container
after a stand was established.
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-14-
TABLE 2. LOCATIONS OF EXPERIMENTAL GROWTH CONTAINERS
Site designation
Location
Widows Creek
Crossville
Colbert
Greenhouse
4 km SE of the TVA Widows Creek coal-fired
power plant near Stevenson, Alabama
At the Auburn University Experiment Station
near Crossville, Alabama, and 70 km SSW of
Widows Creek Power Plant
3 km N of the TVA Colbert coal-fired power plant
near Barton, Alabama
Air Quality Research greenhouse at
Muscle Shoals, Alabama
During heavy rainfall, water drained through the growth medium to
the collecting bottles inside the garbage can. This drainage water was
returned to its respective growth container after the soil moisture con-
tent had been reduced below field capacity by evapotranspiration.
Supplemental irrigation was provided in the field by adding deionized
water as needed to maintain adequate soil moisture. Deionized water was
added daily to maintain optimum soil moisture in the greenhouse.
The entire portion of the plants above ground was harvested on
August 29, 1977, dried at 70°C for 72 h in a forced-air oven, weighed,
and ground to pass a 20-mesh screen. Plant S concentration was measured
with the Leco furnace method, and radioactivity assay was made on the
same sample. The potassium sulfate fertilizer solution labeled with 35S
was analyzed for both stable and radioactive sulfur. The specific
activity (the ratio of 35S to 32S) of the fertilizer solution, expressed
as counts per minute per milligram of S, was calculated by dividing the
total counts per minute by the total S content. Experimental protocols
used in 1976 and 1977 are summarized in Table 3.
Sulfur-Supplying Capacity of Soils
A quantity of soil was collected from two depths--0 to 30 cm and 30
to 60 cm--at each location shown in Table 4.
-------
TABLE 3. SUMMARY OF EXPERIMENTAL PROTOCOLS USED IN 1976 AND 1977
Growth medium preparation
Site location
Year
Crop
Data analysis
Method I low-S soil
Method II S-depleted soil
Method III S-depleted soil
+ 100 mg S labeled with 35S
Low-S soil + 100 mg S
labeled with 35S
Sand culture—nutrient
solution labeled with 35S
4 km from Widows Creek
a
70 km from Widows Creek
Greenhouse (Muscle Shoals)
4 km from Widows Creeka
70 km from Widows Creeka
Greenhouse (Muscle Shoals)
a
4 km from Widows Creek
70 km from Widows Creek
Greenhouse (Muscle Shoals)
a
4 km from Widows Creek
•a
70 km from Widows Creek
3 km from Colbert
Greenhouse (Muscle Shoals)
3 km from Colbert3
1976 Soybeans Technique I
1976 Soybeans Technique I
1976 Soybeans Technique II
1977 Cotton, Techniques I, II, and III
fescue
1977 Cotton, Technique III
fescue
Coal-fired power plants.
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-16-
TABLE 4. COLLECTION SITES FOR SOIL USED IN EXPERIMENT TO DETERMINE
SULFUR-SUPPLYING CAPACITY
Site number
1
2
3
4
5
6
7
Location relative to Widows
Distance
(km)
3.0
3.6
6.3
44.0
70.0
31.0
9.0
Creek Power Plant
Azimuth
(degrees)
102
158
220
190
200
272
348
Soil Treatment--
The soil from each location and depth was mixed individually with
sufficient CaC03 to adjust the pH to 6.0 to 6.5. Three sulfur-free
fertilizers were mixed with 6-kg (oven-dry weight) portions of each test
soil: 3 g ammonium nitrate, 4.37 g CSP, and 1.9 g KC1. These materials
provided 1 g each of N, P, and K.
A control treatment that would supply sufficient S for optimum
growth was prepared with soil collected from the top 15 cm of Mountview
silt loam. This soil received the same amount of ammonium nitrate and
CSP as the test soil; 1 g K and 200 mg S were supplied as potassium
sulfate.
After each harvest, 500 mg N and 500 mg K, as a solution of ammonium
nitrate and potassium chloride, were added to each test soil, and 500 mg
N, 500 mg K, and 200 mg S, as a solution of ammonium nitrate and potassium
sulfate, were added to the control soil.
Experimental Procedure—
Duplicates of each test soil and the control were placed in 10-in.
greenhouse pots and planted to Kentucky 31 fescue on November 18, 1976.
Soil moisture content was maintained at 20 percent by daily weighing the
pots and adding the amount of deionized water necessary to return the
weight to the predetermined level.
Four weeks after plant emergence, vegetative growth was harvested
5 cm above the soil surface and allowed to regrow. Additional harvests
were made at 8, 12, 16, 21, and 27 weeks after emergence. Plant material
was dried at 70°C in a forced-air oven, weighed, ground to pass a 20-mesh
screen, and analyzed for S with the Leco furnace method. Cumulative S
was calculated by adding the S content of a harvest to the total S in
all previous harvests.
-------
-17-
SECTION 4
RESULTS AND DISCUSSION
SULFUR TRANSFER FROM ATMOSPHERE TO AGRO-ECOSYSTEM
The field data are presented in chronological order to demonstrate
the development of a technique to measure S transfer from the atmosphere
to the agro-ecosystem.
Field Study--1976
Technique I—
The total S contents of soybeans grown at three locations and in
soil prepared by three methods were used to evaluate this technique
(Table 5).
TABLE 5. VEGETATIVE PRODUCTION AND SULFUR CONTENT OF SOYBEANS
GROWN AT THREE LOCATIONS IN SOIL PREPARED BY THREE METHODS
Soil preparation
I — Low-S soil
II — S-depleted soil
III--S-depleted soil
+ 100 mg S
Location
4 km3
70 kma
Greenhouse
4 kma
70 km3
Greenhouse
4 kma
70 kma
Greenhouse
Oven-dry
weight
(g>
13.3
17.0
64.0
17.3
25.0
91.6
27.0
26.0
93.3
Sulfur
concentration
(%)
0.143
0.163
0.097
0.153
0.110
0.080
0.153
0.137
0.140
Total
sulfur
(mg)
19
28
62
27
28
73
41
36
131
Distance from coal-fired power plant.
Dry matter yields, in terms of biomass, for soybeans grown at the
field locations were only 20 to 30 percent of those for soybeans grown
in the greenhouse. A lack of free drainage through the growth containers,
which resulted in temporary flooding after heavy spring rains, caused the
growth rates of soybeans to be lower in the field than in the greenhouse.
-------
-18-
The validity of this technique depends on the amount of plant S
derived from the soil being the same in both the presence and absence of
atmospheric S. In this experiment, soybeans were grown in the green-
house to obtain a value for soil-derived S for use at all locations.
The greenhouse plants were found to contain two to three times as much
S as the field plants, primarily because the vegetative production was
higher in the greenhouse than in the field. Therefore, the total S
content of plants grown in the absence of atmospheric S could not be
used as a true value for soil-derived S in plants grown in the presence
of atmospheric S. Estimating the accumulation of atmospheric S by this
technique is questionable if biomass differs between growth sites.
Technique II--
Data from soybeans grown in the soil prepared by method III were
used to test the value of this technique for estimating accumulation of
atmospheric S by plants. These plants meet the requirement that
concentrations of plant S must be similar at all locations.
The concentration of plant S derived from the fertilizer was cal-
culated by dividing the total radioactivity in 1 g of plant material by
the specific activity of S in the fertilizer. The concentration of
[soil S plus atmospheric S] was obtained by subtracting [fertilizer S]
from [plant S] (Table 6).
TABLE 6. SOURCES OF SULFUR IN SOYBEANS GROWN AT THREE LOCATIONS
Soil S plus
Plant S Fertilizer S atmospheric S
Location (mg/100 g, dry wt) (mg/100 g, dry wt) (mg/100 g, dry wt)
4 kma 153 58 95
70 kma 137 82 55
Greenhouse 140 67 73
Distance from coal-fired power plant.
If the accumulation of atmospheric S by soybeans grown in the
greenhouse were completely eliminated, the value for [soil S plus atmos-
pheric S] in greenhouse plants was the concentration of S derived from
the soil. With this technique, it was assumed that the concentration of
soil-derived S in greenhouse and field plants was the same and that
[atmospheric S] in field plants was equal to [soil S plus atmospheric S]
in field plants minus [soil S] in greenhouse plants. In this experiment,
the concentration of soil-derived S in greenhouse soybeans was higher
-------
-19-
than the concentration of soil S plus atmospheric S in soybeans grown 70
km from the power plant. Therefore, the data from soybeans grown in the
greenhouse are not a correct estimate of the amount of S derived from
the soil at the other sites.
The higher value for [soil S plus atmospheric S] in greenhouse plants,
as compared with that in soybeans grown 70 km from the power plant, may
have been due to a higher rate of S mineralization from soil organic
matter or to another source of S in the greenhouse. The rate of S
mineralization may have been higher in the greenhouse than in the
field because the sides of the growth containers were exposed to the
greenhouse air and because soil temperature would have been higher in
the greenhouse. Decomposition of soil organic matter increases as the
soil temperature increases. The presence of very low concentrations of
SC>2 in the atmosphere is also a possible source of S since the green-
house is located only 20 km from the TVA Colbert coal-fired steam plant.
In the summer, temperature in the greenhouse is controlled by moving air
through a bank of charcoal filters, through evaporative cooling pads,
across the plant growing area, and out the opposite side. The system
operates almost continuously during daylight hours in the summer, and
any trace of S02 in the ambient air could result in a measurable
accumulation of S by plants.
Because soil containers were inserted into the soil in the field,
the rates of S mineralization, and thus the concentrations of soil-
derived S, at the two field sites should have been similar. The
soybeans grown 4 km from the power plant accumulated 40 rag more S per
100 g (dry wt) than did the soybeans grown at 70 km. The difference in
the means at the two field locations is statistically significant at the
97.5 percent confidence level.
Field Study—1977
Data from cotton and fescue grown in 1977 are presented in detail
to evaluate the advantages and disadvantages of three techniques for
measuring accumulation of atmospheric S by plants.
Cotton—
Technique I--Total biomass and S content of cotton grown at four
sites were used to estimate accumulation of atmospheric S by plants by
measuring the difference in total S content between plants grown in the
presence of atmospheric S and those grown in the absence of atmospheric
S (Table 7).
Some variability between replicates is expected in an experiment of
this type, but apparent anomalies that appeared at three growth sites
require special attention. Vegetative production and S concentration of
the cotton in replicate 4 at Crossville and replicate 3 at Widows Creek
were higher than in the other replicates at the respective sites.
Although several factors could have caused a higher growth rate, the
increased S concentration in the plant concomitant with the higher yield
-------
-20-
indicates a source of S for these plants that was not available to
plants in the other replicates. The source of the additional S was
either the soil or the atmosphere, and data presented later in the
report will show that it was not the soil. At Colbert Steam Plant,
cotton grown in replicate 2 with both the soil and sand culture had
lower dry weight, S concentration, and total S uptake than did cotton
grown in the other replicates at their respective sites. This indicates
that plants grown in replicates 1, 3, and 4 accumulated S from a source
other than the soil or sand more readily than did those in replicate 2.
All four replicates at each growth site were used in calculating
the mean for each parameter in Table 7 to demonstrate this technique of
estimating the contribution of atmospheric S to the total plant S. The
mean for total plant S is a mean of the four replicate values rather
than a product of mean oven-dry weight and S concentration.
Cotton was grown in a greenhouse with charcoal-filtered air to
obtain a value of S accumulation from the soil that could be used as an
estimate of soil-derived S in cotton grown at each field site. The
amount of S accumulated by field-grown cotton in excess of the amount
accumulated by greenhouse-grown cotton was considered to be the amount
of S accumulated from the atmosphere.
Total S in cotton grown in the greenhouse was higher than that in
cotton grown at Crossville, partly because of a larger biomass, but also
because of the higher concentration of plant S in the greenhouse cotton.
Therefore, estimating the amount of atmospheric S in cotton grown at
Crossville by measuring the difference in total plant S in the two
sets of plants was not possible. Although the total plant S in cotton
grown in soil at Widows Creek and Colbert Steam Plants was higher than
that in cotton grown in the greenhouse, the validity of using S content
of greenhouse cotton as an estimate of soil-derived S at those locations
was questionable.
Although the use of this technique is limited when measuring the
amount of atmospheric S accumulated by plants, a proper interpretation
of differences in S concentrations between plants grown at different
sites, but with the same supply of soil S, will show the presence of a
source of S other than the soil. Results of the 1976 study (Table 5)
showed that, when soybean plants were grown with a limited supply of S
(soil preparation methods I and II), the higher biomass of greenhouse
plants was associated with a reduction in S concentration in the plant
tissue, indicating a dilution of plant S because of increased growth.
When fertilizer S was applied, the S concentration in the larger green-
house plants was similar to that in the smaller plants grown in the
field. These observations, plus a knowledge of basic principles of
plant mineral nutrition, led to the conclusion that, when plants are
grown with a finite supply of S, an increase in biomass is associated
with a concentration of plant S that is equal to or lower than that in
plants with the smaller biomass. An increase in both biomass and
concentration of plant S strongly suggests a supply of S from some
source other than the soil.
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-21-
TABLE 7. VEGETATIVE PRODUCTION AND SULFUR CONTENT
OF COTTON GROWN AT FOUR SITES
Site
Crossville
Widows Creek
Colbert
(soil)
Colbert
(sand)
Greenhouse
Replicate
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
Oven- dry
weight
(8)
87
90
88
204
(117)
112
136
244
125
(154)
396
182
412
436
(356)
222
115
201
207
(186)
170
173
140
158
(160)
Sulfur
concentration
(%)
0.11
0.11
0.12
0.15
(0.12)
0.15
0.16
0.32
0.13
(0.19)
0.30
0.24
0.33
0.25
(0.28)
0.28
0.15
0.28
0.30
(0.25)
0.15
0.18
0.22
0.19
(0.18)
Total
plant S
(ing)
96
99
106
306
(152)
168
218
781
162
(332)
1188
437
1360
1090
(1019)
622
172
563
621
(494)
255
311
308
300
(293)
-------
-22-
In 1977, the total biomass of cotton was not the same at all growth
sites (Table 7). Although these differences could have been caused by a
number of environmental factors, the simultaneous increase in both plant
S and biomass indicates accumulation of S from the atmosphere and a
possible growth response to atmospheric S. Jordan and Bardsley14
reported a "critical" S concentration of 0.20 percent for cotton; the
plants with the lower weights in this experiment also had S concentra-
tions below the critical level.
Technique II--The second technique for measuring the accumulation
of S from the atmosphere consists of separating the plant S into two
sources—[fertilizer S] and [soil S plus atmospheric S].
The anomalies within replicates shown in Table 7 are again apparent
in the data in Table 8. In replicate 4 at Crossville and replicate 3 at
Widows Creek, the concentration of plant S and the amount of S in each
gram of plant material that was derived from the [soil S plus atmospheric
S] was higher than in the other replicates at the respective sites. This
observation is significant because of the manner in which the concentration
of plant S and the fertilizer-derived S changed as a result of the increased
growth. It was concluded above that, if the S supply were finite and low,
increased growth would result in dilution of plant S. The concentration
of fertilizer-derived S in cotton was lower in replicate 4 at Crossville
and replicate 3 at Widows Creek, which shows that this source of S was
diluted in the plant tissue, as would be expected with the increased
growth. The soil-derived S should also have been diluted in the plant
tissue to the same extent as the fertilizer S; therefore, a higher value
for [soil S plus atmospheric S] would represent a decrease in soil S
and an increase in atmospheric S. The same reasoning applies for
interpreting the anomalies at Colbert.
If atmospheric S in greenhouse cotton was zero, the value of [soil
S plus atmospheric S] was the concentration of soil-derived S in the
plant. If soil S in a unit weight of plant material is assumed to be
the same at all locations, then the amount of S accumulated from the
atmosphere can be calculated by subtracting soil S in greenhouse cotton
from [soil S plus atmospheric S] in field cotton. In this experiment,
the concentration of soil S in greenhouse cotton was higher than the
concentration of S from all sources in cotton grown at Crossville;
therefore, the greenhouse data are not a correct estimate of the amount
of S derived from the soil at the other sites.
Although the accumulation of atmospheric S by plants cannot be
quantified by this technique, it has some advantages over technique I in
demonstrating that a greater amount of atmospheric S was accumulated by
plants growing at one site relative to those growing at another site.
Plants that accumulate the higher amount of atmospheric S will always
have a higher concentration of [soil S plus atmospheric S] and an equal
or lower concentration of fertilizer S than plants that accumulate the
lower amount of atmospheric S. This relationship is independent of the
total amount of S in the plant.
-------
-23-
TABLE 8. SOURCES OF SULFUR IN COTTON GROWN AT FIVE SITES
Site
Crossville
Widows Creek
Colbert
(soil)
Colbert
(sand)
Greenhouse
Repli- Radioactivity
cate (cpm/g,
dry wt)
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
301,140
345,960
348,090
194,400
311,220
339,200
114,240
247,470
66,080
249,690
60,000
100,300
65,520
189,970
58,560
57,840
202,120
133,560
253,260
235,620
Soil S plus
Fertilizer S Plant S atmospheric S
(M8/8, (H8/8, (H8/8,
dry wt) dry wt) dry wt)
176
202
204
114
(174)
182
198
67
145
(148)
39
146
35
59
(70)
38
111
34
34
(54)
118
78
148
138
(120)
1100
1100
1200
1500
(1225)
1500
1600
3200
1300
(1900)
3000
2400
3300
2500
(2800)
2800
1500
2800
3000
(2525)
1500
1800
2200
1900
(1850)
924
898
996
1386
(1051)
1318
1402
3133
1155
(1752)
2961
2254
3265
2441
(2730)
2762
1389
2766
2966
(2471)
1382
1722
2052
1762
(1730)
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-24-
In this experiment, cotton growing near coal-fired power plants had
a higher concentration of [soil S plus atmospheric S] and a lower concen-
tration of fertilizer S than cotton grown at Crossville, which is located
70 km from the nearest power plant. The source of S in the growth
medium of cotton grown in sand at Colbert was limited to the fertilizer,
and with soil S equal to zero, the value for [soil S plus atmospheric S]
is the amount of S accumulated in each gram of plant material from the
atmosphere.
Technique III—Cotton was grown in a greenhouse with charcoal-
filtered air to establish the specific activity of available soil S, but
data in Tables 7 and 8 indicate that these plants accumulated S from
some other source—either the atmosphere or the soil organic matter.
The relative dilution of the specific activity at the various
growth sites was tested by dividing total plant S into the total radio-
activity at each site. The mean values for specific activity of plant S
at the four sites were (1) Crossville, 25.15 x 104 cpm/mg S; (2) Widows
Creek, 16.14 x 104 cpm/mg S, (3) greenhouse, 11.20 x 104 cpm/mg S, and
(4) Colbert (soil), 4.61 x 104 cpm/mg S. Colbert (sand) was not included
because the specific activity of S in the plants that was derived from
the growth medium was the same as the specific activity of the fertilizer.
The specific activity of S in cotton grown at Crossville was the highest,
which showed that greater dilution occurred at the other sites because
of S accumulation in the plants from a source other than the soil. Con-
tinuous monitoring at the Crossville site showed no measurable concentra-
tion of S02 in the ambient air, but 41 mg S was deposited by rainfall
and particulate deposition on a surface area equal to the growth con-
tainers. At Widows Creek and Colbert, 30 and 47 mg S, respectively,
were deposited in this manner. Although cotton at Crossville probably
accumulated some S from the atmosphere, the specific activity of plant
S was more comparable to the specific activity of soil S than at any
other location. Therefore, the specific activity of plant S at Cross-
ville was assumed to be equal to the specific activity of soil S at
the other sites for the purpose of demonstrating this method of
calculating S accumulation from the atmosphere.
The specific activity of S in cotton grown at Crossville was calcu-
lated by dividing total radioactivity by total plant S for each repli-
cate (Table 9). The value for specific activity in replicate 4, which
is much lower than values for the other replicates, is further evidence
of a source of S other than the soil for cotton grown in that container.
The total radioactivity of cotton in each replicate at the other
sites was divided by the mean specific activity of S in cotton grown at
Crossville to obtain the amount of soil-derived S in the plants (Table
10). Soil-derived S in cotton grown in sand culture at Colbert was
calculated by dividing the total radioactivity in the plants by the
specific activity of the fertilizer (171 x 104 cpm/mg S).
Evaluation of the data from Widows Creek by using techniques I and
II indicated that cotton in replicate 3 accumulated S from some source
other than the soil. The data in Table 10 show that a much larger per-
centage of the total plant S was derived from the atmosphere in replicate
-------
TABLE 9.
-25-
DETERMINATION OF SPECIFIC ACTIVITY OF SULFUR
IN COTTON GROWN AT CROSSVILLE
Replicate
1
2
3
4
Mean
Total
radioactivity
(cpm x 104)
2620
3114
3063
3966
Total
plant S
(mg)
96
99
106
306
Specific activity
(cpm x 104/mg S)
27.29
31.45
28.89
12.96
(25.15)
TABLE 10. SOURCE OF SULFUR IN COTTON GROWN AT THREE SITES
Site
Widows Creek
Colbert
(soil)
Colbert
(sand)
Greenhouse
Repli-
cate
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
Total
radioactivity
(cpm x 104)
3,486
4,613
2,787
3,093
2,617
4,544
2,472
4,373
1,454
2,184
1,177
1,197
3,346
2,311
3,546
3,723
Soil-
derived S
(mg)
138
183
111
123
(139)
104
181
98
174
(139)
8
13
7
7
(9)
137
92
141
148
(130)
Total
plant S
(mg)
168
218
781
162
(332)
1188
437
1360
1090
(1019)
622
172
563
621
(494)
255
311
308
300
(294)
Atmosphere-
derived S
(mg)
30
35
670
37
(193)
1084
256
1262
916
(880)
504
159
556
614
(458)
118
219
167
152
(164)
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-26-
3 than in the other replicates. At Colbert, the lower values for total
plant S in cotton grown in replicate 2 of both the soil and sand cultures
were associated with lower values for atmospheric-derived S.
Fescue
Techniques I and II--The limitations of using these two methods of
calculation to measure accumulation of atmospheric S were discussed
above. Total vegetative production and S content of fescue (Table 11)
and concentrations of the different sources of S in fescue (Table 12)
were determined so that these data could be compared with the data from
cotton and soybeans. Analysis of these results confirms the conclusion
that these techniques have limited use as methods for measuring accu-
mulation of atmospheric S by plants.
Technique III--The rationale for this technique was discussed above
for cotton; therefore, this discussion will be limited to the calculation
of data for fescue.
The specific activity of S in fescue grown at Crossville was cal-
culated (Table 13) and used as the specific activity of soil S at all
other growth sites. Note that the total plant S varied from 44 to 75 rag
between replicates, but the specific activity only varied from 31.95 to
33.13 x 104 cpm/mg S. This shows that fertilizer S and native soil S
were accumulated by the plant in the same proportion even though the
total S uptake varied between replicates. The primary advantage of this
technique is that the only purpose for growing plants in the absence of
atmospheric S is to establish the specific activity of soil S.
The mean specific activity of S in fescue grown at Crossville
(Table 13) was higher than the value calculated for cotton (Table 9).
However, the mean for replicates 1, 2, and 3 for cotton was 29.21 x 104
cpm per milligram of S. If the soil is the only source of S, the
specific activity of S in the plant should be independent of the crop
species. Because cotton accumulated atmospheric S more efficiently than
did fescue at the other sites, it was not unexpected that the specific
activity would be lower in cotton than in fescue at Crossville. This
difference in specific activities between plant species emphasizes the
necessity of growing plants in the absence of atmospheric S to obtain a
true specific activity of soil S.
The soil-derived S was calculated by dividing the total radio-
activity in fescue grown at each site by the mean specific activity of
plant S in fescue grown at Crossville (Table 14).
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-27-
TABLE 11. VEGETATIVE PRODUCTION AND SULFUR CONTENT
OF FESCUE GROWN AT FOUR SITES
Site
Crossville
Widows Creek
Colbert
(soil)
Colbert
(sand)
Greenhouse
Replicate
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
Oven- dry
weight
(g)
44
37
50
39
(42)
64
67
46
63
(60)
45
51
55
48
(50)
41
50
49
36
(44)
8
18
21
11
(14)
Sulfur
concentration
(%)
0.12
0.12
0.15
0.14
(0.13)
0.18
0.18
0.20
0.21
(0.19)
0.16
0.18
0.16
0.19
(0.17)
0.15
0.23
0.17
0.18
(0.18)
0.15
0.18
0.15
0.09
(0.14)
Total
plant S
(mg)
53
44
75
55
(57)
115
120
92
132
(115)
72
92
88
91
(86)
62
115
83
65
(81)
12
32
32
9
(21)
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-28-
TABLE 12. SOURCES OF SULFUR IN FESCUE GROWN AT FIVE SITES
Site
Crossville
Widows Creek
Colbert
(soil)
Colbert
(sand)
Greenhouse
Repli-
cate
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
Radioactivity
(cpm/g,
dry wt)
399,040
379,996
480,060
459,991
351,430
412,750
471,500
423,200
272,160
372,000
387,720
431,730
124,230
441,600
369,360
310,000
421,200
409,500
282,720
20 , 160
Fertilizer S
(M8/8,
dry wt)
233
222
281
269
(251)
206
241
276
247
(242)
159
218
226
252
(214)
73
258
216
181
(182)
246
239
165
12
(165)
Plant S
(Mg/g,
dry wt)
1200
1200
1500
1400
(1325)
1800
1800
2000
2100
(1925)
1600
1800
1600
1900
(1725)
1500
2300
1700
1800
(1825)
1500
1800
1500
900
(1425)
Soil S plus
atmospheric S
(Mg/8,
dry wt)
967
978
1219
1131
(1073)
1594
1555
1724
1853
(1683)
1441
1582
1374
1648
(1511)
1427
2042
1484
1629
(1643)
1254
1561
1335
888
(1260)
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TABLE 13.
-29-
SPECIFIC ACTIVITY OF PLANT SULFUR FOR
FESCUE GROWN AT CROSSVILLE
Replicate
1
2
3
4
Mean
Total
radioactivity
(cpm x 104)
1756
1406
2400
1794
Total
plant S
(rag)
53
44
75
55
Specific activity
(cpm x 104/mg S)
33.13
31.95
32.00
32.62
(32.42)
TABLE 14. SOURCE OF SULFUR IN FESCUE GROWN AT THREE SITES
Site
Widows Creek
Colbert
(soil)
Colbert
(sand)
Greenhouse
Total
Repli- radioactivity
cate (cpm x 104)
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
1
2
3
4
Mean
2,249
2,765
2,169
2,661
1,225
1,897
2,130
2,072
509
2,208
1,810
1,116
337
737
594
22
Soil-
derived S
(ing)
69
85
67
82
(76)
38
59
67
64
(57)
3
13
11
7
(8)
10
23
18
0.7
(13)
Total Atmosphe re-
plant S derived S
(mg) (mg)
115
120
92
132
(115)
72
92
88
91
(86)
62
115
83
65
(81)
12
32
32
9
(21)
46
35
25
50
(39)
34
33
21
27
(29)
59
102
72
58
(73)
2
9
14
8
(8)
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-30-
General Discussion
The primary objective of this experiment was to select a technique
for measuring the accumulation of S by plants, but other significant obser-
vations should be considered. The data from cotton and fescue were summa-
rized with the source of plant S calculated by technique III (Table 15).
Cotton was more efficient than fescue in accumulating S from the
atmosphere, as shown by the higher concentration of atmospheric S in
cotton than in fescue grown at each site. These data suggest that the
amount of S accumulated from the atmosphere was influenced by the
relationship between the supply of soil S and the S requirement of the
crop. Cotton has a relatively high S requirement, and the soil supply
was not sufficient to maintain the S concentration above the "critical"
concentration of 0.20 percent in the cotton grown at Crossville.
Because the supply of soil S was limiting, the cotton grown near the
coal-fired power plants accumulated more S from the atmosphere than from
the soil and therefore acted as a "sink" for atmospheric S. In both the
soil and sand at Colbert, the supply of S in the growth medium was
limiting, and the concentrations of atmospheric S in the cotton were
similar.
Fescue has a lower S requirement than cotton; therefore, the supply
of soil S relative to the S requirement was higher for fescue than for
cotton. Because the supply of soil S was more nearly adequate to meet
the S requirement of fescue, the capacity to accumulate additional S
from the atmosphere was less for fescue than for cotton. Fescue grown
near the power plants accumulated more S from the soil than from the
atmosphere. Further evidence of this relationship was obtained by
comparing accumulation of atmospheric S by fescue grown in soil with
that by fescue grown in sand at Colbert. Fescue grown in soil accumu-
lated 57 mg S from the soil, but only 29 mg S from the atmosphere, and
the concentration of atmospheric S in the plant was 58 mg/g (dry wt).
Fescue grown in sand, with a low S supply, accumulated only 8 mg S from
the growth medium, but 73 mg S from the atmosphere, and the concentration
of atmospheric S in the plant was 165 mg/g (dry wt). Fescue acted as a
"sink" for atmospheric S, as did cotton, only when the supply in the
growth medium was low relative to the S requirement of the plant.
Cotton and fescue were grown in the greenhouse to measure S accu-
mulation from the soil in the absence of atmospheric S. The accumulation
of 102 and 57 mg of atmospheric S per 100 g (dry wt) by cotton and
fescue, respectively, shows why the total S content of these crops could
not be used as an estimate of the soil-derived S in plants. This
technique does not differentiate between a higher rate of S mineraliza-
tion and the atmosphere as the source of "atmospheric S" in greenhouse
plants, but in either case, the specific activity of S in the greenhouse
plants was not the same as the specific activity of soil S at the other
growth sites. Plants grown in the absence of atmospheric S and in soil
with the same rate of S mineralization rate as that in the field are
required to quantify the accumulation of atmospheric S by plants. In
this report, only the amount of S accumulated from the atmosphere by
cotton and fescue grown near the power plants in excess of atmospheric S
accumulated at Crossville was calculated.
-------
TABLE 15. VEGETATIVE PRODUCTION, SULFUR CONTENT, AND SOURCE OF PLANT SULFUR FOR
COTTON AND FESCUE GROWN AT FOUR SITES
Growth site
Crossville
Widows Creek
Colbert (soil)
Colbert (sand)
Greenhouse
Crossville
Widows Creek
Colbert (soil)
Colbert (sand)
Greenhouse
Oven- dry
weight
(g)
117
154
356
186
160
42
60
50
44
14
Sulfur
concentration
(%)
Cotton
0.12
0.19
0.28
0.25
0.18
Fescue
0.13
0.19
0.17
0.18
0.14
Total
sulfur
(mg)
152
332
1018
494
294
57
115
86
81
21
Source of plant sulfur
Soil
(ng)
152
139
139
9
129
57
76
57
8
13
Atmosphere
(•g)
0
193
854
485
164
0
39
29
73
8
(mg/100 g,
dry wt)
0
125
240
260
102
0
65
58
165
57
I
LO
-------
-32-
SULFUR-SUPPLYING CAPACITY OF SOILS
Cumulative S uptake was calculated for fescue grown in soils col-
lected from the 0- to 30-cm depth at each site (Figure 3). The uptake
rates of S by these plants were used to estimate the size of the sulfate
pools and the rates of S mineralization from the soil organic matter.
Sulfur accumulation by fescue grown in the topsoil from site 4 was
used to demonstrate how the two sources of S supply were separated
(Figure 4). The decreasing rate of S uptake during the first 16 weeks
of growth reflects the depletion of the sulfate pool. Between 16 and 27
weeks, the rate of S uptake was constant, representing the rate of S
mineralization from the soil organic matter. The size of the sulfate
pool in the 6 kg of soil at the beginning of the experiment was estimated
by extrapolating the linear portion of the curve to zero time and reading
33 mg S at the point of interception with the y-axis. The S-supplying
capacity of the soil is equivalent to the rate of S mineralization and
was estimated by calculating the slope of the linear portion of the S
accumulation curve. The topsoil from site 4 supplied 1 mg S per kilo-
gram of soil during the 27 weeks of growth. At this rate of S minerali-
zation into the sulfate pool, it would take about 3 years to replenish
the sulfate pool to its original level.
Although size of the sulfate pools varied between the different
soils, the rates of S mineralization were similar for topsoils collected
at sites 1, 3, 4, 5, and 7 (Figure 3). The relatively large sulfate
pools in soil collected from sites 2 and 6 were not depleted during the
growth period, and this prevented a determination of rates of S minerali-
zation for these two soils.
Cumulative S uptake was calculated for fescue grown in soils col-
lected from the 30- to 60-cm depth at each site (Figures 5 and 6). The
sulfate pools at this depth were larger than in the corresponding 0- to
30-cm depth. This observation is consistent with results reported by
Bardsley and Kilmer,15 who used chemical analysis to assay available
sulfate in soils. They found that, in 17 of 21 soils studied, acetate-
soluble sulfate accumulated between the 30- and 60-cm depth. In this
experiment, the sulfate pools were not depleted in soils collected from
the 30- to 60-cm depth; consequently, neither the size of the sulfate
pools nor the rates of S mineralization could be calculated.
The soil was removed from the greenhouse pots, and plant residue
was removed; the soil was repotted and planted to fescue. The procedure
used in this experiment will be repeated to deplete the sulfate pool and
measure the rate of S-supplying capacity of these soils.
-------
-33-
3 O O
2 5 O
•
A
O
D
*
A
•
O
Site No.
1
2
3
4
5
6
7
C O NTRO I
8 12 16
AGE (Weeks)
2 1
27
Figure 3. Sulfur accumulation by fescue grown in soil
collected from the 0- to 30-cm depth.
-------
-34-
4O -
3O -
O3
E
V—'
z
o
u
u
2 O
8 12 16 21
AGE (weeks)
2 7
Figure 4. Sulfur accumulation by fescue grown in soil collected
from the 0- to 30-cm depth at site 4.
-------
-35-
4 8 12 16 21 27
AGE (W e e ks")
Figure 5. Sulfur accumulation in fescue grown in soil
collected from the 30- to 60-cm depth at
three sites.
-------
-36-
24 O -
O)
E
z
O
u
u
a:
CO
180 -
12O -
12 16 21
AGE (Weeks)
27
Figure 6. Sulfur accumulation in fescue grown in soil
collected from the 30- to 60-cm depth at
four sites.
-------
-37-
REFERENCES
1. Ensminger, L. E., and H. V. Jordan. The Role of Sulfur in Soil
Fertility. Adv. Agron., 10:408-434, 1958.
2. Bettany, J. R., J.W.B. Stewart, and E. H. Halstead. Assessment of
Available Soil Sulfur in an 35S Growth Chamber Experiment. Can.
J. Soil Sci., 54:309-315, 1974.
3. Beaton, J. D., S. L. Tisdale, and J. Platou. Crop Response to
Sulfur in North America. The Sulfur Inst. Tech. Bull. 18, 1971.
4. Fried, M. The Absorption of Sulfur Dioxide by Plants as Shown by
the Use of Radioactive Sulfur. Soil Sci. Soc. Am. Proc., 13:135-
138, 1949.
5. Cowling, D. W., L.H.P. Jones, and D. R. Lockyer. Increased Yield
through Correcting of Sulfur Deficiency in Ryegrass Exposed to
Sulfur Dioxide. Nature, 243:479-480, 1973.
6. Olsen, R. A. Absorption of Sulfur Dioxide from the Atmosphere by
Cotton Plants. Soil Sci., 84:107-111, 1957.
7. Alway, F. J., A. W. Marsh, and W. J. Methley. Sufficiency of Atmo-
spheric Sulfur for Maximum Crop Yields. Soil Sci. Soc. Am. Proc.,
2:229-238, 1938.
8. Payrissat, M., and S. Beilke. Laboratory Measurements of Sulfur
Dioxide by Different European Soils. Atmos. Environ., 9:211-217,
1975.
9. Roberts, S., and F. E. Koehler. Sulfur Dioxide as a Source of
Sulfur for Wheat. Soil Sci. Soc. Am. Proc., 29:696-698, 1965.
10. Yee, M. S., H. L. Bohn, and S. Miyamats. Sorption of Sulfur Dioxide
by Calcareous Soils. Soil Sci. Soc. Am. Proc., 39:268-270, 1975.
11. Jordan, H. V., C. E. Bardsley, Jr., L. E. Ensminger, and J. A.
Lutz, Jr. Sulfur Content of Rainwater and Atmosphere in Southern
States. U.S.D.A. Tech. Bull. 1196, 1959. 16 pp.
12. Beaton, J. D., G. R. Burns, and J. Platou. Determination of Sulfur
in Soils and Plant Material. The Sulfur Inst. Tech. Bull. 14,
1968. 55 pp.
13. Todemann, A. R., and T. D. Anderson. Rapid Analysis of Total Sulfur
in Soils and Plant Material. Plant Soil, 35:197-200, 1971.
14. Jordan, H. V., and C. E. Bardsley. Response of Crops to Sulfur on
Southeastern Soils. Soil Sci. Soc. Am. Proc., 22:254-256, 1958.
15. Bardsley, C. E., and V. J. Kilmer. Sulfur Supply of Soils and Crop
Yields in the Southeastern United States. Soil Sci. Soc. Am. Proc.,
27:197-199, 1963.
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TECHNICAL REPORT DATA
(Please read Inttructions on the reverse before completing)
I. REPORT NO.
EPA-600/7-79-I09
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
ACCUMULATION OF ATMOSPHERIC SULFUR BY PLANTS AND
SULFUR-SUPPLYING CAPACITY OF SOIL
6. REPORT DATE
April 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOH
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