Most of my experience has been with leguminous tree crops,
not annuals, but I'll share a few lessons. As you stated, there
are both specialists and generalists among crops in terms of
their Rhizobium needs for nodulation. Some plants require a
particular species of R. while others do not. I have forgotten
the details for the annuals you list, so rather than mis-speak
I'll just say that this is an initial step to take: determine if
your crop is a specialist or generalist for fixing bacteria.
Soil acidity has been the most limiting factor in places I've
worked, more than overwintering problems. Your soils may
be fine, but this is something else to look into. Another factor
can be soil moisture. Rhizobia do not take drying well at all.
Generally, I don't believe it is necessary to inoculate every
year, unless you know that the Rhizobium species for your
crop does not carry over well due to winter, pH, dryness, Mg
balance, or any of a number of other factors.
Try a small experiment in which you inoculate half a field
every year and don't inoculate the other half but every three
years. After a decade or so, you should know what works
best. I would hesitate to use the results of greenhouse or pot
experiments (done in much shorter time) because the main
factors you suspect as potentially limiting: winter, acidity
(affected by rainfall and other variables), soil moisture, etc.
cannot be controlled under growing conditions as they would
Your objective, after all, is not to publish a peer reviewed
paper in Ecology showing statistical significance between
treatments, but to find out what is going to work in farmers'
fields. It may very well be different from one field to the next.
I'm sure to get flamed for this by inoculant salespeople and
probably by some researchers. Anyway, there's my 2 bytes
worth. Try calling the Nitrogen Fixing Tree Association at
Winrock's offices in Morrilton, Arkansas. They have done
more work with Rhizobia than any other group that I'm aware
of. Another good source of info is NITRAGIN Co., a division of
Lipha Chemicals, Inc. 3101 W. Custer Ave., Milwaukee, WI
53209. 1-800-558-1003. Ask for Technical Bulletin 102,
Rhizobia inoculants for various leguminous species, R.S.
Smith, S. Tholman, and R. Randall. The NifTAL project in
Hawaii published an extension bulletin back in 1989 that may
be useful -- Roskoski, Joann P. 1989 Biological Nitrogen
Fixation (BNF): Commonly asked questions and answers
pub. #4 Illustrated concepts in agric. biotech. series, NifTAL
project, Univ. of Hawaii.
Best of luck,
Todd R. Johnson
>>> Carol A. Miles <firstname.lastname@example.org> 26 June 1996 2:12
I am often asked if it is necessary to inoculate legumes
soybeans, vetch, clover, etc.) every seeding when the soil
has a history of
growing these crops and the crop has previously formed
I understand Rhizobium does not necessarily overwinter well
and that there
are soil predators which feed on it. We are in a mild climate
generally do not freeze although we do get a dusting of snow)
day tempertures average in the 70's.
Is there a general rule of thumb, i.e., if the crop nodulated
last year, no
need to inoculate this year. Or, if you have had the crop
within the last
3 years and it nodulated, no need to inoculate this year. Or,
every year regardless of crop/nodule history. Or, to
perhaps certain plant species need inoculum every year
while others don't.
I look forward to some learned opinions.
Carol A. Miles, Ph.D.
Washington State University
Extension Agricultural Systems
360 NW North Street
Chehalis, WA 98532
PHONE 360-740-1295 FAX 360-740-2792