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Polyacrylamide (PAM) is a water-soluble,high molecular weight (5 to 30 Mg•mol-1,or 6 to 33 tons•mol-1), long-chain, syn-thetic, organic polymer that is producedfrom natural gas. When applied to soil, itinteracts largely with the clay fraction, withthe effect controlled by properties of boththe polymer and the soil (Seybold, 1994).Some soil properties that impact the effec-tiveness of PAM are the amount and types ofclay present, pH, soil solution ionic strength,and the type of ions in solution.

The polymer largely works by helping tokeep the soil in a flocculated state, as well asby strengthening soil aggregates from physi-cal and chemical disruption. The PAMreduces repulsive forces among clay particlesand creates bridges between soil aggregateparticles through bonding with the particles

(Ben-Hur, 1994). Because fewer aggregatesare broken down, fewer small clay and siltparticles are available to move into and clogsoil pores. Thus, much higher infiltrationrates can usually be maintained on surfacestreated with PAM, which reduces runoffrates and erosion potential.

Anionic polyacrylamide has been shownto be the most effective type at reducing sealformation and maintaining high infiltrationrates (Shainberg and Levy, 1994), and it alsohas a longer temporal effect than cationicPAM (Levy et al., 1992). Anionic PAM alsoposes little danger to off-site water organ-isms, unlike cationic PAM.

Use of anionic polyacrylamide for erosioncontrol has been studied by a number ofresearchers over the past 30 years. Some ofthe earliest work with PAM was conducted

by Gabriels et al. (1973). In laboratorystudies under simulated rainfall, they foundthat 38 kgha-1 (34 lbs ac-1) anionic polyacry-lamide effectively reduced runoff and soil losson soil at a 9% slope. Wallace and Wallace(1986) also conducted laboratory studies onsmall plots at 58% slopes, with PAM appliedat rates ranging from 16 to 161 kgha-1 (14 to144 lbsac-1), and found that soil loss rates con-tinued to decrease with increasing rates ofPAM application.

Some of the most successful research andreal-world use of PAM has been on agricul-tural land that receives furrow-irrigationwater. Polyacrylamide has been studiedextensively for use in furrow irrigation (Lentzet al., 1992; Lentz and Sojka, 1994;Trout etal, 1995; Sojka et al., 1998; Lentz and Sojka,2000), and this technology is now being usedthroughout regions of the western UnitedStates and elsewhere. Research studies havealso examined the potential for use of PAMin sprinkler-irrigation water to reduce runoffand erosion (Levy et al., 1991; Levy et al.,1992; Aase et al., 1998; Bjorneberg et al.,2000; Bjorneberg and Aase, 2000).

PAM field studies on rainfed, dryland agri-cultural systems have had mixed results.Mitchell et al. (1996) applied 18 kg ha-1

(16 lbsac-1) of anionic PAM to 3% slope fieldplots in Illinois on a silt loam soil undernatural rainfall conditions. They observed nosignificant treatment effect on runoff or sedi-ment yield but suggested that greater applica-tion rates of the PAM might be needed to be effective. However, in a field study onlow-slope plots, Fox and Bryan (1992)applied 25 kg ha-1 (22 lbs ac-1) anionic PAMon disturbed soil, and this treatment waseffective in reducing runoff and soil loss.

Zhang and Miller (1996) studied the effectof anionic polyacrylamide on soil erosion in

Using polyacrylamide to control erosion on agricultural and disturbed soils inrainfed areasD.C. Flanagan, L.D. Norton, J.R. Peterson, and K. Chaudhari

ABSTRACT: Use of anionic polyacrylamide (PAM) as an erosion control soil amendment has beenstudied at the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS), NationalSoil Erosion Research Lab since the early 1990s. An initial field experiment in Indiana usingsimulated rainfall on a sloping silt loam soil found that 20 kg ha-1 of PAM could reduce sedimentloss by more than 60% from the first storm event from an agricultural silt loam soil, as well asprovide control from rill detachment for inflows of water up to 60 L min-1. More recent studieshave examined use of PAM on areas prone to excessive erosion (highway embankments, landfillcaps, etc.) to provide control while vegetation is being established. A simulated rainfall studyfound that 80 kg ha-1 PAM application on a 3:1 silt loam soil embankment reduced runoff by 86%and soil loss by 99% in a severe storm event (69 mm h-1 for 1 hour) on initially dry soil. The PAMcontinued to be effective at controlling runoff and soil loss through a series of simulated rainfallapplications, reducing runoff by an average of 40% and soil loss by an average of 83% over theentire experiment. Two associated natural rainfall studies found similar erosion control benefits,as well as improved vegetation establishment. Polyacrylamide at 80 kg ha-1 was also found to beeffective at preventing earthen channel erosion and degradation on a preformed trapezoidalchannel at a 1% slope at inflows of water up to 760 L min-1. Application of PAM as a liquid spraythat is allowed to dry on the soil surface is more effective than an application of dry PAM granulesfor immediate erosion control. Recent laboratory experiments have been targeted towarddetermining the optimal rates of PAM to control rill erosion and minimize cost.

Keywords: PAM, polyacrylamide, soil amendments, soil erosion control

Dennis C. Flanagan is an agricultural engineer andL. Darrell Norton is a soil scientist with the U.S.Department of Agriculture-Agricultural ResearchService, National Soil Erosion Research Laboratoryin West Lafayette, Indiana. Joel R. Peterson is aformer graduate research assistant with the Depart-ment of Agricultural and Biological Engineering atPurdue University in West Lafayette, Indiana. He isnow employed as an environmental engineer withthe U.S. Army Corps of Engineers in Rock Island,Illinois. Kiran Chaudhari is a former graduateresearch assistant with the Department of Agricul-tural and Biological Engineering at Purdue Universi-ty in West Lafayette, Indiana. He is now employedas a remediation engineer with BP-Group Environ-mental Management Company in Carson, California.

Reprinted from the Journal of Soil and Water ConservationVolume 58, Number 5

Copyright © 2003 Soil and Water Conservation Society

JOURNAL OF SOIL AND WATER CONSERVATION S|O 2003302

This work is reported in detail in Flanaganet al. (1997a, 1997b).

Examination of the use of PAM was part ofa larger study aimed at determining theimpacts of rainfall simulator water quality oninfiltration, runoff, and soil loss results. Threelevels of water quality (deionized, tap water,and tap water with 10 ppm PAM added on awhole product basis) and three soil surfacetreatments were evaluated. The treatmentsand treatment codes used are detailed in Table 1. Electrical conductivity of the tapwater was approximately 600 µS cm-1 (1500µS in-1), and for the deionized water it was 10 µScm-1 (25 µSin-1) or less to simulate nat-ural rainwater. The domestic tap water con-tained approximately 440 ppm of iron, 140ppm of strontium, 130 ppm of manganese, 88ppm of calcium, 30 ppm of magnesium, 29

furrows on a Cecil sandy loam soil at 11% slope gradient. Using simulated rainfallon 3.5 by 0.9 m (11.5 by 3.0 ft) plots, theyfound that both 15 and 30 kg ha-1 (13 and 27lbs ac-1) of PAM reduced rill formation anddetachment by about 98% on initially drysoil, and by 48% to 66% in two subsequentevents. Zhang et al. (1998) found that PAMat 20 kgha-1 (18 lbsac-1) was more effective atreducing runoff than soil loss from naturalrainfall events on tilled 3.5 x 2 m (11.5 by 6.6 ft) flat plots on the same Cecil sandy loamsoil, and the PAM had a persistent effect overa 5-month period.

Often, the effectiveness of polyacrylamidecan be enhanced by applying it in combina-tion with an electrolyte source of multivalentcations. These cations that go into solutionact to bridge the negatively charged soilparticles and the PAM together (Laird, 1997).This effect was demonstrated by Shainberg etal. (1990). They studied the interactionbetween PAM at rates up to 40 kgha-1 (36 lbsac-1) alone and enhanced electrolyte concen-tration at the soil surface through use of 5 Mgha-1 (2.2 tons ac-1) of phosphogypsum. Ontheir clayey soils at 5% slopes, the PAM wasmuch more effective at reducing runoff rateswhen applied with the phosphogypsum.

Stern et al. (1991) also studied the effect of phosphogypsum and PAM applications.On loamy soils in small plots under naturalrainfall conditions, PAM was applied at 20 kgha-1 (18 lbs ac-1) in combination withphosphogypsum at 5 Mg ha-1 (2.2 tons ac-1).PAM and phosphogypsum had less runoffthan either the control or phosphogypsumalone treatments.

Research has been conducted on the useof polyacrylamides for soil erosion control by the USDA-ARS, National Soil ErosionResearch Laboratory (NSERL) since theearly 1990s. In particular, the NSERL hasbeen examining the feasibility of using PAMunder rainfed, dryland agricultural and con-struction conditions. The objective of themultiple research studies is to determine theeffectiveness of PAM and other soil amend-ments as erosion control measures, and toultimately develop a set of guidelines for theiruse to achieve desired levels of erosion con-trol. The purpose of this article is to describeand summarize the important findings ofseveral experiments and detail current lines ofresearch. Many of the studies, in particularmost of the field experiments, were meant toexamine PAM effectiveness on plot sizes,

slopes, and with inflow rates of water notexplored in research by others.

Field ExperimentsSilt loam soil in an agricultural field. Someof the earliest work with polyacrylamide bythe NSERL was conducted in the summer of1991 on a Russell silt loam soil in an agricul-tural field located about 10 km (6 mi) west ofWest Lafayette, Indiana. Soil texture was 12%sand, 68% silt, 20% clay, and 1.6% organicmatter. Plot slopes ranged from 6% to 9%.Soil was in a freshly tilled condition, and sub-plots consisted of three small interrill subplots(0.8 m by 0.6 m [2.6 ft by 2.0 ft]) and threelonger rill subplots (0.8 m by 10.7 m [2.6 ftby 35 ft]) underneath a rainfall simulator. Astraight shank chisel plow was used to pre-form the furrows on a 0.8 m (2.6 ft) spacing.

Table 1. Experiment treatments in agricultural field study.

Code Rainfall water type Soil surface treatment Reps.

DC Deionized Control 5

TC Tap Control 10

PC Tap + 10 ppm PAM Control 6

DG Deionized 5 t•ha-1 FBCBA 5

DP Deionized 20 kg•ha-1 PAM 5

TP Tap 20 kg•ha-1 PAM 5

Figure 1Rainfall minus runoff rate (estimated infiltration rate) versus time for rill subplots on agriculturalfield study.

Rai

n—R

unof

f R

ate

(mm

/hr

)

80

70

60

50

40

30

20

10

010 20 30 40 50 60 70 80 90 100

Time (minutes)

PCDP

DGDC

TP

TC

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ppm of boron, and less than 10 ppm of potassium, sodium, and zinc.The PAM soil surface treatment used was 20 kg ha-1 (18 lbs ac-1) of anionic polyacry-lamide on a whole product basis (PAM usedwas Magnifloc® 836A from CYTECIndustries Inc. of Stamford, Connecticut),applied as a liquid solution with a backpacksprayer. The polymer had a molecularweight of 16 Mgmol-1 (18 tonsmol-1) and acharge density of 18%. The liquid PAMsolution was allowed to air dry on the soilsurface before rainfall simulation. FluidizedBed Combustion Bottom Ash (FBCBA) wasapplied to the soil surface as an alternativeamendment to provide a source of multiva-lent cations to reduce soil chemical dispersionand promote flocculation. (See Table 1.)

Simulated rainfall was applied using aprogrammable rainfall simulator described by Foster et al. (1982) at an intensity of about64 mm h-1 (2.5 in h-1). Flow discharge wasmeasured using small, precalibrated HS-flumes with direct float-to-pen linkage chartrecorders. The first rainfall event was appliedto initially dry soil in a loose, aggregatedcondition until steady-state runoff wasachieved for a minimum of 5 minutes.Sediment samples were collected every 3minutes in 1 liter plastic bottles, and sedimentconcentration was determined gravimetrically.

Results presented in Figure 1 describe theimpact of the various water and soil amend-ment treatments on measured runoff ratesand estimated infiltration rates from theinitially dry soil for the long rill subplots. Forall treatments, runoff began after about 25minutes into the rainfall simulation. The PCtreatment maintained high infiltration ratesfor a very long time, and simulations wereended after about 100 minutes, even thoughit was not clear that steady-state runoff hadalways been achieved. (Water supply treatedwith 10 ppm PAM was nearly exhausted.)Final runoff rates on the rill subplots were notsignificantly different for any of the treat-

ments, and only PC had a significantly higherinfiltration rate (Note: Measured rainfallapplication rates were slightly different onevery plot. Individual plot rainfall rates wereused in calculating individual plot infiltrationrates, which were subsequently used in thestatistical analyses.)

Sediment concentrations and steady-statesediment discharge rates (Table 2) weresignificantly less from the PAM-treated(DP and TP) furrows, compared with thecontrols (DC and TC). The interrill subplotserosion results showed no differences inmeasured detachment rates for any of thetreatments under deionized or regular tapwater rainfall. Thus, the PAM surface treat-ments were controlling soil loss throughcontrol of rill detachment.

An interesting result was that the additionof 10 ppm of PAM in the rainwater (PC)acted to increase the sediment concentrationsand sediment discharge to the highestobserved levels in both the interrill and rillsubplots (Table 2). The PC sediment con-centrations were significantly higher thanthose from the TC control. Apparently theconstant application of the tap water withPAM, with no time for drying, left the soilsurface in a loose and more easily erodedstate. When runoff ultimately occurred (aftera very long period of rainfall application andhigh infiltration) because of saturation of thesoil, sediment easily moved with the runoffwater. This probably would not be a seriousconcern in practice with a sprinkler-irriga-tion system, for example, as much less waterwould be applied than was here.

Subsequent rainfall simulations at the sameintensity were conducted on wet soil approx-imately one hour after the end of the initialsimulation run on dry soil. When steady-state runoff was achieved, a series of inflowruns were conducted. The DC and DP fur-rows received inflow of deionized water,while the PC furrows received inflow of tapwater with 10 ppm PAM. The TP furrows

received inflow of tap water, as did five of theTC furrows. The other TC furrows receivedinflow of tap water with 10 ppm PAM.Inflow rates of 8, 15, 30, and 60 Lmin-1 (2, 4,8, and 16 gpm) were used. Each inflow levellasted approximately 8 minutes.

The PAM surface treatments (DP and TP)significantly decreased both average andsteady-state sediment concentrations across allinflow levels compared with the controls (DC and TC). Table 3 shows the sedimentconcentration and sediment discharge valuesfor the highest inflow level (60 L min-1 [16gpm]), and Figure 2 shows three of the rillsubplots after application of this high inflowlevel. Polyacrylamide was very effective atpreventing rill initiation and headcutting.There were some localized areas of nick-points visible in the left furrow in Figure 2;however, the center and right furrows were completely scoured out. Also, only 20kg ha-1 (18 lbs ac-1) was used in this experi-ment, with a minimal amount of drying time(less than one hour), so longer drying and/orhigher rates of application might have furtherprotected the soil surface.

This field experiment showed that anionicPAM at relatively low rates could be veryeffective at controlling rill initiation anddetachment for large flows (that could repre-sent long slope lengths). The interrill and rillerosion results indicated that surface-appliedPAM controlled soil loss for this situationmainly by preventing rill initiation and devel-opment. Runoff rates across all treatmentsfrom initially dry soil were not different fromone another, and inflow rates were uniformfor each furrow. With the dramatic decreasein sediment concentrations and dischargerates for the surface-applied PAM, the controlmechanism of the PAM has to be through astrengthening of the soil surface, effectivelythrough a decrease in rill erodibility and/oran increase in critical shear stress.

Steep slope embankments. With the suc-cessful results of using PAM in an agricultural

Table 2. Mean sediment concentrations (Cs) and sediment discharge rates (Ds) on 10.7 m long rill subplots on agricultural field study fromsimulated rainfall applied to initially dry soil.

Rainfall water Soil surface Average Cs Steady-state Cs Steady-state Ds

Code type treatment (g•L-1)* (g•L-1)* (g•s-1)*

DC Deionized Control 69.2b 78.1ab 7.24a

TC Tap Control 51.4c 58.6bc 5.06b

PC Tap + 10 ppm PAM Control 87.5a 98.2a 7.20a

DG Deionized 5 t•ha-1 FBCBA 47.8c 53.8cd 4.76bc

DP Deionized 20 kg •ha-1 PAM 24.8d 36.8d 2.67c

TP Tap 20 kg •ha-1 PAM 28.2d 38.6cd 2.83c* Means in same column followed by same letter are not significantly different using LSD multiple comparison test at P < 0.10 level.

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block design experiment with three replicatesof each treatment was used. Plots were3 m wide by 9 m long (10 ft by 30 ft). Fulldetails on this experiment can be found inFlanagan et al. (2002a).

The same programmable rainfall simulator(Foster et al., 1982) was used as in the previ-ous study, and deionized water was applied toall plots. PAM used in this study was a com-mercially available product, Percol® 336 (nowMagnafloc® 336) produced by Ciba SpecialtyChemicals of Suffolk, Virginia. The PAMwas anionic,with a charge density of 32% anda very high molecular mass of 20 Mg mol-1

(22 tons mol-1). The PAM granules weredissolved in deionized water to produce a0.25% solution (whole product basis), thensprayed onto the plots using a speciallyconstructed sprayer. The sprayer consisted ofa 2.2 kW (3 hp) motor that powered a rollerpump, and the polymer solution was sprayedthrough 30 m (100 ft) of rubber hose and a spray wand with a Teejet® 8006 nozzle tip. Once applied, the PAM solution wasallowed to dry a minimum of 24 hourson the soil surface before rainfall sim-ulations commenced.

A series of three rainfall simulation eventswere used: a run for one hour on initially drysoil at a target rainfall intensity of 64 mmh-1

(2.5 inh-1), a run on wet soil for one hour at64 mmh-1 (2.5 inh-1) an hour after the end ofthe dry run, and a final run on very wet soilat three rainfall intensities. The very wet runbegan 30 minutes after the end of the wet runand consisted of 15 minutes of rainfall at 64mmh-1 (2.5 inh-1), 15 minutes of rainfall at 28mmh-1 (1.1 inh-1), and 15 minutes of rainfallat 100 mmh-1 (3.9 inh-1). Simulated rainfallapplications began on July 25 and were com-pleted on August 20, 1998.

The PAM (P) and PAM with Gypsum(PG) treatments had significantly less runoffand soil loss compared with the untreatedcontrol (C), as shown in Table 4. For some of

setting demonstrated, other types of moreserious erosion control were considered.One of the most important problems in ero-sion control is stabilization of the soil duringcritical periods of vegetation establishment,particularly on very steep embankments asso-ciated with highway construction, landfills,timber harvesting, etc. If anionic PAM waseffective at relatively gentle agricultural slopegradients, how would it perform under verysteep (3:1 to 2:1) slope conditions, typical ofconstruction sites with disturbed soils? CouldPAM be used to reduce the potential forcatastrophic failure of a newly constructedslope that had been seeded with grass and/orother seeds for long-term vegetative erosion

control? Would the PAM not only help tominimize erosion, but also to enhance (or atleast not to inhibit) vegetation growth?

Sets of both rainfall simulator and naturalrainfall experiments were designed to answerthese questions. A rainfall simulator studywas conducted in 1998 on a constructed 32%slope using a silt loam topsoil (21% sand, 61%silt, 18% clay, 2.94% organic matter) strippedfrom another location as the surface soil.Soil treatments were a control, 80 kg ha-1

(71 lbs ac-1) of anionic PAM applied as aliquid spray, and 80 kg ha-1 (71 lbs ac-1) ofanionic PAM applied as a liquid spray com-bined with 5 Mg ha-1 (2.2 tons ac-1) of drygranular gypsum. A randomized complete

Table 3. Mean sediment concentrations (Cs) and sediment discharge rates (Ds) on 10.7 m long rill subplots of agricultural field study fromsimulated rainfall and a flow addition of 60 L per minute applied to wet soil.

Rainfall water Soil surface Inflow water Average Cs Steady-state Cs Steady-state DsCode type treatment type (g•L-1)* (g•L-1)* (g•s-1)*

DCD Deionized Control Deionized 116ab 108a 118.ab

TCT Tap Control Tap 128ab 122a 146.a

TCP Tap Control Tap + 10 ppm PAM 138ab 129a 165.a

PCP Tap + 10 ppm PAM Control Tap + 10 ppm PAM 160a 153a 163.a

DGT Deionized 5 t•ha-1 FBCBA Tap 109b 108a 119.ab

DPD Deionized 20 kg•ha-1 PAM Deionized 54.0c 55.5b 61.2bc

TPT Tap 20 kg•ha-1 PAM Tap 33.6c 32.6b 35.4c• Means in same column followed by same letter are not significantly different using LSD multiple comparison test at P < 0.10 level.

Figure 2View of 10.7 m long rill subplots of agricultural field study after final inflow rate of 60 liters perminute was applied. Subplot on left had surface treatment of 20 kg ha-1 PAM, while subplots incenter and right had no surface treatment. Left and right rills had tap water inflow, while centerrill had inflow of tap water plus 10 ppm PAM.

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the rainfall intensity levels in the very wetrun, there was significantly less runoff fromthe PG plots compared with the P, indicatingimproved effectiveness of the PAM and gyp-sum combination. Mean values of sedimentyield were always lower for the PG treatmentthan for P, but the differences were not signif-icant at the P<0.05 level. Representativeplots for each treatment are shown in Figure 3, and one can see that rill formationand development were almost completelycontrolled by the P and PG amendments.

These results demonstrated that anionicpolyacrylamide could be successfully used asan erosion control practice on very steepslopes, under worst-case conditions. Theinitial rainfall event on dry soil (1 hr at 64mmh-1 [2.5 inh-1]) represents a storm havinga return period of 25 years for west-centralIndiana, and the cumulative applied rainfall of176 mm (6.9 in) over 4.25 hours represents astorm event with a return period exceeding100 years (Huff and Angel, 1992).

Natural rainfall field experiments were also conducted to determine how effectivethe PAM treatments would be for erosioncontrol under real-world rainfall conditions.Additionally, information on the longevity ofany treatment effect and impacts on vegeta-tion establishment and growth was desired.Two of these studies were conducted—one in1997 and one in 1998.

In 1997, a cut slope at an IndianaDepartment of Transportation (INDOT)highway site near Logansport, Indiana, was

used as an area to install nine experimentalplots. Newly exposed clay loam subsoil wasspread over the cutslope surface area to adepth of 25 cm (10 in) with a bulldozer. Thesoil was composed of 22% sand, 50% silt,28% clay, and 1.23% organic matter. Theerosion plots were delineated using 20 cm (8 in) high sheet corrugated sheet metal andwere 2.96 m wide by 9.14 m long (9.7 ft by

30 ft). Plots were arranged in a completelyrandomized design using the same threetreatments (C, P, PG) and PAM formulationas described earlier for the rainfall simulatorstudy. Final slope gradient for the nine plotswas 35%. In addition to the anionic poly-acrylamide and gypsum soil amendments, astandard INDOT Type R grass seed mix(Kentucky fescue, perennial rye grass, Jasper

Table 4. Comparison of total runoff and sediment yield between treatments for steep-slope rainfall simulator study.

Reduction of runoff Total Reduction of sedimentTotal compared with sediment yield yield compared with

Simulation Run Treatment runoff (mm) control (%) (Mg•ha-1) control (%)

Dry C 41.5a* 76.3a*

P 5.9b 86 1.0b 99

PG 4.7b 89 0.7b 99

Wet C 60.0a 71.5a

P 44.2b 26 11.3b 84

PG 35.0b 42 8.8b 88

Very wet (64 mm h-1) C 13.5a 11.3a

P 10.6ab 22 3.4b 70

PG 8.3b 39 2.2b 81

Very wet (28 mm h-1) C 6.8a 3.1a

P 5.9a 13 1.0b 69

PG 3.9b 43 0.4b 85

Very wet (100 mm h-1) C 26.7a 48.3a

P 23.1b 14 18.4ab 62

PG 19.2c 28 7.2b 85* When followed by the same letter, runoff depth and sediment yield for a given run are not significantly different at P < 0.05 using paired

t-tests for multiple means comparisons.

Figure 3View of representative plots from steep slope rainfall simulator study after completion of all rain-fall simulations. From left to right, treatments were: C—untreated control; P—80 kg ha-1 PAM;and PG—80 kg ha-1 PAM and 5 Mg ha-1 Gypsum. Rills were painted and image color modified toenhance visibility.

JOURNAL OF SOIL AND WATER CONSERVATION S|O 2003306

were 17 runoff events. The P and/or PGtreatments significantly reduced runoff com-pared with the control in 12 of the 17 events.The PG treatment had significantly loweraverage total runoff of 181 mm (7.1 in); the Ptreatment had average total runoff of 212 mm(8.3 in), which was not significantly less thanthe control runoff of 250 mm (9.8 in). Forthe entire period, the gypsum significantlyreduced runoff in combination with PAMbelow runoff from plots receiving only atreatment of PAM alone.

The P and/or PG treatments significantlyreduced sediment loss in 14 of the 17 events.Total average sediment loss for the controltreatment was 212 Mg ha-1 (95 tons ac-1),while for P it was 128 and for PG was 99 Mgha-1 (44 and 57 tons ac-1), for reductions of40% and 53%, respectively. The addition ofgypsum did not produce a significant reduc-tion in total sediment yield between the Pand PG treatments, though in a few stormevents PG was less than either C or P treat-ments. Grass growth was consistently betteron the P and PG plots on each of six obser-vation dates. Using a rating procedure thesame as that described earlier for the cutslopesite, the overall vegetation establishment rat-ings for this site were 7.9 for C, 4.1 for P and3.0 for PG. (1 = best, 9 = worst.) Figure 4shows grass establishment on representativeplots three weeks after seeding and after 130mm (5.1 in) of rainfall. The reader is refer-enced to Flanagan et al. (2002b) for a fulldescription of all of the results.

PAM application method study. Anionicpolyacrylamide typically comes from themanufacturer as a dry, granular powder. Theusual approach that has been followed in ourfield studies has been to slowly dissolve aknown mass of powder in a known volumeof water, and then apply the liquid solution toa freshly tilled dry soil. The wetted soilsurface is then allowed to air dry for someperiod of time, from 1 to 24 hours or morebefore any experiments would commence.Other researchers have suggested that PAMcould be applied as a dry powder, and thenactivated by rainfall to provide erosioncontrol over a substantial period of time(Roa-Espinosa et al., 2000).

A field rainfall simulator experiment wasconducted on a 17% constructed fill slope(simulated embankment) using a silty claytopsoil (18% sand, 40% silt, 42% clay, 3.4%organic matter). Anionic PAM was appliedat a rate of 60 kgha-1 (53 lbs ac-1) as either a

red fescue) was broadcast on the plots at 190kg ha-1 (170 lbs ac-1). Dry granular fertilizer(12-12-12) was also hand broadcast at a rateof 900 kgha-1 (803 lbsac-1).

A two-barrel runoff collection system,described by Mitchell et al. (1996), was usedto collect and measure runoff and sedimentloss from the plots. Runoff from each plotwas directed down a sloping metal channel toa 230 L (60 gal) plastic barrel. Once this firstbarrel filled, a flow divisor was used to direct1/9 of the overflow to a second 230 L (60 gal)barrel. Full details on the experimental proce-dures can be found in Flanagan et al. (2002b).

Nine runoff-producing rainfall eventsoccurred from the time of plot establishment(June 1997) until the study was completed inSeptember 1997. In eight of these nineevents, the PAM treatments significantlyreduced sediment yield below that from thecontrol; however, runoff was only significantlyreduced in five of the nine events. Over allstorm events, the P and PG treatmentsreduced runoff by about 33% and reducedsediment yield by 45% to 54%. The PAMtreatments were most effective at reducingsediment yield compared with the control inthe storm events earlier in the season. Theaddition of the gypsum with the PAMshowed no added benefit at this site whencompared with use of PAM alone,most likelybecause of the presence of electrolytes(calcium, etc.) in the surface soil on all plots.

Grass establishment was checked at 17 dif-ferent times on these experimental plots.Photographs were taken to allow furtherassessment of grass-stand quality and visualranking of grass health. The nine pictures foran individual observation day were rated on ascale from 1 (best) to 9 (worst), and then anaverage rating for each treatment was calcu-lated for each observation day. Grass estab-lishment on the PG and P plots consistentlyranked better than that on the control plotsfor all 17 dates and over the entire growingseason. Average vegetation establishmentratings were 7.9 for C, 4.4 for P, and 2.7 forPG. (Lower numeric values are better.)

In 1998, a similar natural rainfall studywas conducted on a fill slope at a sanitarylandfill near Logansport, Indiana. The sametreatments were used in a randomized com-plete block design, with nine experimentalplots and the same runoff and sediment col-lection equipment. The fill soil here was asilt loam topsoil (21% sand, 61% silt, 18% clay,1.63% organic matter) stripped from anotherarea of the landfill, then placed at the studysite with scrapers and spread to a 60 cm depthwith a bulldozer. Plots were again 2.96 mwide × 9.14 m long (9.7 ft by 30 ft) and hada final slope gradient of 45%. Runoff andsediment samples were collected from lateMay to November.

During the 5.5-month period, 636 mm (25 in) of rainfall fell on the plots and there

Figure 4View of representative plots of steep slope natural study at landfill site (45% slope) three weeksafter seeding and following 130 mm of cumulative rainfall. From left to right, treatments were:PG—80 kg ha-1 PAM and 5 Mg ha-1 Gypsum; C—untreated control; P—80 kg ha-1 PAM.

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dry formulation or in a 0.1% liquid solution.An additional source of multivalent cationswas applied with the PAM. There were four treatments in all: untreated control; dryPAM at 60 kgha-1 (53 lbsac-1), along with dryNutraAsh® (PAMD+NA); wet PAM at 60 kgha-1 (53 lbs ac-1), along with dry NutraAsh(PAMW+NA); and wet PAM at 60 kg ha-1

(53 lbs ac-1), along with dry Soiler-Lime® (PAMW+SL). NutraAsh (NA) is areclaimed material marketed as a liming/fer-tilizer supplement that is manufactured fromponded class C fly ash that has been mined,crushed, and sieved to produce various-sizeproducts. SoilerLime (SL) is a liming/fertiliz-er amendment made by blending compostedalkaline coal ash from the Purdue Universitypower plant with fermentation by-productsfrom the Eli Lilly Corp. in Lafayette, Indiana.NutraAsh and SoilerLime were applied atrates to provide a calcium amount equivalentto 5 Mg ha-1 (2.2 tons ac-1) gypsum. Fulldetails on this experiment can be found inPeterson et al. (2002a).

A programmable rainfall simulator (Fosteret al., 1982) was used to apply rainfall in threesimulation subruns: initial dry run of 75 mmh-1 (3.0 inh-1) for 1 hour, followed bya 1 hour break, followed by a wet run of 75 mmh-1 (3.0 inh-1) for 1 hour, followed bya 30 minute break, followed by a very wet runat three intensities—75 mmh-1 (3.0 in h-1) for15 minutes, 28 mm h-1 (1.1 in h-1) for 15 minutes, and 100 mmh-1 (3.9 inh-1) for 15minutes. Runoff rates and sediment concen-trations were determined gravimetrically.

Figure 5 shows some representative plot soilsurface conditions before and after all of therainfall simulations. The image at the upperleft of the figure shows the soil surface typicalof all the treatments, in which the soil is in aloose and well-aggregated condition with alarge amount of pore space. In the upperright is a control plot surface, in which mostof the large soil aggregates have beendestroyed and the soil surface smoothed andapparently sealed. The dry PAM treatment(lower right) resulted in a similar appearancesoil surface to the control, apparently becausethe large storm event and rapid wetting didnot allow time for the dry PAM particles toactivate and protect the soil surface. Soil sur-faces that had been treated with a liquid sprayof PAM (and dry NA) maintained muchmore aggregation and did not appear to havemuch surface sealing (image at lower left).

Surprisingly, total runoff was greatest from

the soil surfaces that had been treated with thedry PAM and NA (Table 5). The dry PAMgranules apparently acted in some way toimpede infiltration and enhance runoff. Aviscous solution of high-concentration PAMmay have plugged the soil pores as waterhydrated the PAM granules. Runoff from thedry PAM treatment was 64% greater than thecontrol. The wet PAM application treat-ments, however, significantly reduced runoff,by 62% to 76% compared with the control.Figure 6 shows average treatment runoff rateswith time for the runs on initially dry soil.Here the wet PAM applications clearlydelayed initiation of runoff, decreased peakrunoff rates, and decreased total runoff. Thewet PAM treatments also significantly reducedsediment yield, by 93% to 98% comparedwith the control. There were no significantdifferences between the total sediment lossfrom the control and dry PAM treatments.

This field experiment demonstrated theimportance of applying polyacrylamide as aliquid solution that is allowed to dry on thesoil surface before a large rainstorm event.Application of PAM as dry granules actuallyincreased runoff and soil loss under the condi-tions of this experiment, making things worsethan if no soil amendment had been applied.This type of rainfall simulation experimentapproximates what might be caused by a largethunderstorm typical of the midwesternUnited States. For other regions where thereare prolonged periods of low-intensityrainfall, dry PAM applications may be feasible,if the material can be activated properly.

Earthen channel PAM experiment.The previous agricultural and steep-slopefield studies showed the ability of PAM toreduce rill formation and rill detachment.Another area of possible use for the polymermight be in concentrated flow areas, such as

Figure 5View of representative plots from PAM application method experiment before (upper left) andafter completion of all rainfall simulations. The treatments shown here were control (upperright), liquid PAM and NA (lower left), and dry PAM and NA (lower right).

Table 5. Total runoff and sediment loss from PAM application method experiment.

Runoff % Runoff Sed. yield % SedimentTreatment depth (mm) reduction (Mg•ha-1) reduction

Control 74.9b* 43.0a*

PAMD+NA 123.a -64 29.6a 31

PAMW+NA 28.7c 62 3.0b 93

PAMW+SL 17.8c 76 0.90b 98• Values in same column followed by same letter are not significantly different at P < 0.05

using Tukey multiple comparison method.

JOURNAL OF SOIL AND WATER CONSERVATION S|O 2003308

newly-seeded grass waterways, emergencyspillways for dams, and possibly directly onephemeral gullies.

To study how effective anionic PAMmight be at controlling detachment by largechannel flows, a cooperative study was con-ducted with the USDA-ARS HydraulicEngineering Research Unit in Stillwater,Oklahoma. A large, outdoor, 29 m (95 ft)long, 1.8 m (6 ft) wide, and 2.4 m (8 ft) deep,reinforced concrete flume (see Robinson andHanson, 1996) was used. This same flumeand the soil conditions in our study were verysimilar to work by Bennett et al. (2000) thatexamined characteristics of eroding ephemeralgullies. A local red clay loam soil (37% sand,35% silt, 28% clay) was placed in layersapproximately 10 cm (4 in) deep, then packedto a bulk density of 1.92 gcm-3 (120 lbs ft-3) Atotal soil depth of 0.8 m (2.6 ft) in the base ofthe flume was desired, which required from 7to 9 layers. The soil was screeded to a uni-form 1% slope using iron rails attached to thewalls of the concrete flume as a guide.

Two parallel trapezoidal channels were cutinto the soil bed using a specially designed,hydraulically powered tiller attached to thefront of a skid-steer loader. The same railsused to support the screed were also used toguide the tiller. Channels were 0.6 m (24 in)wide at the top, 0.1 m (4 in) wide at thebottom, 0.13 m (5 in) deep, and 15.2 m (50 ft) long. The loose soil displaced by thetiller from the channel cross sections wascarefully removed by hand. A carriage sus-pended from rails on the top of the flumewalls allowed free access to the soil surfacewith no contact to the test bed.

The soil treatments in this study were 80kg ha-1 (71 lbs ac-1) anionic PAM and anuntreated control, replicated three times, andwith a control and PAM treatment being runconcurrently. The PAM used in this studywas anionic Magnafloc® 156 (Ciba SpecialtyChemicals Corp., Suffolk, Virginia) having~30% charge density and molecular weight ofabout 18 Mg mol-1 (20 tons mol-1). ThePAM was applied to the soil surface as a 0.1%solution using a power sprayer the day beforethe inflow experiments.

Water from a nearby lake was used asinflow to the flume, and four inflow rateswere applied (96, 190, 380, and 760 L min-1

[25, 50, 100 and 200 gpm]). The change ineach channel’s shape at multiple cross sectionswas measured with a point gauge (at 3, 6, 9,and 12 m [10, 20, 30, and 40 ft] from the

Run

off

Rat

e (L

/m

in)

Time (min)

Control PAMW+NA PAMW+SL PAMD+NA

25

20

15

10

5

00 10 20 30 40 50 60

Figure 7Outflow from PAM experiment in large outdoor flume in Stillwater, Oklahoma, with untreatedcontrol channel on left, and channel on right treated with 80 kg ha-1 anionic PAM. Both channelshere were receiving same inflow rate of water at 380 L min-1. Notice high sediment concentrationin water outflow on left, as well as channel incision and widening.

Figure 6Runoff rate versus time for runs on initially dry soil for PAM application method field rainfallsimulator experiment.

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point of inflow). Sediment samples werecollected in 1 L (0.26 gal) plastic bottles atthree times during each inflow rate. Detailson the experimental methods and results canbe found in Peterson et al. (2002b).

PAM was very effective at controllingerosion in the earthen channels. Averagesediment yield rate for the treated channelswas significantly (P < 0.05) reduced, by 93%to 98% compared with the control, across allinflow rates. There were only very minimalchanges in the PAM-treated channel crosssections, while for the control channelsextensive incision and channel wideningoccurred (Figure 7).

This experiment showed that anionicPAM could effectively control detachmentcaused by very large flow rates, which mightbe typical of ephemeral gullies or grass water-way channels in agricultural fields. Morework is needed to determine what theoptimal amount of PAM might be for thesesituations and whether the material wouldcontinue to provide protection for steeper-slope channels experiencing high inflows.

Laboratory flume study on erodibilityparameters. To better understand the impactof anionic polyacrylamide on soil resistanceto detachment, a series of laboratory experi-ments was conducted in 2001 and 2002 on a4.5 m (15 ft) long flume with 15 cm (6 in)wide simulated rill channels set on a 10%slope. The seven soils used (Table 6) had awide range of physical and chemical charac-teristics. A minimum of four different PAMapplication rates from 0.1 to 80 kg ha-1

(0.1 to 71 lbs ac-1) were applied to the soil asa 0.075% liquid solution that was allowed todry for 24 hours. The PAM used in thisstudy was Magnafloc® 156 (Ciba SpecialtyChemicals Corp., Suffolk,Virginia).

On the day of the experiment, an initialsimulated rainfall was applied at an intensityof 30 mmh-1 (1.2 inh-1) to minimize effectsof antecedent moisture content, as well asprovide a condition similar to a natural rill.Following the prewetting, rainfall wasstopped and then inflow at the top of thechannels was started. Water inflow ratesranged from 4 to 56 Lmin-1 (1 to 15 gpm).Flow discharge and sediment samples were

collected at the exit of each rill channel. Thesediment discharge data were analyzed toestimate detachment rates as a function ofapplied flow shear stress (assuming an excessflow shear stress detachment relationship),resulting in values for critical hydraulic shear(τc) and rill erodibility (kr) (Table 7). Figure8 shows an example set of results for the Barnes loam soil for the 20 kg ha-1

(18 lbs ac-1) PAM treatments, a definite shift-ing to a higher critical shear stress is evident.Details on the experimental procedures andadditional results can be found in Petersonand Flanagan (2002) and Peterson (2002).

The data and relationships developed fromthis study are being used to determine func-tions to estimate baseline erodibility and shearstress, as well as adjustment factors to accountfor the effect of anionic PAM on kr and τc. Aninitial equation to predict the multiplicativeadjustment factor for τc is (Peterson 2002):

(1)

τ*cp=3.17+0.0119 e +0.497(P)(d 2)(CLAY )(Ca)106,

16

CLAY10

Table 6. Selected lab flume study soil physical and chemical properties.

Organic BraySoil Type Location Texture Sand Silt Clay matter P1 K Mg Ca pH CEC

———— % ———— % ———— ppm ———— meq/100g

Local Soil Indiana Clay loam 26 40 34 3.0 32 138 390 4600 7.7 26.6

Cecil Georgia Sandy loam 65 19 16 1.6 60 170 50 450 5.3 5.5

Tifton Georgia Loamy sand 81 11 8 1.3 29 96 50 300 6.5 2.2

Heiden Texas Clay 19 21 60 3.1 5 203 120 14800 7.9 75.5

Barnes Minnesota Loam 43 33 24 4.3 29 134 415 2550 6.6 17.8

Mexico Missouri Silty clay loam 11 59 30 3.7 36 168 315 2500 7.0 15.6

Nansene Washington Silt loam 15 67 18 2.7 33 538 250 1200 5.5 14.3

Table 7. Average critical shear stress (Pa) and rill erodibility (s•m-1 * 1000) for laboratory rill flume study by treatment using weightedleast squares regression.

———————— PAM Application Rate (kg•ha-1) ————————

Soil Type 0 0.1 0.25 0.5 1 2.5 5 10 20 30 40 80

Local Soil τc 3.00 — — — — — — — 4.65 — 3.11 3.13Kr 20.4 — — — — — — — 17.9 — 4.4 1.7

Tifton τc 1.72 — — — — — 4.71 — 0.67 — 5.58 —Kr 59.2 — — — — — 18.7 — 0.2 — 1.3 —

Cecil τc 0.94 — — — — — 3.60 3.09 4.94 3.25 2.67 —Kr 26.7 — — — — — 13.9 33.1 39.5 16.0 12.9 —

Heiden τc 0.58 — — — — — — — 3.83 2.81 3.42 —Kr 11.5 — — — — — — — 21.7 8.6 7.8 —

Barnes τc 0.82 — — — — 4.33 4.45 4.30 3.95 — — —Kr 9.4 — — — — 7.2 6.2 11.1 12.2 — — —

Nansene τc 1.48 2.28 2.75 4.02 — — — — — — — —Kr 8.3 7.4 7.6 6.9 — — — — — — — —

Mexico τc 0.58 — — — — 4.59 — 3.10 — — — —Kr 5.7 — — — — 43.2 — 1.6 — — — —

JOURNAL OF SOIL AND WATER CONSERVATION S|O 2003310

ments are examining the interaction betweenPAM application rates and soil aggregate size,because the polymer appears to be moreeffective when applied to smaller size aggre-gates. This may lead to guidelines for optimalPAM rates for given soil conditions.

Summary and ConclusionMore than ten years of research studies at theUSDA-ARS, National Soil Erosion ResearchLaboratory have demonstrated the effective-ness of anionic polyacrylamide at controllingsoil erosion. In particular, these studies haveidentified that PAM affects rill detachmentprocesses more than interrill ones and cangreatly decrease rill formation and detach-ment rates. Use of a liquid solution that isallowed to dry on the soil surface is muchbetter than use of dry PAM granules at con-trolling erosion from a large rainfall eventoccurring soon after application. PAM wasable to control detachment from flows ofwater up to 760 L min-1 (200 gpm) in anearthen channel, indicating that it may be ableto be used to control erosion in ephemeralgullies, newly established grass waterways,and other concentrated flow channels.Laboratory studies have been and are cur-rently being conducted to quantify the effectof PAM application rates on rill erodibilityand critical hydraulic shear. Ultimately,results of current research are planned to beused for development of guidelines for PAMrates needed to control erosion for a particu-lar soil, soil condition, slope, and climaticregion. Current costs of PAM may limit itseconomic feasibility for general agriculturalapplications, but it may fit well as a tool for protecting embankments and newly-constructed earthen channels.

Endnote1The use of trade names does not constitutean endorsement from the U.S. Departmentof Agriculture-Agricultural Research Serviceor Purdue University.

References CitedAase, J.K., D.L. Bjorneberg, and R.E. Sojka. 1998.

Sprinkler irrigation runoff and erosion control withpolyacrylamide-Laboratory tests. Soil Science Societyof America Journal 62(6):1681-1687.

Ben-Hur, M. 1994. Runoff, erosion, and polymer applica-tion in moving-sprinkler irrigation. Soil Science158(4):283-290.

Bennett, S.J., J. Casali, K.M. Robinson, and K.C. Kadavy.2000. Characteristics of actively eroding ephemeral gulliesin an experimental channel. Transactions of the AmericanSociety of Agricultural Engineers 43(3):641-649.

where τ*cp is the factor to multiply times the

baseline critical shear to get the adjustedvalue, CLAY is the percent clay in the soil, Pis the PAM application rate in kgha-1, d16 is arepresentative aggregate diameter in mm, andCa is the calcium content in mg kg-1. Theequation should be set equal to one if noPAM is applied. Using the data from theexperiment, the equation had an R2 of 0.821and an adjusted R2 of 0.800 (n=90), and allcoefficients were significant at the P < 0.05level. As this is a preliminary equation, usinga limited set of soils, the values used in theequation should be in the range of the datafor this research. Also, very low PAM appli-cation rates (e.g., < 1 kgha-1 [< 0.9 lbs ac-1])in combination with large values of d16 (e.g.,> 0.3 mm [> 0.01 in]) will probably lead tomeaningless results.

The rill erodibility of a PAM-treatedsurface was conceptualized as a function ofsurface roughness, strength of the soil surface,and depth of the PAM-treated soil layer.Once failure of the PAM-treated soil surfaceoccurs, the rate at which the scour hole(s)develops is related to the soil strength, or

cohesion, at the soil surface, as well as thecohesion of the underlying soil. The initialequation to predict PAM effect on rill erodi-bility is (Peterson 2002):

(2)

krp=1.28–(32.2) + (0.164)d84,

where krp is the factor to multiply rill erodi-bility by to reflect the polymer effect, Cp is thePAM concentration in ppm and d84 is a repre-sentative aggregate diameter in mm.Parameter values used with this equationshould be in the range used in this research.Combinations of high PAM application rateswith low PAM concentrations will give erro-neous negative results. In this equation, all ofthe regression coefficients were significant atthe P < 0.05 level, and the equation provideda modest fit with the observed data with an R2

of 0.497 and an adjusted R2 of 0.438 (n=90).Further analysis of the data from this exper-

iment, refinement of the prediction equations,and continued experiments in the rill flumeare continuing. In particular, new experi-

PCp

Figure 8Example sediment discharge rate versus shear stress graph for control and 20 kg•ha-1 PAM treat-ments for the Barnes soil in the laboratory flume experiment. Notice the definite effect of PAMon the critical shear stress for this soil.

q s(k

g s-1

m-2)

Tau (Pa)

P20 Control

0.1

0.08

0.06

0.04

0.00

0

0 1 2 3 4 5 6 7 8 9 10

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