Plastic Mulch: Harmful or Helpful?
Tomato beds mulched with plastic.
Many gardeners and homeowners use wood chips, paper, or
other shredded materials as mulch around their plants to reduce weed
growth and enhance storage of soil moisture. Though fields of large-scale
commercial produce farms look very different from the typical backyard
veggie garden, they too use mulch. But tomato producers, for instance,
use plastic sheeting instead of wood chips as mulch on large parts of
their fields to prevent the same kinds of problems.
Both the pro and the backyard gardener often have something
else in common: They use pesticides to combat weeds and insect pests.
But when used in combination with pesticides, the plastic mulch favored
by many commercial growers can have unintended effects. Unfortunately,
plastic mulch, which can cover between 50 percent and 70 percent of
a field, increases surface water runoff from both rainfall and irrigation.
That means more of the pesticides applied on plastic-mulched fields
makes it into runoff leaving the field.
Chemists Cathleen Hapeman
(left) and Jennifer Fetcho
collect water samples from
Biscayne Bay to determine
Cathleen Hapeman of the Environmental Quality Laboratory
in Beltsville, Maryland; Pamela Rice of the Soil and Water Management
Research Unit in St. Paul, Minnesota; and Don Wauchope of the Southeast
Watershed Research Laboratory in Tifton, Georgia, are collaborating
in comparing various management practices to find ways to reduce or
possibly eliminate pollution from agricultural practices. To get a handle
on the solution, the scientists have to first find out what happens
to the pesticides applied to the fields. Specifically, they want to
determine the environmental fate of the pesticides. To do this, they
use computer simulation models to predict pesticide movement and then
identify management practices to reduce that movement.
Model predictions of the effects of agricultural practices
on water quality are being compared with experimental measurements at
ARS locations nationwide and in
other countries, as well.
Hapeman and Rice are exploring a computer model's application
to the fate and transport of pesticides. Rice, formerly of the Environmental
Quality Laboratory, and now with the Soil and Water Management Laboratory
in Minnesota, is using a model in conjunction with her research on the
effect of agricultural management practices on pesticide movementspecifically
Pesticides applied to crops
may inadvertently end up in
groundwater. The work of
chemist Cathleen Hapeman
(ARS Environmental Chemistry
Laboratory, Beltsville, Maryland)
will be used to develop
management practices to better
protect sensitive ecosystems.
Copper, applied as copper hydroxide, is the most widely
used fungicide-bactericide for control of tomato diseases. Copper from
this pesticide formulation has been found in runoff from fields that
have plastic mulch. Unfortunately, elevated levels of copper can harm
shellfish, finfish, and other aquatic organisms. More than 80 percent
of the copper measured in runoff was attached to soil particles in the
runoff. Rice is inputting all variables from the fieldsuch as
acreage, crop type, and pesticides appliedinto the computer model
to determine whether it will predict the same type of runoff seen in
her data. Her research will be used to develop management practices
to reduce the movement of soil particles in runoff.
More than 12 years ago, ARS plant physiologists Aref Abdul-Baki
and John R. Teasdale, of the Sustainable Agricultural Systems Laboratory
in Beltsville, developed hairy vetch as an alternative to plastic mulch
in tomato plots in the Northeast. More recently, these scientists have
conducted cooperative research with the University of Florida in Homestead.
Tomato plants in the hairy vetch system were vigorous and had a 25-percent
increase in yield. Hairy vetch can be used as a sustainable management
practice, unlike plastic mulch, which contributes to soil loss, increased
runoff volume, and off-site pesticide loading. Hairy vetch helps soil
retain moisture, prevents destructive insects from taking hold in the
soil, and allows less fertilizer use.
Researchers found that vegetative mulches like hairy
vetch reduced the amount of dissolved pesticides in runoff. Another
method to slow pesticide movement from the field is to plant a different
type of vegetation, like cereal rye, between the rows of plastic mulch.
Several management systems were investigated for their environmental
impact: plastic mulch only; plastic mulch with rye grown between rows;
or hairy vetch.
"There's a lot of pesticide use in Florida by both
commercial growers and private citizens. We wanted to provide a new
way to reduce that use," says Hapeman.
In a 2-year study, Rice and Hapeman found that there was
less runoff volume, less sediment in the runoff, less soil erosion,
and less pesticide in runoff when cereal rye was used along with plastic
mulch. This mechanism can reduce runoff concentrations and still allow
use of plastic mulch. In another study, there was 30 percent less soil
loss and 10 times less water runoff with hairy vetch mulch than with
The ongoing struggle is to prevent harm from pesticides
by providing information about their environmental fate and giving growers
alternatives to plastic mulch.
"We need a baseline level to find out the impact
of the pesticides," says Hapeman. "Only with a full understanding
of the proportion of pesticides that are present in runoff can effective
alternatives to plastic mulch be completely investigated and used."
The research group will continue to study vegetative mulches
to assist commercial farmers. "The goal is to provide an environmentally
friendly management practice that has minimal impact on production,"
says Hapeman.By Sharon
Durham, Agricultural Research Service Information Staff.
This research is part of Water Quality and Management,
an ARS National Program (#201) described on the World Wide Web at www.nps.ars.usda.gov.
Cathleen Hapeman is with the USDA-ARS Environmental
Quality Laboratory, Bldg. 007, Room 224, 10300 Baltimore Ave., Beltsville,
MD 20705; phone (301) 504-6511, fax (301) 504-5048.
"Plastic Mulch: Harmful or Helpful?" was published
in the July
2003 issue of Agricultural Research magazine.