plants
Article
Alfalfa Responses to Gypsum Application Measured
Using Undisturbed Soil Columns
Rebecca Tirado-Corbalá 1,2, *, Brian K. Slater 1 , Warren A. Dick 3 and Dave Barker 4
1
2
3
4
*
School of Environment and Natural Resources, The Ohio State University, Columbus, OH 43210, USA;
slater.39@osu.edu
Agro-Environmental Science Department, University of Puerto Rico, Mayagüez, Puerto Rico, 00681, USA
School of Environment and Natural Resources, The Ohio State University, 1680 Madison Avenue,
Wooster, OH 44691, USA; dick.5@osu.edu
Department of Horticulture and Crop Science, The Ohio State University, Columbus, OH 43210, USA;
barker.169@osu.edu
Correspondence: rebecca.tirado@upr.edu; Tel.: +1-787-370-9179
Academic Editor: Jim Moir
Received: 18 May 2017; Accepted: 10 July 2017; Published: 11 July 2017
Abstract: Gypsum is an excellent source of Ca and S, both of which are required for crop growth.
Large amounts of by-product gypsum [Flue gas desulfurization gypsum-(FGDG)] are produced from
coal combustion in the United States, but only 4% is used for agricultural purposes. The objective of
this study was to evaluate the effects of (1) untreated, (2) short-term (4-year annual applications of
gypsum totaling 6720 kg ha−1 ), and (3) long-term (12-year annual applications of gypsum totaling
20,200 kg ha−1 ) on alfalfa (Medicago sativa L.) growth and nutrient uptake, and gypsum movement
through soil. The study was conducted in a greenhouse using undisturbed soil columns of two
non-sodic soils (Celina silt loam and Brookston loam). Aboveground growth of alfalfa was not affected
by gypsum treatments when compared with untreated (p > 0.05). Total root biomass (0–75 cm) for
both soils series was significantly increased by gypsum application (p = 0.04), however, increased
root growth was restricted to 0–10 cm depth. Soil and plant analyses indicated no unfavorable
environmental impact from of the 4-year and 12-year annual application of FGDG. We concluded that
under sufficient water supply, by-product gypsum is a viable source of Ca and S for land application
that might benefit alfalfa root growth, but has less effect on aboveground alfalfa biomass production.
Undisturbed soil columns were a useful adaptation of the lysimeter method that allowed detailed
measurements of alfalfa nutrient uptake, root biomass, and yield and nutrient movement in soil.
Keywords: alfalfa; gypsum; no-tillage; nutrient uptake; undisturbed soil columns
1. Introduction
Gypsum is a common mineral in sedimentary environments [1], and has been used as an
amendment on agricultural soils for over 250 years [2,3]. Synthetic gypsum, or flue gas desulfurization
gypsum (FGDG), is produced by coal-fired power plants when SO2 is scrubbed from the exhaust gases.
The production of gypsum in the US was stimulated as a result of the Clean Air Act Amendments
of 1990, which mandated a reduction of 6.4 million tons of SO2 emissions by electricity utilities from
1990 to 2010. In the USA, more than 30 million Mg of FGDG was generated in 2014 [4]. Of this total,
around 49% of FGDG produced was beneficially used in industrial applications, such as highway
repairs [5], manufacturing of wallboard, and as a filler ingredient in some food products [6], a small
fraction (4%, 1.2 million Mg) was used in agricultural applications, and the remainder FGDG was
discarded as waste.
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Gypsum has been recognized for its potential to improve soil quality and agricultural
productivity [7–9]. Gypsum amendments benefit soils (especially sodic or heavy clay soils with
poor structure) by promoting soil flocculation, reducing runoff by increasing water infiltration rates,
and reducing surface sealing and crusting [10–12]. Gypsum applied to the soil surface increases the
electrolyte concentration of the infiltrating water, compressing the electric double layer, and providing
Ca to the exchange complex where it has selectivity over Mg and Na in most soils [13,14]. Gypsum can
also help ameliorate problems associated with subsoil acidity due to its moderate solubility and its
removal of toxic Al3+ ions by complexation instead of pH adjustment [15–17]. Consequently, gypsum
treatments enhance deep rooting and improve the ability of plants to access adequate supplies of water
and nutrients during drought [18].
Gypsum is an excellent source of Ca and S, two essential macro-elements needed for plant
nutrition [7,19]. Many gypsum products, also including FGDG, also provide other essential trace
nutrients such as B, Fe, Mo, and Zn. Although FGDG gypsum contains heavy metals such as Pb and
Cr [19,20], the concentrations and availability of these metals are generally much lower than regulatory
levels specified for soils [21].
Previous studies considered the hydrology and downward transport of gypsum components,
and the potential short-term environmental impacts of trace elements in FGDG products, when the
products are surface applied or mixed into the top 20 cm of soil [20,22]. However, less information is
available about the long-term effects of gypsum, including FGDG, in the whole soil profile [23].
This greenhouse study aimed to provide information of the soil properties and alfalfa growth
responses in undisturbed soil columns taken from fields where annual gypsum applications from 0
to 12 years had been applied to two fields managed with no-tillage. The specific objectives were to
measure, (1) the movement of gypsum components in soil and (2) the mineral uptake and growth of
shoots and roots of alfalfa planted in undisturbed soil columns.
2. Results and Discussion
2.1. Soil Chemical Properties
Exchangeable Ca, total S and SO4 -S were measured but only exchangeable Ca and total S
were significantly increased by gypsum application at all soil depths (Table 1). Measurements of
exchangeable Ca and total S revealed that dissolution products of surface-applied gypsum had moved
throughout the Brookston and Celina profiles compared with CT soils (Tables 1 and 2). Higher
exchangeable Ca and total S were found in gypsum-treated soils compared with CT in both soils
(Table 2). For exchangeable Ca, the interaction of gypsum treatment by depth was statistically
significant (p = 0.035) in Celina soil. Gypsum-treated soils had more exchangeable Ca than CT
soils at depths greater than 20 cm. Gypsum-treated soils had at least 0.4 to 1.4 times more exchangeable
Ca [LT (3.21 g kg−1 ) and ST- gypsum (3.19 g kg−1 ) treated soils, respectively] at 60–75 cm than CT
soils (1.69 g kg−1 ) (Table 2). In Brookston soils, exchangeable Ca main effects (gypsum treatment,
soil depth) were statistically significant (Table 1). Higher concentrations of exchangeable Ca were
observed in ST and LT gypsum treated soils compared with CT (Figure 1). Also, higher concentrations
of exchangeable Ca were observed at 20–60 cm soil depth (Figure 1). For Total-S, the interaction of
gypsum treatment by depth was statistically significant (p < 0.0001) in Brookston soil (Table 1). Total-S
values oscillated between 2.54 and 5.25 g S kg−1 in gypsum-treated soils where higher values were
encountered in the first 40 cm of soil in ST-gypsum treated soils compared with CT (Table 2). In Celina
soils, total- S main effects (gypsum treatment, soil depth) were statistically significant (Table 1). Higher
total-S concentrations (>13.6 g·S·kg−1 ) were encountered at deeper soil depths (> 40 cm) (Figure 2).
Total-S concentrations were at least two times higher on gypsum-treated soils (13.9 and 10.9 g S kg−1
in ST and LT-gypsum, respectively) compared with CT (4.62 g S kg−1 ) (Figure 2).
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Table 1. Probability levels for testing of treatment effects calculated from analysis of variance of alfalfa root dry weight and chemical properties of two Ohio soil series
treated with three levels of gypsum.
pH
P-Bray 1
TC †
EC
Ca
Mg
K
Total-S
SO4 -S
Root Dry Weight
0.629 ‡
0.030
0.990
0.118
<0.001
0.333
0.0003
<0.0001
<0.0001
0.139
0.959
0.997
0.002
0.005
0.696
0.0004
<0.0001
0.028
0.173
0.141
0.550
0.0001
0.0007
<0.0001
0.814
0.698
0.955
<0.0001
0.045
<0.0001
0.239
0.005
0.934
0.246
<0.0001
0.112
<0.0001
<0.0001
<0.0001
0.528
0.954
0.904
<0.0001
<0.0001
0.035
0.0009
0.004
0.002
0.060
0.001
0.018
0.012
0.0001
0.082
0.680
0.958
0.979
<0.0001
<0.0001
<0.0001
Soil
Brookston
Gypsum
Depth
Gypsum Depth
Celina
Gypsum
Depth
Gypsum Depth
†
TC= Total carbon, EC=Electrical conductivity; ‡ All values were compared to an alpha of 0.05.
Table 2. Total (C) and macronutrients (Ca, Mg, K and S) in two Ohio soil profiles receiving three levels of gypsum.
Soil/Depth
cm
Brookston
0–20
20–40
40–60
60–75
Celina
0–20
20–40
40–60
60–75
†
TC †
Ca
Mg
K
S
g·kg−1
g·kg−1
g·kg−1
g·kg−1
g·kg−1
CT a
19.0 aA‡
13.6 bB
12.0 aB
7.1 bC
ST
20.5 aA§
20.6 aA
6.7 bB
3.5 cB
LT
17.7 aA
14.9 bA
13.2 aB
11.8aB
CT
2.37
3.03
2.56
2.28
ST
2.66
3.76
3.39
2.85
LT
2.61
3.11
3.18
2.85
CT
4.64 bC
8.31 aA
8.31 aA
7.65 aB
ST
6.05 aC
7.41 bB
8.04 bA
7.19 bB
LT
2.96 cC
5.06cB
7.09 cA
7.32 bA
CT
1.49
1.42
1.23
1.24
ST
1.53
1.12
0.88
0.86
LT
1.30
1.12
1.24
1.28
CT
4.47 bA
2.84 cB
2.07 cC
2.10 bC
ST
5.25 aA
4.60 aB
3.34 aC
2.54 aD
LT
3.77 cA
3.93 bA
3.00 bB
2.85 aB
12.2 aB
4.4 cC
3.4 cC
30.6 bA
11.3 aC
31.9 aB
44.1 aA
46.0 aA
13.0 aC
6.9 bD
22.7 bB
47.8 aA
1.14 aA
1.20 cA
1.88 cA
1.69 bA
1.76 aC
2.04 aBC
3.07 aAB
3.19 aA
1.52 aC
1.59 bC
2.10 bB
3.21aA
2.25 bC
4.28 aB
7.78 aA
4.19 aB
4.92 aA
5.32 aA
3.05 bB
1.77 bC
1.87 bC
2.51 bB
3.38 bA
1.61 bC
0.67 bB
0.67 bB
0.87 aA
0.52 aC
1.22 aA
0.80 aB
0.43 cC
0.42 bC
0.70 bA
0.65 bA
0.52 bA
0.26 cB
2.51
1.65
5.44
8.86
2.73
2.06
23.6
27.1
2.67
2.47
11.8
26.8
CT = control, no gypsum application; ST = four years of gypsum application at 1680 kg·ha−1 ·year−1 , totaling 6720 kg·ha−1 , and LT = 12 years of gypsum application at 1680 kg·ha−1 ·year−1 ,
totaling 20,200 kg·ha−1 , TC= Total carbon; ‡ Means followed by the same lower case letter or no letter in a row between treatments for each chemical variable are not significantly different
by Tukey test at p < 0.05; § Means followed by the same upper case letter or no letter in a column for each treatment on each chemical variable are not significantly different by Tukey test at
p < 0.05.
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3.5
3.5
Brookston
a
a
3.0
b
b
b
b
2.5
Ca (g kg )
2.5
-1
-1
Ca (g kg )
a
Brookston
a
3.0
2.0
1.5
2.0
1.0
1.0
0.5
0.5
0.0
ab
1.5
a
0.0
CT
ST
0-20
LT
20-40
Gypsum treatment
60-75
40-60
Soil Depth (cm)
Figure 1. Calcium means values of Brookston soils in for each gypsum treatment (left) and in each
soil layer (right). Means followed by the same letter or no letters for each soil and soil layer are not
significantly different by Tukey’s test at p < 0.05.
16
25
Celina
Celina
a
14
a
a
12
10
-1
S (g kg )
-1
S (g kg )
20
8
6
b
15
b
10
a
b
4
5
c
2
c
0
0
CT
ST
0-20
20-40
60-75
40-60
LT
Gypsum treatment
Soil Depth (cm)
Figure 2. Sulphur mean values of Celina soils for each gypsum treatment (left) and in each soil layer
(right). Means followed by the same letter or no letters for each soil and soil layer are not significantly
different by Tukey’s test at p < 0.05.
No differences in soil pH were observed among gypsum treatments for each soil depth (Table 1);
although pH increased with depth in both soils (p = 0.03)
long-term surface
− (Table 1, Figure 3). Also,
−
applications of gypsum to Brookston (0.36 dS m−1 ) and− Celina (0.39 dS m−1 ) −−soils did not result in
significantly different EC values compared to CT soils (0.54 and 0.46 dS m−1 for −Brookston and Celina,
respectively) (Table 1). Studies by Farina and Channon [24], Toma et al. [17], and Caires et al. [25] found
minimal or no effect on soil pH when gypsum was applied to soil systems dominated by permanent
charges. Bray-1 P was statistically different for soil depth in both soils (p < 0.001) (Table 1). The highest
Bray-1 P was found at the 0–20 cm depth of both soils (Figure 4). However, values decreased with
depth in both soils (Figure 4).
8.5
8.5
Celina
Brookston
8.0
8.0
7.5
7.5
a
pH
pH
ab
7.0
7.0
a
6.5
6.5
ab
6.0
b
b
6.0
ab
b
5.5
5.5
0-20
20-40
40-60
Soil Depth (cm)
60-75
0-20
20-40
40-60
60-75
Soil Depth (cm)
Figure 3. pH values of Brookston and Celina soils in each soil layer. Means followed by the same letter
or no letters for each soil and soil layer are not significantly different by Tukey’s test at p < 0.05.
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40
40
a
Brookston
Celina
P (mg kg )
30
-1
-1
P (mg kg )
30
20
b
10
20
a
10
b
b
b
c
c
0
0
0-20
20-40
40-60
0-20
60-75
20-40
40-60
60-75
Soil Depth (cm)
Soil Depth (cm)
Figure 4. Phosphorous (P) concentration of Brookston and Celina soils in each soil layer. Means
followed by the same letter or no letters for each soil and soil layer are not significantly different by
Tukey’s test at p < 0.05.
For total carbon, the interaction of gypsum treatment by depth was statistically significant
(p < 0.0001) in both soils (Table 1). In the Brookston soil, higher TC values were found for the
−
ST-gypsum treatment in the 0–20 and 20–40 cm depths (TC >20.0 g kg−1 ) but values decreased
−
−
dramatically below 40 cm (TC <6.7 g·kg−1 ) when compared with the other two treatments
(13 < TC > 7 g·kg−1 ) (Table 2). No consistent response of TC was observed in the surface soil layer for
the gypsum-treated Celina soil (Table 2). However, ST and LT-gypsum treated Celina soils had higher
TC (4.60 and 4.78%, respectively) for the deeper horizons (60–75 cm) when compared with CT soils at
the same depths (3.06%) due to presence of calcium carbonates. Soil under the LT-gypsum treatment
had higher calcite (calcium carbonates) content as a percentage (%) of total C (8.1 ± 1.1) than the soil
under the ST-gypsum treatment (3.9 ± 0.3) and CT soil (1.3 ± 0.2) [23]. Wang and Anderson [26] found
applying water with high electrolyte concentration due to presence of gypsum to a calcareous system
could increase the calcium concentration in solution above calcite equilibrium, dissolve Ca, Mg and
carbonates under saturated conditions, and precipitate some of the dissolution products as secondary
carbonates under unsaturated conditions.
Lower concentrations of exchangeable K were observed at depths below 40 cm in both gypsum
treatments in the Celina soil compared with the CT treatment (Table 2). No statistical difference
was observed for exchangeable K in Brookston soil (Table 1). For exchangeable Mg, the interaction
of gypsum treatment by depth was statistically significant in both soils (Tables 1 and 2). Lower
concentrations of exchangeable Mg were observed in LT-gypsum treated Brookston soil compared
with CT (Table 2). Although, in Celina soils, lower concentrations of exchangeable Mg were observed
at depths below 40 cm in both gypsum treatments in the Celina soil compared with the CT treatment
(Table 2). Lower concentrations of exchangeable K and Mg are likely due to Mg and/or K replacement
on the exchange sites by Ca. It resulted in reductions in exchangeable Mg and K, mainly in the upper
part of the profile [9,24,27].
2.2. Plant and Root Responses
The average cumulative dry weight and average plant height for the Brookston soil were
−
−
2561 g·m−2 and 17.2 cm, respectively; and for Celina soil were 1,820 g m−2 and 14.4 cm, respectively.
However, no significant difference among treatments (p > 0.28) was observed for both soils. A similar
result for yield was found by Sloan et al. [20] where FGDG applied to alfalfa in the upper Midwest
(i.e., Minnesota, Wisconsin, Michigan, North and South Dakota, Indiana, Illinois, Iowa, and northern
−
Ohio) at agronomic rates (up to 3,750 kg ha−1 ) did not affect yield, but increased the S content of alfalfa
plants relative to alfalfa grown on untreated soil. In addition, O’Leary and Rehm [28] found alfalfa dry
weight was not affected by gypsum application on silt loam soils in Wisconsin. The higher Brookston
plant yield and height were attributed to the Brookston soil having a more optimum amount of K for
−
plant growth. The optimum soil K for most crops in Ohio is 100 to 200 mg·K·kg−1 soil [29], and alfalfa
−
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has a particularly high K requirement [22]. We found that in the Brookston soil-K concentration was
higher than 100 mg·kg−1 in all treatments in the first 40 cm of soil (Table 2). However, for the Celina
soil, the CT and LT gypsum treatments resulted in soil K concentrations that were lower than the
optimum in the 0–20 cm soil depth.
Total root biomass for alfalfa in each soil was significantly improved by gypsum application
(Tables 1 and 3). However, the positive gypsum effect on root biomass was mostly restricted in the
0–10 cm soil depth where approximately 60% of the root biomass occurred (Table 3). At deeper depths,
there was no significant effect of gypsum. In our experiment, water was not limited. Thus, root
exploration into deeper soil layers was not stimulated by drought conditions (Table 3). The increased
root biomass in the 0–10 cm depth would likely have made uptake of nutrients from this nutrient rich
soil layer more efficient. If gypsum had stimulated root growth deeper into the soil profile during
drought conditions, as reported by Wendell and Ritchey [30], then the combination of improved
nutrient and water uptake brought about by improved rooting depth with gypsum additions may lead
to crop yield increases [31].
Table 3. Root dry weight per depth and total of alfalfa plants grown in a greenhouse for 180 days in
intact cores of two Ohio soils treated with three levels of gypsum.
Soil/Depth
CT †
Brookston
0–10
10–20
20–40
40–60
60–75
Total ¶
Celina
0–10
10–20
20–40
40–60
60–75
Total
ST
LT
kg·m−3
cm
83.3 b‡ A
43.3 aB
19.1 aC
12.1 aC
4.7 aC
162 b
110 aA§
62.0 aB
14.9 aC
9.9 aC
4.2 aC
201 a
129 aA
59.9 aB
13.2 aC
12.0 aC
4.7 aC
219 a
70.0 bA
41.0 aB
10.0 aC
12.0 aC
4.5 aC
138 b
76.0 bA
46.0 aB
9.9 aC
8.6 aC
3.9 aC
144 b
125 aA
55.5 aB
12.0 aC
4.9 aC
4.7 aC
202 a
† CT = control, no gypsum application; ST = four years of gypsum application at 1680 kg·ha−1 ·year−1 , totaling
6720 kg·ha−1 , and LT = 12 years of gypsum application at 1680 kg·ha−1 ·year−1 , totaling 20,200 kg·ha−1 ; ‡ Means
followed by the same lower case letter or no letter in a row between treatments are not significantly different by
Tukey test at p < 0.05; § Means followed by the same upper case letter or no letter in a column for each treatment
are not significantly different by Tukey test at p < 0.05; ¶ Total root dry weight for the root samples collected from
0–75 cm soil depth.
2.3. Alfalfa Nutrient and Trace Element Concentrations
2.3.1. Major Nutrients
Calcium is an important nutrient for good root growth [17,32], especially responsible for
strengthening cell walls and for developing root tips (Fisher, 2011). Calcium concentrations in
gypsum-treated soils (Table 2) were higher compared with CT soils in both soil series but alfalfa
tissue Ca concentrations were not statistically different (p > 0.05), even though large amounts of Ca
were added to the soil as gypsum (Table 4). A similar result for Ca concentration in alfalfa was found
by Chen et al. [22] when Wooster silt loam (Typic Fragiudalf) soil was treated with FGDG, ag-lime, or
left untreated. The authors attributed these opposite-to-expected results to the Ca uptake rate which
did not surpass the rate of plant growth and accumulation of this element in the plant tissue.
Higher tissue concentrations of S relative to the CT were measured in alfalfa receiving ST and LT
gypsum treatments in the alfalfa growing in the Brookston soil, but not the Celina soil (Table 4). This
result was not surprising as gypsum is an excellent source of S and its application to soil is expected to
be reflected in plant tissue, especially for crops growing in S-deficient soils. However, the addition of S
had no positive or negative effect on cumulative dry weight (Table 3).
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Table 4. Mean concentrations of major plant nutrients (Ca, K, Mg, P, S, and N) in alfalfa shoots grown
in a greenhouse at the end of harvest (180 days after planting) in intact cores of two Ohio soils treated
with three levels of gypsum.
Soil
Treatment †
Ca
K
Mg
P
S
g·kg−1
N
%
Brookston
CT
ST
LT
P>F
15.3 ‡
15.2
15.4
0.68
23.4 ab
27.2 a
22.2 b
0.035
3.60 a
3.63 a
3.18 b
0.006
2.88 b
3.62 a
2.94 b
0.002
4.34 b
4.69 a
4.78 a
0.005
4.76
4.82
4.74
0.82
Celina
CT
ST
LT
P>F
18.0
16.3
18.4
0.17
15.8 b
21.9 a
18.6 a
0.007
4.76 a
4.12 b
3.75 c
0.005
2.33
2.49
2.15
0.42
4.73
4.68
5.04
0.17
4.68
4.66
4.53
0.08
† CT= Control, no gypsum application, ST = 4 years annual gypsum application (6,720 kg/ha total; 1,680 kg/ha
per year) and LT = 12 years annual gypsum application (20,200 kg/ha total; 1,680 kg/ha per year), and N= Total
nitrogen; ‡ Means followed by the same letter or no letters in a column for each soil are not significantly different by
Tukey’s test at p < 0.05.
Significantly higher K concentration was measured in alfalfa tissue for the ST treatment, compared
to the control, especially in Celina soil (Table 4). In the LT treatment, the tissue concentration of K in
alfalfa was maintained in the Celina soil (Table 4), even though the exchangeable K concentrations in
the soil were decreased by gypsum and soil depth (Table 2). The gypsum seemed to have displaced the
K and made it more available to alfalfa. For Mg, lower tissue concentrations were generally observed
in alfalfa growing in both the gypsum-treated Brookston and Celina soils, compared to the CT (Table 4).
Similar results were found by Chen et al. [22] where the Mg concentration in alfalfa tissue significantly
decreased when soil was treated with FGDG containing vermiculite and slightly decreased when
treated with FGDG by-products containing perlite compared to control. The rate of Mg uptake tends
to be depressed by its competition with cations such as Ca, K, and Mn [22,33].
No statistical difference (p > 0.05) was found among treatments in both soils for alfalfa tissue
N (Table 4). A lower tissue P concentration was found for the LT treatment (2.94 g·kg−1 ) compared
with the ST treatment (3.62 g·kg−1 ) in the Brookston soil. No statistical difference was found among
treatments in the Celina soil. Alfalfa plants growing in the Celina soils were slightly P deficient
(<2.6 g·P·kg−1 ) based on the critical tissue ranges given by Pickerton et al. [34]. The possible P
deficiency is important to note because there has been concern expressed that gypsum may reduce
available P for plant uptake, but this seems not to be the case for Celina soils. Brauer et al. [35] found
that gypsum did not change soil test P values.
2.3.2. Selected Elements
The FGDG provided B (~26.7 mg·kg−1 ), an essential element for plant growth, so that higher B
concentrations were found in alfalfa receiving ST and LT gypsum treatments in each soil (Table 5).
Alfalfa growing in gypsum-treated soil had greater tissue B concentrations than alfalfa growing in soil
that received no gypsum (Table 5); however, these concentrations were not considered phytotoxic [36].
Jones et al. [37] reported that alfalfa leaf concentrations above 30 mg·kg−1 were sufficient for alfalfa.
Concentrations of Cu, Mn, Mo, and Zn in alfalfa tissue (Table 5) were affected by the gypsum
treatments and within accepted concentrations for healthy plants in Brookston soil [33]. In the case of
Cu and Mn, the concentrations were lower under LT and ST application of gypsum compared to CT
treatment (Table 5). Higher concentrations of Mo and Zn were found in alfalfa grown in the Brookston soil
that received the ST gypsum treatment. Although there were no statistically significant treatment-related
concentration differences for Cu, Mn, and Ni in alfalfa growing in the Celina soils (Table 5).
Alfalfa tissue Mo concentration was sufficient for plant growth (Table 5). Molybdenum
concentrations are particularly important to legumes because Mo is a constituent of the nitrogenase
enzyme. Adequate levels of Mo in aboveground alfalfa tissue have been reported to range from 0.15 to
1.30 mg·kg−1 [34].
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The Cu concentrations in alfalfa tissues were mostly below the critical deficiency levels (Table 5).
The critical deficiency level of Cu in vegetative plant parts generally ranges from 1–5 mg·kg−1 dry
weight, depending on plant species, plant organ, developmental stage and N supply [38]. Based
on Pickerton et al. [34], our plants might have experienced Cu deficiency (<4 mg·kg−1 ). In general,
the critical deficiency level in the youngest emerged leaf is less affected by environmental factors than
older leaves.
There were no significant differences among gypsum treatments for Al and Cr concentrations in
alfalfa (Table 5). Higher concentrations of Cd were found under ST-gypsum treated soils in Brookston
soil, while lower concentrations of Ba were found in alfalfa growing in the Brookston soil receiving
LT–gypsum (Table 5). There was no statistical difference among treatments for tissue Ba concentration
for alfalfa growing in the Celina soil (Table 5). Concentrations of As (1.28 mg·kg−1 ), Pb (0.77 mg·kg−1 ),
and Se (2.32 mg·kg−1 ) were below detection limits which are shown here in parentheses. Chen et al. [7]
found similar results to our outcomes for concentrations of Cr, Pb, and Se which exhibited no effect of
FGDG by-products or ag-lime treatments. However, plant Al, Ba and Cd concentrations significantly
decreased in alfalfa growing in plots treated with FGDG by-products or ag-lime.
3. Materials and Methods
3.1. Study Site
In late March to the beginning of April 2008, twenty-four, 30.5 cm i.d. and 75 cm long undisturbed
soil columns [schedule 40 polyvinyl chloride (PVC) pipes] were collected in a commercial farm
from two nearby soil series with three gypsum management systems (two soil series × three gypsum
treatments = six fields) in a uniform prime agricultural landscape in southwest Ohio, USA (39◦ 45′ 17′′ N,
84◦ 40′ 28′′ W). The soil series were Brookston (fine-loamy, mixed, superactive, mesic Typic Argiaquolls,
1% slope) and Celina (fine, mixed, active, mesic Aquic Hapludalfs, <6% slope) soil series associations
that are commonly found in the glaciated Ohio landscape and southeastern Indiana. Twelve columns of
each soil series were collected. Fields from both soil series had been managed by the farmer in a similar
cropping history since 1996, comprising rotations of corn (Zea mays L.) and soybean (Glycine max L.).
Only corn received annual fertilizer application (178, 43, 65, and 11 kg·ha−1 of N (Ammonium nitrate,
34-0-0), P (Monoammonium Phosphate, 11-52-0), K (Potassium oxide, 0-0-60), and S (Ammonium
thiosulfate, 12-0-0-26), respectively, during each April since 1996). The farm had been converted from
conventional (i.e., chisel tillage) to no-tillage cultivation in 1996.
The three gypsum treatments were: (1) control treatment (CT), no gypsum application;
(2) short-term treatment (ST), consisting of annual applications of gypsum at a rate of 1680 kg·ha−1
over the previous 4 years for a total of 6720 kg·ha−1 (i.e., since 2004); and (3) long-term treatment (LT),
consisting of annual applications of gypsum at a rate of 1680 kg·ha−1 for the previous 12 years for a
total of 20,200 kg·ha−1 . For the LT treatment, the first six gypsum applications were waste drywall
gypsum (WDG). The subsequent six applications of gypsum on the LT fields and all four applications
on the ST fields were made using FGDG. All gypsum applications for the ST and LT treatments were
applied each year during the month of December. Both WDG and FGDG were applied to the fields
using a double spinner lime spreader.
The FGDG was of high purity with <3% water insoluble residues and trace element concentrations.
The chemical contents of FGDG determined by Midwest Laboratories from samples collected from
Zimmer Station Wet FGDG By-Products (Station from where the farmer gets the FGDG) were 19.8,
0.02 and 16.2% for Ca, Mg and S, respectively; and the concentrations of P and B were 16.7 and
26.7 mg·kg−1 , respectively. Dontsova et al. [19] reported that WDG concentrations were 21.9, 0.22 and
18.9% for Ca, Mg and S, respectively. The waste drywall gypsum P and B concentrations were 51.6 and
7.3 mg·kg−1 , respectively. Also, Don Dontsova et al. [19] reported that FGDG had a smaller and more
uniform particle size (40 µm), a lower cost, and better flow characteristics than the WDG.
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Table 5. Mean concentrations of selected elements (Al, B, Ba, Cd, Cr, Cu, Fe, Mn, Mo, Ni, and Zn) in alfalfa shoots grown in a greenhouse at the end of harvest (180
days after planting) in intact cores of two Ohio soils treated with three levels of gypsum.
Soil
Treatment †
Al
B
Ba
Cd
Cr
Brookston
CT
ST
LT
P>F
298 ‡
649
437
0.49
27.3 b
33.9 a
36.4 a
0.012
27.1 b
30.3 a
21.4 c
0.0003
0.26 b
0.48 a
0.19 b
0.0013
0.71
1.05
0.64
0.55
Celina
CT
ST
LT
P>F
206
411
226
0.59
14.3 b
19.6 a
26.6 a
0.018
0.90
0.90
0.90
N/A
0.10
0.14
0.06
0.07
0.73
0.79
0.65
0.89
Cu
mg·kg−1
1.36 a
1.94 a
0.85 b
0.004
1.55
0.87
0.59
0.32
Fe
Mn
Mo
Ni
Zn
341
445
451
0.72
88.6 a
41.4 b
51.4 b
0.003
1.43 b
3.05 a
0.92 b
0.0001
4.10
3.25
3.60
0.093
341
445
451
0.72
300
446
367
0.74
76.2
77.9
73.8
0.79
1.65
0.73
1.26
0.11
2.89
3.05
2.31
0.19
300
446
367
0.74
† CT = Control, no gypsum application, ST = 4 years annual gypsum application [6720 kg/ha total; 1680 kg/ha per year] and LT = 12 years annual gypsum application [20,200 kg/ha total;
1680 kg/ha per year]; ‡ Means followed by the same letter or no letters in a column for each soil are not significantly different by Tukey’s test at p < 0.05.
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3.2. Field Sampling Prior Soil Columns Collection
Composite duplicate soil samples from each field were collected from four depths (0–20, 20–40,
40–60, and 60–75 cm) using a 3” regular auger, air-dried and sieved by hand through a 2-mm screen
prior to the collection of soil columns to characterize the soil. Exchangeable Ca2+ , Mg2+ , and K+
were extracted using 1 mol·L−1 NH4 OAc [39] and available P by Bray-1 extractant [40]. Soil pH
was measured in a 1:1 (v:v) soil–water mixture [41]. Total S was determined via inductively coupled
plasma spectrometry (ICP) (Teledyne Leeman Labs Prodigy Dual, Hudson, NH) after Perchloric acid
digestion [42,43]. Soluble Sulfate-S was measured by ion chromatography (Dionex DX 120, Sunnyvale,
CA, USA) following monocalcium phosphate extraction [44]. Soil electrical conductivity (EC) was
determined in a 1:5 (v:v) soil–water suspension [45]. Triplicate soil samples from each treated field
area and soil depth were used to measure total C (TC) via the combustion method [46]. Calcium
carbonate equivalence (CCE) were measured by the gasometric method of Dreimanis [47] employing a
Chittick apparatus.
3.3. Soil Column Collection
Four columns from each of the three gypsum treatments for two soil series (a total of 24 columns)
were collected from the commercial farm using a free standing, portable hydraulic ram designed by
Hutton et al. [48]. The hydraulic ram was powered using a tractor mounted 775–900 kg skid loader
(model 317, John Deere Manufacturing Company, Moline, IL, USA) with closed-center configuration
as described in Tirado-Corbalá et al. [23]. All samples in each site were collected within a close
geographical radius of 0.25 km to reduce possible spatial variability. Once the PVC pipes were inserted,
a backhoe was used to dig a trench between two lines of columns and the columns lifted from the soil.
Once all the soil columns were lifted, excess soil from each column was removed from the outside of
the PVC pipes followed by the installation of an end cap with 5–7 cm layer sand to prevent compaction
or any disturbance of the soil during transportation. The secured soil columns were loaded onto a
truck and transported to a greenhouse at The Ohio State University, Columbus, OH.
3.4. Alfalfa Greenhouse Experiment Using Collected Soil Columns
Although 24 soil columns were moved to the greenhouse, damage to some columns resulted in
only 18 columns being used for the soil columns study (July 2008 to January 2009). A block factorial
design was used, that included all combinations of three gypsum treatments (CT, ST, and LT), two soils
(Celina and Brookston), and three replicates. Treatments were randomized within each replicate
block. “Evergreen-3” alfalfa was grown from 200 seed column−1 planted on July 1, 2009, that was
subsequently thinned to 150 seedlings column−1 . This was approximately double the rate for a field
planting due to the short-term nature of this experiment, in which plants did not attain the full size
that might be expected from mature field plants. Alfalfa seed had been pretreated with a commercial
preparation of Sinorhizobium meliloti to ensure nodulation.
For the first three-month growing period (July–September, 2008), water was applied in the
greenhouse at the same rate as the daily average precipitation was calculated using 30 years of data.
Climatological data for Eaton, OH, the closest weather station to the fields where the soil columns were
collected, were obtained from the National Oceanic and Atmospheric Administration (NOAA). For the
subsequent three months (October–December, 2008), water was applied at four times the average
30-year precipitation rate to simulate wetter conditions and greater leaching. A total of 2063 mm of
water was applied to each soil column during the six-month period.
Natural illumination was used from July to October 2008 and artificial illumination was used
from 14 October 2008 to 20 January 2009 to provide a minimum day length of 14 h. Temperature was
recorded during the research period to ensure the greenhouse temperature was 23.0 ± 2.0 ◦ C.
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3.5. Alfalfa Analysis
Alfalfa yield was measured six times during the study (2008–2009) as total aboveground
(5-cm cutting height) dry biomass per column. The first harvest was performed at the first flowering.
Five subsequent harvests were made at about 35-d intervals. Alfalfa height was recorded the day
before each harvest. Alfalfa tissue from each harvest was dried at 60 ◦ C for 4 d and weighed to
determine dry weight harvest−1 and total dry weight summed across all six harvests. At 180 days after
seeding alfalfa (harvest #6), plant tissue (10 g) from each soil x gypsum treatment combination was
grounded to pass through a sieve with 0.1 mm openings and analyzed for P, K, Ca, Mg, S, Fe, Mn, Al,
Na, B, Cu, Mo, and Zn by ICP spectrometry (Teledyne Leeman Labs Prodigy Dual view ICP Hudson,
NH) after Perchloric acid digestion [43]. Total N and C were determined by combustion analysis.
After the sixth harvest, two of the three columns of each treatment were vertically bisected, using
a reciprocating saw, to allow roots to be sampled for measurement of root biomass. Soil from one
half of each vertically bisected column was sectioned into five horizontal depth increments (0–10,
10–20, 20–40, 40–60, and 60–75 cm). The roots within each section were gently washed free of soil
with tap water and given a final rinse with deionized water. Later, the cleaned roots were dried at
65 ◦ C in a paper bag and weighed to determine the dry mass per depth, and total dry mass of each
column/treatment.
3.6. Statistical Analysis
For statistical purposes, the gypsum application duration (i.e., 0, 4, or 12 years) was treated
as being randomly assigned to field areas and variability was assumed to be primarily due to soil
and gypsum rate. For soil chemical properties analysis and root dry weight (per depth), gypsum
treatment (0, 4, or 12 years duration) and soil depth increment were treated as fixed factors and
replicate was considered as random factor. The analysis of variance (ANOVA) was performed by soil.
The alfalfa growth response variables that were statistically analyzed, as affected by treatments in
the soil columns, were cumulative plant dry weight, plant height, total root dry weight, and alfalfa
shoot nutrient concentrations. The ANOVA and Tukey’s test (p < 0.05) for mean comparisons were
performed using the Statistical Analysis System JMP Version 9.0 (SAS Institute, Cary, NC, USA).
4. Conclusions
In summary, the increased root mass stimulated by the gypsum addition suggests that under
water and/or nutrient limiting conditions, the alfalfa would respond favorably to gypsum application.
Positive soil fertility and alfalfa growth responses were observed, but the responses were not strong
or always consistent across the two soils or under the different total amounts of gypsum application.
Application of gypsum had no measurable effect on alfalfa yield and generally little effect on
macronutrient status, except for increased S uptake. Also, because gypsum is an excellent source of S,
the application of gypsum to soils where availability of this element is limited should lead to improved
alfalfa production.
Acknowledgments: The authors would like to thank Delk Crosier for access to his farm and to Ag-Spectrum
Company, and especially to Cliff Ramsier, for financial support of some aspects of this study. Likewise, the Ohio
Coal Development Office (Columbus, OH) supported a portion of this research. The senior author thanks
Joseph Ringler and Pall Kolka for their assistance with the fieldwork and Larry Brown for access to the hydraulic
ram used for core collection. Sandy Jones provided expert technical assistance in the Soil Characterization
Laboratory at The Ohio State University.
Author Contributions: Rebecca Tirado-Corbalá designed the experiment with feedback from Brian K. Slater,
Warren Dick, David Barker and Edward McCoy. Rebecca Tirado-Corbalá conducted all the field and greenhouse
samplings and analysis of the experimental work with the feedback from Brian K. Slater, Warren Dick,
David Barker. Rebecca Tirado- Corbalá wrote the manuscript, and all the authors revised it.
Conflicts of Interest: The authors declare no conflict of interest.
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