Against Pollutants and Pathogens
Soil microbiologist Jim Entry
(left) and soil scientist Bob
Sojka discuss data showing
that PAM decreases the
concentration of enteric
bacteria in irrigation water
flowing from pastures into
the Snake River.
An environmentally friendly
compound nabs nutrients and troublesome microbes before they can escape from
farmers' fields and make their way to ponds, lakes, streams, or rivers. Known
as a polyacrylamide, or PAM, this powder can help keep nutrientssuch as
the phosphorus in fertilizersfrom traveling beyond the farm in irrigation
runoff. Similarly, PAM helps keep disease-causing microbes, like those in cow,
pig, or fish manure, from being swept beyond the confines of farmyards or
That's according to investigations by ARS scientists with the Northwest
Irrigation and Soils Research Laboratory in Kimberly, Idaho. Researchers there
are already world leaders in discovering safe, practical, and affordable
PAM-based tactics that prevent soil particles from ending up in irrigation
water. Without PAM's help, particles can become dislodged when farmers irrigate
Findings from the team's laboratory and outdoor experiments have prompted
U.S. growers to put PAM to work on more than 1 million acres of irrigated
farmland. "Growers who mix PAM with irrigation water can expect to reduce
erosion from their furrow-irrigated fields by 80 to 99 percent," says
Rodrick D. Lentz, an ARS soil scientist at Kimberly. "One ounce of PAM
anchors as much as 1,000 pounds of topsoil that might otherwise be carried away
by irrigation water."
Agricultural engineer Dave
Bjorneberg demonstrates a
PAM application method for
furrow irrigation. About
2 tablespoons of PAM would
be used per 1,000 feet of
Says Kimberly colleague David L.
Bjorneberg, "We achieved slightly less dramatic results with sprinkler
irrigation." Bjorneberg is an ARS agricultural engineer.
The idea of using PAM to thwart erosion from furrow-irrigated fields dates
back to about 1975. But the Kimberly studies, begun in 1991, were the first to
determine precisely how much PAM farmers should use, as well as when, where,
and how to apply it. In fact, their work has led to PAM's being hailed as
"possibly the most successful soil-conservation practice ever developed
for furrow irrigation."
Now, new information from ARS soil microbiologist James A. Entry and ARS
soil scientist Robert E. Sojka shows that pairing PAM with other compounds
boosts its ability to fasten onto nutrients in runoff. "It's a matter of
when a nutrient becomes a pollutant," says Entry, in explaining their
interest in keeping nutrients in fields. "On the farm, nitrogen and
phosphorus are regarded as nutrients plants need to thrive. If these same
natural chemicals make their way into water as it leaves the farm, however,
they may become pollutants."
Jim Entry (left) and Dave
Bjorneberg record sediment
concentrations from furrow
irrigation runoff samples.
The darker sample on the
left is from an untreated
PAM Catches Nutrients
Nitrogen and phosphorus in runoff, for example, can become culprits behind
algal blooms in ponds or lakes. Fueled by these pollutants, algae flourish.
Later, their decay uses up oxygen needed by fish and other aquatic dwellers. So
some statesin setting pollution limits for runoffspecify not only
the allowable amount of sediment, but also the permitted amount of these
potentially polluting nutrients.
PAM helps growers avoid exceeding these "Total Maximum Daily
Loads" for sediments and nutrients. Entry and Sojka, building on the
Kimberly lab's earlier nutrient-pollution studies, tried some new PAM-chemical
combinations to see whether they would bolster PAM's pollution-fighting
prowess. In these nutrient-loss trials, they combined PAM with aluminum sulfate
or calcium oxide.
Why match PAM with these other chemicals? Explains Entry, "We already
knew, from work others had done, that chemicals like aluminum sulfate
and calcium oxide can slow the loss of phosphorus. We also knew, from
textbook chemistry, that they would help PAM bind to phosphorus."
Biological technician Sheryl
Ver Wey prepares to count
colonies of fecal coliform
bacteria in a water sample.
Entry and Sojka put PAM in furrows containing cow, pig, or fish manure.
They irrigated the field and then analyzed the runoff. Entry reports,
"PAM alone did a good job of removing nutrients, as we've seen
before. But the new PAM combinations were even more effective."
Waterborne nutrients can either flow overland or move down through
the soil and potentially pollute underground water. "In a washed-sand
study in our laboratory," Entry notes, "we mimicked the flow
of nutrients as they leach through soil."
Sand Columns Simulate Nature
Entry and Sojka assembled 48 plastic columns, each 18 inches high and 4
inches in diameter. They added clean, loosely packed sand to each column.
To some columns, they added a small amount of either PAM or PAM mixed with
one of the other chemicals. On top of that, they placed some cow or pig manure
from local farms, or fish droppings from a nearby hatchery. Then they poured
distilled water into the columns and captured this leachate as it flowed out
the bottom into flasks.
"This is a tough challenge for PAM," says Entry, because water
drains through clean sand faster than through most soils. The fast rate of flow
means PAM has much less time to grab onto nutrients.
"We found that water
draining from sand columns that had PAM alone contained significantly fewer
nutrients from the cow or pig manure," says Entry. "But columns with
the PAM combinations held back twice as many nutrients from those manures. None
of the treatments reduced already-low levels of target nutrients in
flow-through from fish manure."
Sojka comments, "Earlier, our outdoor studies had suggested that if
nutrient concentrations in runoff are low to begin with, there's less chance
that the nutrients will contact binding sites on PAM molecules. We think that
might be the case with the fish manure leachates."
Even though they provide needed nutrients, manures can pose a problem: they
usually harbor microbessome of which can cause disease. That's why Entry
and Sojka have newly explored PAM's ability to grasp such pathogenic microbes
from runoff. They did this by analyzing microbes from the column leachate and
PAM Works on Manure
"PAM alone significantly reduced bacterial microbes in these water
samples," Entry points out. "Specifically, PAM alone reduced
populations of total and fecal coliform and fecal streptococci in the cow and
pig leachate from the column experimentsas well as from our outdoor
runoffby about 90 percent."
The PAM combinations did even better. PAM plus aluminum sulfate and PAM plus
calcium oxide reduced total and fecal coliform bacteria and fecal strep by
about 99 percent. "From a practical water-treatment standpoint, that means
the PAM combinations were far more effective than PAM used alone. That's the
same thing we observed in our nutrient studies," says Entry.
Says Sojka, "We think these findings have important implications for
keeping microbes from moving away from farms or places where animal manure
accumulates. For instance, if producers use manure on their fields, they could
apply PAM with their irrigation water."
Entry adds, "We want to find
out if PAM might be used effectively around the perimeter of farmyards or
feedlots. Farmers and feedlot managers already do many things to control losses
of nutrients and pollutants from manure. But sometimes their systems fail.
Let's say a manure pond breaks or overflows during a storm or flood. When that
happens, you need an emergency measure. We plan to determine whetherunder
these conditionsputting down a layer of PAM could help limit the spread
of microbes that otherwise might flow into streams or groundwater.
"Keeping the microbes in place helps protect the health of water users
downstream," emphasizes Entry. "PAM doesn't kill microorganisms. With
or without PAM, they die off at the same rate. The advantage of PAM is it keeps
down the number of these microbes in farm runoff.
"PAM's performance in clinging to microbes in water in confined spaces,
such as sewage-treatment plants, is already well-known," Entry says.
"But our data are likely the first about PAM's interaction with microbes
in water flowing over land."
More information about these and other PAM results from the Kimberly
scientists is presented on the World Wide Web at
Wood, Agricultural Research Service Information Staff.
This research is part of Soil Resource Management, an ARS National
Program (#202) described on the World Wide Web at
Rodrick D. Lentz,
David L. Bjorneberg,
James A. Entry, and
Robert E. Sojka are with the
USDA-ARS Northwest Irrigation and
Soils Research Laboratory, 3793N 3600E, Kimberly, ID 83341; phone (208)
423-5582, fax (208) 423-6555.
||"PAM Protects Against Pollutants and
Pathogens" was published in the
issue of Agricultural Research magazine.