Soybean yields are higher
after seed inoculation
with the Nod+ nitrogen-
fixing strain of bacteria.
Developed by ARS, this
inoculant has been rapidly
growing in popularity.
A lowly bacterium first cultured 2 decades ago by ARS
researchers is now enjoying celebrity status as a commercial soybean
Behind that success is Urbana Laboratories, a St. Joseph, Missouri,
company that has sold nearly 14 million acres' worth of the inoculant
since obtaining a license from ARS to market the bacterium in 1994.
A Bradyrhizobium species, the bacterium converts (fixes) gaseous
nitrogen into forms that soybean plants can use for optimal growth and
higher yield. In return, the plant shelters and nourishes the bacterium
inside root nodules, where nitrogen fixation occurs.
ARS microbiologists L. David Kuykendall and William J. (Jim) Hunter
originally developed, tested, and in 1991 patented the bacterium as
an improvement over Bradyrhizobium strains being used by soybean
In the laboratory, they used nitrous acid to trigger gene mutations
in a liquid culture of B. japonicum strain I-110. Through a similar
process called direct selection with one of the resulting mutant strains,
they settled on a strain called TA11Nod+ (or Nod+) as their final choice.
Interestingly, use of this bacterial genetics approachrather
than a recombinant onemay have contributed to the mutant strain's
acceptance among farmers, notes Hunter, with ARS' Plant, Soil and Nutrient
Research Unit, Fort Collins, Colorado.
Nod+, also called the USDA Patented Strain, "is derived through
nonrecombinant means, so you don't have to worry about foreign genes
in the bacterium's DNA," adds Kuykendall, with ARS' Molecular Plant
Pathology Laboratory in Beltsville, Maryland.
Promising results from field studies also boosted acceptance by growers.
For example, against B. japonicum I-110a top soybean inoculant
itselfthe Nod+ strain formed 44 percent more nodules and fixed
50 percent more nitrogen. Generally speaking, a well-nodulated crop
helps save on synthetic fertilizer costs and nourishes soils at rates
less likely to affect groundwater, Hunter notes.
Large-scale testing of the Nod+ strain began shortly after Urbana began
selling it in 1995. Based on those field trials, conducted by extension
scientists at 377 sites in 18 states, the inoculant's use increased
soybean yields by 2 to 3 bushels per acre.
In 1995, the first year of sales, Urbana inoculants containing the
Nod+ strain were used on 220,000 acres of soybeans. Over 4 million acres'
worth of inoculant was produced for 2001a 20-fold increase. Since
its introduction, Hunter estimates, the new inoculant has raised yields
by nearly 30 million bushels. At $5 per bushel, this means an additional
$150 million gross income for farmers.
In February, Hunter and Kuykendall received an ARS award for "superior
effort" in transferring the inoculant technology to market.
Noting the 100-year history of soybean inoculants, Kuykendall comments
that "the new strain's impact has been strong enough to show that
we improved on an old, sustainable process and that what's good for
the environment can actually make good economic sense as well."By
Agricultural Research Service Information Staff.
This research is part of Plant Biological and Molecular Processes,
an ARS National Program (#302) described on the World Wide Web at http://www.nps.ars.usda.gov.
To reach scientists mentioned in this article, contact Jan
Suszkiw, USDA-ARS Information
Staff, 5601 Sunnyside Ave., Beltsville, MD 20705; phone (301) 504-1630,
fax (301) 504-1641.