Azotobacter Question and Answer June 2007

Tom Miles

Azotobacter Question and Answer June 2007
Richard Haard, Four Courner Nursery, Bellingham, Washington, June 11, 2007

Question by Sean Barry:
RH ". . .Learning about potential for enrichment culture of Azotobacter and trying to measure available nitrogen in this situation."

Here you mention promoting the growth of nitrogen fixing Azotobacter. I have always been interested in the possibility of inoculating charcoal with mycorrhizal fungi.

Do you think it might be possible that you could isolate, culture, and propogate enough of both types of microorganism species from the soil in your area, then enrich or inoculate charcoal with it, and put that charcoal into plant growth trials? I have seen some FDA ARS (Agricultural Research Service) documentation about developed and patented methods to do this (propogate soil fungi) kind of thing. The charcoal you have on the forest floor with the litter (I believe I've seen this picture); is it incorporated into the soil containing the fungus? Or just on top with the litter? Are there any plants growing in it? Are there also Azotobacter in that soil (along with the mycorrhizal fungi) ?

Answer by Richard Haard:

As Alan has stated there are numerous commercial sources of mycorrhizial fungi. The most common VAM species, Glomus interadices is utilized by crop plants and grown on host plants in greenhouse culture then used as harvested roots and a carrier in inocculum. In addition, commercial inocculum may contain collected spore material of known ectomycorrhizial species such as Rhizopogon, Scleroderma and Psilothus.

Depending on the requirements of your crop you can do all or any of above. I seem to recall you live in upper midwest and you should be able to find Rhizopogon and Scleroderma this summer and fall. I would be happy off-list to help you find these if interested.

At our farm, and also as described by Dr. Ogawa, we inocculate recently sterilized soil with collected leaf litter, rotting wood and surface soil from a healthy forest understory as my crop plants are native trees and shrubs, hosts for ecto and endomycorrhizial (VAM) fungi.

As I understand things these organisms do not fix atmospheric nitrogen but do make nitrogen available to plants.

Charcoal may indeed be helpful in establishing suitable habitat for these beneficial fungi.

There are two additional classes of nitrogen fixing organisms that are of interest to me.

Frankia is an actinomycete that forms nodules on a number of host plants including red alder and sweet gale, Ceanothus sp, plants we grow at 4CN. We have had interesting results with tests of collected, mashed alder roots combined with charcoal. Not conclusive because both treatments worked fairly well.

Azotobacter species A. chroococcum,and A. vinelandeii are a class of free living bacteria that convert atmospheric nitrogen to ammonia.
They are aerobic and found in soils and in association with plants.

Azotobacter is interesting to me because in pure culture it can fix 10 mg of nitrogen/g of sugar and in organic matter rich soils and in association with root exudates may be a source of natural fertilizer.

Charcoal and its cellular structure may provide habitat for this beneficial bacterium.

Lastly Sean the status of my tote of charcoal now residing under hemlock and douglas fir trees.

We want to age this material in a natural way and use in in some tests sometime next year. Right now it is sitting on top of the ground. Before 1995 we piled many truck loads of leaves, garden debris and it has rotted into a high organic matter layer that the conifer tree roots have grown into. Every fall this forested place supports heavy fruiting of the mushrooms Lepiota, Collybia and Tricholoma and digging into the soil it is easy to find tree roots and dense mycelium.

So the plan is to bury our charcoal in this place and let it age in this environment. Early next spring I will be moving this organic rich soil and charcoal soil mix into raised beds for commercial propagation of a native plant, Coryalidis scouleri which occurs in moist, organic rich under-story soils in our region.

See Soil Microorganism thread in discussion archive June 2007.