Effects of four soil surfactants on four soilwater properties in sand and silt loam
T.L. Mobbs, R.T. Peters, J. Davenport, M. Evans, and J. Wu
Abstract: Soil surfactants are wetting agents designed to improve infiltration, water distribution, and water retention. This industry-independent study evaluates the effects on soil-water
properties of four surfactants commonly used in the Pacific Northwest: Wet-Sol #233
(Schaeffer), WaterMaxx II (Aquatrols/Western Farm Services), Ad-Sort RST (Simplot), and
ADVANTAGE Formula One (Wilbur-Ellis). These surfactants were tested at labeled rates
on two sifted soils with no known water repellency issues: a Warden silt loam and a Quincy
sand. No significant differences were found among the means of treatment variables of any of
the surfactants or the control (irrigation water only) in the tests of infiltration rate and water
holding capacity, at a significance level of α = 0.05. Significant differences were found for
the tests of unsaturated hydraulic conductivity (p = 0.009) and capillary rise (p = 0.048) in
the sand samples only. Lower unsaturated hydraulic conductivity was inferred from the results
for Wet-Sol samples compared to the control and all other samples. Additionally, Formula
One performed significantly better than Wet-Sol and Water Maxx in unsaturated hydraulic
conductivity, but differences compared to the control were insignificant. In capillary rise tests,
the rise height of samples treated with WaterMaxx, Ad-Sorb, and Formula One were significantly lower than that of the control samples. Hence, the use of surfactants did not benefit
water penetration or soil-water distribution (up to 24 hours) according to the statistical tests
on the four soil physical properties. Furthermore, the surfactants did not perform consistently
across the different experiments.These findings indicate that a single application of these four
anionic, nonionic, and block polymer surfactants does not improve the movement and conservation of soil-water in these hydrophilic soils.
Key words: hydraulic conductivity—soil surfactants—water holding capacity—water infiltration
Since the 1960s, researchers have investigated using surfactants in soils to combat
common problems of water penetration
and distribution in the soil matrix, but
data are still lacking for making clear recommendations. Agricultural surfactants are
well known as “spreaders and stickers” that
help fertilizers, pesticides, and soil conditioners spread through the soil matrix, sorb to soil,
or adhere to plant leaves (Ishiguro and Fujii
2008). However, a subgroup known distinctly
as soil surfactants has achieved varied levels of
success in improving water infiltration (Feng
et al. 2002), preferential flows (Oostindie et
al. 2008), runoff and excess channel seepage
(Lentz 2003, 2007), and water use efficiency
(Starr et al. 2005; Cooley et al. 2009).
The structure and function of the molecules of the wide number of surfactants
273
JULY/AUGUST 2012—VOL. 67, NO. 4
vary widely, yet all possess a hydrophilic
“head” group and a hydrophobic “tail” group
(Karagunduz et al. 2001). Their heads bond
strongly with water, while their tails adsorb to
surfaces such as clay minerals, air molecules in
pores, or hydrophobic organic substances in
soil (Kuhnt 1993;Tumeo et al. 1997).The net
effect is an apparent lowering of the interfacial tension between air-water and soil-water
surfaces (Rosen 1989; Karagunduz et al.
2001). This is especially noticeable when the
soil particles have hydrophobic, or water
repellent, coatings (Doerr et al. 2007; Kostka
et al. 2007; Hallett 2008). Surfactants can
thus help some surfaces wet more easily. Soil
surfactants used as wetting agents are both
anionic and nonionic, with nonionic surfactants showing stronger and longer-lasting soil
sorption (Kuhnt 1993; Park and Bielefeldt
PROOF—NOT FOR DISTRIBUTION
2003). Block polymers are a class of nonionic
surfactants specially formulated to enhance
the surfactant’s sorption to soil and remain
active in the soil matrix longer than other
nonionic surfactants (Schmoka 1977).
Laboratory tests have shown soil surfactants to affect infiltration rates and flow
patterns. Vertical infiltration rates increased
with the concentrations of two commercial
soil surfactants applied to water repellent soil
(Feng et al. 2002). In horizontal soil columns,
flow was induced in direct proportion to
surfactant concentration (Henry et al. 1999,
2001; Bashir et al. 2008). Nonionic AquaGro
L (Aquatrols Corp., Cherry Hill, New Jersey)
produced a uniform, 11 cm (4.3 in) wetting front in a chamber of mixed sands that
previously showed preferential flow paths
(Nektarios et al. 2002). Golf course soil cores
treated with an Aquatrols copolymer showed
complete wettability over two years, while
untreated cores showed significant water
repellent regions interspersed with wettable
regions (Oostindie et al. 2008).
Researchers have reported both increases
and decreases in hydraulic conductivity due
to surfactants, and the mechanisms of action
have been debated since 1969 (Tumeo 1997).
Researchers have postulated that surfactants
either increase or decrease aggregate stability in soils, depending on soil composition
(Tumeo 1997). Although the surface tension
reduction achieved by surfactants should
in theory increase hydraulic conductivity, decreases in hydraulic conductivity are
reported often in literature. Studies of 4
anionic and 11 nonionic surfactants showed
reductions in hydraulic conductivity of up to
two orders of magnitude in loamy soils and
up to 58% in sand (Allred and Brown 1994,
1995). Adsorption isotherms for nonionic
Soil Penetrant 3685 and Aqua Gro indicated
that hydraulic conductivities decreased at
higher surfactant concentrations near the
critical micelle concentration in hydrophoTamara L. Mobbs is a science consultant with
Enjoy Water Company and works from Pullman,
Washington. R. Troy Peters is an extension irrigation specialist and assistant professor, and
Joan Davenport is a professor of soil science for
the Irrigated Agriculture Research and Extension
Center, Washington State University, Prosser,
Washington. Marc Evans is a professor in the
Department of Statistics, and Joan Wu is a professor in Biological Systems Engineering, Washington State University, Pullman, Washington.
JOURNAL OF SOIL AND WATER CONSERVATION
bic samples, but no changes were observed
in hydrophilic samples (Miller et al. 1975).
Surfactants often produce the opposite effect
on the hydraulic conductivity of waterrepellent soils than is seen in hydrophilic soils
(Tumeo 1997).
Direct changes in water content have
also been observed after surfactant applications. Higher volumetric water content was
observed in soil cores treated with a nonionic
copolymer compared to untreated cores
(Oostindie et al. 2008). The anionic polymer
XPAM increased water retention: seepage rates decreased with increasing XPAM
dosages in five soil types (Lentz 2007). A soilremediation surfactant that was formulated
to increase drainage, Triton-X, produced
the opposite effect by substantially reducing
soil water content (Karagunduz et al. 2001).
Adding an anionic surfactant to seed-germinating growth media increased the media’s
total water holding capacity in proportion
to surfactant dosage, and the available water
increased significantly after the application
of surfactant (even at the lowest dose) to the
media (Urrestarazu et al. 2008).
Capillary rise was found to decrease
significantly when anionic and nonionic surfactants were tested in sand columns, with
the decrease in direct proportion to surfactant concentration (Wiel-Shafran et al. 2006).
Capillary rise significantly decreased in loam
and sandy loam columns treated with an
anionic surfactant, while the solid-liquid
contact angle increased; in the same study,
no significant impacts were observed for a
nonionic surfactant (Abu-Zrieg et al. 2003).
Upward infiltration rates and contact angles
were affected differently in different materials
when tested with varying concentrations of
anionic surfactant (Ishiguro and Fujii 2008).
In hydrophilic sand and glass, the upward
infiltration rate decreased with increasing
concentration due to surfactant adsorption.
In hydrophobic peat moss and polyethylene particles, contact angles decreased with
increasing surfactant concentration until
they were similar to those of the hydrophilic
materials, indicating that the hydrophobic
materials grew increasingly wettable; the
upward infiltration rates increased as the
contact angles became smaller (Ishiguro and
Fujii 2008).
In the field, positive results have been seen
in hydrophobic turfgrass and potato plots.
Severe dry spots were reduced in 36 sandbased golf tees treated with an Aquatrols block
JOURNAL OF SOIL AND WATER CONSERVATION
polymer (Kostka 2000). Another Aquatrols
surfactant increased soil water uniformity
and overall water savings in a putting green
(Karcher et al. 2005). Regular monthly applications of surfactants consistently maintained
low dry spot levels in turfgrass (Miller 2002).
Pacific Northwest potato yields increased
significantly in hydrophobic soil plots treated
with an Aquatrols block polymer (O’Neill
2005). In two Wisconsin studies, researchers found that nitrate leaching was reduced
and water content and yields increased after
treating hydrophobic sands with surfactants
(Kelling et al. 2003; Lowery 2005).
In contrast, discouraging results were
found in several field studies involving other
cropping soils. The anionic soil conditioner
AgriSci (Four Star Agricultural Services
Inc., Bluffton, Indiana) did not significantly
improve the hydraulic conductivity, sorptivity, water retention, organic matter content,
or 48-hour aeration porosity over two years
of observation in a fallow silt loam plot with
incorporated corn residue (Fitch et al. 1989).
An Aquatrols and an Advantage surfactant
achieved no significant increases in water
contents or pinto bean yields in Southwestern
sandy loam plots (O’Neill 2005).Three nonionic wetting agents advertised to improve
nutrient availability and crop yield (WEX,
Basic H, and Amway Spray Adjuvant) were
tested in Wisconsin corn, soybean, and
potato plots (silt loam and loamy sand); over
several years of study, no significant increases
in crop yields, crop protein levels, or foliar
nutrient content of N, P, and K were found
in surfactant-treated crops (at varying application rates) compared to untreated crops
(Wolkowski et al. 1985). Additional studies
were included in a review of wetting agents
in which surfactants did not significantly
increase the yield or nutrient content of
corn, potatoes, soybeans, wheat, and grain
sorghum (McFarland et al. 2005).
While all the studies reporting positive results were conducted in problematic
hydrophobic soils, the wettability or hydrophobicity of the soils in the other field studies
was not discussed. A review of wetting agents
for the Cooperative Extension Services of
10 Midwestern states warns growers against
“blanket endorsements” of surfactants that
do not specify soil or other field conditions
that may alter the effectiveness of the agents
(Sunderman 1988). Sunderman (1988)
reports two of his own research studies and
reviews several other studies in which wetting
PROOF—NOT FOR DISTRIBUTION
agents either produced no effect or adversely
affected the wetting of hydrophilic soils.
Sunderman reasons that the reduction in capillary rise produced by surfactants in normally
wettable soils may actually lower the infiltration of water into hydrophilic soil pores.
Many studies of soil surfactant effectiveness
are disseminated to the public online and in
printed brochures by private and university
researchers whose funding is often provided
by the surfactant manufacturers or distributers. As these studies are not published by
peer-reviewed journals, their conclusions do
not add to the published body of academic
research knowledge and their scientific validity may be called into question by skeptical
growers and researchers.
The objective of this study was to evaluate the effects of several soil surfactants on
infiltration rate, water holding capacity,
unsaturated hydraulic conductivity, and capillary rise in two wettable (nonwater repellent)
soils typically productive for high-value crops
in the United States Pacific Northwest. Our
null hypothesis (Ho) for each experiment is
equality of the mean values of each test variable across all surfactants treatments, while
the alternative hypothesis (Ha) is that at least
one mean value differs from the others.
Materials and Methods
Our study focused on typical soils used to
grow high-value crops of potatoes, onions,
dry/green beans, and vine/tree fruits in
Eastern Washington and Oregon, a Warden
Series silt loam and a Quincy Series sand.
The soil samples were air dried for approximately three months (at a mean temperature
of 30°C [86°F]) and were sieved (0.5 cm [0.2
in] mesh size) to ensure uniformity between
replications before all tests.
Four agricultural soil surfactants commonly marketed and used in Eastern
Washington and Oregon were tested as
described in table 1. The surfactants were
expected to be mixed with water for application to the soil via the regular method of
surface, drip, or sprinkler irrigation. To replicate this in the laboratory, a sample volume
of the surfactant, Vs, was calculated by scaling
down the median rate (qt ac–1) on the product label to the area-equivalent rate (µl cm–2)
for our 14.4 cm (5.7 in) diameter soil sample.
Treatment solutions were produced by mixing each sample volume of surfactant with
sufficient irrigation water (161 ml [5.4 fl
oz]) to wet the entire surface of a sample and
JULY/AUGUST 2012—VOL. 67, NO. 4
274
Table 1
Brand names, classifications, manufacturers, and amounts of the four surfactants applied in the experiments.
Chemical
Active
Surfactant
type
Manufacturer
ingredients
Surfactant
volume (Vs)
added to each
sample (µl)
Concentration
(%)
Wet-Sol #233
Nonionic
Schaeffer Manufacturing
Co. (St. Louis, Missouri)
25% Alkyl phenyl-hydroxy
polyoxyethylene
0.3% Polydimethyl-siloxane
11.5
0.007
WaterMaxx II
Block
polymer
Aquatrols Corp.
(distributed by Western
Farm Services,
Fresno, California)
30% Blend of
propanediol and
glycosides ingredients
7.66
0.005
Ad-Sorb RST
Reverse
block polymer
J.R. Simplot Manufacturing
Co., Plant Health
Technologies (Boise, Idaho)
10% Alkoxylated polyois
7% glucoethers
3.83
0.002
30% Ammonium
alkyl ether sulfate
1% Alkyl aryl polyethoxylates
0.72
0.0004
ADVANTAGE
Anionic
Wilbur-Ellis Co.
Formula One
(Fresno, California)
Note: Concentration = volumetric concentration (Vs ÷ 161 ml water).
Figure 1
Schematic of key elements in experimental setup for testing infiltration rate.
Marriotte reservoir
Marriotte siphon
Level of air-intake tube
Pond level
Soil level
(soil pretreated with surfactant)
Wetting front
penetrate the soil about 1 cm (0.4 in). Hence,
each soil sample was effectively treated as if
it were a small part of a large field receiving
the manufacturer-recommended surfactant
dosage. The sample volumes and treatment
solution concentrations after mixing with
water are included in table 1.
In total, the soil samples were subjected
to five treatments: four different surfactants
added to irrigation water and a control treatment of irrigation water without added
surfactant. Each variable (infiltration rate,
water holding capacity, etc.) was measured
on four replicate soil samples for each com-
275
JULY/AUGUST 2012—VOL. 67, NO. 4
bination of the five treatments and soil types
(i.e., 20 total samples for each soil type) in a
completely randomized design with a twoway treatment structure. In addition, the test
variables for infiltration rate, unsaturated
hydraulic conductivity, and capillary rise
were observed over time in order to model
temporal change.
Infiltration Rate. For the infiltration rate
experiments, 52 cm (20.5 in) of sifted soil
was added to each open plexiglass column
that was 14.4 cm (5.7 in) in diameter. Soil
was shaken from a cup and the columns lifted
and dropped regularly to ensure uniform set-
PROOF—NOT FOR DISTRIBUTION
tling of soil and consistency across samples. A
mesh screen with 0.04 cm2 (0.006 in2) holes
and filter paper that was 14.4 cm in diameter
with a 0.15 μm pore diameter was used to
retain the soil but allow liquid to drain into
a pan beneath the column stand. Prior to
the experiments, each surfactant was mixed
with 161 ml (5.4 fl oz) of water to produce
treatment solutions with the concentrations
reported in table 1. The surfactant treatment
solutions, or water alone for the control
treatments, were sprinkled on top of the dry
soil samples and allowed to penetrate.
Marriotte reservoirs that were 14.4 cm
(5.7 in) in diameter and 61 cm (2 ft) tall supplied tap water via siphons to the top of the
soil columns to maintain constant ponding
heights varying from 1.3 to 3.8 cm (0.5 to 1.5
in), depending on the heights of reservoir airintake tubes (figure 1). The reservoirs’ water
levels were recorded every 2 to 10 minutes,
depending on how rapidly the water infiltrated (infiltration rate decreased over time
and was higher for sand than for silt), until
drainage began and the siphons were removed.
The decline in reservoir water level over time
matched the rate that water infiltrated the soil.
The infiltration rate is theoretically described
by the Lewis-Kostiakov equation:
i(t) = bkt b–1 + fo,(1)
where i(t) is the infiltration rate (cm min–1)
versus intake opportunity time t (min), b
and k are empirical parameters, and fo is the
steady-state value (cm min–1) (Sepaskhah and
Afshar-Chamanabad 2002).
JOURNAL OF SOIL AND WATER CONSERVATION
Table 2
Calculated values of gravimetric water content (θm), volumetric water content (θv), and bulk density (Pb) for replicates R1 through R4.
Treatment
Replication
θm (g g–1)
θv (cm3 cm–3)
Ρb (kg m–3)
Silt loam samples
θm (g g–1)
θv (cm3 cm–3)
Ρb (kg m–3)
Sand samples
Wet-Sol #233
WaterMaxx II
Ad-Sorb RST
ADVANTAGE
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
R1
0.2800.399
1,425 0.1460.246
1,690
0.267
0.3851,439
0.154
0.2581,678
0.246
0.3601,455
0.153
0.2581,687
0.2330.345
1,479 0.1620.272
1,675
0.277 0.397
1,429 0.1400.237
1,692
0.2790.399
1,427 0.1470.246
1,678
0.2570.376
1,458 0.1410.239
1,689
0.288
0.4081,418
0.150
0.2541,682
0.2820.399
1,409 0.1420.241
1,701
0.280
0.3991,422
0.157
0.2651,682
0.306
0.4221,379
0.152
0.2541,672
0.2430.355
1,457 0.1620.272
1,675
0.274 0.397
1,446 0.1460.247
1,689
Formula One
Control
R2
R3
R4
R1
R2
R3
R4
0.2830.406
1,432 0.1650.275
1,661
0.282
0.4031,425
0.159
0.2681,678
0.2720.392
1,441 0.1610.270
1,678
0.2680.390
1,450 0.1460.249
1,697
0.2950.420
1,420 0.1610.272
1,685
0.3220.448
1,392 0.1610.270
1,675
0.3060.432
1,408 0.1580.264
1,670
Figure 2
Unsaturated hydraulic conductivity experimental setup.
Mini-disk infiltrometer
(containing treatment solution)
Water Holding Capacity. The water holding capacity of the different samples was
examined by weighing the columns before
and after the infiltration rate experiments.The
“dry” weight measurement was taken after the
columns were filled with dry soil and treated
with the 161 mL (5.4 fl oz) surfactant solution.
When the infiltration siphons were removed,
JOURNAL OF SOIL AND WATER CONSERVATION
Ruler
Solution level
the tops of columns were covered with foil
to prevent evaporation, and the bottoms were
covered when drainage ceased. After 48 hours,
the coverings were removed, and a second
“wet” weight was measured. The difference
between the wet and air dry weights (minus
the tare weight of the experimental apparatus
and weight of treatment solution) represented
PROOF—NOT FOR DISTRIBUTION
the mass of water (Mw) that the soil retained.
These measurements were used with the soil
column volume to calculate the volumetric
soil water content achieved after the different
treatments (table 2).
Unsaturated Hydraulic Conductivity.
Plexiglass columns that were 14.4 cm (5.7
in) in diameter were filled with dry soil to 8
cm (3.1 in) of depth in the same manner as
in the previous experiments. Mini-disk infiltrometers from Decagon Devices (Pullman,
Washington) that were 3.18 cm (1.25 in)
in diameter with a 100 mL volume (3.4 fl
oz) capacity supplied the treatment solution
in the same concentrations used previously
(table 1), and water levels were recorded
every 10 seconds for silt and every 5 seconds
for sand (figure 2).The solution did not penetrate to the bottom of the columns during
the experiments, so no drainage occurred.
Cumulative infiltration was represented by
the water level normalized by the infiltrometer’s cross-sectional area.
Tension infiltrometers have been used
by a number of researchers to determine
hydraulic conductivity from infiltration data
(Zhang 1997; Verbist et al. 2009). Based on
the Wooding analysis, the cumulative infiltration, I(t), in centimeters per second is (Zhang
1997;Verbist et al. 2009)
JULY/AUGUST 2012—VOL. 67, NO. 4
276
Figure 3
Capillary rise experimental setup.
Merriotte reservoir
(containing treatment solution)
Ruler
Rise
height
I(t) = C1t 1/2 + C2t.(2)
In equation 2, C1 (cm s–1) is related to sorptivity and C2 (cm s–1) is proportional to K
(cm s–1) as follows:
K (ho) =
C2
A2 ,(3)
where ho (cm) is the tension value of the
infiltrometer (i.e., matric potential at the disk
infiltrometer surface) and the dimensionless
A2 depends on van Genuchten parameters
under fixed soil conditions (Carsel and
Parrish 1988; Zhang 1997; Flury 2007).
Capillary Rise. Capillary rise was measured in open, transparent plastic tubes that
were 3.5 cm (1.4 in) in diameter and 30.5
cm (12 in) tall and filled with soil to the 23
cm (9 in) depth by the same filling method
described previously. A mesh screen with
0.04 cm2 (0.006 in2) hole area was used at
the bottom of each tube to retain the soil.
Marriotte bottles containing the treatment
solutions (at the concentrations reported in
table 1) were placed into uncovered pans that
were 5 cm (2 in) deep, and the soil columns
were placed into the ponds of treatment
solution in the pans (figure 3). As the solution was taken up by the soil, the Marriotte
reservoirs continuously resupplied the solution, and the heights of the rising wetting
fronts were recorded over time.
The Washburn equation characterizes
the vertical rise of the wetting front due to
capillary action (Ishiguro and Fugii 2008;
Matthews 2008; Shang et al. 2008). The
277
JULY/AUGUST 2012—VOL. 67, NO. 4
height of the wetting front in meters, x, is
related to contact angle, θ, as follows:
x2 =
Reff ϒL cosθ
t ,(4)
2η
where Reff is the effective pore radius of the
interparticle capillaries in the porous layer
(m), γL is the surface tension of the test liquid
(J m–2), η is the liquid viscosity (N s m–2), and
t is time (s) (Shang et al. 2008). Simplifying
this equation to represent the height versus
time gives:
x = at 1/2,(5)
Reff ϒL cosθ 1/2
, measured in meters.
2η
⎩
⎭
where a =⎧
⎫
In the experiments, columns were set in
the pan with care and held upward by standing tools. Before the first measurement could
be taken, the water had risen in the column a
small distance.To account for the rise height at
the time of first recording (t = 0), a second constant term, b (m), was added to the equation:
x = at1/2 + b.(6)
Equation 6 thus approximates the height of
the wetting front over time, and the parameter a was calculated to best fit equation 6 to
the measured data.
Statistical Analysis. Model parameters
for the nonlinear models were estimated
PROOF—NOT FOR DISTRIBUTION
by least squares for each replicate separately
using SAS NLIN, while SAS GLM was used
to compute the parameter estimates for the
linear models.The volumetric water content,
θv, was computed directly from the data for
each replicate. The mean values of the fitted
parameters (i.e., treatment variables b–1 for
the Lewis-Kostiakov model of infiltration
rate, C2 for the unsaturated hydraulic conductivity model, and a for the capillary rise
model [tables 3, 4, and 5]) and the mean values of the volumetric water content, θv, were
assessed for differences among the surfactant
treatments using one-way analysis of variance
(ANOVA) and Fisher’s LSD for pairwise
mean comparison. The level of significance
for each test was set at α = 0.05. SAS/STAT
Release 9.1.3 was used for all computations
(SAS Institute Inc., Cary, North Carolina:
2000 to 2004).
Results and Discussion
The overall ANOVA results and the comparison of means are presented in tables 6
and 7, respectively. For the experiments on
infiltration rate and water holding capacity, no overall significant differences among
treatments were found (table 6). No overall significant differences were found for
the unsaturated hydraulic conductivity and
capillary rise experiments in the silt loam
columns either. However, in the experiments
with sand columns, overall p-values indicated
significant differences among treatments for
the unsaturated hydraulic conductivity and
capillary rise (table 6).
For the unsaturated hydraulic conductivity, the mean values for treatment variable C2
were significantly different between Wet-Sol
and all other treatments (table 7). Since C2
is directly proportional to K (equation 3), it
may be inferred that the addition of Wet-Sol
decreased the unsaturated hydraulic conductivity of the samples to an extent that was
significantly different from the other samples’ unsaturated hydraulic conductivities,
including the control’s. In addition, unsaturated hydraulic conductivity of the samples
increased after the addition of Formula One
to an extent that was significant compared
to the Wet-Sol and WaterMaxx samples, but
not significant compared to the control and
Ad-Sorb samples.
Hence, the results indicate that adding
a surfactant does not improve unsaturated
hydraulic conductivity compared to using
water alone. Only Formula One is associated
JOURNAL OF SOIL AND WATER CONSERVATION
Table 3
Values that best fit the Lewis-Kostiakov equation (equation 1) to the data for the four replicates (R1 through R4) and the associated sum of squared
error (SSE) for each fit.
TreatmentReplication
bk
fo (cm s–1)SSE
b–1
bk
fo (cm s–1)SSE
b–1
Silt loam samples
Sand samples
Wet-Sol #233
WaterMaxx II
Ad-Sorb RST
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
10.6
0.94
0.96
0.41
0.61
0.54
0.82
0.68
1.20
0.93
0.59
8.40
−1.40
−0.60
−0.64
−0.41
−0.42
−0.42
−0.71
−0.47
−0.69
−0.53
−0.40
−1.40
0.064
0.016
0.018
0.024
0
0
0.036
0
0.032
0
0
0.054
0.35
0.007
0.001
0.001
0.01
0.01
0.01
0.01
0.01
0.03
0.02
0.003
2.2
9.2
4.4
2.7
2.03
3.7
1.8
6.7
1.5
4.9
2.4
3.0
−0.78
−1.08
−1.60
−0.54
−0.55
−1.06
−0.52
−1.10
−0.66
−0.77
−0.58
−0.95
0.18
0
0.43
0
0.11
0.40
0.025
0.20
0.19
0
0
0.30
0.02
1.2
0.06
0.14
0.22
0.17
0.11
0.02
0.1
0.07
0.03
0.03
ADVANTAGE
Formula One
Control
R1
R2
R3
R4
R1
R2
R3
R4
1.40
0.82
0.77
0.68
0.62
0.34
0.86
0.73
−0.78
−0.50
−0.58
−0.48
−0.47
−0.34
−0.52
−0.54
0.04
0
0.022
0
0
0
0
0
0.01
0.02
0.02
0.01
0.01
0.005
0.05
0.05
2.7
6.0
1.3
4.8
6.7
2.4
6.8
2.8
−1.00
−1.07
−0.27
−1.30
−1.70
−0.95
−1.40
−0.71
0.24
0.25
0
0.29
0.36
0.25
0.40
0.22
0.01
0.04
1.0
0.01
0.04
0.05
0.001
0.001
Table 4
Calculated values of C1 and C2, coefficients that best fit the cumulative infiltration equation (equation 2) to the data for replicates R1 through R4 with
associated sums of squared errors (SSE) for the unsaturated hydraulic conductivity tests.
TreatmentReplication
C1 (cm s–½)
Wet-Sol #233
WaterMaxx II
Ad-Sorb RST
ADVANTAGE
Formula One
Control
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
JOURNAL OF SOIL AND WATER CONSERVATION
C2 (cm s–1)SSE C1 (cm s–½)
Silt loam samples
C2 (cm s–1)SSE
Sand samples
0.3680.0180.80
0.7930.0680.68
0.371 0.0300.10
0.183 0.2300.61
0.343
0.035
0.070.245
0.188
0.35
0.342
0.027
0.410.211
0.171
0.25
0.3290.0210.58
0.0260.2920.34
0.3280.0200.48
0.3850.1820.50
0.321
0.040
0.130.275
0.231
0.86
0.374 0.0220.53
0.067 0.2980.52
0.281
0.037
0.080.186
0.290
0.26
0.2920.0290.53
0.2680.2100.25
0.333
0.041
0.140.133
0.292
0.23
0.344 0.0340.28
0.190 0.2930.12
0.338 0.0400.06
0.323 0.3230.11
0.388 0.0390.44
0.264 0.3020.11
0.309 0.0380.17
0
0.3990.02
0.291 0.0330.11
0.085 0.3340.17
0.3490.0301.16
0.0670.2960.92
0.316
0.031
0.460.117
0.158
1.08
0.313
0.041
0.140.153
0.272
0.06
0.328 0.0460.10
0.221 0.2950.07
PROOF—NOT FOR DISTRIBUTION
JULY/AUGUST 2012—VOL. 67, NO. 4
278
Table 5
Values of a and b that best fit the Washburn equation (equation 6) to the data and the sums of squared errors from the regression.
TreatmentReplication
a (cm s–½)
b (cm)
SSE
Silt loam samples
a (cm s–½)
b (cm)
SSE
Sand samples
Wet-Sol #233
WaterMaxx II
Ad-Sorb RST
ADVANTAGE
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
R1
2.322.83
9.76
3.673.10
13.1
2.39 2.897.11
3.19 3.807.95
2.72
1.03
7.593.01
5.18
8.96
2.39
3.70
9.103.31
5.04 14.0
2.600.52
12.0
3.252.80
5.30
2.83015.2
3.094.00
4.31
2.25
5.11
0.423.24
5.31 13.6
2.355.41
1.17
2.905.01
3.75
2.77
0
14.73.25
3.87 29.3
2.60
1.07
6.683.30
3.90 12.7
2.58
0.64
7.932.97
4.77
7.61
2.84
0.05 11.62.80
5.28 9.67
2.54 1.985.15
3.19 5.405.20
Formula One
Control
R2
R3
R4
R1
R2
R3
R4
2.295.21
5.56
3.025.86
7.22
2.52
1.67 11.43.18
4.65 2.98
2.44 0.723.89
2.93 6.726.18
2.65
0.62
2.903.76
1.19 13.1
2.76
0
7.293.68
4.40 35.6
2.74
0.60
6.204.00
2.01 31.6
2.700.13
4.83
3.046.49
9.74
Table 6
Probability results from the ANOVA for comparison of surfactant treatments (α = 0.05).
Experiment
Test variables
Infiltration rate
Power constant b–1 for Lewis-Kostiakov curve,
i(t) = bk t b−1 + Fo
0.50
0.52
Slope constant bk for Lewis-Kostiakov curve,
i(t) = bk t b−1 + Fo
0.54
0.81
Water holding capacity
Volumetric water content, θv
0.060.10
Unsaturated hydraulic
conductivity
C2 in cumulative infiltration curve,
I(t) = C1 t ½ + C2 t
0.08
0.01*
Capillary rise
* Statistically significant < 0.05
Slope constant a in Washburn equation,
x=at½+b
0.08
0.049*
with an increase in unsaturated hydraulic
conductivity, but that increase is only with
respect to those samples (treated with Wet-Sol
and WaterMaxx) that experienced decreased
hydraulic conductivity compared to the
control sample. Compared to the control,
Formula One did not significantly improve
unsaturated hydraulic conductivity, while
Wet-Sol, on the other hand, significantly
lowered unsaturated hydraulic conductivity
compared to the control.
For the experiments on capillary rise, the
mean value of the variable a was signifi-
279
Overall p,Overall p,
silt loam
sand
JULY/AUGUST 2012—VOL. 67, NO. 4
cantly higher for the control samples than
for WaterMaxx, Ad-Sorb, and Formula One
(table 7). Since a relates directly to the height
of the rising wetting front (equation 6), these
results indicate that the columns treated with
these three surfactants experienced a significant decrease in capillary rise compared to
the control samples.This finding is consistent
with previous studies of surfactant adsorption
in sand (Wiel-Shafran et al. 2006; Ishiguro
and Fujii 2008).
This study is limited to a single application of surfactant. Different results might be
PROOF—NOT FOR DISTRIBUTION
achieved under repeated water applications
or surfactant doses. Studies support the continual use of surfactants in water-repellent
soils, but data is lacking for hydrophilic soils.
In water-repellent sand previously treated
with surfactant, higher infiltration rates were
achieved in a rewetting experiment (Feng
et al. 2002). Other researchers recommend
the use of surfactants with strong adsorption to gradually convert hydrophobic soil
particles to hydrophilic, although they also
caution that residual surfactant will eventu-
JOURNAL OF SOIL AND WATER CONSERVATION
Table 7
Mean values of the fitted variables, averaged over four replicates for unsaturated hydraulic
conductivity (C2) and capillary rise (a), using the GLM least squares procedure. Values with the
same letters next to them are not significantly different (p ≥ 0.05).
Mean of C2 (cm s )
Mean of a (cm s )
Treatment
Silt loam
Silt loam
–½
Sand
Allred, B., and G.O. Brown. 1994. Surfactant-induced
reductions in soil hydraulic conductivity. Groundwater
–½
Monitoring and Remediation 14(2):174–184.
Sand
Wet-Sol
0.028ab0.16a
2.454ab3.29ab
WaterMaxx 0.026bc0.25b
2.51abc 3.12a
Ad-Sorb
0.035ab0.27bc
2.70ac 3.08a
Formula One
0.038a
0.34c
2.450b
3.08a
Control
0.037a0.26bc 2.7c 3.62b
Note: Values with the same letters next to them are not significantly different (p ≥ 0.05).
Allred, B., and G.O. Brown. 1995. Surfactant-induced
reductions of saturated hydraulic conductivity and
unsaturated diffusivity. Surfactant-Enhanced Subsurface
Remediation—Emerging
Technologies.
ACS
Symposium Series 594:216–230.
Bashir, R., J.E. Smith, and D.F. Stolle. 2008. Surfactantinduced unsaturated flow: Instrumented horizontal
flow experiment and hysteretic modeling. Soil Science
Society of America Journal 72(6):1510–1519.
Carsel, R.F., and R.S. Parrish. 1988. Developing joint
ally counter the surfactant’s ability to increase
infiltration (Urrestarazu 2008).
Researchers have theorized that soil surfactants may not be profitable in healthy,
hydrophilic soils (Miller et al. 1975;
McFarland et al. 2005). Structurally, surfactants interact well with problematic
conditions, such as hydrophobicity or dense
surface clods (Kuhnt 1993). Although the
soil conditions in an advertisement may be
ideal for a product’s action, the same results
may not be achieved in a field with different
soil composition and history.
To determine whether the surfactants
will behave differently in a problem soil,
we should repeat these same experiments
in hydrophobic, compacted, or crusty soils
in future studies. In those cases, differences
might emerge between the anionic, nonionic, and block polymer surfactants due to
their different mechanisms of soil sorption
and soil-water movement. Testing under different soil conditions is critical to obtaining
a complete picture of the possible effectiveness of these wetting agents in conserving
soil-water.
Summary and Conclusions
Existing research has demonstrated that soil
surfactants or wetting agents can improve the
infiltration of water into water repellent, or
hydrophobic, soil as well as the distribution
of water as it spreads through the soil matrix.
These benefits were not achieved, however, by the four commercial soil surfactants
applied to hydrophilic silt loam and sand in
this study.
In the experiments in which surfactants
remained longest in the soil (from a few
hours to overnight), no statistically significant
differences were found among treatments in
silt loam or sand. In 52 cm (20.5 in) soil columns, the infiltration rate of water was not
significantly different between any columns
JOURNAL OF SOIL AND WATER CONSERVATION
pretreated with surfactant or the control (no
added surfactant). The same columns likewise did not show significant differences in
water holding capacity (measured by water
content) among the treatments.
Significant differences were found among
treatments in sand columns only (not silt
loam) for the tests of unsaturated hydraulic conductivity and capillary rise, but the
changes due to surfactants were not beneficial to soil-water movement overall. The
empirical parameter related to hydraulic
conductivity was actually lower in Wet-Sol
#233 than in all other treatments, including
the control. Hence, water movement either
saw no significant change under surfactant treatment compared to the control, or
was hindered (for Wet-Sol). Reduction in
unsaturated hydraulic conductivity might be
useful for soil-water retention in areas with
high drainage losses, but no corresponding increases in volumetric water content
were seen in the experiments testing the
water holding capacity of sand columns.
Additionally, the parameter related to capillary rise was lower in most surfactant-treated
samples compared to control samples, suggesting that the surfactants decreased the
surface tension in the sand columns (but not
in the silt loam). However, the reduced capillary rise heights for the sand columns were
not matched with significant increases in
infiltration rate, as would be expected. Based
on these results, the four surfactants tested
did not consistently improve the soil-water
movement to help conserve irrigation water
in these hydrophilic cropping soils.
probability distributions of soil water retention curves.
Water Resources Research 24:755–769.
Cooley, E.T., B. Lowery, K.A. Kelling, P.E. Speth, F.W.
Madison, W.L. Bland, and A. Tapsieva. 2009. Surfactant
use to improve soil water distribution and reduce nitrate
leaching in potatoes. Soil Science 174:321–329.
Doerr, S.H., C.J. Ritsema, L.W. Dekker, D.F. Scott, and D.
Carter. 2007. Water repellence of soils: New insights
and emerging research needs. Hydrological Processes
21:2223–2228.
Feng, G.L., J. Letey, and L. Wu. 2002. The influence of two
surfactants on infiltration into a water-repellent soil. Soil
Science Society of America Journal 66:361–367.
Fitch, B.C., S.K. Chong, J. Arosemena, and G.W. Theseira.
1989. Effects of a conditioner on soil physical properties.
Soil Science Society of America Journal 53:1536–1539.
Flury, M. 2007. Soil Physics Laboratory Manual. Pullman,
WA: Washington State University.
Hallett, P.D. 2008. A brief overview of the causes, impacts,
and amelioration of soil water repellency. Soil and Water
Resources 3:S21–S29.
Henry, E.J., J.E. Smith, and A.W. Warrick. 1999. Solubility
effects on surfactant-induced unsaturated flow through
porous media. Journal of Hydrology 223:164–174.
Henry, E.J., J.E. Smith, and A.W. Warrick. 2001. Surfactant
effects on unsaturated flow in porous media with
hysteresis:
Horizontal
column
experiments
and
numerical modeling. Journal of Hydrology 245:73–88.
Ishiguro, M., and T. Fujii. 2008. Upward infiltration into
porous media as affected by wettability and anionic
surfactants. Soil Science Society of America Journal
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Karagunduz, A., K.D. Pennell, and M.H. Young. 2001.
Influence of a nonionic surfactant on the water retention
properties of unsaturated soils. Soil Science Society of
America Journal 65:1392–1399.
Karcher, D., J. Miller, M. Richardson, and B. Leinauer. 2005.
Irrigation frequency and soil surfactant effects on a sand-
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