Adapted from:Lentz, R.D., T.D. Stieber, and R.E. Sojka. 1995. Applying polyacrylamide
(PAM) to reduce erosion and increase infiltration under furrow irrigation.
p. 79-92. InL.D. Robertson, P. Nolte, B. Vodraska, B. King, T. Tindall, R. Romanko,
J. Gallian (ed.) Proc. Winter Commodity Schools - 1995. University of Idaho
Cooperative Extension, Moscow, Idaho.
APPLYING POLYACRYLAMIDE (PAM) TO REDUCE EROSION AND INCREASE INFILTRATION
UNDER FURROW IRRIGATION
R.D. Lentz: Mail
1, T.D. Stieber
2, and R.E. Sojka
Polyacrylamide (PAM) has received widespread attention in the last 3-4
years as a potential new tool for virtually halting irrigation-induced
erosion in furrow irrigated agriculture when added in small amounts to
the advance phase of water application. When used properly, 3-7 lbs of
PAM per acre per year can reduce erosion from typical furrow irrigated
fields in Idaho an average of 94%. Because PAM in irrigation water retards
surface sealing, it also generally increases net infiltration and lateral
movement of infiltrated water. Season-long infiltration totals for PAM-treated
fields in Idaho have averaged 15% higher than non-treated fields.
Research by the USDA Agricultural Research Service in Kimberly, Idaho
has documented the effectiveness of PAM and provided general guidelines
for safe use (5, 6, 7, 13, 14, 15, 16, 17, 18, 19). The October 1994 issue
of Soil Sciencedeals comprehensively with PAM-use efficacy and environmental safety (1,
2, 3, 4, 5, 7, 8, 10, 12, 15). Another recent review (11) covered the topic
independent of the symposium reported in Soil Science. Basic familiarity with PAM-use in irrigation water, can be obtained
from two publications (7 & 14) available from the authors. Recent work
(Stieber) with farmers using PAM has shown the need for certain cautions
regarding field scale applications of PAM. These are discussed later in
Commercial formulations of PAM are now available as soil amendments under
approved labels in Idaho and several other Western states. An interim conservation
standard was approved in January 1995 for PAM-use in furrow irrigation
for the Western US by the NRCS (formerly SCS). It is expected that this
will pave the way for cost sharing in some areas. Local NRCS and Consolidated
Farm Service Agency (formerly ASCS) offices should be contacted for specific
Overall Before considering PAM-use a farmer should read the PAM label, the interim
west-wide conservation standard and supporting literature (e.g. 7 &
14) mentioned above. PAM requirements for sprinkler application have not
been thoroughly researched to date. It is generally assumed, however, that
application rates for results similar to those seen with furrow irrigation
may require several times the per acre application rate. PAM will perform
better in high quality irrigation water than in waters impaired by high
sediment content and/or high sodium adsorption ratio (SAR). PAM works best
on silt to clay textured soils, and may have little effect on sandy soils.
Proper mixing and uniform application of PAM are essential to proper performance.
Although thorough cost benefit analysis for PAM use has not been performed,
the practice is regarded as economical and possibly profitable. The cost
of PAM to farmers at this writing is expected to be $4-6 per pound (@ 3-7
lbs/year anticipated application requirements for complete erosion control).
Yield increases may result from water infiltration benefits and through
enhanced retention of plant nutrients. A thorough economic analysis must
include the reduced need for furrow reshaping and the decreased need for
settling-pond or return-flow ditch cleaning.
Water Quality - Chemistry Salinity per se (i.e. electrical conductivity, or EC) is seldom a problem
if the alkalinity (SAR) remains low, within the range of EC acceptable
for irrigation water. In fact, a slight electrolyte content (small measurable
EC) of divalent cations (e.g. Calcium or Magnesium ions) will improve PAM
efficacy compared to distilled water. The PAMs currently labeled for use
in furrow irrigation are moderately anionic. Divalent cations have small
hydrated radii compared to the hydrated sodium ion. Thus divalent cations
"bridge" the anionic PAM and soil adsorption sites whereas sodium's lower
charge and greater volume impairs bridging. Thus high SAR or very low EC
could require addition of more PAM for desired effectiveness, or addition
of a divalent electrolyte to irrigation water to aid PAM efficacy (e.g.
addition of gypsum--CaSO
Water Quality - Suspended Sediment PAM is a potent industrial flocculent--a powerful settling agent for suspended
solids. If water supplied at the head ditch contains appreciable amounts
of suspended sediment, the addition of PAM to the water will cause the
suspended sediments to settle rapidly to the bottom of the ditch. If sediment
loads are particularly high (>5 g/l), the settled sediment can fill-in
large reaches of the head ditch in only a few hours. Even for moderately
turbid water (1-5 g/l) addition of PAM to the water may increase the intervals
of required ditch maintenance.
Presence of suspended solids need not preclude the use of PAM, but it
will require certain precautions. If possible, rather than adding PAM directly
to the ditch, PAM can be added in a small holding pond along side of the
ditch at the upper reaches of the field. This can allow the treated flow
to drop-out its sediment load in the confined area without risk of damming
up the head ditch. When PAM is not being added, the flow need not run through
the pond, and captured sediment can be spread on the field.
Where possible, PAM can be added near the point of water entry into gated
pipe. Water flowing through pipe will usually retain a higher velocity
than in an open ditch and flocculated sediments will be carried further
in the flow. A large fraction of these flocculated sediments will be flushed
through the open gates and deposited within a few feet of the furrow inlets
across the upper end of the field. A farmer should inspect his gated pipe
when using PAM to determine the possible need for flushing the pipe at
the end of an irrigation. PAM should not be added to high sediment bearing
water being delivered great distances via gated pipe at low head, as the
risk of loading the pipe with sediments will be greatly increased. Research
is underway using modified drip lines to deliver PAM stock solutions to
individual furrows, avoiding the large scale sedimentation of bulk flows
in head ditches.
Soil Properties Soil salinity, structure, texture, organic matter content and mineralogy
are all factors that may effect PAM effectiveness. These factors have not
been thoroughly researched. It is generally thought that high exchangeable
sodium percentage (ESP), high amounts of shrinking-swelling clays (smectites,
e.g. montmorillonite or "bentonite"), or high amounts of organic matter
in soils increase the amount of PAM needed in irrigation water to achieve
erosion control. Structure and texture effects are somewhat better documented.
Structure Polyacrylamide acts to stabilize soil structure that is present at the
time of treatment. For optimal effect PAM should be applied to well structured
soils, ie. after tillage or cultivation operations done at appropriate
soil water contents. Treatment of freshly cultivated furrows is important
because the application will help preserve the high infiltration and surface
roughness characteristics that reduce furrow runoff and soil losses.
Texture PAM is thought to control erosion and increase infiltration best on medium
textured soils (sandy loams, silt loams, loams, silty clay loams). Sandy
soils with little or no silt or clay (loamy sands, sands) may show considerably
less PAM efficacy and PAM will have little or no impact on infiltration.
Clayey soils will see a greater relative impact of PAM on infiltration
and may see a smaller relative impact on erosion.
Slope Steeper slopes, breaking slopes, and longer slope runs, have the greatest
potential to see benefit from PAM-use. Extensive research has shown that
10 ppm of PAM in the advance phase water will control erosion on slopes
up to 3.5%. Greater slopes may need higher rates.
Subsoil layers If shallow subsoil layers have poor infiltration properties, PAM will
still help prevent erosion, but may have little net effect on infiltration
once the soil above the restrictive layer is wet. PAM cannot increase infiltration
into an already restrictive layer. The PAM infiltration benefits are the
result of structure stabilization in the surface few millimeters of soil.
Application Timing To achieve the maximum benefit of both erosion control and increased infiltration,
10 ppm PAM should be in the advancing water of the first irrigation. If
PAM is not applied until after water has begun to flow down the furrow,
or if added at lower rates, some of the surface soil structure will be
damaged by the non-treated water, reducing the PAM's effectiveness. PAM
should be reapplied in the same manner after soil disturbance (e.g., traffic
or cultivation). Best results are usually obtained on well formed, moderate
depth wheel track furrows. PAM application cannot overcome the effects
of excessive wheel track compaction.
Lower rates of PAM (1-5 ppm) in the advance water may prove beneficial
during irrigation on undisturbed previously irrigated furrows. Each irrigation
of undisturbed previously irrigated furrows without any PAM in the advance
water will result in a 50% loss of treatment effect. In the absence of
soil disturbance, the need for PAM treatment will decline as the season
progresses. This is because furrow sediment transport generally declines
later in the season as furrows become more stable, and/or vegetative material
enters the furrow.
Infiltration PAM treatment maintains water infiltration rate into the soil. Net increases
in infiltration with PAM-use reported in scientific studies are on a comparative
basis. Compared to irrigating without PAM, the season-long infiltration
totals obtained by irrigating with PAM are greater. Both non-treated water
and PAM-treated water cause gradual sealing of the soil surface, causing
the actual infiltration rate to decline with time. PAM treatment of water
simply slows that decline in infiltration rate, compared to non-treated
water. The difference is referred to as an "increase" in infiltration rate
with use of PAM.
In Idaho, PAM has increased infiltration an average of 15% on medium to
fine textured soils, and should be similarly effective on a range of soil
textures, including sandy loams, loams, silt loams, and silty clay loams.
The PAM treatment may have little or no effect on more coarse-texture soils
(loamy sands and sands). When dissolved in water, PAM thickens the solution
and makes it more viscous. At higher PAM concentrations, flow of treated
water through soils can be greatly inhibited by the attendant increased
viscosity. Label recommended rates will provide soil surface stabilization
without impeding water entry. PAM treatment at the 10 ppm rate in advance
water has proven effective on slopes up to 3.5%.
For furrows of approximately 4 inches in depth, PAM has increased lateral
wetting an average of 25%. This is because prevention of furrow downcutting
and sealing of the furrow wetted perimeter provides a stronger gradient
for lateral movement of water. This allows for a shorter irrigation set
time early in the season, when water movement to the seed zone is all that
is required. Similar increases in lateral wetting have not been seen in
deeper furrows (e.g. with potato hills). In these instances the shape and
depth of furrow and bed prevent measurable differences in lateral movement
Erosion In Idaho, using recommended application strategies, field sediment losses
have been reduced an average of 94% (range 80-99%). Because erosion is
greatly reduced, furrow configuration is much more stable, reducing the
need to reshape furrows as often through the season. PAM enhances other
management practices designed to reduce erosion. For example settling ponds
will require emptying far less frequently since most soil will remain on
the field. PAM benefits will be enhanced if stream size cut-back is practiced
(i.e. treat the advance with 10 ppm at a high rate of flow, then, when
runoff begins, cease applying PAM and cut the water stream back to a lower
flow rate). PAM-use is an effective means of helping farmers meeting water
quality goals, by decreasing return flow sediment, lowering biological
or chemical oxygen demand (BOD or COD), and preventing loss of phosphate
into streams, rivers, reservoirs and riparian areas. Data from California
(9) also show reduced loss of soil-adsorbed pesticides. These effects will
ultimately help improve Snake River water quality.
Irrigation Water Management Since PAM-use increases net furrow infiltration, water management may
need to be adjusted to avoid excessive water application. In fields with
steeply sloping furrows (> 2%), infiltration tends to be lower and water
normally advances rapidly down the field. Improved infiltration and longer
furrow advance times resulting from PAM treatment are not likely to be
a problem here. Although, on very steep fields, PAM may increase net infiltration
enough to warrant reducing irrigation set times. In fields with gently
sloping furrows (0-0.5%) and especially for non-trafficked furrows, infiltration
can be relatively high and advance times excessively long -- leading to
nonuniform, down-furrow water application. PAM technology can overcome
this nonuniformity problem because PAM allows irrigators to increase inflows
without increasing furrow erosion losses. Enlarging initial stream size
greatly reduces advance time and equalizes infiltration-opportunity-times
for the top and bottom of the field. On the other hand, if PAM is applied
to flat fields withoutchanging water management, it will further reduce water application uniformity
and may cause excessive water application and leaching at the field head.
Also, PAM will usually accentuate the difference between wheel track and
non-wheel track furrow advance times and infiltration rates.
Fields with variable slopes generally have improved infiltration uniformity
in the entire field - sometimes providing economic return from previously
marginal field areas where steep slopes prevented adequate infiltration
and/or were deeply eroded by season's end.
Commercial PAM Products Most states (Idaho is one) require that agricultural chemicals (including
soil amendments such as PAM) meet safety and state labeling requirements.
The PAMs currently labeled are water-soluble, anionic (11-20%), high (10-15
million) molecular weight compounds meeting EPA and FDA monomer limits
below 0.05%. PAM is available in several forms: dry powder or granules
containing 80-95% active ingredient (AI); inverse oil-emulsion liquid concentrates
containing 30 to 50% AI (PAM is dissolved in water droplets that float
in an oil matrix; and pre-mixed PAM-water solutions containing <3% PAM.
Consult the label for current approved use recommendations.
When should PAM be applied? As a minimum PAM should be used on the first irrigation and when soil
is disturbed by traffic and/or cultivation. Additional applications at
or below label amounts may be considered to provide complete erosion control
for the entire season. If PAM is applied in the first irrigation and subsequent
irrigations have no PAM in the water, then erosion control and infiltration
effects can be expected to decline approximately 50% with each non-treated
irrigation. Thus, by the third irrigation little effect remains. For those
crops in which erosion naturally subsides during mid season (e.g., potatoes
when vines elongate) PAM need not be applied after the natural erosion
reducing properties ensue.
Applying PAM to Irrigation Water Regardless of what form of PAM is supplied to the farmers (dry material,
concentrated material, or pre-mixed stock solution) it is important to
provide aggressive mixing (agitation) at the point of application of PAM
to the water sources. The agitation requirement increases as the concentration
of stock solution increases and is greatest for use of direct dry PAM application.
Agitation should be provided by use of a stream drop and multiple flow
obstructions near the point of injection. With vigorous turbulent flow
25-50 ft of ditch canal should be allowed for stock solution mixing before
the first siphon tube withdrawal or gate. Dry PAM may need longer ditch
runs for adequate mixing. If using gated pipe, the first length of gated
pipe after the point of PAM injection should have one or two baffles to
enhance mixing. PAM should not be added upstream from weed screens or filters of any kind.Heating of water or stock solution greatly enhances PAM dissolution and
Choosing Which Form of PAM to Apply - Pre-mixed Solution, Liquid Concentrate;
Pre-Mixed PAM-Water Solution Application
- easy to calculate and meter exact rates
- easy to keep track of amounts applied, since volume
applied can easily be recorded
- requires minimal "in the ditch" mixing to work well
- slower to clog weed screens, filters or narrow siphons
- low risk of exposure if operator doesn't handle dry
- applications can be accomplished without specialized
mixing or metering equipment
Disadvantages (Pre-Mixed Solution Application)
- may be more expensive than granular method due to
increased handling cost
- requires bulkier equipment that isn't manually portable
- large stock solution volumes needed for large fields,
or where advance rate is slow
- mixing field solution from concentrate takes considerable
time and requires 'dedicated' equipment
Liquid Concentrate (oil-emulsion) Application
- small volumes needed for large fields, or where advance
rate is slow
- easy to keep track of amounts applied, since volume
applied can easily be recorded
- application equipment must be more sophisticated (compared
to that for pre-mixed solutions) to obtain uniform metering rates
- includes oil and surfactant components that provide
no known benefits to crops
- requires more vigorous mixing than pre-mixed solutions
for dissolution and uniform application
- currently more expensive than dry PAM
- portable equipment that can be moved manually
- a season's supply of dry PAM can be purchased and
- may be the least expensive form of PAM
- less need to rely on suppliers to refill tanks on
farm (as for pre-mixed solutions) for irrigation sets
- application equipment may tend to plug
- requires more vigorous mixing than pre-mixed solutions
for dissolution and uniform application
- will rapidly plug weed screens and filters
- there is some danger of choking from inhalation of
PAM dust while filling machine
- need to purchase or build application equipment
- greater PAM losses from the field since there is less
control of dissolution
- poorer uniformity of distribution than with liquid
PAM-WATER SOLUTION APPLICATIONS
Preparing PAM-Water Stock Solutions Proper mixing equipment is required to prepare aqueous PAM solutions from
dry granules. The mixer should be capable of producing a distinct vortex
in the water volume contained in a full mixing tank. It is imperative that
dry PAM granules be added slowly to the vigorously agitated water volume,
ensuring that granules are dispersed individually in the solvent. Best
results are obtained when the solution is agitated for 60 min after all
PAM has been introduced. If possible, the solution should be allowed to
stand over night, to ensure that the PAM is fully hydrated and dispersed.
Stock solutions can be prepared from pre-mixed PAM-water solutions using
a recirculating nurse tank. Pre-mixed PAM-water solutions are generally
2.25% PAM and are the consistency of cold honey. Furrow treatment strength
is obtained by first diluting to field solution strength in a nurse tank
and the final dilution takes place in the ditch or pipe on the way to the
(Table 1). Usually a 9:1 dilution ratio is used and resulting field concentration
kept below 2500 ppm to ensure easy handling in the field.
|STOCK SOLUTION ---->
||FIELD SOLUTION ---->
Diluting Stock Solutions in a Nurse Tank
- Start with a clean nurse tank 1000 gallons or larger that is set up to recirculate. Plumb a delivery hose and float box or valve to the tank if it will be used for applying PAM to fields.
- Add 200-300 gallons of water and start recirculation.
- Begin to add 2.25% stock solution slowly while recirculating. Add 100 gallons total.
- Fill tank to 1000 gallons with water while recirculating.
- Resulting 2250 ppm PAM solution will not require continuous recirculation.
Calculating PAM-Water Solution Application Rate The rate of PAM to apply depends on 1) irrigation flow rate,
2) concentration desired in water, and 3) concentration of PAM field solution.
Worksheet #1 to calculate the flow rate of the PAM-water solution to inject. Advantages
of a worksheet are that it can also serve as a record keeping tool that
allows adjustment of PAM delivery based on field observation.The equation to calculate liquid PAM injection rate is relatively simple:
PAM Injection Rate (gpm) = [Irrigation flow (gpm) x Desired Inflow ppm)]
/ [PAM Stock (ppm)]
Volume of PAM-Water Solution Required to Treat a Field Using the rate of application of 2250 ppm field strength PAM from your
Worksheet #1 and predicted irrigation advance rate, volume of PAM solution can quickly
be determined using
Table 1. For early irrigations when the desired PAM inflow rate is 10 ppm or
greater, the volume of liquid PAM can be quite high. For fields larger
than 20 acres, more than 1000 gallons of PAM stock solution may be needed
(Table 1). Volume of PAM solution can be reduced by increasing field solution concentration
to its maximum based on handling limitations; around 3000 ppm PAM.
Many furrow irrigators use 24-hour sets. Some use 12-hr sets. Advance
rates typically range from 6 to 18 hours for a first irrigation and 4 to
8 hours subsequent irrigations. Surface irrigation is most efficient when
advance time is one 1/4 to 1/3 of the total set time. Larger inflows can
be used with PAM-treated water, thereby decreasing advance time, yet without
risk of erosion. Irrigations may be reduced to twelve hour sets on some
fields when PAM is applied. These management changes could also reduce
leaching of N.
Pre-Mixed PAM-Water Solution Metering Devices
1. Poly tanks should be a minimum of 1000 gal. size but a 1500 gal. tank
would fit most situations and doesn't cost appreciably more. Trailer or
pickup-mounted poly tanks can prove a useful convenience, however, actual
tanker trucks that sit at a specific field during irrigation may be over-kill.
Remember that tanks may need refilling between irrigation sets on some
2. Flow of PAM solution from the poly tank to the irrigation supply ditch
will usually be from 1 to 4 gpm. Accuracy of delivery should be 0.1 gpm,
especially in the 0 to 2.5 gpm application range. Rapid adjustability is
important if the system will be moved between fields.
3. Although "float boxes" (constant delivery rate gravity flow boxes)
are desirable to keep outflow constant, they are not essential equipment.
A timer shutoff may pay for itself. A complete application system would
include a shutoff timer, flow gauge, and totalizing flow meter.
LIQUID CONCENTRATE (OIL EMULSION) APPLICATIONS
Metering Devices Note that small water quantities contacting an oil-emulsion liquid
concentrate cause the liquid to gel. Thus applicator discharge tubes must
be protected from water contact to prevent them from being plugged. One
means of accomplishing this is to install a check valve at the end of the
discharge tube to prevent backflow into the tube and storage tank. The
viscosity of an oil-emulsion liquid changes significantly with temperature.
Therefore, if applicators that dispense oil-emulsion concentrates via gravity
flow are calibrated early in the morning, they will tend to apply excess
PAM as the day progresses, because air temperature increases and the liquid
flows more readily. This problem is greatly reduced if the applicator employs
a positive-displacement pump to dispense the oil-emulsion.
Calculating oil emulsion injection Rates Use
USDA-ARS NISRL Station Note #01-98 to compute the volume of oil-emulsion liquid concentrate applied per minute
to head ditch or pipe flows.
DRY PAM APPLICATIONS
Several commercially available applicator devices have been designed specifically
for applying granular PAM. It is very difficult to meter unconditioned
granular materials. Products such as fertilizer and granular insecticides
were manufactured to be easy to meter in granular form. When exposed to
humidity, polyacrylamide granules tend to stick to each other and to drop
tubes which can then plug. The flow rate for granular PAM ranges from 2
to 33 grams per minute depending on irrigation flow and desired concentration
in the irrigation water. A small error in the rate of metered PAM will
lead to large differences in concentration in irrigation inflow water.
Despite having some problems, several producers have successfully adopted
the use of granular PAM application equipment and operate several machines
on the same farm. General Dry PAM Applicator Considerations: 1) dispensing rates of 1 to 35 grams/min; 2) simple and reliable operation;
3) precalibrated or easily calibrated for fast setup in the field; 4) portability;
5) lasting power supply, small sealed battery packs are less tempting to
thieves than auto batteries.
Calculating oil emulsion injection Rates: Use
USDA-ARS NISRL Station Note #01-96 (Revised) to determine the PAM application rate needed to a given head ditch or
pipe flow to obtain a target furrow stream PAM concentration. Use
Worksheet #2 to calculate dry granular rates needed in head ditch or pipe to obtain
a target pounds per acre.
PAM APPLICATION RATE IN POUNDS PER ACRE UNITS
Numerous USDA-ARS studies have shown that consistent, excellent control
of furrow-irrigation induced erosion results when irrigators include 10
ppm PAM in furrow advance flows (ie. in water that first wets-up the dry
furrow soils). The PAM applications were stopped once runoff began leaving
the fields, and untreated irrigation water was used for the remainder of
the irrigation. In general, these same studes indicate that total PAM application
for successful PAM treatments ranged from 0.6 to 2 lbs/ac
The total field PAM application (lbs/ac) is a function of the total volume
of treated irrigation water used per irrigated area, which in turn is a
function of the head ditch flow rate, PAM concentration, and treatment
period. Since PAM-treated inflows produce little erosion and sediment loss,
irrigators should increase their treated inflows to speed furrow advance
and improve irrigation uniformity. Irrigators can use the 1 lb/ac PAM application
value as a general guide to determine what their furrow advance period
should be, and whether inflows should be increased (to reduce furrow advance
time) or decreased (to increase furrow advance time.
Irrigators can use USDA-ARS NISRL Station Note #04-96 [Page 1. 0-6 Hr & 6-12 Hr] to determine how a change in irrigation advance time affects the total
PAM amounts applied to fields of a given size, when head ditch flows
are treated with given PAM concentrations.
TROUBLE SHOOTING GUIDE
The following is a list of possible reasons why a given PAM application
does not achieve desired results. Most of the common problem areas are
addressed here, but other complicating factors may also be involved.
1. Inadequate Mixing of PAM Concentrate- Liquid PAM solutions require considerable mixing during dilution. Field
solutions should be clear and free from small jelly globules called "fisheyes"
which would indicate undissolved concentrate.
2. Not Enough PAM Was Applied- Rate of PAM addition must be based on total irrigation inflow rate,
erosion potential for a field, and desired injection concentration. Also
consider #3 and #4.
3. Losses of PAM During Application, Mud Ditches- Several factors can decrease the concentration of PAM delivered to the
furrow. PAM will adhere to the sides of a mud ditch and to siphon tubes
since PAM is attracted to metals. Preliminary data indicate that ditch
losses are highest during the first "PAM" application and can be 20 to
30% during the first hour of an irrigation event. Measurements taken during
the third PAM application indicated negligible losses to the ditch.
4. Losses of PAM During Application - Sediment in Irrigation Water- As discussed earlier, PAM injection will settle suspended sediment in
irrigation water. This will reduce the amount of PAM applied to the field
since some PAM is 'deactivated'. Further research is needed to relate the
amount of PAM deactivated by suspended sediment in irrigation water. Groundwater
high in metallic salts may also deactivate some PAM and slightly reduce
5. Poor Mixing of Applied PAM with Irrigation Water- Inadequate mixing of PAM may result in highly concentrated PAM being
applied in the first few furrows and insufficient PAM in the furrows furthest
from the point of injection. For open ditch systems, multiple tins or dams
can be used to mix PAM prior to application to the furrow; one or two dams
have proven adequate for liquid applications. Three to four dams and at
least 100 feet of ditch are recommended to adequately mix granular applied
PAM. PAM must be mixed well prior to entering a gated pipe system since
water does not mix as well in a pipe. If PAM cannot be mixed prior to entering
a gated pipe system then multiple in-line control boxes should be installed.
Plastic in-line control boxes are available (K Box, Fruitland, Idaho) that
will provide turbulent mixing and a place to inject polymer and fertilizer.
Field testing indicates that a weed screen should not be used to mix PAM
treated water since it can easily plug the screen.
6. Poor Prediction of Advance Time- The use of automated timers or liquid shutoff valves can be problematic
for controlling PAM injection because it is difficult to accurately predict
furrow advance time. If advance time is slower than expected, the bottom
portion of the fields will not be treated with PAM. If furrow advance is
faster than expected more PAM than necessary will be applied and PAM losses
in runoff water could occur.
7. Cold Irrigation Water- Irrigation water from a well will be colder than surface water. It is
more difficult to dissolve PAM in cold water than in warm water. Greater
time and agitation will be required to dissolve PAM in cold water.
THE COST OF PAM TECHNOLOGY
Cost of PAM-use will vary between sites and operators depending on the
amount and type of PAM applied and management costs.
Amount and Type of PAM
- desired level of erosion control
- field and soil characteristics
- cost for PAM
- carriers or additives added to pure PAM
- pick-up and delivery costs
- mixing costs for liquid PAM
- regulation of PAM injection
To achieve 8 to 10 ppm in the irrigation advance water generally requires
1 to 2 pounds PAM per acre. Since the rates per acre are low, it is easy
to over apply PAM. Therefore calibration and monitoring of your injection
equipment is important. The cost for PAM may justify changes in irrigation
practices to facilitate a rapid irrigation advance, thus lowering the amount
of PAM required.
If all irrigations following soil disturbance are treated, row crops will
require from 3 to 5 PAM applications for the season. This results in a
seasonal cost of $15 to $50 per acre if PAM costs to the producer is $5.00
per pound (Table 4).
|Table 4. Seasonal costs for PAM at $5.00 per pound
|Injections per season
||Amount of PAM applied
||Seasonal cost per acre
||(lbs per acre per application)
Cost estimates in Table 4 are conservative since they do not include management
costs or inefficiency factors associated with PAM-use. Adhesion to mud
ditches, failure to shut off tanks in a timely manner, and disposal of
"left-over mix" will increase the amount of PAM used. For pesticide applications
it is common to mix from 5 to 15% greater volume than is needed based on
exact calculations. Equipment costs to apply PAM were not included in Table
4. A good quality 1500 gallon tank with plumbing can be obtained for about
$950 and an granular applicator for $250-500.
Note: These are COSTS only, but do not reflect possible reductions in
other field management costs (e.g. soil replacement or reduced nitrate
losses); nor do they reflect possible improved gross returns (e.g. yield
increases on steep slopes due to improved infiltration).
1. Barvenik, F.W. 1994. Polyacrylamide characteristics related to soil
applications. Soil Sci. 158:235-243.
2. Ben-Hur, M. 1994. Runoff, erosion, and polymer application in moving-sprinkler
irrigation. Soil Sci. 158:283-290.
3. Bicerano, J. 1994. Predicting key polymer properties to reduce erosion
in irrigated soil. Soil Sci. 158:255-266.
4. Grula, M.M., May-Lin Huang and G. Sewell. 1994. Interactions of certain
polyacrylamides with soil bacteria. Soil Sci. 158:291-300.
5. Lentz, R.D., Shainberg, I., Sojka, R.E., and Carter, D.L. Preventing
irrigation furrow erosion with small applications of polymers. Soil Sci.
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1.Soil Scientists, USDA-Agricultural Research Service, Northwest Irrigation
and Soils Research Laboratory, 3793 N. 3600 E. Kimberly, ID 83341.
* Corresponding Author. E-mail:
2.University of Idaho, Extension Educator