Above, organically grown corn
has more weeds late in the
season, since no herbicides
were used. But yields were
similar to those of conventionally
grown corn, below. Weeds are
managed with cover crops and
cultivation in the organic
plots and with herbicides and
cultivation in the conventional
Soil Microbes Do the Dirty Work
Beneficial soil microbes help plants get the nutrients they need to
flourish. Now ARS studies may show that soil microbes are helped both by
organic fertilizers and conservation tillagelong-standing practices of
organic farms and some conventional farms.
All-natural, organic fertilizers are those approved for producing certified
organic crops. Larry M. Zibilske, a soil scientist in the Integrated Farming
and Natural Resources Research Unit at Weslaco, Texas, and Joe M. Bradford,
head of the unit, are examining how organic fertilizers help soil microbes do
the job of increasing the uptake of nutrients by plants. They are working with
specialists from three companies that produce organic-based fertilizers:
Earthwise Organics, Inc., of Harlingen, Texas; Ag Organics, Inc., of Houston,
Texas; and Gardenville Fertilizer Corp., of San Antonio, Texas. These
specialized fertilizers include compost and processed animal manure pellets.
The studies of these products are taking place in greenhouses, using
strawberries as a model plant.
"We are impressed with the high levels of nutrients in the organic
fertilizers and the rates at which the nutrients are released into the
soil," says Zibilske. "We don't know yet exactly how the microbes
free up or release the nutrients. But the microbes seem to release the
nutrients at the time when the developing strawberry plant needs them
In other experiments, Zibilske and Bradford have successfully used
conservation tillage to boost the enzymatic zeal of microbes, which helps
plants take more nutrients from the soil. Unlike traditional tillage,
conservation tillage requires leaving the crop residue on the field surface
after harvest. This plant material provides several benefits while it slowly
"We've improved the uptake of phosphorus, iron, and other nutrients in
both corn and cotton," Zibilske says.
Bradford notes further, "Our studies have shown that leaving crop
residue decreases wind and water erosion, prevents water loss through
evaporation, and doesn't hurt crop growth or yield in subtropical environments
like southern Texas. And, of course, by not plowing under the crop residue,
the farmers save on costs of labor, fuel, and tractors and other equipment."
Superb Soybeans for Silky Tofu
Organically grown soybeans intended for the tofu market won't pass muster if
they're stained. In 1998, only 5 percent of Iowa's large-seeded, high-protein,
organic soybean crop was rejected for the purpose of making silky tofu because
of unsightly purple stains. But in 1999, rejection rates increased dramatically
to about 50 percent.
Douglas L. Karlen and his colleagues at Ames, Iowa, are intent on solving
the problem of soybean staining. Part of the Agricultural Land Management
Research Unit, they are working with scientists at Iowa State University and
with the Heartland Organic Cooperative, a group of organic farmers in the
Normally, blemish-free soybeans command premium prices in Japan for making
silky tofu. Unlike firm tofu, which is used for cooking stir-fry dishes, for
example, silky tofu has a soft, custardlike consistency and is eaten raw or
used in soups and desserts.
Both forms of tofu are made from soybeans that have been soaked, then ground
and cooked. The cooked soymilk is formed into bean curd, much like making
cottage cheese from milk.
In this past year, conventionally produced soybeans sold for about $4.55 per
bushel, whereas the large-seeded, high-protein, organic soybeans sold for about
$14.50. That's lower, however, than the $19 per bushel that this type of
organic soybean has sold for in the past.
Recent analysis by Karlen and his associates pinpointed the soybean leaf
beetle as the culprit. This pest transmits the bean pod mottle virus to healthy
plants. Notes Karlen, "Because of warmer-than-average winter temperatures
in 1997, 1998, and 1999especially in the southwestern area of the
statethe overwintering beetle population increased rapidly. The resulting
beetle population, first and second generations, created much greater insect
pressure during the subsequent growing season, causing the unusual increase in
"We found that there were lower beetle populations and
little-to-moderate staining of soybeans in the northeastern portion of the
state where winter temperatures were colder."
In a series of experiments, Karlen and his co-workers are testing nine
all-natural compounds to boost plant vigor or otherwise help combat the insect
or the virus. These include applications of molasses to increase plant sugars
and thus insect resistance, baking soda to kill pathogenic microbes, garlic for
insect control, and organic compost to minimize plant stress. The compost was
applied to the soil before planting, while the other treatments were applied
directly to the plants every 2 weeks from July to mid-September.
The researchers are also examining botanically based Neem and rotenone to
control insects naturally, hydrogen peroxide to control microorganisms, and
humic and fulvic acids to stimulate plant vigor and counteract plant diseases.
Preliminary findings suggest that rotenone or the humic and fulvic acid
treatments can slightly reduce staining. Karlen's team expects to finish
analyzing further results this year. They are doing much of the work on five
organic farms across Iowa.
Beefing Up Organic Herds
Nick Maravell's 165-acre organic farm is nestled in a valley near the
charming village of Buckeystown, Maryland. He grows organic hay, edible
soybeans, corn, barley, rye, and hairy vetch. He also has a small herd of Angus
cattle he is raising for beef.
Maravell runs the largest operation of the several farmers working with ARS
researchers John R. Teasdale, Michel A. Cavigelli, and Mark G. Davis. The
scientists are based at the Sustainable Agricultural Systems Laboratory in
Beltsville, Maryland. Their work involves comparing several organic farming
systems to conventional methods. For instance, Cavigelli and co-workers are
looking at the effects of cover crops on weeds, erosion, and nitrogen.
Everything on Maravell's farm is organic. "We don't use any commercial
fertilizers, herbicides, insecticides, parasiticides, antibiotics, or growth
hormones. Everything our cows eat all the time is organically
grownwhether they are grazing on grass or eating baled hay,"
"There are state and new national regulations on what it takes to
produce organic meat. Cattle that are grown for beef must be raised organically
their entire lives. But cattle that are grown for breeding can be raised
conventionally until the last third of each pregnancy. At that point the rules
kick in, and the cow cannot be given any antibiotics, growth hormones, or
parasite medicines. But we don't use any of these treatments at any
timeeven though we legally could," he says.
Maravell has begun working with another ARS researcher, Louis C. Gasbarre, a
microbiologist in the Immunology and Disease Resistance Laboratory in
Beltsville. Gasbarre is developing methods to identify those cattle genetically
prone to higher-than-usual parasite infestations.
Gasbarre's work will help farmers to convert their herds from
"all-natural" to "organic." All-natural herds can receive
parasiticides, but organic cattle cannot. Both kinds of herds are fed only
organic grass and other organic feeds.
Gasbarre is identifying the species of parasites in each herd, deciphering
how they are being transmitted, and determining which animals have the most. He
has discovered that a few individual cows have most of the parasites in cattle
herds, and this trait is strongly influenced by the animals' genes.
"This means," says Gasbarre, "that growers can reduce their
use of parasiticides by removing or treating the few high-parasite animals once
they're identified." The farmer would either cull the vulnerable calves
or, if they are valuable for other reasons, treat them for parasites and then
sell the meat in the nonorganic market.
In addition, Gasbarre is using the susceptible animals to find the genes and
gene markers for parasite susceptibility. Gene markers are pieces of genetic
material that are inherited with the trait of interest. The gene markers can be
used to develop rapid and inexpensive tests for vulnerability to parasites.
"Our goal," says Gasbarre, "is to minimize use of
parasiticides and keep production levels as high as possible."By
Chavez, and Don Comis,
Agricultural Research Service Information Staff.; and Jennifer Arnold,
formerly with ARS.
This research is part of Soil Resource Management (#202) and Integrated
Agricultural Systems (#207), two ARS National Programs described on the World
Wide Web at http://www.nps.ars.usda.gov.
Read more about organic farming by contacting the web site of the ARS
National Agricultural Library's Alternative Farming Systems Information Center
To reach scientists mentioned in this article, contact Marcia Wood,
USDA-ARS Information Staff, 5601
Sunnyside Ave., Beltsville, MD 20705-5129; phone (301) 504-1662, fax (301)