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Exchangeable Na, polymer, andwater quality effects on waterinfiltration and soil lossM. Ben‐Hur a , P. Clark b & J. Letey b

a Institute of Soils and Water , The Volcani Center , P.O.Box 6, Bet‐Dagan, 50–250, Israelb Department of Soil and Environmental Science ,University of California , Riverside, CA, 92521, USAPublished online: 09 Jan 2009.

To cite this article: M. Ben‐Hur , P. Clark & J. Letey (1992) Exchangeable Na, polymer,and water quality effects on water infiltration and soil loss, Arid Soil Research andRehabilitation, 6:4, 311-317, DOI: 10.1080/15324989209381325

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Arid Soil Research and Rehabilitation, Volume 6, pp. 311-317 0890-3069/92 $3.00 + .00Printed in the UK. All rights reserved. Copyright © 1992 Taylor & Francis

Exchangeable Na, Polymer, and Water QualityEffects on Water Infiltration

and Soil Loss

M. BEN-HUR

Institute of Soils and WaterThe Volcani CenterP.O. Box 6Bet-Dagan 50-250, Israel

P. CLARKJ. LETEY

Department of Soil and Environmental ScienceUniversity of CaliforniaRiverside, CA 92521, USA

Abstract Increasing exchangeable sodium percentage (ESP) contributes to in-creased soil dispersion and swelling of clay, which reduces the infiltration rate andincreases runoff. Synthetic polymers are available that may decrease soil dispersion.A study was conducted to determine the effect of three polymers dissolved in water at10 or 50 mg L-1 concentrations and applied through a rainfall simulator on theinfiltration rate, erosion, and soil migration through the layer of a soil at ESP equalto 8.5 and 30.6. The polymers were a cationic polysaccharide and two anionicpolyacrylamides with different negative charge densities. The infiltration rate de-creased with time and approached a final steady-state infiltration rate (FIR). Therunoff water and associated sediment were captured and measured. Water comingthrough the soil layer and the amount of particulates contained in the water weremeasured. The FIR was significantly lower for the soil at ESP equal to 30.6 than atESP equal to 8.5. There was no statistically significant effect of the polymer type orconcentration on FIR. The amount of soil loss through erosion was significantlyaffected by the soil ESP, polymer type, and polymer concentration of the polymerapplication. More soil was in the runoff for the higher ESP than for the lower ESP.The polymer treatment effects on soil loss were in the following order: cationicpolysaccharide > untreated > low anionic PAM > higher-charged anionic PAM.Soil loss from application of the polymer at 50 mg L-1 was significantly less than at10 mg L-1. The amount of soil migrating through the soil layer with the percolatewas significantly higher for the higher ESP soil, whereas there was no significanteffect of polymer treatment on this parameter.

Keywords soil conditioner, polyacrylamide, polysaccharide, sodicity

Received: April 20, 1992; accepted: May 27, 1992.Address correspondence to J. Letey.

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312 M. Ben-Hur et al.

Introduction

Exchangeable sodium percentage (ESP) of the soil and water quality are important fac-tors that control water infiltration and movement in soils (Shainberg and Letey 1984).Low electrolyte concentration in soil solution and high ESP increase dispersion andswelling of clay, which enhance breakdown of soil structure and reduction of hydraulicconductivity and infiltration rate (IR). Under water drop impact conditions (rain orsprinklers), the reduction of the IR may also be caused by physical disruption of aggre-gates leading to seal formation on the soil surface (Morin et al. 1981). The term seal isused to denote a layer of particulates at the soil surface that results in small pores withlow water permeability.

Chemical amendments may improve or maintain soil structure. Ben-Hur and Letey(1989), Ben-Hur et al. (1989), Helalia and Letey (1988), and Helalia et al. (1988) foundthat addition of cationic polysaccharides and anionic polyacrylamides (PAM) to waterthat was applied by a rainfall simulator in the laboratory to soils with low ESP increasedthe IR as compared to the control.

Soil erosion by water involves two major processes: (1) detachment of soil materialfrom the soil surface by raindrop impact and/or runoff shear, and (2) transport of theresulting sediment by raindrop splash and/or overland flow (Baver et al. 1972). HighESP and low electrolyte concentration in the irrigated water decrease IR and increaserunoff (Kazman et al. 1983). As a result, runoff transport capacity and runoff shear bothincrease, which may increase the soil erosion. However, high ESP and low electrolyteconcentration enhance seal formation. The seal increases the shear strength of the soilsurface (Marshall and Holmes 1979) and, consequently, soil erosion could be decreased.

Singer et al. (1982) found that soil loss increased with increasing ESP up to 12 andthen remained relatively constant up to an ESP of 80. Warrington et al. (1989) found thatphosphogypsum spread over sandy loam soil dissolved in rain of distilled water andreduced erosion by 60% as compared to the control. Bradford et al. (1987) conducted astudy on 20 soils and found that surface sealing caused a reduction in infiltration rate andan increase in shear strength resulting in a decrease in total soil loss. Similar results werereported by Moore and Singer (1990). Total soil loss, splash, and wash were highlyintercorrelated. Ben-Hur et al. (1990) found under rainfall simulator conditions thataddition of a cationic polysaccharide to the applied water decreased seal formation andincreased soil loss and the sediment concentration in the runoff.

The objectives of this study were to investigate (1) the effect of ESP and waterquality on erosion and infiltration rate, and (2) the effect of cationic polysaccharide andanionic PAM on infiltration rates and soil loss for soil with various ESP values.

Materials and Methods

An Arlington sandy loam (Haplic Durixeralf) soil was collected from the upper 0.2-mlayer in Riverside County, California. The soil was 10% clay, 31% silt, and 59% sandand had a cation exchange capacity of 18 cmolc kg"1 and CaCO3 content < 0.1%. Toget soil with various ESP values, water with various SAR and electrolyte conductivity(EC) was applied to different plots in the field before soil sample collection. The soilwas leached as described by Kazman et al. (1983). The resultant ESP values were 2.8,8.5, and 30.6.

The soil samples were crushed and sieved through a 4.0-mm-size screen. The sievedsoil was packed 2 cm deep at a 1.47-mg m"3 bulk density in 12 x 20-cm perforated

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Exchangeable Na and Polymer Interactions 313

trays over a fiberglass sheet placed on the tray bottom. Trays were placed in a sprinklerinfiltrometer at a slope of 5% with duplicates for each treatment. The infiltrometer andsoil trays were as described by Helalia and Letey (1988) and Kleijn et al. (1979). Briefly,water drops were released from hypodermic needles in a random manner so that dropsdid not continuously hit the same spot. The mechanical parameters of the applied sprin-kler water were as follows: instantaneous application of 30 mm h"1 with standard devia-tion of 0.8 mm h"1, water drop final velocity of 4.0 m s"1, and total kinetic energy of240 J m"2 h"1.

The soil was first saturated from the bottom with tap water (EC = 0.7 dS m"1 andSAR = 1 ) and then received a storm of 60 mm by the rain simulator. The volumes ofwater percolating through the soil were recorded for each 2.5 mm of water application tocompute the IR. The runoff was collected and measured after the 60-mm storm. Theparticle size distribution of the eroded material and the total soil loss were measured bypassing the runoff gently through different sieve sizes (0.05 to 4 mm) and drying andweighing the particulates on each sieve and those passing through the smallest sieve size.

Tap water and saline water with EC equal to 5 dS m"1 and SAR = 0 (CaCl2

solution) were used in the study along with three polymers provided by Hi-Tek PolymerCorporation (Louisville, KY). The polymers were a cationic guar derivative with molec-ular weight of 0.2 to 2 X 106, and two polyacrylamide (PAM) polymers with molecularweight of 10 to 15 X 106 and with two negative charge densities. The anionic charge ofthe PAM was obtained by substituting a proton on the amino group with a carboxylateion. The cationic polysaccharide will hereafter be referred to as C-17. The two PAMsused in this study, 2J and 40J, had 2 and 40% substitution, respectively. Stock solutionsof 500 mg L"1 of each polymer were prepared and then diluted to concentrations of 10or 50 mg L"1 for application with the infiltrometer. The polymers were tested with tapwater only and on soils with ESP of 8.5 and 30.6.

Results and Discussion

The effects of the various treatments on soils with different ESP values are illustrated inFigs. 1-3 for the final infiltration rate, soil loss through erosion, and soil migrationthrough the soil layer with the percolating water. A summary of the analysis of varianceis presented in Table 1.

The FIR was significantly lower for the soil at ESP 30.6 than 8.5. This result isconsistent with increased dispersion and swelling of clay with increasing ESP values(Shainberg and Letey 1984). There were no significant effects of polymer type or con-centration on the FIR. Also, the interactions were not statistically significant. Ben-Hurand Letey (1989) found that 10 mg L"1 of C-17 in tap water increased the final infiltra-tion rate from 12 to 30 mm h"1 in Arlington soil with an ESP = 2.0. The average FIRfor C-17 was higher than for untreated water at ESP 8.5, but not for ESP = 30.6 (Fig.1). Thus, there is a trend for the polymers applied in this manner to have decreasedrelative effectiveness with increasing soil ESP.

The soil loss by erosion was significantly affected by ESP and polymer type andconcentration (Table 1). The soil loss by erosion pooled for all treatments was signifi-cantly higher for ESP equal to 30.6 than for 8.5. The increasing loss at the higher ESPvalue was associated with more runoff. When the erosion was computed on the basis ofaverage concentration of sediment in the runoff water, there was no difference betweenthe soils at the two ESP levels.

The type of polymer pooled for soil ESP and concentration significantly affected the

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314 M. Ben-Hur et al.

• Tap Water• Saline Waler

C-17 lOmgL'1

C-17 SOmgL"'

50 mg r'2J O L " 1

E l 2J 5OmgL

8.5 30.6

EXCHANGEABLE SODIUM

PERCENTAGE( ESP )

Figure 1. The final infiltration rate of various solutions in soils of different ESP levels.

BB Tap Water• Saline Water

C-17 lOmgL'1

C-17 50mgL"'E3 40J

40J 50 mg L'1

2J lOmgL'

2J 50 mg L"'

30.6

EXCHANGEABLE SODIUM

PERCENTAGE (ESP)

Figure 2. Soil loss in the runoff of various solutions on soils of different ESP levels.

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Exchangeable Na and Polymer Interactions 315

15

O Î

ceo

oCO

10

• Tap Water• Saline WalerE2 C-17 lOmgf'ES C-17 50mgl/'\Z} 40J 10mgL''S 3 <0J 50 mg L"'S 2J 10mgL"'D l 2J 50 rng f1

2.8 8.5 30.6

EXCHANGEABLE SODIUM

PERCENTAGE (ESP)

Figure 3. Soil migration with various percolating solutions through soils of different ESP levels.

amount of erosion. The order of treatment effect with the average amount of soil loss ing m"2 listed in parentheses was in the following order: C-17 (160) > untreated (128) >2J (90) > 40J (45). The effect of type of polymer on erosion cannot be related to theamount of runoff, because there was no significant effect of polymer type on finalinfiltration rate (Table 1). The size distributions of the particulates in the runoff for thevarious treatments are presented in Fig. 4. The runoff from the untreated waters ischaracterized by a very high percentage (70-80) of particulates smaller than 0.053 mm.The polymers were effective in decreasing the extent of dispersion into the finest size

Table 1Analysis of Variance for FIR, Soil Loss, and Soil Migration as Related to

Experimental Variables

ESPPolymer typeConcentrationESP x Polymer typeESP X Polymer concentration

FIR

***

NSNSNSNS

Soil Loss

*****NSNS

SoilMigration

***

NSNSNSNS

*,•••Significance at the p — .05 and p — .001 levels, respectively. NS, no significance at the p — .05level.

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316 M. Ben-Hur et al.

Ü

100

80

60

OLUrrLU

TA

G

LUOceLUQ_j

X

WE:

40

20

0

100

eo

60

40

20

0

TAP WATER

2.8 8.5 30.6

C-17

100

80

eo

40

20

0

100

80

eo

40

20

0

SALINE WATER

2J

>1mm

0.5-1

0.25-0.5

0.1-0.25

0.053-0.1

<0.053

40J

EXCHANGABLE SODIUM PERCENTAGE

Figure 4. Weight percentage frequency of participates in the runoff from soils of different ESP levels for twowaters and tap water containing 10 mg L of three polymers.

fractions. C-17, however, had considerably more of the finest participates than 2J or40J.

Soil erosion appears to be affected by complex interactions. The finer particulatesare more easily transported by the flowing water, but the finer particulates can create aseal, which increases the shear strength, thus reducing erodibility. El-Morsy et al.(1991) found significant interactions between treatments and the amount of erosion whenthe variables were the electrical conductivity and the sodium adsorption ratio of theapplied water, both with and without C-17 polymer. The increase in erosion with the C-17 polymer is in agreement with the results previously presented by Ben-Hur et al.(1990). A decrease in erosion using PAM polymers is consistent with results achieved byLevin et al. (1991) and Levy et al. (1991). Thus, it appears that the polymer type is.avery significant factor in erodibility. The cationic polysaccharide with lower molecularweight than the anionic polyacrylamide was less effective (actually negative effect) thanPAM in reducing soil erosion.

The amount of soil migration with the effluent was significantly higher for the soil atESP 30.6 than 8.5. There were no significant effects of polymer type or concentrationon these results. Higher migration in the soil at the higher ESP is associated withenhanced dispersibility of that soil producing fine particulates that would be mobile inthe water flowing through the pores. The amount of fine particulates in the runoff wasnot affected by soil ESP (Fig. 4). However, the particulates in the runoff were the resultof both dispersion caused by the chemical interaction between the soil and water and alsothe impact energy of the drops, which physically dispersed the soil. On the other hand,as the water passes through the soil layer, impact energy would not be a factor except atthe surface. Helalia et al. (1988) reported that the amount of paniculate percolatedthrough the soil was dependent on the water quality and not the polymer treatment. Itwas postulated that the polymers become adsorbed near the sol surface layer and are nolonger effective in preventing dispersion as the water flows through the layer.

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Exchangeable Na and Polymer Interactions 317

Acknowledgments

The research was supported by Bi-National Agricultural Research and Development andthe University of California Kearney Foundation of Soil Science.

References

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