Gnservation TillageFEBRUARY 199

Official Publication for State Conservation Tillage Associations and Districts

PA toIrrigaition SystemsGreatly Eliminates

Erosionfr •

New Icitation IncreasesCropping Options

Challenging the SoybeanYield Barrier

•

...ADRICK LENTZ • AD,SDA/ARS PKG 0417

J793 N 3600 E SACK 26.. IMBERLY ID • 83341-5076A.11.11.1.1.11.1.144.1.11.1.14,11.AH

E

rosion is one of the banes ofagriculture; it just won't goaway. Its curse has hunkered

over tillers of the soil for thousands ofyears, stealing soil, nutrients andproductivity. Soil erosion is highlydetrimental, both on and off site. Ithas been blamed for the loss of peo-ples and the collapse of civilizations.Now, a technology that uses an off-the-shelf chemical flocculent providesa convenient and economical meansof fighting back. The chemical floccu-lent is PAM, short for polyacrylamide.Field studies conducted since 1991 bythe USDA's Northwest Irrigation and •Soils Research Laboratory (Kimberly,Idaho) demonstrated PAM's ability topractically eliminate water erosion onfÜrrow irrigated fields. These find-ings have stimulated the imagina-tions of other scientists and farmers,who are exploring PAM's potential for •controlling erosion and increasinginfiltration under sprinkler irrigation •and on construction sites and impr . ,, ,ing emergence of row crops.

PAM belongs to a class of materiak-,called polymers. Polymers are • verylarge molecules made from smaller

66

identical building blocks that arechemically linked together. The PAMused in erosion control is made fromtwo types of building-block units.Several hundred thousand of theseunits are linked together into a longchain to produce a water-soluble, "I in-ear" copolyiner. It is this linear PAMthat is used to control erosion.Unfortunately, the linear PAM isoften confused with a related "cross-linked" form th.:t has very differentproperties. The Itiked" PAM isproduced when ; Aividual

poly J ! ;: together .

used as a soil conditioner to increaseplant available soil water or as anabsorbent in disposable diapers.However, it is the water soluble, lin-ear PAM that is used in this erosioncontrol technology and discussed inthe remainder of this article.

The PAM molecule's size and chargecharacteristics are important becausethey determine how PAM reacts withsoil. The linear PAM used in erosioncontrol has a very high molecularweight of 12-15 million grams permole. When dissolved in water, about18% of the PAM'S building-block sub-

ts ionize, giving the molecule a•,gative (anionic) charge. This PAM.•,:ibilizes and strengthens soils and

settling agent. A . settlin t rContinued on p. 24

... PAM may eventually beeconomically useful in

rainfed agriculture."

POLYACRYLAMIDE (PAM)FOR EROSION CONTROL

Continued from p. 21agent causes individual soil particlessuspended in the flowing water tostick together, forming larger andheavier soil clumps thatsettle to the furrow bottom.PAM was tested in a three-year ARS study conductedin Idaho. Applying aboutone pound PAM per acre inirrigation water cut fieldsoil losses by 94% andincreased net infiltrationinto furrows by 15%. Thecombined effect of reducedfurrow down cutting andgreater infiltration,increased lateral watermovement toward theplanted row by 25%. PAMtreatment greatly improvedrunoff water quality.Treated furrow runoff wasclear, having little sedi-meat and markedly lowerconcentrations of phospho-rus, nitrate and organicmaterials.

PAM works most effec-tively when it is dissolvedin the irrigation water thatfirst flows down the fur-rows and wets the soil.PAM concentration in irri-gation water should be 10ppm (i.e. 10 parts PAM forevery million parts water).Typically, PAM-treatedwater is used only duringthe furrow advance phase,that period in the early partof the irrigation whenwater first overruns andwets (treats) the dry soil.Then untreated irrigationwater is used for the remainder of theirrigation. During initial wetting,PAM in infiltrating water contactsand becomes bound to a thin layer ofsoil on the surface I.rf furrow clods andalong the wetted furrow. The treatedsoil is more cohesive and stable, andis less likely to rupture, disintegrate,or move downstream in flowingwater. Any fine soil particles in thefurrow stream adhere to one anotherand form larger particles that . settleout of the flow. Compared to untreat-ed furrows, PAM-treated soils have acoarser structure, furrow surfaces arerougher, and the depositional layerthat forms along the furrow bottom,is more porous. This allows infiltra-tion rates to remain high, maintains

lower runoff rates and helps preventerosion and soil loss. Not all irriga-tions need be treated, but we recom-mend that irrigations done early in

the season, and those on disturbed:;oils be treated with PAM.

PAM use for preventing furrow irri-gation-induced erasion is growingrapidly in the irrigated West. MostFarmers buy granular PAM from localfarm suppliers in 55 lb, bags at a costthat ranges from $3.50 to $5.00 perpound. The PAM is applied to thewater supply using home-built or pur-chased devices that include a storagebin and a battery-powered Gandy©applicator or auger-screw system thatdrops PAM crystals into the waterflow at a uniform rate. Turbulence isintrodticed in. the water just down-stream from the point of applicationto help dissolve and disperse thePAM. Flow drops or dams placed in

the downstream flow produce suffi-cient turbulence in most cases. PAMis also available in either 30% or 50%inverse oil emulsion concentrates

that dissolve more easilywhen dribbled into flowingwater.PAM is an environmentallysafe material. At concentra-tions used in field applica-tion, it has no known toxiceffects on humans or othermammals, aquatic verte-brates or invertebrates, orplant life. It has been listedby U.S. EPA as an"Acceptable Drinking WaterAdditive" and has gained avariety of FDA approvals forfood additive applications.In soil, PAM acts like othernaturally occurring, persis-tent forms of organic mat-ter, degrading to H2O andCO 2 at a rate of approxi-mately 10% per year.

There are a number of dif-ferent types of polyacry-lamides available for sale.Farmers should verify thatthe PAM they purchase foranti-erosion is the anionic,high molecular weight,water soluble type and con-tains less than 0.05% of themonomer, acrylamide,which is regulated by law.At these levels, the acry-lamide monomer, a manu-facturing contaminant,poses no • threat to soils or

• surface waters. Unlike poly-acrylamide, the acrylamidemonomer rapidly biode-

. grades in soil or water,decomposing in a matter of hours,

Some farmers have already usedPAM in center pivot sprinkler sys-tems to increase infiltration andreducerunoff and erosion. An emulsi-fied PAM concentrate is injected intothe sprinkler source flow to obtain a10 ppm concentration, which is deliv-ered to the field in varying amountsofwater. The farmers saw definiteimprovements using the PAM.Scientists are currently researchingthis new application method. In addi- : .tion. engineers have successfully usedPAM on disturbed construction-sitesoils to increase infiltration andreduce erosion from rainfall. Moreinvestigation needs to be dime, butthese successes. suggest that PAM

24 Nup FEBRUARY IW)7

11

may eventually be economically use-ful in rainfed agriculture. While PAMis not the ultimate solution to agricul-tural erosion, it is a convenientlyapplied technology that can be usedimmediately to dramatically reducesoil losses and nonpoint source pollu-tion. As such, it is one of the mostexciting and effective new weaponsavailable in our agricultural arsenal.The final solution to agricultural ero-sion most likely will rely on a systemapproach that utilizes conservation

tillage techniques and residue man-agement to build up and maintainsoil strength and structure. Eventhen, sonic rotations that include alow-residue crop will probably requireadditional protection, like that sup-plied by PAM. •

Rick Lentz and Bob Sojka. are soil sci-entists at the USDA AgriculturalResearch Service, NorthwestIrrigation and Soils ResearchLabortatory, Kimberly, Idaho.

COMIY BRIOBARACTERISTIC

t yield potentialr ear retentioning plant Heath

Maturity 1(18-110

odium full seasonelding • Good dry-dow

Npproximate Maturity 112 Days

Eio 460 d dry-down of grainsistent performancemate Ma turity 111 Days

lEi• '90 relent plant health

b standabilityield potentialMaturity 111 Days

SOYBEANVARIETIES

Freedom 4437 CN Has shown to he a leader inbeating the best in yields.

Freedom 4498 CNProduces top yields in

southern soybean growing areas.

Director of MarketingTOM D•NNEY

Neoga, ILPh.: 217/895-2191Fax: 217/895-2853

BOB TAYLOR

BIG BAY AGXenia, If

Grantsburg, IL618/662-9452

618/949-2857

JOHN B. DAVISHardin, IL

618/576-9339

FREEDOM WHERE EVERYBAG IS PLOT SEED

i1/4EEDOM SEEDCOMPANY

U.S. Route 24 EastAstoria, IL 61501

1-800-262-4480

NCTD FEBRUARY 1997 25

At Left: Farrow irrigation without PAM treatment.Below: Farrow irrigation with PAM treatment.