Lincoln, Nebraska
December 2008
Source:
University of Nebraska -
CropWatch
Jennifer M. Rees,
University of Nebraska-Lincoln
Extension Educator
http://cropwatch.unl.edu/input$/soybean_inoculant.htm
Eliminate soybean inoculant in
fields with a history of beans (save $1.50/acre*)
Inoculating soybeans with
products containing the bacterium Bradyrhizobia japonicum
is a common practice and considered an inexpensive insurance
against soybean yield loss. This bacterium forms a symbiotic or
beneficial relationship with soybean roots in which
nitrogen-producing nodules are formed, allowing for nitrogen
fixation to occur.
As producers strive to find a
“silver bullet” to significantly enhance soybean yields, they
may look to one of the soybean inoculant or combined inoculant
and growth promoter products new to the market. These products
are said to contain more aggressive strains of B. japonicum,
fix more nitrogen, and increase yields over previous inoculant
products.
Added inoculant often
proves unnecessary
UNL research conducted from
2001 to 2004 at the South Central Agricultural Laboratory near
Clay Center, and by the Greater Quad County On-farm Research
group and Nebraska Soybean and Feed Grains Profitability Project
all showed that adding soybean inoculant did not significantly
increase yields on fields with a history of soybeans. The B.
japonicum remained in the soil after previous inoculations
and was able to inoculate the new soybean planting. These fields
had all produced soybeans in the previous four to five years.
In 2005-2006, Greater Quad
County On-farm Research producers tested a few new products to
determine if treated fields would have a significant yield
increase over untreated checks. These studies were conducted in
irrigated soybeans with a field history of soybeans (corn and
soybean rotation).
The products tested in 2005
included
- Cell Tech 2000, a
liquid inoculant;
- Vault, a liquid
seed treatment which includes a biofungicide and plant
activator; and
- SoySuperb, a
peat-based (now liquid) plant growth-promoting
rhizobacteria.
Cell Tech 2000 yielded 75.5
bu/ac compared to the untreated check at 75.4 bu/ac in four
replications with no statistical significant difference. Vault
yielded 77.1 bu/ac compared to the untreated check at 76.1 bu/ac
in 11 replications with no significant difference. The SoySuperb
yielded 76.1 bu/ac compared to 74.2 bu/ac in 19 replications.
This was statistically significant at the 99% level.
In 2006, SoySuperb and Vault
were compared to untreated checks with 12 replications in
producers’ fields. There was no significant difference in yields
with SoySuperb, Vault, and the untreated check yielding 72.7
bu/ac, 73.5 bu/ac, and 72.9 bu/ac respectively. Thus, UNL’s
recommendation remains that in most situations, soybean
inoculants are not needed in fields with a history of soybeans
in the past four to five years.
When to inoculate
If the field has not produced
soybeans in the past four to five years or has never produced
soybeans, an inoculant is needed for nitrogen fixation to occur.
Positive yield results from inoculation also can occur where the
soil environment does not support long-term bacteria survival.
These environmental conditions could be due to
- pH below 5.0 or above 8.0,
- sandy soils,
- fields experiencing
flooding of more than four days, or
- conditions where crops
often experience severe water stress.
In these cases, a yield
response may be possible or likely due to re-inoculation.
To determine if your field
needs re-inoculation, use the Soybean Inoculation Decision
Worksheet for “Old” Fields in the NebGuide,
Soybean Inoculation: Applying the Facts to Your Fields
(G1622).
*Estimated cost/acre of
inoculant |
