Soybeans for Perfect Tofu
February 4, 2002
Organically grown, large-seeded,
high-protein soybeans intended for the high-quality tofu market will not pass
muster if they are stained. In 1999, more than half of these specialty soybeans
grown in Iowa did not make the grade. By comparison, in 1988 just 5 percent of
these soybeans from Iowa were rejected for making silky tofu because of
Now Agricultural Research Service
soil scientist Doug Karlen and colleagues at the ARS National Soil Tilth Laboratory in Ames,
Iowa--working in cooperation with scientists at
Iowa State University and with the
Heartland Organic Cooperative, a group of organic farmers--are looking for the
causes of soybean staining and how to avoid them.
To find out what caused the staining, the team conducted an experimental
study on five farms in several counties across Iowa during the 2000 crop year.
The researchers speculated there were six potential causes for the
purple-colored stains. These included four different fungal
groups--Fusarium, Phomopsis, Alternaria and
Cercospora--as well as bean pod mottle virus and soybean mosaic virus.
Since organic growers cannot use insecticides on their crops, the
researchers tested several natural products on the soybeans to control vectors
and minimize staining.
They determined that feeding by the soybean leaf beetle was the primary
culprit. Due to warmer than average temperatures in 1997, 1998 and 1999,
especially in the southwestern area of the state, the overwintering beetle
population had increased rapidly. This resulted in much greater first- and
second-generation insect pressure during the growing season, thus causing the
increase in soybean staining. In the northeastern portion of the state, where
winter temperatures were colder, there were lower beetle populations and little
to moderate staining of the soybeans.
You can read more about this organic farming research in the
February issue of
Agricultural Research magazine, available on the World Wide Web.
ARS is the U.S. Department of
Agricultures chief scientific research agency.