SULFUR MANAGEMENT IN CORN AND SOYBEAN CROPPING SYSTEMS
By
Luke Luciano Thurgood

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
Crop and Soil Sciences – Master of Science
2014

ABSTRACT
SULFUR MANAGEMENT IN CORN AND SOYBEAN CROPPING SYSTEMS
By
Luke Luciano Thurgood
Earlier planting dates in cooler soils, increased nutrient removal by higher yielding cultivars, and
reductions in atmospheric sulfur (S) deposition suggest that S application may require
reassessment in Michigan for optimal corn (Zea mays L.) and soybean (Glycine max L.) growth.
Field experiments were conducted on corn to examine the effect of a range of S rates with
increasing nitrogen (N) rates on grain yield. The results indicated S availability may be
sufficient when optimal N rates are applied promoting sufficient root growth to exploit the soil
profile and acquire sufficient S quantities for optimal plant growth, however, yield responses to S
may vary with environmental conditions (i.e., soil organic matter, soil texture, soil phosphorus
(P) levels, and crop rotation). Residual soil S, mineralization of soil organic matter, S deposition
from rainfall, and possible sub-soil S accumulation should all be considered for potential S
contributions to determine when S application is justified. A soybean field trial investigated S
placement at 25 lbs S/acre while evaluating the presence of a starter fertilizer (20 lbs N and 50
lbs P2O5/acre) in a 2 × 2 inch band. Although starter fertilizer had no significant effect on
soybean grain yield or quality, in both study years soybean canopy density and greenness were
greater with starter fertilizer application prior to V4. No significant effect on grain yield from S
placement occurred in either study year suggesting sufficient S was cycling in the soil profile for
optimal soybean growth to occur. Evaluating residual soil S and organic matter levels at the time
of planting may be necessary to determine if S application is justified for optimal corn and
soybean growth.

ACKNOWLEDGMENTS

I would like to thank Dr. Kurt Steinke for serving as my major advisor during my
graduate studies at Michigan State University. Dr. Steinke’s guidance and unfailing charisma in
agricultural research has promoted greater knowledge and skills in my professional career. I
thank Dr. Christy Sprague and Dr. Daniel Brainard for serving on my guidance committee and
contributing there knowledge and experience to make my thesis a success.
I want to especially thank Andy Chomas for all the work he put in to helping me develop
my field experiment layout, establishing the trials, and collecting data. Andy offered practical
knowledge that was beneficial in field management and collecting quality data, his input was
greatly appreciated. Thank you goes to the Michigan Soybean Promotion Committee, Corn
Marketing Program of Michigan, Michigan State University’s AgBioResearch and Project
GREEEN for providing the funds to support this research.
Many undergraduate and graduate students contributed to my education during the last 2
years at MSU. I give a special thanks to Brian Stiles for his consistent diligence in helping me
collecting samples. I would also like to thank Vance Gawel, Gavan Leinhart, Brandon Mezzo,
and Dan Quinn. Additionally, I would like to thank past and current graduate students Laura
Lindsey, Alex Lindsey, and Mike Swoish.
I would like to thank my parents and my in-laws for the aid they provided as I have
worked to complete my education. The greatest gratitude belongs to my wife Vanessa for all the
support she provided through the challenging times of completing this degree.

iii

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................................... vi
LIST OF FIGURES ..................................................................................................................... viii
CHAPTER 1 – LITERATURE REVIEW .......................................................................................1
Introduction ..........................................................................................................................1
Sulfur in Plants.....................................................................................................................2
Soybeans and Sulfur ............................................................................................................3
Sulfur in Corn ......................................................................................................................5
Organic Sulfur ......................................................................................................................7
Elemental Sulfur ..................................................................................................................8
Sulfate Fertilizers ...............................................................................................................10
Losses of Available Sulfur .................................................................................................11
Applying Sulfur .................................................................................................................12
Residual Sulfur...................................................................................................................13
Soil Testing ........................................................................................................................14
Testing for Sulfur in Plants ................................................................................................14
REFERENCES ..................................................................................................................17
CHAPTER 2 – EFFECTS OF SULFUR ON CORN YIELD AT DIFFERENT NITROGEN
RATES ...........................................................................................................................................23
Abstract ..............................................................................................................................23
Introduction ........................................................................................................................24
Materials and Methods .......................................................................................................26
Results and Discussion ......................................................................................................29
Environmental Conditions .....................................................................................29
Nutrient Uptake Responses ....................................................................................31
Greenness Indices ..................................................................................................35
Corn Grain Yield....................................................................................................37
Agronomic Efficiency of Nitrogen Fertilizer ........................................................40
Conclusions ........................................................................................................................41
APPENDIX ........................................................................................................................42
REFERENCES ..................................................................................................................45
CHAPTER 3 – SOYBEAN RESPONSE TO SULFUR PLACEMENT AND STARTER
FERTILIZER .................................................................................................................................49
Abstract ..............................................................................................................................49
Introduction ........................................................................................................................49
Materials and Methods .......................................................................................................51
Results and Discussion ......................................................................................................53
Environmental Conditions .....................................................................................53
Plant Tissue Analyses ............................................................................................55
iv

Root Nodule Assessment .......................................................................................57
Plant Greenness ......................................................................................................58
Grain Yield, Quality and Components...................................................................59
Conclusions ........................................................................................................................61
REFERENCES ..................................................................................................................63
CHAPTER 4 – CORN RESPONSE TO SULFUR IN HIGH PHOSPHORUS SOILS ................68
Abstract ..............................................................................................................................68
Introduction ........................................................................................................................68
Materials and Methods .......................................................................................................70
Results and Discussion ......................................................................................................73
Corn Growth Response and Nutrient Uptake ........................................................73
Grain Yield Response to Sulfur .............................................................................75
Factors Affecting Sulfur Response ........................................................................77
Conclusions ........................................................................................................................79
REFERENCES ..................................................................................................................81

v

LIST OF TABLES

Table 2.1. Growing season (May – Sept.) and 30-yr mean precipitation and temperature
data for East Lansing, MI, 2012 – 2013.............................................................................30
Table 2.2. Corn whole plant (V6) and ear leaf (R1) nutrient analysis as affected by sulfur
rate. Nutrient concentrations were averaged across six nitrogen rates, East Lansing, MI,
2012 – 2013........................................................................................................................32
Table 2.3. Effects of nitrogen and sulfur rate on corn stalk nitrate concentrations at
physiological maturity, East Lansing, MI, 2012 – 2013 ....................................................34
Table 2.4. Nitrogen by sulfur interaction on corn stalk nitrate concentrations at
physiological maturity, East Lansing, MI, 2013 ................................................................34
Table 2.5. Total vegetative nitrogen uptake at physiological maturity as affected by
nitrogen and sulfur rate, East Lansing, MI, 2012 – 2013 ..................................................35
Table 2.6. Effects of nitrogen and sulfur rate on V6 relative normalized difference
vegetation index, East Lansing, MI, 2012 – 2013 .............................................................36
Table 2.7. Nitrogen by sulfur interaction on V6 relative normalized difference vegetation
index, East Lansing, MI, 2013 ...........................................................................................37
Table 2.8. Interaction between nitrogen and sulfur application on corn grain yield, East
Lansing, MI, 2012-2013 ............................................................................................................. 38
Table 2.9. Corn R1 ear leaf nitrogen analysis, East Lansing, MI, 2012 – 2013 ................39
Table 2.10. Main effects of nitrogen and sulfur on agronomic efficiency of nitrogen, East
Lansing, MI, 2012-2013 ....................................................................................................40
Table 3.1. Mean May – Sept. and 30-yr average precipitation and temperature data, East
Lansing, MI, 2012 – 2013 ..................................................................................................54
Table 3.2. Petiole R1 nutrient concentrations as affected by S placement and starter
fertilization, East Lansing, MI, 2012 – 2013 .....................................................................56
Table 3.3. Soybean R3 root nodule counts as affected by S placement and starter
fertilization, East Lansing, MI, 2012 – 2013 .....................................................................57
Table 3.4. Soybean grain yield and moisture as affected by S placement and starter
fertilization, East Lansing, MI, 2012 – 2013 .....................................................................59

vi

Table 3.5. Soybean grain oil and protein as affected by S placement and starter
fertilization at East Lansing, MI in 2012 and 2013 ...........................................................61
Table 4.1. Mean May – Sept. precipitation and 30-yr mean with irrigation, Entrican,
MI, 2012 – 2013 .................................................................................................................71
Table 4.2. Corn V6 whole plant and R1 ear leaf N and S concentrations as affected by S
rate, Entrican, MI, 2012 – 2013 .........................................................................................74
Table 4.3. Stalk nitrate concentration as influenced by N and S applications, Entrican,
MI, 2012 – 2013 .................................................................................................................75
Table 4.4. Grain yield and moisture as affected by S rate, Entrican, MI, 2012 –2013 ......75
Table 4.5. Corn grain yield response to N × S interaction, Entrican, MI, 2013 ................76
Table 4.6. Main effects of S on R1 N:S ratios, Entrican, MI, 2012 – 2013.......................77

vii

LIST OF FIGURES

Figure 2.1. Daily precipitation May – Sept. for (a) 2012 and (b) 2013, East Lansing,
MI.......................................................................................................................................30
Figure A.1. Corn grain yield regressed against nitrogen rates for (a) 2012 and (b) 2013.
Convergence criteria was not met for the 45 kg S rate in 2012 and not presented, East
Lansing, MI ........................................................................................................................44
Figure 3.1. Daily precipitation May – Sept. for (a) 2012 and (b) 2013, East Lansing,
MI.......................................................................................................................................54

viii

CHAPTER 1
LITERATURE REVIEW

Introduction
The state recommendations for S application in Michigan corn and soybean production have not
been updated in the last 30 years. As one of the 17 essential plant nutrients S has an important
role in many internal plant functions. Since the last update of Michigan S recommendations
more stringent clean air laws have been mandated, thus requiring power plants and industrial
facilities to significantly reduce the levels of contaminants emitted through smoke stacks (i.e.,
sulfur dioxide). Deposition of sulfate and hydrogen sulfide through rain fall has traditionally
supplied agricultural soils with sufficient S to meet plant requirements. In the early 1970s
Wisconsin field studies demonstrated that alfalfa obtained optimal yields when receiving as
much as 44% of necessary S from the atmosphere (Hoeft et al. 1972). However, the U.S.
Environmental Protection Agency (EPA) reports that from 1980 to 2010 S emissions have been
reduced by as much as 83% (National Atmospheric Deposition Program, 2012). Sulfur escape
into the atmosphere has been reduced by flue gas scrubbing technology. When coal is
combusted the sulfur that is naturally present will combine with oxygen forming SO2. Before
exhaust gas is released into the atmosphere it passes through a mixture of lime or limestone and
water. The SO2 will react with the lime mixture and is removed from the exhaust. Data
collected from the southern half of Michigan has shown that S-deposition (wet weight) has been
reduced from 30 kg ha-1 in 1980 to less than 10 kg ha-1 in 2010 (National Atmospheric
Deposition Program, 2012).

1

Reductions in S deposition are not the sole cause of more frequent occurrences of S
deficiency. Single super phosphate (SSP, 0-9-0-12S) was once commonly used as a phosphorus
source since its development in the 1800s. However, comparable cost between single super
phosphate and higher analysis P sources has caused growers to use triple super phosphate (TSP,
0-45-0) and more commonly mono-ammonium phosphate (MAP, 11-52-0) (Hagstrom, 1986).
The change to high analysis sources has resulted in less incidental S application with fertilizer
mixtures.
In addition to the declines in sulfur deposition and incidental S application a concurrent
increase of corn yields has occurred requiring greater S quantities to reach optimal yields. In
1970 the national average corn yield was 4.5 Mg ha-1, in 2011 it was 9.2 Mg ha-1 (Capehart,
2013). Similar increases in average soybean yield have occurred over the same period of time
increasing from 1.7 Mg ha-1 (1974) to 2.7 Mg ha-1 (2009). The increase of corn and soybean
yields results in higher rates of S removal in grain.
Sulfur in Plants
Within plants S is well known as a component of amino acids cysteine and methionine (Taiz and
Zieger, 2010). Sulfate (SO4), the plant available form of S, when taken up by the plant
undergoes reduction before reacting with o-acetylserine (OAS) to form the amino acid cysteine.
Nitrogen’s dependence on S is associated with OAS. In the event that a plant should become Sdeprived, OAS will accumulate causing transporters of S to be up-regulated (increased
expression of a gene to create plant organelles) to increase S uptake (Smith et al., 1997).
Conversely when N becomes limited and the production OAS decreases, however, there is not a
consequential increase of N transporters (Reuveny et al., 1980). An S deficiency will primarily
limit N assimilation to form cysteine, but will not hinder N uptake (Zhao et al., 1998).

2

Apart from amino acid production S is essential for the reduction of nitrate. When plants
take up nitrate (NO3) it is reduced to form organic N (ammonium, NH4). The pathway to convert
nitrate to ammonium is a two-step process. First, nitrate reductase will reduce nitrate to nitrite, a
highly reactive form of N that can be toxic. Plants will immediately transport the nitrite from the
cytosol to the chloroplasts in leaves and plastids in the roots. In these compartments nitrite is
converted to ammonium via nitrite reductase. Sulfur is a component of nitrite reductase. Nitrite
reductase is a single polypeptide (long continuous, un-branched, chain of amino acids linked by
amide bonds) containing a heme (a non-protein chemical compound that is bound to
a protein and is required for the protein's biological activity) and an iron-sulfur compound known
as ferrodoxin (Fe4S4) (Taiz and Zieger, 2010). Without available S plants would be limited in
their ability to reduce nitrate.
Soybeans and Sulfur
Cysteine and methionine have an important role in soybeans due to higher marketable contents in
this crop, as soybean seed typically averages 40% protein and 20% oil (Krishnan, 2005). In the
United States, a large percentage of the soybean produced is used as livestock feed to satisfy the
high S requirement of poultry and swine diets (Chung and Baker, 1992; Waldroup and Hellwig,
1995). The use of genetic technologies has been investigated to promote more favorable traits
and pathways that may potentially increase the S-containing amino acids of soybeans and
improve protein content (Krishnan and Chronis, 2003; Krishnan, 2005). However, one of the
constraints preventing the development of soybean cultivars with higher protein potential is the
inverse relationship between seed protein and yield in both determinate and indeterminate
cultivars (Wehrmann et al. 1987). Determinate variety traits may enhance the ability to

3

overcome the inverse relationship to produce high-yielding soybean cultivars with seed protein
concentrations in excess of 450 g kg-1 (Wilcox and Guodong, 1997).
Sulfur uptake and remobilization at seed set in soybeans can be up to 800 μg S plant-1 d-1
(Sexton et al., 1998a). A large proportion (56 to 59%) of total plant S accumulates in late
vegetative development and is remobilized shortly thereafter for seed fill with only 10 and 20%
being supplied from the pods and leaves, respectively (Naeve and Shibles, 2005). A reduction in
seed protein quality occurs by the production of the β-subunit from the β-conglycinin storage
protein which is frequently encountered in S deficient environments due to the lack of S
containing amino acids (Tierney et al., 1987). However, even in high S providing environments
10 to 20% of the seed storage proteins consisted of the β-subunit of β-conglycinin (Sexton et al.,
1998b). The high percentage of low grain quality leads to the hypothesis that in high Senvironments the production of high quality seed protein is limited by the reduction of sulfate
and synthesis S-containing amino acids (Sexton et al., 1998b).
The timing of S availability may be crucial in protein development. The ratios of
glycinin to β-conglycinin are the same for soybeans S deficient throughout vegetative growth
stages and then received adequate S throughout reproductive stages as soybeans that received
adequate S throughout the entire plant life cycle (Sexton et al., 1998c). A greater part of S
assimilation occurs in the reproductive stages, thus the magnitude of S assimilation and synthesis
of S-containing amino acids may be limited if the majority of S is acquired over a short period.
The contribution of mobilized N on soybean seed quality and yield was assayed and an N
mobilization efficiency of 70% was achieved which illustrated that the availability of N in
aboveground plant biomass was two to four times greater than what was required in mature seeds
(Loberg et al., 1984; Vasilas et al., 1995; Naeve et al., 2008). Therefore, acquiring S may be a

4

greater limiting factor than N to obtain greater soybean yields. Sulfur has also demonstrated
effects on soybean root development and the plant-soil microbial relationship (Zhao et al., 2008).
In a greenhouse study S applications of 30 and 60 mg kg-1 responded with an 8.6 – 25.2% and
10.9 – 33.2%, respectively, increase in soybean lateral root quantities. At 60 mg kg-1 the nodule
count per plant was significantly higher than 30 mg kg-1 and no application of S (Zhao et al.,
2008). A similar response accounted for a 60% increase in nodule activity when 45 kg S ha-1
was applied to kidney beans (Phaseolus vulgaris L.) (Janssen and Vitosh, 1973). The
accumulation of free N compounds with marginal S availability suggests an inability to
synthesize proteins resulting in a repression of nitrogen fixation.
Sulfur in Corn
Sulfur uptake and partitioning in corn (Zea mays L.) has recently been reassessed in a field trial
using six commercial hybrids (Below et al., 2013). Total S uptake for 12.0 Mg ha-1 corn yield
averaged 26 kg S ha-1 resulting in 15 kg S ha-1 removed with harvestable grain. Sulfur was
determined to accumulate at 0.7 kg ha-1 d-1 and by R1 48% S-uptake was complete. Corn
hybrids demonstrated more aggressive uptake following V10 and rate of uptake declined slightly
at R1. In a previous field trial aerial accumulation of S reached 40 kg S ha-1 when corn grain
yield was 16.3 Mg ha-1 (Karlen et al., 1988). At physiological maturity plants were separated by
lower leaves, upper leaves, stalk and tassel, and ear and shank to demonstrate that S was
partitioned within the respective plant parts at 11, 12, 13, and 64%. Minimal translocation from
upper plant parts occurred during early grain fill and only 2 kg S ha-1 was provided from the
lower leaves. The data suggested that if S sources are not adequate to meet aggressive S
demands during the reproductive corn growth stages a topdress application should be considered
to limit deficiency.

5

In the Atlantic Coastal Plains of the U.S., field research demonstrated that when residual
soil S was equal to 1.5 mg kg-1 at planting the application of 22 and 44 kg S ha-1 imcreased corn
yields 1 to 28% (Reneau, 1983). A critical N:S ratio of 16:1 suggested that the ratio may be a
better measurement of S sufficiency due to variability in S concentration at different growth
stages. Ammonium sulfate applied at 0, 34, 67, and 101 kg S ha-1 improved yield at only three of
twelve locations (Kline et al., 1989). Differences were most prominent between 0 and 67 kg S
ha-1 with yield increasing by 0.9 – 1.4 Mg ha-1. The lack of yield response was attributed to high
availability of S from other sources (e.g. rainfall, irrigation, and subsoil S accumulation).
When S response has been investigated in corn production where plant stresses are present
increasing corn yield is difficult to demonstrate (Chen et al., 2008). A four year trial was
performed with two S rates (0 and 33 kg S ha-1) applied in conjunction with seven N rates (0, 67,
100, 133, 167, 200, and 233 kg N ha-1). Soil samples revealed that water soluble S was 3.8 mg
kg-1 indicating that the site was likely to demonstrate a response based off the critical waterextractable soil S concentration of 5.6 mg kg-1 (Fox et al., 1964). Severe drought resulted in a
average 2.6 Mg ha-1 grain yield with no S and a significant increase to 3.0 Mg ha-1 grain yield
with S application. In 2003 effects from no S application demonstrated corn yields of 10.7 Mg
ha-1 with a significant increase to 11.6 Mg ha -1 with S application. Separating differences
between S rates among all N rates demonstrated significant yield increases from S application
occurring in 3 of 4 years at the 100 kg N ha-1 (2003) and 133 kg N ha-1(2004 and 2005). There
seemed to be few effects from S at low N rates of 0 to 100 kg N ha-1 and none at N rates higher
than 200 kg N ha-1.

6

Organic Sulfur
Organic forms of soil S are found in plant residues and humus. Within organic matter there exist
one of two sources of S; carbon-bonded sulfur and organic sulfates (Freney, 1961). Sulfur is also
commonly bound in organic matter as S esters and is converted to sulfate by sulfatase enzymes
by the following reaction:
R-O-SO3- + H2O

sulfatase

R-OH + HSO4-

The measure of S in soil organic matter is closely correlated to N in an N:S ratio of about 8:1,
varying from 5 to 13 across North America (Tabatabai, 1984). The strong relationship of N and
S in plants may help explain why an 8:1 ratio remains constant for many cultivated regions. In a
silty clay loam, continuous corn was grown for 11 years. At the end of each year plant residue
was removed from each plot followed by treatment application rates of 2, 4, 8, and 16 Mg corn
stover ha-1 yr-1 (stover nutrient analysis: 0.77, 0.17, and 0.09% N, S, and P respectively) with a
standard 202 kg N ha-1 applied plus an additional 11.2 kg N ha-1 for each Mg of stover applied.
After the 11 year trial the organic S in the soil had increased by 9% from the addition of 2 Mg
residue ha-1 yr-1, and 40% when 16 Mg residue ha-1 yr-1 was applied (Larson et al., 1972). The
return of S from corn stover has led some scientists to hypothesize that agricultural systems may
cycle S adequately to meet plant requirements.
Organic S can be added to the soil through the applications of animal manure. Sulfur
concentration will vary depending on the manure form applied. Pig slurry ranges between 300 –
660 mg S kg slurry-1 but solid manures may range between 0.69 – 1.4 kg S Mg-1 (Eriksen et al.,
1995, Steineck et al., 1999). Discrepancies of S concentration in animal manures will vary based
on animal diet. The determining factor in the availability of organic S sources is typically the
carbon to sulfur ratio (C:S). A net mineralization or release of organic S results at a C:S ratio

7

less than 200, whereas a net immobilization (conversion of inorganic nutrients to organic
complexed nutrients) occurs at a C:S ratio greater than 400 (Freney, 1967). The change in plant
available S that occurs between mineralization and immobilization ratios is either so small that it
is negligible or there is no net change. The annual mineralization rate of organic S is estimated
to be near 2% of total organic S as this is the annual mineralization rate of soil organic matter
(McGrath and Zhao, 1995). However, S mineralization each year can be estimated, for example,
a soil with 1% organic carbon in the top 20 cm of the soil profile with use of the following
equation (McGrath and Zhao, 1995):
1kg org C
100 kg soil

10 4 m 2
ha

0.2m depth bulk density

1kg org S
2 kg S min
100 kg org C 100 kg org S

kg S min
ha

This equation can be adjusted to calculate S mineralization based on more specific properties of
any given soil.
Elemental Sulfur
Synthetic fertilizers and soil amendments can also provide available S to plants. While many S
sources come with additional nutrients elemental S (ES) is the exception. Elemental S is a
widely accepted S source due to high analysis (99% S) and slow release properties (Germida and
Janzen, 1993). However, for ES to become plant available it must undergo oxidation:
S0→S2O3-2→S4O6-2→SO4-2
Elemental sulfur availability may be impacted by temperature, physical and chemical soil
properties, amendment particle size, and management practices (Germida and Janzen, 1993).
Research has demonstrated temperature may affect the oxidation of ES. When applied to
a sandy loam soil and incubated at 30°C, after 30 days ES had four times as much S oxidized
than when incubated at 23°C (Li and Caldwell, 1966). Elemental sulfur has demonstrated
oxidation 2 to 6 times faster at 30°C than at 5°C and was 2 to 4 times faster when temperatures
8

were increased from 15°C to 30°C (Nor and Tabatabai, 1977). However, temperature effects on
the rate of S oxidation vary by year and throughout the growing season making availability
predictions difficult.
Soil properties including soil texture, soil micro-biota, soil pH, organic matter content,
and soil moisture can lead to differences in oxidation. Some experimentation has reported no
specific relationship between ES oxidation and soil texture (Rehm and Caldwell, 1969;
McCaskill and Blair, 1987). However, other studies have found that S oxidation and sand
content are directly related while S oxidation and clay content were inversely related (Janzen and
Bettany, 1987).
To a limited extent S oxidation occurs by abiotic means, but is dominantly performed by
soil micro-biota. The different microorganisms involved in S oxidation can be divided into three
groups 1) chemolithotrophs, 2) photoautotrophs, and 3) heterotrophs (Germida and Janzen,
1993). As the overall heterotrophic microbial biomass increases the rate of S oxidation will also
increase (Lawrence and Germida 1988). The rate of increase was observed among a range of
soil clay content (8-75%), soil pH (5.5-7.8), and available organic C (9-35 mg kg-1).
Particle size of ES can have an effect on S oxidation. Sulfur oxidation can be accelerated
by increasing the surface area. Sulfur oxidation is a surficial process and soil microbes are
limited to access only those atoms on the exterior of fertilizer particles. Spreading ES powder
has demonstrated to be as effective as gypsum application in alfalfa trials in Nebraska (Fox et al.,
1964). However, fine powders of ES are a potential explosive hazard when exposed to abrasion
(Chien et al., 2011). Elemental S amendments with different particle sizes may have the
potential to affect the efficiency and rate of S oxidation. If a higher surface area to mass ratio is

9

ideal, then the manipulation of ES to produce thin plates may be preferable over spheres
(Watkinson, 1989; Germida and Janzen, 1993).
Sulfate Fertilizers
Other S-containing sources such as ammonium sulfate (AS), ammonium thiosulfate (ATS),
single super phosphate (SSP), and gypsum differ in their ability to provide S as each contains 24,
26, 12, and 18% S, respectively. Sulfur supplied through SSP is phosphate rock that has been
acidulated with sulfuric acid (H2SO4) to form gypsum. This process further illustrates that there
are only two main fertilizers sources that supply S in the plant available form SO4, ammonium
sulfate and calcium sulfate (gypsum). A negative aspect to using SO4 based fertilizers includes
leaching ability when excessive amounts of water are applied from precipitation or irrigation
(Konopka et al., 1986).
Current conventional agriculture practices tend to use more high analysis fertilizers that
contain high percentages of N, P2O5, and K2O without other additives. One example would be
the use of MAP in place of SSP. Single super phosphate supplies 11-12% S but only provides 16
to 20% P2O5, whereas MAP will provide 52% P2O5. Another example is the comparison
between urea and AS. Ammonium sulfate is 21% N and 24% S while urea is 46% N with no
significant S content. Historically low S recommendations have led growers to solely use high
analysis fertilizers, resulting in minimal additions of S and greater opportunity for deficiencies.
A yield response to S has primarily been demonstrated in coarse textured low organic
matter on soils that have no historic S application (Fox et al., 1964b, O’Leary and Rehm, 1990).
Sulfur research has demonstrated that an early season S application, when S mineralization is
limited, can encourage early season plant development in corn and influence yield (Rehm, 2005).
Two S sources, ammonium sulfate (21-0-0-24) and ammonium thiosulfate (12-0-0-26), were

10

placed either in a band 2.5 cm to the side and 5.0 cm below the seed at planting and with the
seed. The two S sources were applied at 0, 6.7, 13.4, and 20.1 kg S ha-1. Treatments that
received thiosulfate demonstrated a reduction in emergence as the S rate increased when S was
applied with the seed and in coarse textured soils. Early season S uptake also seemed to be
diminished with thiosulfate when compared to ammonium sulfate. The increase in S uptake by
using ammonium sulfate instead of thiosulfate ranged from 10 to 40%. No definite conclusion
was given why greater S uptake occurred with ammonium sulfate, but oxidation of thiosulfate
may have delayed sulfate availability. The data demonstrate that an early season S application
may improve yield beyond no S application, however, caution should be taken when applying S
with the seed in coarse textured soils especially when using thiosulfate.
Losses of Available Sulfur
Research has demonstrated that there may be differences in leaching ability among S soil
amendments. In a pot study gypsum and three S containing N fertilizers (Ureas, Urea+ES
powder, and AS) were tested in clay and loamy sand soil textures to determine S movement from
the root zone (Dijksterhuis and Oenema, 1990). Ureas, which is a trademarked product (80%
urea and 20% AS), demonstrated the greatest amount of leached S followed by AS and gypsum.
The increased amount of S leached from pots treated with Ureas was believed to have occurred
to due to the temporary pH increase caused by the hydrolysis of urea. Temporary pH increases
may limit S adsorption and result in more S movement in solution.
Factors such as soil texture and soil moisture may also effect S lost through leaching.
Coarse-textured soils with high sand content are more prone to S leaching due to high water pore
velocity and limited exchange sites for S adsorption (Dick et al., 2008). The ability for water to
move rapidly through soil pores allows solutes to be carried from the root zone to lower soil

11

horizons where S is not easily recovered. Other conditions such as water logging of soil could
potentially reduce sulfate and lead to volatilization of S (Banwart and Bremner, 1975).
However, sulfur lost from the soil in gas form is typically less than 1 kg S ha-1 yr-1 for nonwetland soils (Noggle et al., 1986).
Applying Sulfur
When a corn field trial in the coastal plains of Virginia was performed, a positive yield response
to S application occurred (Reneau, 1983). Sulfur was surface applied as calcium sulfate and
incorporated in moderately-well to well-drained soils. Sulfur was applied at 0, 22, 44, and 66 kg
S ha-1 with a standard rate of 224 kg N ha-1 pre-plant and incorporated with a rotary tiller. Grain
yield results demonstrated that maximum yield was obtainable with 22 kg S ha-1. Conversely,
four S rates (0, 34, 67, and 101 kg S ha-1) applied in a Delaware corn field trial in three
increments did not demonstrate a significant yield response (Kline et al. 1989). However, no
response may have been due to annual applications of poultry manure for 5 years previous to the
study being performed.
A field study, investigating four N rates (56, 112, 168, and 224 kg N ha-1) and four S
rates (0, 22, 44, and 66 kg S ha-1), was performed to determine N and S interaction effects on
corn yield. Nitrogen was applied as 28 kg N ha-1 as ammonium nitrate at planting and the
remainder at 50 cm corn while S was applied pre-plant broadcast as calcium sulfate (Rabuffetti
and Kamprath, 1977). As the S rate increased from 0 to 66 kg S ha-1 when applying 56 kg N ha-1
yield decreased. When higher S rates (44 and 66 kg S ha-1) were applied in conjunction with
higher N rates (168 and 224 kg N ha-1) significant yield increases occurred. Optimum yields for
this experiment were obtained at 44 kg S ha-1 and 168 kg N ha-1.

12

The effects of 0, 6.7, 13.4, and 20.1 kg S ha-1on S uptake and yield were monitored using
ammonium thiosulfate and ammonium sulfate placed near the seed in a 2.5 x 5 cm band or with
the seed (Rehm, 2005). The study was conducted to determine the effect of rate, source, and
placement of S fertilizers on corn yield. In the preceding autumn N, P, and K were added in a
dry band application of 22, 9.9, and 37.2 kg ha-1, respectively, 10 cm below the seed row.
Additional N was side-dressed as urea to obtain optimal yields, total N applied ranged from 150
to 180 kg N ha-1 among the six sites. Ammonium thiosulfate caused yield reductions at two
locations when higher rates (13.4 and 20.1 kg S ha-1) were placed with the seed. The two
locations that demonstrated reduced yield when ammonium thiosulfate was applied with the seed
were characterized by a loamy fine sand texture, whereas other sites with loam, sandy loam, and
silt loam didn’t show significant reductions in corn yield. Both sources applied at 6.7 kg S ha-1
demonstrated an average yield increase of 11% from the check at five of the six locations. Sulfur
source only demonstrated an effect on yield when placed with the seed in which case ammonium
thiosulfate reduced yields in coarse textured soil, loamy sand. Additional S application research
in soils with organic matter content of 20 g kg-1 or less have revealed that a rate of 13 kg S ha-1 in
a 5 x 5 cm band or broadcast applying 28 kg S ha-1 may provide a sufficient quantity of S for
corn (Rehm and Clapp 2008).
Residual Sulfur
Sulfur application to crops may be carried over into subsequent years providing some S to the
second year rotation crop. In a pot study different soils were used to determine the effects of soil
colloids, pH, and presence of phosphorus on sulfate adsorption in Cecil, White Store, and Nipe
soils (Kamprath et al., 1956). In 1:1 type clay minerals, such as kaolinite, an increase in sulfate
adsorption was demonstrated and was attributed to a larger quantity of free iron and aluminum

13

oxides. Hydrated aluminum oxides have especially demonstrated a high capacity for adsorbing
sulfate (Ensminger, 1954). Increased sulfate adsorption was demonstrated at pH less than 6 and
was the highest at pH 4. The presence of phosphate also has a significant effect on sulfate
adsorption. As the sulfate concentration remained constant at 5.4 meq 100g-1 and phosphate
concentration was increased from 0 to 3.6 meq 100g-1 all adsorbed sulfate was displaced by
phosphate. The displacement of S by P suggests that soils generally have a greater affinity for P
than S. Thus high pH and high P containing soils may limit S retention whereas high
concentrations of aluminum and iron oxides may increase S adsorption.
Soil Testing
As many as 20 different chemical extractants have been studied and tested to determine soil S
including water, calcium or potassium phosphate, potassium chloride, and sodium bicarbonate
(Dick et al., 2008). Soil S has most consistently been analyzed by extraction with calcium
dihydrogen phosphate, Ca(H2PO4)2 (Hoeft et al., 1973). The steady ability P has at displacing
adsorbed SO4 supports why calcium dihydrogen phosphate has been commonly used as an
extractant (Ensminger and Freney, 1966). Many soil tests used today will extract sulfate with
water in order to determine primarily plant available S.
Testing for Sulfur in Plants
The critical S level in corn plant tissue is between 1.2 - 2.0 g kg-1 (Jones, 1986). Tissue samples
were collected from both the leaf opposite and below the ear at early silking and analyzed for
total S and N:S ratio (Reneau, 1983). Values obtained from these samples demonstrated total
tissue S was not as useful of a predictor as the N:S ratio for yield. When actual corn yield
increases from each treatment were compared to tissue N:S a linear correlation was observed
with R2-value of 0.82.

14

Currently the only method for measuring plant S concentration is tissue sampling.
However, because S use in plants is related to N, tools to assess N availability may be useful in
assessing S sufficiency (Smith et al., 1997). Methods, such as plant tissue sampling, chlorophyll
meters (measures light transmittance through plant leaves), and active sensing (use of sensor
receptors to measure reflectance of near-infrared light), are all useful tools for predicting N status
of plants. To better detect S deficiency recent research has demonstrated monitoring S in corn
by using a Minolta SPAD-502 chlorophyll meter (Pagani and Echeverria, 2011). In order to
prescribe general S recommendations by using chlorophyll meter readings (CMR) the data had to
be normalized to reduce variability that is incurred by factors other than S availability. The
normalization of readings can be performed by the establishment of reference areas within the
field or area of interest eliminating variation in data that can be caused by environmental
conditions, plant hybrids, or different growth stages (Blackmer and Schepers, 1995). By
compensating for deficiencies with reference strips the CMR may appropriately demonstrate if S
deficiencies exist. As much as 15% variance exists between CMR among plants making it
necessary to collect samples from several plants to obtain more accurate measurements (Peterson
et al., 1993).
Active sensing can be effective at determining N levels in plants and improve S
management (Bausch and Diker, 2001). Active sensors function by using near-infrared light
(NIR, ~770 nm). Near Infrared light has high reflectance and transmittance whereas visible light
has low reflectance and transmittance (Gausman, 1974; Chappelle et al., 1992; Slaton et al.,
2001). A comparison was performed between plant tissue sampling, chlorophyll meter reading,
and active sensing (Bausch and Duke, 1996). The objective was to examine canopy reflectance
on irrigated soils to determine N status, while simultaneously comparing the results from the

15

three methods of canopy N status measurements (plant tissue sampling, chlorophyll meter
reading, and active sensing). A 1:1 relationship between the reflectance index of remote sensing
and the N sufficiency index was reported for CMR between V11 and R4 corn. An appropriate
timing for active sensing use has been investigated to determine a growth stage when NDVI can
be measured and yield predicted (Teal et al., 2006). Measuring NDVI at the eighth vegetative
stage (V8) revealed a strong relationship with yield (R2=0.77). All NDVI measurements
collected before or after V8 showed weak exponential relationships.

16

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17

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22

CHAPTER 2
EFFECTS OF SULFUR ON CORN YIELD AT DIFFERENT NITROGEN RATES

Abstract
Earlier planting dates in cooler soils, increased nutrient removal through greater yielding
cultivars, and reductions in atmospheric sulfur (S) deposition suggest that S application may
require reassessment for optimal corn (Zea mays L.) growth. In 2012 and 2013 a field study was
initiated on a loam soil to evaluate corn response to S application by investigating nutrient
uptake, grain yield, and agronomic efficiency (AE) at six rates of nitrogen (N) fertilizer. The
study was arranged as a split-plot randomized complete block with four replications. Main plots
consisted of three S rates (0, 23, and 45 kg S ha-1) while sub-plots consisted of six N rates (0, 56,
112, 169, 225, and 281 kg N ha-1). Corn tissue S concentrations were sufficient in one of two
years, but did not accurately predict a yield response from S treatments. These data suggest that
tissue tests may not be an adequate measurement for determining when a yield response to S
application may occur. Significant yield differences were demonstrated between the 0, 23, and
45 kg S rates without N fertilizer in 2012 (6.7, 7.7, and 9.5 Mg ha-1) and in 2013 (3.2, 5.7, and
3.5 Mg ha-1), respectively. In 2013, a significant yield increase occurred from S application at 56
kg N ha-1, but at N rates greater than 56 kg ha-1 S did no significantly impact yield. Averaged
across N fertilizer rates there was no significant response to S application. These data suggest
that soils with an organic matter content ≥ 28 g kg-1 and residual S ≥ 6-8 mg kg-1 are sufficient
for optimal corn growth when optimal N rates (> 56 kg N ha-1) are applied.

23

Introduction
During the last 15 years S application has been found to increase corn grain yields throughout the
upper Midwest Corn Belt (Chen et al., 2008; Kim et al., 2013). Data from southern Michigan
has shown that S-deposition has been reduced from 30 kg SO4 ha-1 in 1980 to less than 10 kg
SO4 ha-1 in 2010 (wet wt.) (National Atmospheric Deposition Program, 2012). Increased
observations of S deficiency have been partially attributed to the increased use of high analysis
fertilizers containing little or no S (Hagstrom, 1986; Chien et al., 2011). Corn yield has steadily
increased over the last 30 years with the mean national corn yield increasing from 4.5 Mg ha-1 in
1970 to 9.2 Mg ha-1 in 2011 (Capehart, 2013). Increased corn yield at greater rates of N
application creates a larger sink for plant nutrients and results in a greater demand for plant
available S to achieve optimal corn yield (O’Leary and Rehm, 1990; Ciampitti and Vyn, 2013).
Current S removal in corn grain ranges from 1.0 – 1.2 g S kg grain-1 (Chen et al., 2008;
Bender et al., 2013). Research has found that in high yielding corn environments (≥ 12.0 Mg ha1

) total vegetative S uptake at physiological maturity may range from 26 – 40 kg ha-1 within

yields of 12.0 – 19.3 Mg ha-1 (Karlen et al., 1988; Bender et al., 2013). Positive yield responses
to 33 kg S ha-1 have been observed in corn production with greater increases in yield occurring
from S application at less than 133 kg N ha-1 (Chen et al., 2008). Sulfur fertilization (33 kg S ha1

) with 100 kg N ha-1 as compared to 200 kg N ha-1 has resulted in similar grain yields when soil

S concentrations were less than or equal to 8 mg kg-1 (Fox et al., 1964; Chen et al., 2008). More
recent research has found that 28 kg S ha-1 applied with 157 kg N ha-1 increased grain yield 0.9
Mg ha-1 at one of four locations when S was pre-plant incorporated while mean yield increases of
1.3 Mg ha-1 were found at three of four locations with S application in a 5 × 5 cm band at
planting as compared to treatments without S (Kim et al., 2013). However, literature during the

24

last 20 years has reported yield responses with or without S application with little attention to
multiple S rates or S response as influenced by N application.
To determine optimum N and S management programs in corn, research has investigated
the use of N:S ratios, tissue sufficiency ranges at various growth stages, and partitioning of N
and S in vegetative tissue and grain. Nitrogen and S plant ratios have been considered optimum
between 16 -25:1 with sufficient plant tissue S concentrations ranging from 2.1 – 4.0 g kg-1 at V6
and R1 (Reneau, 1983; Kline et al., 1989; Oenema and Postma, 2003; Chen et al., 2008). More
recently, non-destructive methods such as SPAD chlorophyll meters and greenness indices have
been used as S diagnostic tools to determine S sufficiency but detecting plant nutrient status with
these instruments may be limited by environmental conditions (Rodriguez et al., 2005;
Schlemmer et al., 2005). Although plant tissue levels may be critical to monitoring S availability
early in the season before canopy closure prevents mid-season fertilizer applications, the use of
SPAD chlorophyll meters has been suggested as an alternative tool for quicker assessment of S
sufficiency in plant tissue (Pagani et al., 2009; Pagani and Echeverria, 2011). A range of S rates
and higher degrees of soil S deficiency (soil organic matter (OM) < 49 g kg-1) have been
suggested for further investigation in corn S management (Pagani et al., 2009).
Soil testing has previously been the standard indicator for recommending S applications
(Hoeft et al., 1973). However, S recommendations based on SO4 soil testing have not shown a
good relationship with grain yield in Minnesota (Kim et al., 2013). Although soil testing may be
the best method for determining soil S availability at the time of planting it does not predict
critical soil S concentrations or grain yield response to applied S as growing conditions are not
consistent from year to year (Pagani and Echeverria, 2011; Kim et al., 2013). The objective of

25

this field study was to determine the influence of S and N rate on nutrient uptake, plant greenness
grain yield, and agronomic efficiency (AE) of N fertilizer.

Materials and Methods
Field studies were conducted in 2012 and 2013 at the Michigan State University research
agronomy farm in East Lansing, MI on a Capac loam (fine-loamy, mixed, active, mesic Aquic
Glossudalfs). Soil characteristics over both study years included 7.0-7.3 pH, 45-51 mg kg-1 P
(Bray-1 P), 124-127 mg kg-1 K, 1513-1669 mg kg-1 calcium (Ca), 6-8 mg kg-1 S (extracted with
Ca(H2PO4)2), 11-12 cmolc kg-1 cation exchange capacity (CEC), and 27-28 g kg-1 soil organic
matter. Fields were previously cropped to corn in both study years and autumn chisel plowed
after harvest followed by spring tillage using a soil finisher at a 10 cm depth.
Individual six row plots measured 4.5 m in width by 12.1 m in length. The experimental
design was a split-plot randomized complete block with four replications. Individual replications
contained 18 experimental units. Sulfur fertilizer rate was the main plot factor and was pre-plant
incorporated to a depth of 10 cm using calcium sulfate at rates of 0, 23, and 45 kg S ha-1. Main
plots were split vertically to evaluate six N fertilizer rates (0, 56, 112, 169, 225, and 281 kg N ha1

). Forty percent of the total N rate was pre-plant incorporated using urea (46-0-0) on the day of

planting. Starter fertilizer was applied at planting in a 5 x 5 cm band with 23 kg P2O5 and 56 kg
K2O ha-1. Sixty percent of the total N rate was sidedressed at V4 corn (31 May 2012 and 6 June
2013) using urea coated with a urease inhibitor [CO(NH2)2 + n-(n-butyl) thiophosphoric
triamide] banded on the soil surface 10- to 15-cm to the side of the corn row (Koch Agronomic
Services, LLC, Wichita, KS). The corn hybrid used over both study years was Dekalb DKC4812 RIB (98 d relative maturity) (Monsanto Co., St. Louis, MO). Plots were planted on 11 May
2012 and 7 May 2013 to achieve a final plant population of 79,000 seeds ha-1. Weed control
26

consisted of acetochlor [2-chloro-N-ethoxymethyl-N-(2-ethyl-6-methylphenyl)acetamide],
atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)], and glyphosate [N(phosphonomethyl)glycine] applied to 5 cm weeds (30 May 2012 and 24 May 2013) followed by
a second application of glyphosate [N-(phosphonomethyl)glycine] the first week of July in both
study years. Environmental data were recorded throughout the growing season and obtained
from the Michigan Automated Weather Network (http://www.agweather.geo.msu.edu/mawn/,
Michigan State University, East Lansing, MI).
Chlorophyll meter readings were collected at V6 and R1 using a Minolta SPAD-502
chlorophyll meter (Spectrum Technologies Inc., Plainfield, IL). Twenty-five plants per plot were
sampled and the average recorded. Chlorophyll measurements were collected from the youngest
most fully developed leaf with a visible collar at V6 and from the R1 ear leaf half-way between
the mid-rib and the leaf margin and midway between the stalk and the leaf tip (Blackmer and
Schepers, 1995; Pagani et al., 2009). A relative greenness index (RGI) was calculated as:
RGI=GIfield/GIFT NS
The GIfield is the index of greenness for treatments that may be deficient in N or S, and the GIFT NS
is the index of greenness for treatments that have adequate N and S (45 kg S and 281 kg N ha-1)
(Pagani et al., 2009). Canopy normalized difference vegetation index (NDVI) was also collected
at V6 using a Greenseeker® handheld red-band optical sensor (Trimble Navigation Ltd.,
Sunnyvale, CA). From row two or five, 60 to 80 NDVI readings were collected per plot and
used to develop a relative greenness index for determining treatment effects on plant growth and
color (Teal et al., 2006). Plant height measurements were collected from 20 plants per plot at V6
(height of leaf curve apex in youngest most fully developed leaf with an exposed collar) and R1
growth stages.

27

Plant tissue samples were collected for nutrient analysis at V6 (10 whole plants plot-1),
R1 (25 ear leaves plot-1), and R6 (6 whole plants plot-1). Tissue samples collected at V6 and R1
were dried at 60° C, ground to pass through a 1-mm mesh screen and analyzed for N, P, K, and
S. Whole plant sampling at R6 had cobs and grain removed but husks returned to the sample.
Vegetative fresh weights were collected, samples were pulverized with a gas powered flail
grinder, homogenous sub-samples were collected, and sub-sample fresh weights were recorded.
Whole plant sub-samples were analyzed for N using a micro-Kjeldahl digestion method and
colorimetric analysis through a Lachat rapid flow injector autoanalyzer (Nelson and Sommers,
1973; Bremner 1996) (Lachat Instruments, Milwaukee, WI). Fifteen basal stalk samples were
collected per plot to evaluate stalk nitrate concentration by removing stalk sections 15 cm above
the soil surface and 20 cm in length (Binford et al., 1992; Fox et al., 2001). Stalk samples were
dried at 60° C and ground to pass through a 1-mm mesh screen. A 10-g stalk sub-sample was
added to 1 M KCl and shaken for 30 minutes at 3.33 hertz. Stalk extracts were filtered through
Whatman #2 filter paper (12.5 cm diameter) and nitrate concentrations were determined with
colorimetric analysis through Lachat rapid flow injector autoanalyzer (Huffman and Barbarick,
1981).
The center two rows of each plot were harvested with a Massey Ferguson 8XP small plot
combine to determine grain yield, moisture, and test weight (Kincaid Equipment Manufacturing,
Haven, KS). Final grain yields were corrected to 150 g kg-1 moisture. Agronomic efficiency
(AE) of N was calculated to measure the effect of S rate on grain yield at different N rates. The
AE was calculated by subtracting the grain yield of the untreated check from the yield of a
treatment and dividing by the N rate of the treatment (Wortmann et al., 2011; Sorenson et al.,
2012).

28

The data were subjected to analysis of variance using PROC MIXED in SAS (SAS
Institute, Cary, NC). Normality of the residuals was evaluated by examination of normal
probability and stem-and-leaf plots. Homogeneity of the variances was determined with
Levene’s test (P ≤ 0.05). The data were determined to be significantly different by year (P ≤
0.05) and were analyzed individually. A nonlinear model was fit to yield data using PROC
NLIN in SAS to determine differences in yield plateaus caused by S rate. When ANOVA
generated a significant F-value (P ≤ 0.05) means were separated using Fisher’s least significant
difference test.

Results and Discussion
Environmental Conditions
Mean 2012 growing season (May – Sept.) precipitation was 23 cm less than the 30-yr mean
(Table 2.1, Fig. 2.1a). Monthly mean air temperatures (May – Aug.) during 2012 were 2° C
greater than 2013 and 2° C above the 30-year mean for this time period (Table 2.1). Warmer air
temperatures in combination with 50% less precipitation may have limited corn growth in 2012.
Rainfall in 2013 was near normal May – Aug., but May and June precipitation resulted in five
rainfall events greater than 2 cm, three of which occurred over a single 3 day period (Fig. 2.1b).
Temperatures in 2013 were consistent with the 30-yr mean but were 2° C cooler in Aug. and 1°
C warmer in Sept. than normal. Annual precipitation measurements indicate S deposition for
southern Michigan is 0.13 kg SO4 (wet wt.) cm rain-1 (National Atmospheric Deposition
Program, 2012). When S concentrations and annual precipitation data were used to calculate S
deposition, mean S deposition during the 2013 growing season would have been 5.4 kg S ha-1
(wet wt.) versus 2.7 kg S ha-1 in 2012 due to less precipitation.

29

Table 2.1. Growing season (May – Sept.) and 30-yr mean precipitation and temperature data for
East Lansing, MI, 2012 – 2013.
May
June
July
August
September
Total
_____________________________________
__________________________________________
cm
Precipitation
2012
1.0
2.8
6.4
4.9
5.9
21.0
2013
7.6
15.4
6.8
9.7
2.1
41.6
30-yr ave.
9.1
9.1
7.6
9.1
9.1
44.0
________________________________________
_____________________________________________
°C
Temperature
2012
17
21
23
21
16
2013
16
19
21
19
18
30-yr ave.
16
19
21
21
17
Precipitation data was collected from Michigan Automated Weather Network
(http://www.agweather.geo.msu.edu/mawn/). 30-yr averages come from the PRISM climate
group (http://prism.oregonstate.edu/normals).

Figure 2.1. Daily precipitation May – Sept. for (a) 2012 and (b) 2013, East
Lansing, MI.

30

Figure 2.1(cont’d)

Nutrient Uptake Responses
Over both study years as N rate increased from 0 to 281 kg ha-1 vegetative N increased from 29
to 42 g kg biomass-1 at V6 and 20 to 29 g kg biomass-1 at R1 (P ≤ 0.01) (data not shown).
Sulfur rate had a direct relationship (P ≤ 0.05) in 2012 with V6 total N uptake and in both study
years with V6 S uptake (Table 2.2). In 2012 and 2013, 45 kg S ha-1 increased V6 S uptake by 8
and 45%, respectively (P ≤ 0.01), but S concentrations were within the sufficiency range (0.21 –
0.40% S) in all treatments. Limited precipitation (< 3.8 cm prior to July 1) during 2012 may
have reduced soil S leaching explaining the sufficient S tissue concentrations despite the absence
of S fertilization. Data in 2013 suggest S uptake may not have been sufficient prior to V6 as
tissue concentrations were low (≤ 2.0 g kg-1) but not necessarily deficient where no S was
applied (Table 2.2). May and June 2013 precipitation totals exceeded 20 cm which may have
increased residual S leaching beyond developing corn roots despite 3 kg S ha-1 (wet weight)
deposited from rainfall during the same period. Bender et al. (2013) found that corn required
approximately 3 kg S ha-1 by V6 suggesting that S availability may be a greater concern in wet
31

years when residual soil S is more readily leached and S-deposition simultaneously continues to
decrease. In 2012, 23 and 45 kg S ha-1 increased V6 N concentration by 0.7 and 1.6 g kg-1,
respectively (P ≤ 0.05), which concurs with Salvagiotti et al. (2009) who found that wheat N
uptake increased by 26 to 28% when 30 kg S ha-1 was applied with 52 to 104 kg N ha-1.
Ear leaf R1 N concentrations were not significantly increased (P ≤ 0.05) by S in either study
year (Table 2.2). In one of two study years R1 S concentration increased (P ≤ 0.05) at the 45 kg
S rate but both years resulted in low S concentrations (≤ 1.8 g kg-1) despite S fertilization.
Oenema and Postma (2003) suggested that the critical S concentration for corn ear leaf at silking
was 1.0 g kg-1, yet S concentrations were considered low between 1.0 and 2.0 g kg-1. Tissue S
concentration from V6 to R1 decreased by 30 and 15% without S as compared to 28 and 40%
reductions with S application in 2012 and 2013, respectively.
Table 2.2. Corn whole plant (V6) and ear leaf (R1) nutrient
analysis as affected by sulfur rate. Nutrient concentrations
were averaged across six nitrogen rates, East Lansing, MI,
2012 – 2013.
V6
R1
N
S
N
S
2012
_________________
Sulfur (kg ha-1)
g kg-1 ______________
0
39.6 a
2.4 a
24.9 a 1.7 a†
23
40.3 ab
2.4 a
25.7 a 1.8 a
45
41.2 b
2.6 b
26.4 a 1.8 a
Significance (Pr>F)
S
0.03
<0.01
0.36
0.44
N×S
1.00
0.54
0.49
0.85
2013
_________________
Sulfur (kg ha-1)
g kg-1 ______________
0
36.0 a
2.0 a
25.4 a 1.7 a
23
38.0 a
2.9 b
24.1 a 1.7 a
45
36.0 a
2.9 b
25.2 a 1.8 b
Significance (Pr>F)
S
0.31
<0.01
0.28
0.04
N×S
0.21
0.17
0.07
0.27
†
Means in the same column followed by the same letters for
each year are not significantly different at P ≤ 0.05.
32

A build-up of tissue S early in corn growth (e.g. prior to V6) followed by moderate declines (≥
2.1 g kg-1 at V6 to 1.7 g kg-1 by R1) may increase opportunities for a positive yield response.
Reneau (1983) indicated larger corn yield increases occurred when ear leaf S concentrations
were below 1.7 g kg-1 at early silking. Few other studies have identified an optimum S
concentration at R1 but have indicated an optimum S concentration range for corn as wide as 1.5
to 5.0 g kg-1 at silking (Pagani and Echeverria, 2011). Thus optimal S management may require
S sufficiency concentrations to be maintained more critically during early corn growth (2.1 to 3.0
g kg-1 near V6) followed by S decreases to moderate concentrations (1.5 to 2.0 g kg-1) near R1
due to growth dilution.
A 98% increase in 2013 precipitation as compared to 2012 may have caused a 35 to 90%
decrease in stalk nitrate concentrations (Table 2.3). In 2012 stalk nitrate concentrations showed
a direct relationship with S rate and were within the optimum range (250-2000 mg kg-1), but the
relationship was not significant (Binford et al., 1992; Fox et al., 2001). In 2013, stalk nitrate
concentrations resulted in an N × S interaction (P ≤ 0.01) (Table 2.4). Stalk nitrate
concentration was 80 and 35% less as the S rate increased to 45 kg ha-1 at 225 and 281 kg N ha-1,
respectively, compared to similar N rates with no S. The data suggest that at 225 and 281 kg N
ha-1, N assimilation may have increased as S application increased. Kim et al. (2013) reported
that 28 kg S ha-1 pre-plant incorporated increased N uptake and grain N by 6% at three of four
and one of four locations, respectively. Despite 98% more precipitation in 2013 increasing
vegetative N uptake by 12-156% from 2012, S application did not affect total vegetative N at
physiological maturity (Table 2.5). These data suggest N uptake and partitioning may be more
affected by soil moisture than actual S availability (Derby et al., 2005).

33

Table 2.3. Effects of nitrogen and sulfur rate on corn
stalk nitrate concentrations at physiological maturity,
East Lansing, MI, 2012 – 2013.
2012
2013
Nitrogen (kg ha-1) ___________ kg N ha-1 ___________
0
42 c
4 a†
56
240 c
3a
112
529 c
44 a
169
1462 b
277 a
225
1971 b
849 b
281
2593 a
1690 c
Sulfur (kg ha-1)
0
989 a
601 a
23
1042 a
560 a
45
1387 a
272 b
Significance (Pr>F)
N
<0.01
0.01
S
0.57
<0.01
N×S
0.30
0.01
†
Means followed by the same letters within a column
are not significantly different at P ≤ 0.05.

Table 2.4. Nitrogen by sulfur interaction on corn
stalk nitrate concentrations at physiological maturity, East
Lansing, MI, 2013.
2013
_____________
kg S ha-1 ____________
0
23
45
___________
Nitrogen (kg ha-1)
mg kg-1 ____________
0
4 aA
3 aA
3 aA†
56
1 aA
1 aA
8 aA
112
18 aA
112 aA
1 aA
169
355 aA
285 abA 191 aA
225
1504 bB
736 bA
308 aA
281
1726 bB 2224 cB
1118 bA
Significance(Pr>F)
N×S
0.01
†
Means in a column followed by the same lowercase letters
are not significantly different at P ≤ 0.05. Means in a row
followed by the same uppercase letters are not significantly
different at P ≤ 0.05.

34

Table 2.5. Total vegetative nitrogen uptake at
physiological maturity as affected by nitrogen and
sulfur rate, East Lansing, MI, 2012 – 2013.
2012
2013
Nitrogen (kg ha-1) ___________ kg N ha-1 ___________
0
7.2 a
10.6 a†
56
12.6 a
14.1 ab
112
13.1 a
18.2 b
169
12.4 a
25.6 c
225
13.7 a
33.3 d
281
12.7 a
32.5 cd
Sulfur (kg ha-1)
0
11.0 a
22.3 a
23
12.8 a
23.4 a
45
12.1 a
21.5 a
Significance (Pr>F)
N
0.10
<0.01
S
0.81
0.51
N×S
0.85
0.25
†
Means followed by the same letters within a column
are not significantly different at P ≤ 0.05.

Greenness Indices
Sulfur fertilization had no affect (P ≤ 0.05) on SPAD data in either year (data not shown).
Canopy greenness (i.e., SPAD and NDVI measurements) may have been affected by water
availability in 2012 and overestimated chlorophyll content as reported by Rodriguez et al. (2005)
and Schlemmer et al. (2005). Lack of water has been suggested to interfere with nutrient uptake
making SPAD measurements difficult under water deficit conditions (Barraclough and Kyte,
2002; Pagani and Echeverria, 2011). Additionally where S is less mobile in the plant and
deficiencies are more prevalent in the newest growth, greater characterization of S status may
have been possible in both study years by measuring leaves in the upper canopy than the
technique for assessing N status used by Blackmer and Schepers (1995) (Pagani and Echeverria,
2011).

35

In 2012 and 2013 relative NDVI at V6 was not affected by N or S application. An N × S
interaction occurred (P ≤ 0.05) in 2013 but not in 2012 (Table 2.6). As a plant defense
mechanism to reduce plant temperatures under water-limiting conditions, reflectivity of near
infrared light increases with water stress (Schlemmer et al., 2005).

Table 2.6. Effects of nitrogen and sulfur rate on V6
relative normalized difference vegetation index, East
Lansing, MI, 2012 – 2013.
2012
2013
Nitrogen (kg ha-1) ________ relative NDVI ________
0
0.99 a
0.76 a
56
1.00 a
0.86 b
112
1.00 a
0.95 c
169
1.00 a
0.99 d
225
1.00 a
0.97 cd
281
1.00 a
1.00 d
Sulfur (kg ha-1)
0
0.98 a
0.92 a
23
1.00 a
0.93 a
45
1.00 a
0.91 a
Significance (Pr>F)
N
0.17
<0.01
S
0.35
0.55
N×S
0.53
<0.01
†
Means followed by the same letters within a column
are not significantly different at P ≤ 0.05.

Plant response to drought conditions may explain why relative NDVI was 1 to 23% greater in
2012 as compared to 2013. Reductions in plant growth in 2012 from drought stress may have
limited the ability of the Greenseeker® to determine differences in plant greenness caused by N
or S. In 2013 45 kg S ha-1 with zero and 112 kg N ha-1 reduced relative NDVI by 12 and 5%,
respectively, compared to the NDVI results obtained with the same N rates at 23 kg S ha-1 (Table
2.7).

36

Table 2.7. Nitrogen by sulfur interaction on V6
relative normalized difference vegetation index, East
Lansing, MI, 2013.
2013
_____________
kg S ha-1 ____________
0
23
45
__________
Nitrogen (kg ha-1)
relative NDVI __________
0
0.80 aB 0.78 aB
0.69 aA
56
0.80 aA 0.88 bA
0.88 bA
112
1.00 bB 0.95 bcB 0.89 bA
169
1.00 bA 0.95 bcA 1.00 cA
225
0.93 bA 1.00 cA
0.95 bcA
281
0.98 bA 1.00 cA
1.00 cA
Significance(Pr>F)
N×S
<0.01
†
Means in a column followed by the same lowercase
letters are not significantly different at P ≤ 0.05. Means in
a row followed by the same uppercase letters are not
significantly different at P ≤ 0.05.
As S rate increased from 23 to 45 kg ha-1 lower relative NDVI values may explain yield
reductions of 2.2 and 0.9 Mg ha-1 with zero and 112 kg N ha-1, respectively. When 2013 relative
NDVI was regressed against grain yield, zero S treatments resulted in an R2 of 0.60. The R2values at 23 and 45 kg S rates increased to 0.78 and 0.79, respectively (data not shown), and may
have been the cause of the 23% greater correlation between relative NDVI and grain yield.
These data agree with Teal et al. (2006) who found that as much as 76% of grain yield variation
was explained by NDVI. Improving the accuracy of determining N sufficiency by maintaining
sufficient plant available S may allow growers to better predict yield variability in the field and
make more informed decisions for in-season N applications (Raun et al., 2001; Samborski et al.,
2009).
Corn Grain Yield
An N × S interaction (P ≤ 0.10) on grain yield occurred in 2012 and 2013 (Table 2.8). Corn
yields in 2013 with 23 and 45 kg S ha-1 at the 56 kg N ha-1 rate were similar to the 2012 grain
37

yields at the zero N rate indicating that several large precipitation events in May and June of
2013 may have resulted in N losses near 45 – 56 kg N ha-1.

Table 2.8. Interaction between nitrogen and sulfur application on corn grain yield, East Lansing,
MI, 2012 – 2013.
2012
2013
____________
_____________
kg S ha-1 ____________
kg S ha-1 ____________
0
23
45
0
23
45
_________________________
Nitrogen (kg ha-1)
grain yield (Mg ha-1) __________________________
0
6.7 aA
7.7 aAB
9.5 aB
3.2 aA
5.7 aB
3.5 aA†
56
8.2 abA
8.5 abA
8.5 aA
6.8 bA
7.3 aAB
9.2 bB
112
8.8 abA
9.7 abA 10.1 aA
11.9 cA 11.7 bA
10.8 bcA
169
9.2 bA
9.4 abA
8.3 aA
12.9 cA 12.8 bcA 12.9 cdA
225
8.5 bA
10.6 bA
9.0 aA
13.2 cA 14.5 cdA 13.2 dA
281
9.0 bA
10.0 bA
9.6 aA
13.6 cA 15.1 dA
14.2 dA
Significance(Pr>F)
N
S
N×S
N
S
N×S
<0.01
0.56
0.07
<0.01
0.37
0.10
†
Means in a column for each year followed by the same lowercase letters are not significantly
different at P ≤ 0.10. Means in a row for each year followed by the same uppercase letters are
not significantly different at P ≤ 0.10.
Sulfur application at the zero and 56 kg ha-1 N rates resulted in a positive yield response in both
study years and in 2013, respectively. Data suggest that in the dry and wet field conditions
during 2012 and 2013, respectively, soil S immobility from lack of mass flow or excessive
mobility and potential S leaching may have occurred to cause a positive yield response from S
application (Bohn et al., 1986; Chen et al., 2008). However, as N rates increased to 56 and 112
kg N ha-1 in 2012 and 2013, respectively, yield differences were moderated and demonstrated no
significant affect from S application. At sub-optimal N rates (56 and 112 kg N ha-1 in 2012 and
2013, respectively) root growth may have been promoted sufficiently to increase plant access to
naturally available S (i.e., residual soil S, mineralized S from soil OM) thus not resulting in a
positive yield response from S application. As corn plants senesce older leaves at sub-optimal N
rates, accelerated protein hydrolysis and greater S mobilization to the upper portion of the plant
38

canopy may occur concealing S deficiency and further limiting yield response to S application
(Loneragan et al., 1976; Marshner, 1995). Yield was not significantly increased from S
application at N rates greater than 56 and 112 kg ha-1 in either 2012 or 2013, respectively.
Greater N rates may increase S demand to satisfy physiological requirements as has been
suggested by O’Leary and Rehm (1990) and Ciampitti and Vyn (2013). However, root growth
may be sufficiently promoted from larger N rates (≥ 56 kg N ha-1) resulting in greater nutrient
exploitation of the soil profile and sufficient S uptake for optimal corn growth and yield (Table
2.9) (Nibau et al., 2008).

Table 2.9. Corn R1 ear leaf nitrogen analysis, East
Lansing, MI, 2012 – 2013.
2012
2013
__________
Nitrogen (kg ha-1)
g S kg-1 ___________
0
1.5 a
1.4 a†
56
1.6 a
1.5 a
112
1.8 b
1.8 b
169
1.8 b
1.8 b
225
1.8 b
1.9 b
281
1.9 b
1.9 b
Significance (Pr>F)
N
<0.01
<0.01
†
Means followed by the same letters within a column
are not significantly different at P ≤ 0.05.

In 2012, convergence criteria were not met to determine a nonlinear model for the 45 kg
S rate and yield plateaus were not significantly different by S rate (P > 0.10) at the zero and 23
kg ha-1 S applications (8.9 and 10.5 Mg ha-1, respectively) (data not shown). Yield plateaus were
not significantly different (P > 0.10) in 2013 with 13.6, 15.8, and 13.7 Mg ha-1 representing
yield maximums at zero, 23, and 45 kg S ha-1, respectively. Nitrogen rate was regressed against
yield at different S rates demonstrating no significant differences (P > 0.10) among slopes

39

caused by S in 2012 (0.38 and 0.49 at the 0 and 23kg S rates, respectively) and 2013 (2.07, 1.98,
and 1.96 at the 0, 23, and 45 kg S rates, respectively).
Agronomic Efficiency of Nitrogen Fertilizer
In both study years agronomic efficiency (AE) decreased by 67 and 51%, respectively, as N rate
increased from 56 to 281 kg N ha-1 (P ≤ 0.01), but no significant main effects occurred from S
application (Table 2.10). In 2012, grain yield increase per kg of N fertilizer applied ranged from
10.3 to 31.0 as N rate decreased from 281 to 56 kg ha-1. Drought conditions during 2012 may
have limited N movement through soil solution decreasing the AE of N fertilizer. In 2013, AE
increased 162 to 284% as compared to 2012 suggesting soil moisture may have influenced AE to
a larger extent than N rate over either study year (Derby et al., 2005).

Table 2.10. Main effects of nitrogen and sulfur on
agronomic efficiency† of nitrogen, East Lansing,
MI, 2012 – 2013.
2012
2013
-1
____
Nitrogen (kg ha )
kg grain kg N-1 ____
56
31.0 b
81.4 c‡
112
25.7 ab
73.7 c
169
13.7 a
57.5 b
225
12.0 a
46.5 ab
281
10.3 a
39.6 a
Sulfur (kg ha-1)
0
15.6 a
56.1 a
23
21.1 a
59.7 a
45
18.9 a
63.3 a
Significance (Pr > F)
N
<0.01
<0.01
S
0.78
0.66
N×S
0.99
0.27
†
Agronomic efficiency (AE) is calculated by
subtracting yield of the control (no nitrogen or
sulfur) from the yield of the treatment and
dividing by the nitrogen rate of the treatment.
‡
Values followed by the same letters within a
column are not significantly different at P ≤ 0.05.

40

Salvagiotti et al. (2009) indicated that S fertilization increased N use efficiency in wheat
and proposed that S application promoted root growth to allow better exploitation of the soil
profile and improve N recovery. Similar reports have been presented (Mandal et al., 2003), but
S-activated root growth is more likely to occur under extreme S deficiency conditions (soil test ≤
1 mg kg-1 and organic matter ≤ 10 g kg-1) in coarse textured soil and not when S is adequately
supplied (Nibau et al., 2008). Data in the current study suggest that increasing S availability will
not significantly increase AE (Table 2.10). Sulfur is an essential nutrient in corn and directly
affects N assimilation as a constituent of enzymes involved in N metabolism (i.e., nitrite
reductase), but nutrient recovery as affected by root growth may be supported to a greater extent
by localized N concentrations and not the presence of S fertilizer (Drew, 1975; Reuveny et al.,
1980; Robinson, 1994; Salvagiotti et al., 2009).

Conclusions
Tissue analyses did not accurately predict a yield response from S treatments, but greater
correlation between yield and NDVI occurred with S fertilization. These data suggest greater
accuracy for determining N sufficiency may occur by maintaining greater plant available S.
However, no significant increase in grain yield resulted from S application despite reports of
decreased S deposition and large nutrient requirements for modern corn cultivars. Soils that
have traditionally been classified as non-responsive to S fertilization (i.e., organic matter ≥ 28 g
kg-1 and soil S ≥ 6 – 8 mg kg-1) resulted in a significant yield increase at sub-optimal N rates (≤
56 kg N ha-1) yet with N rates greater than 56 kg N ha-1 the data suggest sufficient root
exploitation of the soil profile resulting in adequate S uptake for optimal corn growth and yield.

41

APPENDIX

42

Corn grain yield regressed against nitrogen rate in 2012 and 2013 separated by sulfur rate
Yield data from the East Lansing corn study were evaluated at each S rate in 2012 and 2013 to
determine yield plateaus and rate of increase. PROC NLIN and PROC GLM statements in SAS
were utilized to compare yield responses as affected by S rate. The data did not demonstrate a
significant difference in yield plateau or slopes in either study year. In 2012, convergence
criteria was not met to determine a nonlinear model for the 45 kg S rate and yield plateaus were
not significantly different by S rate (P > 0.10) at the zero and 23 kg ha-1 S rates (8.9 and 10.5
Mg ha-1, respectively). Yield plateaus were not significantly different (P > 0.10) in 2013
demonstrating 13.6, 15.8, and 13.7 Mg ha-1 as yield maximums at zero, 23, and 45 kg S ha-1.
Nitrogen rate was regressed against yield at different S rates demonstrating no significant
differences (P > 0.10) among slopes caused by S in 2012 (0.38 and 0.49 at the 0 and 23kg S
rates, respectively) and 2013 (2.07, 1.98, and 1.96 at the 0, 23, and 45 kg S rates, respectively).

43

Figure A.1. Corn grain yield regressed against nitrogen rates for (a) 2012 and (b) 2013.
Convergence criteria was not met for the 45 kg S rate in 2012 and not presented, East Lansing,
MI.

44

REFERENCES

45

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48

CHAPTER 3
SOYBEAN RESPONSE TO SULFUR PLACEMENT AND STARTER FERTILIZER

Abstract
Earlier planting dates, minimal rates of early season nutrient mineralization, increased nutrient
removal, and reductions in atmospheric sulfur (S) deposition have increased concern regarding
early season S availability for optimal soybean [Glycine max (L.) Merr.] growth. A field study
was established to determine the effects of 25 lbs S/acre and a starter fertilizer of 20 lbs nitrogen
(N) and 50 lbs phosphorus (P)/acre on soybean yield and quality. Main plots consisted of S
placement (pre-plant incorporated, at planting in a 2 × 2 inch band, split, and no S) while subplots consisted of N and P starter fertilizer applied at planting (with or without in a 2 × 2 inch
band). Data collection included SPAD chlorophyll measurements (V4, R5), petiole samples
(R1), root nodule counts (R3), grain yield, quality, and yield components (pod producing nodes,
pods/node, beans/pod, weight per 100 seeds). Starter fertilizer did not affect grain yield,
however, root nodule numbers were not significantly reduced and soybean growth prior to V4
appeared to be positively impacted by starter N and P. Sulfur placement did not significantly
affect grain yield in either study year. Sulfur application to soybeans may not affect yield when
pre-plant soil tests demonstrate greater than 6 ppm S with soil organic matter (OM) near 3.0% or
greater.
Introduction
Reports of sulfur (S) applications increasing crop yields have been described throughout the
upper Midwest (Chen et al., 2005; Kaiser and Kim, 2013). Decreased atmospheric deposition of
S, increased purity and usage of concentrated fertilizers, less incidental S in pesticides, and

49

increased usage of minimum tillage systems that delay soil warming and allow accumulating
crop residues to immobilize plant available S have all resulted in a decreased soil supply of S to
crops (Hagstrom, 1986; Whitney, 1997; Rehm, 2005; Chien et al., 2011; National Atmospheric
Deposition Program, 2012). Past research has indicated that S application is not necessary to
achieve optimal soybean yield in Michigan but few recent data are available to substantiate this
claim (Robertson et al., 1976).
Sulfur is particularly important in soybean production due to the high protein content of
the seed (Sexton et al., 1998). By weight, soybean seed averages 40% protein and 20% oil
(Krishnan, 2005). Sufficient available soil S at planting may be critical for optimal soybean
growth as 59% of total S uptake is required by the end of soybean vegetative development
(Naeve and Shibles, 2005). Traditionally soybeans in Michigan have been planted in mid-late
May and early June. However recent research has demonstrated planting in late April to early
May offers significant yield increases lending growers to adjust planting dates to optimize grain
yield potential (Anderson and Vasilas, 1985; Pedersen and Lauer, 2004). As soybean growers in
northerly latitudes attempt to maximize yield through earlier planting dates, S deficiency
becomes a greater concern with cooler soil temperatures and where residual soil S levels are less
than or equal to 8 ppm (Fox et al., 1964). Soil organic matter (OM) may contribute up to 3 lbs
S/acre for every one percent soil OM (McGrath and Zhao, 1995). However, early planting dates
may indirectly create a longer time period where soybeans are S-deficient as mineralization may
be limited by cool soil temperatures (Roberts, 1985; Schoenau and Malhi, 2008). Earlier planted
soybeans may require S fertilization to satisfy vegetative S requirements prior to soil organic S
mineralization but yield response data to S application are limited.

50

Minimal soil microbial activity during early spring conditions may limit the extent of
soybean nodulation and N2 fixation (Lynch and Smith, 1993; Osborn and Riedall, 2006). A
starter fertilizer application of N and P may increase early soybean growth and development
minimizing yield loss potential in what is often difficult growing conditions. Broadcast
application of greater than 100 lbs N/acre at planting or emergence has increased soybean yield
7% (Bly et al., 1998). Concerns are that N application is inconsistent at producing a positive
yield response and may reduce N2 fixation by decreasing nodule number (Salvagiotti et al.,
2008). Phosphorus fertilization at planting may help maintain N2 fixation while promoting
earlier root development for increased S uptake (Cassman et al., 1980; Cadisch et al., 1993;
Kaiser and Kim, 2013). Additional research is needed to investigate how early season N and P
applications in the form of starter fertilizer influence S uptake, yield, and root nodulation. The
objectives of this study were to 1) determine the effects of S placement on soybean growth,
yield, and grain quality and 2) determine the effects of N and P starter fertilizer on early season
nutrient uptake, yield, and root nodule formation.

Materials and Methods
Field studies were established in 2012 and 2013 on a Capac loam (fine-loamy, mixed, active,
mesic Aquic Glossudalfs) at the Michigan State University research agronomy farm in East
Lansing, Michigan. Field sites were previously cropped to corn (Zea mays L.) in both study
years and autumn chisel plowed after previous crop harvest followed by spring tillage with a soil
finisher to a 4 inch depth. Individual plots measured 15 feet in width by 50 feet in length and
were six rows wide with 30 inch row spacing. Soil characteristics over both study years included
6.5-7.3 pH, 31-42 ppm P (Bray-1 P), 132-135 ppm K, 1934-1942 ppm Ca, 6-9 ppm S (extracted
with Ca(H2PO4)2), cation exchange capacity of 13 meq/100g, and 3.0% organic matter.
51

The study was designed as a split-plot randomized complete block with four replications.
Sulfur placement was the main plot factor and consisted of four application intervals including 1)
pre-plant broadcast and incorporated with a soil finisher to 4 inch depth, 2) at planting in a 2
inch band, 3) split with 15 lbs S/acre at planting in a 2

2

2 inch band and 10 lbs S/acre

sidedressed on the soil surface in a band 4 inches to the side of the row at R1 (split), 4) and no
sulfur. All S applications totaled 25 lbs S/acre. The S source for pre-plant application was
calcium sulfate (0-0-0-16) and while the at-planting and split S applications were an ammonium
sulfate based liquid fertilizer (0-0-0-17). Main plots were split vertically to evaluate soybean
response to starter fertilizer (20 lbs N and 50 lbs P2O5/acre) applied at planting in a 2

2 inch

band as di-ammonium phosphate (18-46-0). A maintenance application of 120 lbs K2O/acre was
applied pre-plant and incorporated. The soybean variety was Asgrow 2330 (relative maturity
2.3) in both study years (Monsanto Co., St. Louis, MO). Plots were planted on 21 May 2012 and
9 May 2013 to achieve a final plant population of 154,000 seeds/acre.
Plant height was assessed at V4 and R5 from 20 plants per plot (Osborne and Riedell,
2006). Chlorophyll meter readings were collected from 25 plants per plot using a Minolta
SPAD-502 chlorophyll meter (Spectrum Technologies Inc., Plainfield, IL). Measurements were
collected at V4 and R5 from the youngest most fully developed tri-foliate (Schlemmer et al.,
2005). Petiole samples were taken at R1 collecting 20 petioles per plot selecting the youngest
most fully developed trifoliate (Buckley and Wolkowski, 2012). Samples were dried at 150 °F,
ground to pass through a 1-mm mesh screen, and analyzed for P and S.
Soybean roots were dug at R3 to assess nodulation (Zhao et al., 2008). A shovel was
inserted to the soil 6 inch from the base of the soybean plant down to a 6 to 8 inch depth. Ten
plants per plot were dug and soybean root balls were soaked and washed over a 2-mm mesh

52

screen. Nodules that were removed during washing and retained in the 2-mm mesh screen were
accounted for and averaged with the total number of nodules per plant.
Grain yield was collected from the center two rows of each plot using a small plot
combine (Alamco, Nevada, IA) on 2 October 2012 and 1 October 2013. Grain yield was
corrected to 13% moisture. Grain samples were used to determine grain oil and protein content
with an NIR6500 using WinISI 2 version 1.5 software (Infrasoft international LLC., Eden
Prairie, MN) (Osborne and Riedell, 2006). Ten plants per plot were collected at physiological
maturity to count bean pod producing nodes, pods per node, beans per pod, and weight per 100
seeds.
Data were subjected to ANOVA using the PROC MIXED statement in SAS (SAS
Institute). Normality of the residuals was evaluated by examination of normal probability and
stem-and-leaf plots. Homogeneity of the variances was determined with Levene’s test (P ≤
0.10). When ANOVA generated a significant F-value for a treatment (P ≤ 0.10) means were
compared by Fisher’s least significant difference test (LSD). The data were determined to be
significantly different by year (P ≤ 0.01) and were analyzed separately.

Results and Discussion
Environmental Conditions
Warmer air temperatures in combination with 50% less precipitation may have limited plant
growth in 2012 as compared to 2013 (Table 3.1, Fig. 3.1a). May through August 2013 rainfall
was near or above normal but May and June precipitation resulted in three rainfall events greater
than 1 inch, two of which occurred over a single 2 day period (Fig. 3.1b). Temperatures in 2013
were consistent with the 30-yr. mean but were 3°F cooler in Aug. and 2°F warmer than normal in
Sept. Annual precipitation measurements indicated S deposition for southern Michigan was 0.57
53

lbs SO4 (wet weight) per inch of rainfall (National Atmospheric Deposition Program, 2012).
Sulfate concentrations and annual precipitation data were multiplied to calculate S deposition.
The 2013 growing season received 9.4 lbs S/acre (wet weight) through atmospheric deposition
while the 2012 growing season received 4.7 lbs S/acre due to less precipitation.
Table 3.1. Mean May – Sept. and 30-yr average precipitation and temperature data, East
Lansing, MI, 2012 – 2013.
Month
2012
2013
30-yr ave.
2012
2013
30-yr ave.
_________
___________
__________
precip. (inch)
temperature (°F) __________
May
0.39
3.00
3.60
63
60
61
June
1.12
6.06
3.60
69
67
66
July
2.51
2.66
3.00
74
70
70
Aug.
1.94
3.83
3.60
69
67
70
Sept.
2.32
0.82
3.60
61
65
63
8.30
16.40
17.40
Total
Precipitation and temperature data were collected from Michigan Automated Weather
Network (http://www.agweather.geo.msu.edu/mawn/). 30-yr averages come from the
PRISM climate group (http://prism.oregonstate.edu/normals).

Figure 3.1. Daily precipitation May – Sept. for (a) 2012 and (b) 2013, East
Lansing, MI.

54

Figure 3.1. (cont’d)

Plant Tissue Analyses
In 2012, soybean petiole S concentrations ranged from 0.24% without S to 0.27% with S
application (Table 3.2). Developing soybean tissue acquires S (~25%) from the youngest most
fully developed trifoliate (first trifoliate), and therefore maintaining first trifoliate S
concentrations above 0.25% has been suggested as critical for S assimilation and optimum
soybean growth (Sunarpi and Anderson, 1996). However, in 2012 without S application petiole
concentrations were 0.24% S and grain yield was not significantly reduced. Oenema and Postma
(2003) reported that percent S in the first trifoliate can be as low as 0.21% and remain sufficient
for optimum soybean growth. In 2013, no treatment resulted in a petiole concentration less than
0.32% S. Applying S broadcast or at planting increased petiole S contents by an average of 5%
across these treatments in 2013 and increased grain yield 3% but the differences were not
significant. Data suggest that soybean first trifoliate S concentrations may be sufficient when
residual soil S ranges from 6 – 9 ppm with 3.0% soil OM.

55

Table 3.2. Petiole R1 nutrient concentrations as
affected by S placement and starter fertilization, East
Lansing, MI, 2012 – 2013.
Fertilizer Treatment
2012
2013
_____________
_____________
%S
S Placement
Pre-plant Incorporate
0.26
0.33
At Planting
0.25
0.34
Split
0.27
0.33
No Sulfur
0.24
0.32
Starter Fertilizer
Starter
0.26
0.33
No Starter
0.25
0.33
LSD (0.10)
S Placement
ns
ns
Starter
ns
ns
S Placement × Starter
ns
ns

Increased root branching and elongation from localized placement of N has suggested
that early season S uptake may increase with starter fertilizer application (Nibau et al., 2008).
However without starter fertilizer in either year of the current study, petiole S concentrations
remained above 0.25% and increased by no more than 4% with starter fertilizer application.
Kaiser and Kim (2013) found that starter N fertilizer did not increase percent S at V5 soybeans
but did indicate that S uptake may be greater due to increased biomass from starter N fertilizer
application. Early season biomass was not collected in the current study and may be a
measurement to further elucidate S uptake patterns as affected by starter N fertilizer. Soybean
petiole P concentrations were not deficient averaging 0.32 to 0.46% in 2012 and 2013,
respectively, averaged across starter and no starter fertilizer treatments with no significant effects
from starter fertilizer (P > 0.10) (data not shown). The lack of a P response from starter
fertilizer likely occurred due to pre-plant soil samples demonstrating P levels ranging from
adequate to very high (31-42 ppm Bray-1 P) for optimal soybean growth (Lambert et al., 2006).

56

Root Nodule Assessment
In 2012 and 2013, R3 root nodule numbers were not significantly affected by starter fertilizer (P
> 0.10) (Table 3.3). Research performed in growth chambers has indicated that moderate N
rates (100 lbs/acre) tend to reduce nodule size while larger N rates (300 lbs/acre) seem to
decrease the number of nodules (Harper and Cooper, 1971). Research has shown that N
fertilizer inhibiting N2 fixation has a local effect, which suggests N applied in a 2 × 2 inch band
near the area of nodulation may decrease nodule number (Streeter, 1985; Takahashi et al., 1992).
However the change in nodule number in both study years as affected by starter fertilizer was not
significant, suggesting that 20 lbs N/acre may not be a large enough N rate to limit N2 fixation
despite application near the area of nodulation.
Table 3.3. Soybean R3 root nodule counts as
affected by S placement and starter fertilization,
East Lansing, MI, 2012 – 2013.
Fertilizer Treatment
2012
2013
Nodules per Plant
S Placement
Pre-plant Incorporate
23
24
At Planting
23
24
Split
23
22
No Sulfur
23
24
Starter Fertilizer
Starter
22
24
No Starter
24
23
LSD (0.10)
S Placement
ns
ns
Starter
ns
ns
S Placement × Starter
ns
ns

Root nodulation at R3 averaged 23 and 24 nodules per plant in 2012 and 2013,
respectively, but was not significantly affected by S placement (P > 0.10). Scherer and Lange
(1996) found in a laboratory study that with an S rate of 36 lbs /acre N accumulation from N2
fixation in Broad bean (Vicia Faba L.) was not limited with the presence of N fertilizer at 250

57

lbs N/acre. Research by Zhao et al. (2008) further reported that elemental S promoted nodule
formation when higher rates of S (60 and 120 lbs S/acre) were basal applied. Although no
difference in nodule number resulted from S application in the current study, S may be beneficial
when greater rates of N fertilizer are applied (> 20 lbs N/acre) and maintaining a normal rate of
N2 fixation is a concern.
Plant Greenness
Sulfur at planting increased the 2012 relative SPAD chlorophyll measurement by 2% at V4 (P ≤
0.10), but S did not affect SPAD measurements during other growth stages or in 2013 as all
readings remained above 0.95 (data not shown). Hitsuda et al. (2004) found that chlorophyll
meter readings did not accurately predict the S status of wheat or soybean which may help
explain the minimal variation of the data from the current study. Starter fertilizer application did
not affect soybean greenness in either study year as relative SPAD measurements remained
greater than 0.95. However, visual observations made one week prior to V4 in 2012 and 2013
noted that starter fertilizer resulted in greener and denser plant canopies than plots not receiving
starter N and P applications. Osborne and Riedell (2006) found a similar response as 20 lbs
N/acre applied at planting significantly increased V4 soybean biomass by 10%. Despite the
inability of SPAD to document the visual observations in the current study, starter fertilizer
appeared to positively impact early-season soybean growth and may have a greater impact on
earlier planted soybeans. Future research determining soybean response to starter N and P
fertilizer may be improved by collecting vegetative biomass as compared to SPAD chlorophyll
measurements.

58

Grain Yield, Quality, and Components
Grain yield was not significantly affected from S placement or starter fertilizer in 2012 or 2013
(P > 0.10) (Table 3.4). Pre-plant soil samples demonstrated residual S concentrations ranging
from 6 – 9 ppm while mineralization of the 3% soil organic matter may have contributed up to 9
lbs S/acre as has been suggested by McGrath and Zhao (1995) and Schoenu and Malhi (2008).
Soil data from the current study suggest that 21 – 27 lbs. S/acre were available for soybean
uptake during the growing season. Previous research has indicated that soybean requires 6.5 lbs
S/acre to produce 15 bu (FAO Sulphur Network, 1992; Lantmann and Castro, 2004). Data from
the current study suggest that mean yields of 42 and 64 bu/acre in 2012 and 2013, respectively,
required 18 – 28 lbs S/acre. Pre-plant soil tests indicate that sufficient S was available at the
time of planting and may explain why no significant response to S application was observed in
either study year.

Table 3.4. Soybean grain yield and moisture as affected by S placement and
starter fertilization, East Lansing, MI, 2012 – 2013.
Fertilizer Treatment
2012
2013
2012
2013
________
___________
bu/acre _________
% ___________
S Placement
Pre-Plant Incorporate
45
66
10.9
13.4
At Planting
36
64
10.8
13.3
Split
42
61
10.8
13.4
No Sulfur
42
63
11.0
13.4
Starter Fertilizer
Starter
42
63
10.9
13.3
No Starter
41
64
10.8
13.4
LSD (0.10)
S Placement
ns
ns
ns
ns
Starter
ns
ns
ns
ns
S Placement × Starter
ns
ns
ns
ns

Main effects from starter fertilizer were not significant in 2012 or 2013 (P > 0.10) (Table
3.4). A positive yield response in soybeans from starter N fertilizer has been demonstrated in

59

about one-half of the published studies yet the magnitude of the response does not seem to vary
by different rates of N application (i.e., 0-45, 45-90, or > 90 lbs N/acre) (Salvagiotti et al., 2008).
Osborne and Riedell (2006) found that soybean yield did not respond to starter N fertilizer when
drought conditions occurred, but yield increased 5% in two of three years with 15 lbs N/acre
compared to the untreated check. Timing of N fertilizer may have a more critical role in
increasing yield as soybeans receiving N (20 – 290 lbs N/acre) have increased yield 8 – 12%
when N application occurred during the reproductive stages, most particularly after R3 (Wesley
et al., 1998; Ray et al., 2005). Salvagiotti et al. (2008) further indicated that N supply from N2
fixation is insufficient in high yielding environments (> 70 bu/acre) due to greater N
requirements from increased sink size (i.e., greater biomass and pod set in higher yielding
soybeans). Data in the current study did not demonstrate a significant yield increase but more
consistent yield increases from N fertilizer may occur as different placements of N fertilizer are
utilized (i.e., deep banded (≥ 8 inch) or top dressed during reproductive stages) (Gan et al.,
2002).
Neither S placement nor starter fertilizer affected the number of pod producing nodes
(12-13 and 15-17 in 2012 and 2013, respectively), pods per node (2 pods/node, 2012-2013),
beans per pod (3 beans/pod, 2012-2013), or 100 seed weight (0.56-0.60 oz./100 seeds, 20122013) (P > 0.10; data not shown). No differences in seed oil occurred from starter fertilizer or S
placement in either study year, but percent protein was significantly increased by S broadcasted
or in a 2 × 2 inch band at planting (P ≤ 0.10) in 2013 (Table 3.5). Applying the total 25 lbs
S/acre before or at planting increased protein 1% and may indicate that sufficient S availability at
planting is critical for optimal soybean grain protein production. However Wilson (2004)
reported that soybean grain protein ranges from 34 to 57% with an average of 42%. These data

60

suggest that despite an increase in grain protein from S application in the current study the results
are below average and may not be significant considering the wide range of soybean grain
protein content. Oil and protein were 10 and 12% greater, respectively, from 2012 to 2013
suggesting the 98% increase in precipitation may have been a greater controlling factor for
soybean seed quality than the fertilizer treatments. Results from the current study support
previous research indicating that grain N (protein) and oil concentration were decreased in
drought conditions and may not be significantly affected by N or S fertilization (Sexton et al.,
1998; Osborne and Riedell, 2006).

Table 3.5. Soybean grain oil and protein as affected by S placement and
starter fertilization at East Lansing, MI in 2012 and 2013.
Oil
Protein
Fertilizer Treatment
2012
2013
2012
2013
_________________________
% ________________________
S Placement
Pre-plant Incorporate
20
22
36
41
At Planting
20
22
36
41
Split
20
22
36
40
No Sulfur
20
22
36
40
Starter Fertilizer
Starter
20
22
36
40
No Starter
20
22
36
40
LSD (0.10)
S Placement
ns
ns
ns
0.44
Starter
ns
ns
ns
ns
S Placement × Starter
ns
ns
ns
ns

Conclusions
Grain yield did not respond to starter N and P fertilizer in 2012 or 2013. Although visually
starter fertilizer appeared to improve plant greenness and canopy density in both study years,
soybean SPAD chlorophyll measurements were no less than 95% of maximum with or without N
and P fertilizer. Nitrogen fertilizer may increase early soybean growth when used at 20 lbs

61

N/acre and be a small enough rate to not significantly reduce root nodule formation. Soybean
grain yield did not significantly respond to S application in either study year compared to the
untreated check demonstrating that residual soil S and mineralized S from soil organic matter
were sufficient for optimal plant growth. Alternative options for maintaining sufficient soil S
may include fertilization in alternate rotation years as positive yield responses from S have been
more consistent in corn (Rehm, 2005; Kim et al., 2013). Depending upon S application rate,
sufficient residual soil S may be available in the year following corn application for optimal
soybean growth and development. Prior to S application, consideration of all potentially
available S sources (i.e., soil OM, residual soil S, and S-deposition) may be critical in
determining whether S application is warranted.

62

REFERENCES

63

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Wilson, R.F. 2004. Seed composition. p. 629 – 631. In H.R. Boerma and J.E. Specht (ed.)
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Zhao, Y., X. Xiao, D. Bi, F. Hu. 2008. Effects of sulfur fertilization on soybean root and leaf
traits, and soil microbial activity. J. Plant Nutrition 31: 473-483.

67

CHAPTER 4
CORN RESPONSE TO SULFUR IN HIGH PHOSPHORUS SOILS

Abstract
Sulfur (S) fertilization has traditionally been recommended for Michigan corn (Zea mays L.)
production on coarse textured low organic matter soils, but S recommendations may vary by
crop rotation, sub-soil characteristics, and soil phosphorus (P) concentrations. A two year field
study was initiated on a loamy sand to determine corn yield response to S fertilization by
investigating nutrient uptake, nitrogen (N):S ratios, and grain yield as affected by N fertilizer
rate. Main plots consisted of three S rates (0, 20, and 40 lbs S/acre) while sub-plots consisted of
six N rates (0, 50, 100, 150, 200, and 250 lbs N/acre). Tissue analyses indicated S availability
was optimal to excessive resulting in R1 N:S ratios ranging from 13 – 10:1 as S rate increased
from 0 to 40 lbs/acre, respectively. Reduced N:S ratios from increased S rates were associated
significant 22 and 10% yield losses at the zero and 250 lb N rates, respectively, in one of two
years. Sulfur availability at 12 – 24 inches beneath the soil surface suggested potential for S
accumulation (i.e., pH < 6 and presence of metal oxides) and may need to be considered when
the upper soil profile (0-8 inches) suggests S may be limiting. Inorganic S accumulation within
corn plants was suggested by low N:S ratios which may have caused assimilation competition
between sulfate and nitrate (i.e., sulfite and nitrite reductase) which may explain the negative
yield response from S application in one of two study years.

Introduction
Positive corn yield responses to S fertilization have become more frequent in the upper Midwest
Corn Belt. Yield increases from 14 – 42 bu/acre with applications of 25 – 30 lbs S/acre have
68

been recorded suggesting that S deficiencies may be more prevalent than 10 – 15 years ago
(Chen et al., 2008; Kim et al., 2013). Past research in Michigan has suggested that S application
on corn was not necessary due to sufficiently available S from soil organic matter (OM), S
contributions through atmospheric deposition, or a combination of the two (Robertson et al.,
1976). However, the U.S. Environmental Protection Agency (EPA) has reported that between
1980 and 2010 S emissions decreased by 83% reducing annual sulfate deposition in Michigan
from 25 lbs S/acre to less than 8 lbs S/acre (wet weight), respectively (National Trends Sulfur
Dioxide Levels, 2011). Improved higher-yielding corn germplasm that produces 200 – 250
bu/acre and removes 16 – 20 lbs S/acre with grain harvest in conjunction with decreased S
deposition may create greater opportunities for S deficiency when soil S is not replenished
(Bender et al., 2013).
A large percentage of Michigan’s corn acreage is grown on soils that cannot provide or
retain sufficient S in the root zone due to a coarse soil texture (i.e., loamy sand and sandy loam),
low percent clay (<25%), soil OM less than 2.0%, and pH greater than 6 (Warncke et al., 2009).
Sulfate adsorption is negligible at soil pH’s greater than 6 and is also susceptible to leaching
(Bettany and Steward, 1983; Curtin and Syers, 1990). A portion of Michigan corn production is
in rotation with potatoes (Solanum tuberosum L.) which require high soil phosphorus (P) levels
(75-150 ppm) and may further limit S adsorption due to greater adsorption ability of phosphate
to soil clay particles and iron (Fe) and aluminum (Al) oxides (Schoenau and Malhi, 2008). In
addition, S applications are made in the year of potato production and are exposed to irrigation
which may increase soil S mobility and lead to greater S leaching and accumulation where subsoils indicate greater S adsorption opportunities (i.e., pH > 6 and presence of metal oxides or
clay particles) (Harward et al., 1962; Fox et al., 1971; Bohn et al., 1986). Determining an

69

optimal S rate in soils susceptible to S leaching may be critical to maintaining sufficient plant
available S in the root zone. The objective of this study was to determine the corn response to S
fertilization on a coarse textured, low organic matter soil with high soil P.

Materials and Methods
Field experiments were conducted in 2012 and 2013 at the Michigan State University Montcalm
research center on a Montcalm (coarse-loamy, mixed, semi-active, frigid Alfic Haplorthods) and
McBride (coarse-loamy, mixed, semi-active, frigid Alfic Fragiorthods) loamy sand. Soil
analysis over both study years included 6.1 – 6.2 pH, 151 – 160 ppm P (Bray-1 P), 161 – 194
ppm potassium (K), 567 – 599 ppm calcium (Ca) , 8 – 9 ppm sulfate (SO4, extracted with
Ca(H2PO4)2), 7 meq/100g cation exchange capacity (CEC), and 1.5 – 1.6% soil OM. Field sites
were previously cropped to corn in both study years and autumn chisel plowed, followed by
spring tillage using a soil finisher (4 inch depth). Individual plots measured 15 feet in width by
40 feet in length (six rows) with 30 inch row spacing.
The experimental design was a split-plot randomized complete block with four
replications. Sulfur rate was the main plot factor and was pre-plant incorporated as calcium
sulfate at 0, 20, and 40 lbs S/acre. Main plots were split vertically and evaluated with six N rates
(0, 50, 100, 150, 200, and 250 lbs N/acre), totaling 18 treatments per replication. Forty percent
of the N rate was pre-plant incorporated as urea (46-0-0) the day of planting. Starter fertilizer
was applied at planting in a 2 × 2 inch band at 20 lbs P2O5 and 50 lbs K2O/acre. The remaining
sixty percent of the N rate was sidedressed at V6 using urea with a urease inhibitor [CO(NH2)2 +
n-(n-butyl) thiophosphoric triamide] (Koch Agronomic Services, LLC, Wichita, KS). Sidedress
applications were made on the soil surface by banding the N fertilizer 4 – 6 inches to the side of
the corn row. The corn hybrid used for both study years was Dekalb DKC48-12RIB (98 day
70

relative maturity) (Monsanto Co., St. Louis, MO). Plots were planted on 27 Apr. 2012 and 6
May 2013 to achieve a final plant population of 32,000 plants/acre. Pest control followed
standard management programs used in the region. Mean annual rainfall for this location was
32.4 inches with S deposited annually at a rate of approximately 0.27 lbs SO4 per inch of rainfall
resulting in 8 – 10 lbs. (wet weight) of sulfate deposition per acre (National Atmospheric
Deposition Program, 2012). In the event that precipitation was limited during the growing
season additional irrigation was added through a center-pivot (Table 4.1).
Table 4.1. Mean May – Sept. precipitation and 30-yr mean with irrigation, Entrican,
MI, 2012 – 2013.
Precipitation
Irrigation
2012
2013
30-yr ave.
2012
2013
_____________________
___________________
______
_______
inch
inch
May
0.8
4.5
3.2
0
0
June
2.1
2.3
3.4
2.0
0
July
5.8
1.4
2.9
2.8
3.5
Aug.
5.2
4.1
3.3
1.6
2.6
Sept.
0.3
1.3
3.2
0
0
14.2
13.6
16.0
6.4
6.1
Total
Precipitation data were collected from Michigan Automated Weather Network
(http://www.agweather.geo.msu.edu/mawn/).
http://www.weather.com/weather/wxclimatology/monthly/graph/48858
Chlorophyll meter readings were collected at V6 and R1 using a Minolta SPAD-502
chlorophyll meter (Spectrum Technologies Inc., Plainfield, IL). Twenty-five plants per plot were
sampled and the average recorded. Chlorophyll measurements were collected from the youngest
most fully developed leaf with a visible collar at V6 and from the ear leaf during R1 half way
between the mid-rib and the leaf margin and midway between the stalk and the tip of the leaf
(Blackmer and Schepers, 1995; Pagani et al., 2009). A relative greenness index (RGI) was
calculated as:
RGI=GIfield/GIFT NS

71

The relative greenness index GIfield is the index of greenness for treatments that may be deficient
in N or S, and the GIFT NS is the index of greenness for the treatment that had adequate N and S
(45 kg S and 281 kg N ha-1) (Pagani et al., 2009). Canopy normalized difference vegetation
index (NDVI) was also collected using a Greenseeker® handheld red-band optical sensor at V6
(Trimble Navigation Ltd., Sunnyvale, CA) (Teal et al., 2006). From row two or five, 60 to 80
NDVI readings were collected per plot and a relative greenness index was developed to
determine treatment effects on overall plant growth and color. Plant height measurements were
collected from 20 plants per plot at V6 and R1.
Plant tissue samples were collected for nutrient analysis at V6 (10 whole plants/plot), R1
(25 ear leaves/plot), and R6 (6 whole plants/plot). Tissue samples collected at V6 and R1 were
dried at 150 °F, ground to pass through a 1-mm mesh screen, and analyzed for N, P, K, and S.
Whole plant sampling at R6 had cobs and grain removed but husks returned to the sample.
Vegetative tissue fresh weights were collected, samples were pulverized with a gas powered flail
grinder, homogeneous sub-samples were collected, and fresh weights were recorded. Whole
plant sub-samples were analyzed for N using a micro-Kjeldahl digestion method and
colorimetric analysis through a Lachat rapid flow injector auto-analyzer (Lachat Intruments,
Milwaukee, WI) (Nelson and Sommers, 1973; Bremner 1996). Fifteen basal stalk samples were
collected at R6 to evaluate stalk nitrate concentrations. Stalk sections were cut 6 inches above
the soil surface and were 8 inches in length (Binford et al., 1990; Fox et al., 2001). Stalk
samples were dried at 150° F and ground to pass through a 0.04 inch mesh screen. A 0.35 oz.
stalk sub-sample was added to 1.7 fl. oz. of 1 M KCl and shaken for 30 minutes at 200 rpm.
Stalk extract was filtered through Whatman #2 filter paper (5 inch diameter), and nitrate
concentrations were determined with colorimetric analysis through Lachat rapid flow injector

72

autoanalyzer (Lachat Instruments, Milwaukee, WI) (Huffman and Barbarick, 1981). The center
two rows of each plot were harvested on 9 October 2012 and 29 October 2013 with a Massey
Ferguson 8XP small plot combine to determine grain yield, moisture, and test weight. Final
grain yield was corrected to 15% moisture.
Data were subjected to ANOVA using the PROC MIXED statement in SAS (SAS
Institute, Cary, NC). Normality of the residuals was evaluated by examination of normal
probability and stem-and-leaf plots. Homogeneity of the variances was evaluated with Levene’s
test (P ≤ 0.10). When ANOVA generated a significant F-value for a treatment (P ≤ 0.10) the
means were compared by Fisher’s least significant difference test (LSD). Due to a greater
understanding of corn response to N application, the emphasis of this paper will be on the main
effects of S and N × S interactions.

Results and Discussion
Corn Growth Response and Nutrient Uptake
Plant height and total biomass at V6 and R1 corn were not affected by S application and did not
result in a significant N × S interaction (P > 0.10) (data not shown). Sulfur application rate did
not influence N concentration at V6 or R1 tissue sampling (Table 4.2). Sulfur uptake was
directly related (P ≤ 0.10) with S rate at V6 in 2013 and at R1 in both study years as greater S
rates resulted in increased S uptake. Increased S uptake occurring from S fertilization may be
considered luxury consumption as tissue concentrations were within the sufficiency range (0.21
to 0.40%) without S application (Oenema and Postma, 2003). Data suggest that V6 corn plants
had adequate S available from residual soil S early in the season to meet requirements for
optimal growth. Bender et al. (2013) found that nutrient uptake in corn requires approximately
2.7 lbs S/acre prior to V6.
73

Table 4.2. Corn V6 whole plant and R1 ear leaf N and S
concentrations average across N rates as affected by S rate,
Entrican, MI, 2012 – 2013.
V6
R1
N
S
N
S
2012
S rate (lbs/acre) ____________________ % _____________________
0
3.61
0.25
3.59
0.22
20
3.54
0.25
3.48
0.30
40
3.66
0.26
3.59
0.35
LSD (0.10)
ns
ns
ns
<0.01
2013
S rate (lbs/acre) ___________________ % ____________________
0
2.88
0.21
3.18
0.25
20
2.88
0.23
3.21
0.28
40
2.87
0.25
3.00
0.30
LSD (0.10)
ns
0.02
ns
0.03

Pre-plant soil tests in the current study indicated 16 lbs residual S/acre were available at
planting both study years indicating there was sufficient S to satisfy early corn growth
requirements. Reneau (1983) reported that larger yield increases may be expected when S
fertilization is managed to obtain ear leaf S concentrations below 0.17 % at R1, but no clear
reason was given as to why this was the case. However in the current study no S treatment
resulted in R1 concentrations below 0.21% in 2012 or 2013. Excessive S uptake may have
occurred from fertilization but even without S fertilizer ear leaf concentrations were greater than
0.21% suggesting that other sources may have contributed to S availability and prevented growth
dilution of S in R1 corn.
Stalk nitrate concentrations ranged from 0 to 4887 ppm in 2012 and 0 to 2605 ppm in
2013 (Table 4.3). Past literature has shown that optimal stalk nitrate concentrations range
between 250 to 2000 ppm (Binford et al., 1990; Fox et al., 2001). In both study years a
significant N × S interaction (P ≤ 0.10) occurred affecting stalk nitrate concentrations. Mean
stalk nitrates across N and S treatments were 72% lower in 2013 as compared to 2012 resulting
74

in sub-optimal concentrations for many of the treatments. Lower stalk nitrate concentrations
may explain the 4 – 11% yield reduction observed in 2013 as compared to 2012. However, 20
lbs S/acre may have reduced stalk nitrate accumulation at the supra-optimal 250 lb N rate as
nitrate concentrations were reduced by 2945 and 1505 ppm in 2012 and 2013, respectively. Kim
et al. (2013) reported that S increased N uptake at one of four locations and increased grain N
accumulation at two of four locations, suggesting that in the current study S may have improved
N assimilation at 250 lbs N/acre resulting in lower stalk nitrate accumulation.
Table 4.3. Stalk nitrate concentration as influenced by N and S applications, Entrican, MI,
2012 – 2013.
2012
2013
_____________
____________
lbs S/acre ___________
lbs S/acre ___________
0
20
40
0
20
40
_____________________________________
N rate (lbs/acre)
ppm ____________________________________
0
0
0
0
9
0
0
50
1
0
0
1
0
0
100
16
4
95
2
62
3
150
1609
1661
966
114
247
230
200
3228
3198
4410
621
939
371
250
4887
1942
3520
2605
1100
928
LSD (0.10)
1107
592

Grain Yield Response to Sulfur
Averaged grain yield was 145 – 245 and 139 – 229 bu/acre in 2012 and 2013, respectively. In
2012, S was not necessary to achieve optimal corn yields as neither the 20 lbs. nor the 40 lbs. S
rates resulted in significant yield differences (P > 0.10) from the zero S rate (Table 4.4).
Table 4.4. Grain yield and moisture as affected by S rate, Entrican, MI, 2012 – 2013.
2012
2013
Yield
Moisture
Yield
Moisture
_____
____ ____
____
____
____
____
S rate (lbs/acre)
bu/acre
%
bu/acre
% ____
0
213
18.0
202
22.1
20
208
17.9
194
22.2
40
218
18.1
196
22.1
LSD (0.10)
6.5
ns
ns
ns
75

In 2013 no significant main effects from S occurred, but an N × S interaction was present (P ≤
0.10). Without N application, grain yield decreased 29 and 46 bu/acre at 20 and 40 lbs S/acre,
respectively, indicating a negative yield effect from S application (Table 4.5). Additionally, at
250 lbs N/acre there was a significant 12 and 8% yield loss with the application of 20 and 40 lbs
S/acre, respectively.
Table 4.5. Corn grain yield response to N × S interaction,
Entrican, MI, 2013.
2013
_____________
lbs S/acre ____________
0
20
40
_____
N rate (lbs/acre)
grain yield (bu/acre) ______
0
163
136
118
50
182
169
173
100
201
199
203
150
213
221
229
200
221
234
231
250
239
211
220
LSD (0.10)
18

These data suggest that S may have been provided by other sources (i.e., residual soil S or OM
mineralization) and was sufficient for optimal corn growth at low and high N rates. Nitrogen
and S do not compete for nutrient absorption into corn plants, however, reduced yield from high
application rates of N or S has been suggested as being caused by competition or interference
between nitrite and sulfite reductase in N and S assimilation pathways, respectively. Both nitrite
and sulfite reductase require the same electron donor, ferrodoxin, for reduction processes and
both enzymes’ substrates (NO2 and SO3) are chemically similar (Hoefgen and Hesse, 2008).
Rabuffetti and Kamprath (1977) found that at 50 lbs N/acre S additions negatively affected corn
grain yield, whereas at 150 or 200 lbs N/acre S fertilizer increased yield. An optimum N:S ratio
(16:1) may be necessary for a positive yield response to occur from S application as suggested by
Reneau (1983). Similar to the current study results, Weil and Mughogho (2000) indicated yield
76

reductions when N:S ratios were too low (≤ 8:1) due to excessive S availability. Calculated N:S
ratios from R1 ear leaf concentrations in the current study demonstrated that when averaged
across N rates 40 lbs S/acre resulted in N:S ratios that were 15 and 23% lower in 2012 and 2013,
respectively, than the zero S rate (Table 4.6).
Table 4.6. Main effects of S on R1 N:S ratios, Entrican,
MI, 2012 – 2013.
2012
2013
_____________
S rate (lbs/acre)
R1 N:S _____________
0
13
13
20
12
12
40
11
10
LSD (0.10)
0.5
1.0

Sulfur application decreased N:S ratios below 13:1 in both study years and may have been due
to inorganic S accumulation within the plant as was suggested by Reneau (1983), which was
directly related with the negative yield responses in 2013. Sulfur fertilization may have
increased mid-season (R1) S concentrations to excessive levels but other S sources (i.e.,
precipitation, soil OM, etc.) may have increased S availability beyond S provided from
treatments (Kline et al., 1989). Lower N:S ratios than those calculated in the current study may
have resulted following R1 considering only 48% of S uptake has occurred by this growth stage
as compared to N where 65% of uptake is complete (Bender et al., 2013).
Factors Affecting Sulfur Response
Compared to the zero S treatment, decreased N:S ratios at R1 suggest that other sources may
have contributed to plant available S apart from fertilizer treatments. Based on precipitation data
in 2012 and 2013, S deposition was calculated to be approximately 4.2 and 4.0 lbs SO4/acre (wet
weight), respectively, during the growing season (Table 4.1) (National Atmospheric Deposition
Program, 2012). Residual soil sulfate levels were 8 and 9 ppm providing approximately 16 and

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18 lbs S/acre at planting in 2012 and 2013, respectively. Pre-plant soil tests also demonstrated
OM content of 1.6 and 1.5% in 2012 and 2013, respectively, which may have contributed
approximately 3 lbs S/acre annually for every one percent of soil OM (Roberts, 1985; McGrath
and Zhao, 1995; Schoenau and Malhi, 2008). When examined in total, residual soil S,
mineralized S from soil OM, and S deposition may have provided up to 24 and 25 lbs S/acre
during the 2012 and 2013 growing seasons, respectively. Soil contributions in addition to
atmospheric S deposition may have provided 92 to 96% of the suggested corn S requirement for
190 bu/acre corn yield (Bender et al., 2013). Soil and environmental data suggest that S
application increased S uptake and may have caused N and S competition between assimilation
pathways (i.e., nitrite and sulfite reductase) which may explain why yield was significantly
reduced when S fertilizer was applied at the zero and 250 lbs. N rates in 2013.
Additionally, pre-plant soil sampling demonstrated high soil P levels (> 150 ppm) in both
study years due to the high P requirement of other crops in rotation (i.e., potatoes). Phosphate
has greater adsorption potential than S in the soil and at the current P levels the anion exchange
sites (AEC; positively charged clay surface or minerals where negatively charged compounds
may bind and release) may have been saturated in the upper soil profile (0-8 inch) (Rajan and
Fox, 1975). Additionally growers apply 50 – 100 lbs S/acre in the year of potato production,
which may have resulted in S leaching in previous years especially with high rainfall and
irrigation at the current study field site (Warncke et al., 2009; Bohn et al., 1986). The soil profile
in the current study had two characteristics that may have increased sub-soil S availability to
developing corn roots. At the 9 to 15 inch soil depth, an accumulation of iron (Fe) and
aluminum (Al) oxides has been described which may have offered considerable potential for
sulfate adsorption at soil pH’s less than 6 (Harward et al., 1962; Fox et al., 1971; OSD, 2013).

78

Sub-soil horizons indicated acid pH ranging from 5.1 to 6.0, which may have caused S
accumulation (Gebhardt and Colemnan, 1974; Schoenau and Malhi, 2008). Low N:S ratios at
R1 may have been due to corn root access to sub-soil S mid-season and luxury consumption post
V6. These hypotheses are supported by a previous report indicating that increased percent clay,
amorphous Fe and Al, and AEC at depths of 16 to 24 inches may limit the potential for positive
corn yield responses from S fertilization (Kline et al., 1989).

Conclusions
The field site selected for this study demonstrated what has traditionally been considered to be
optimum S response conditions in Michigan: coarse textured soil (loamy sand), low organic
matter (< 2.0%), and no manure application in the previous 5 years. However, S fertilization did
not seem to be necessary to obtain optimal yield in 2012 and reduced yield by an average 36 and
23 bu/acre at the zero and 250 lb N rates, respectively, in 2013. High soil P levels (> 150 ppm)
in the upper 8 inches of the soil profile may have limited S adsorption and led to leaching in
previous years. Sub-soil characteristics that promote S adsorption (e.g., pH < 6 and presence of
Fe and Al oxides) suggest that S may have accumulated 9 to 15 inches beneath the soil surface
possibly providing sufficient S for optimal corn growth as roots developed during the growing
season. These assumptions were supported by R1 ear leaf concentrations that demonstrated 15
and 23% reductions in N:S ratios as S rate increased from zero to 40 lbs S/acre in 2012 and 2013,
respectively, which may indicate inorganic S accumulation within corn plants and competition
between N and S assimilation pathways (i.e., nitrite and sulfite reductase). These data serve as a
reminder that careful assessment of all available S sources should be considered in corn fertilizer
programs in lieu of recommendations based solely on soil OM and residual soil S. Planting corn
in coarse textured soils (e.g., sandy loam and loamy sand) with large quantities of soil P (> 150
79

ppm) may suggest a high potential for S leaching. Soil sampling 1 – 2 feet beneath the soil
surface to determine if sub-soil S accumulation has occurred may be necessary to adequately
determine all S contributions that may be available to a developing corn plant.

80

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81

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