Perhaps the rhizobia are inactive due to lack of moisture in the soil. I think it's unlikely that once present they wold be extirpated entirely by drought, once moisture returns activity resumes.

I hope some have survived. I did a little research and found that drought and heat will kill some bacteria. I do not know which ones. There is a lot of dead grass in the yard because I did not water. After the rains it still is not decomposing the way it should. The pastures are the same way.
The one thing drought has taught me is how important organic matter is in the soil. Over the past 5 years I have made great efforts to increase the organic matter and have accomplished a much more self sustainable pasture and yard.
Drought breaks up the natural cycle. Because some of the beneficial bacteria will be killed off, thus the organics will not be broken down for plant use. This causes the effects of drought to occur faster in the following year.
Having learned this I think to make for a faster recovery microbes could be added during wet spells for a much faster recovery. This is the same as some farmers now using bio fertilizers to improve crops.
I have found some info. in the permaculture threads and have sent e-mails to some professors a TAMU.

Like us bacteria need certain conditions, food, moisture, and air, to live. Unlike us if those conditions are not there those bacteria will go dormant rahter than die and be ready to spring back when the consitions are optimal.
Trying to put bacteria in where the conditions are not optimal for them is a waste of your time, energy, and money.

Agreed. Areas where clover established itself will incidentally be populated with the appropriate species of rhizobia. After long dry periods they will be dormant.

There are microbes that will grow in the desert and even acid pools in Yellowstone park. There are microbes that go dormant and those that die in adverse conditions. It is a fact that the addition of the proper rizobia for N fixation will help legumes fix more N.
What I have stated is the result of numerous hours of research on the Internet. It does not mean I am right. But I am not totally wrong either.I even found 1 research paper that says there is an increase in microbial action under drought conditions, but that is for certain microbes.
You are correct in that the addition of microbes would have to be during the right conditions. So that is why I would only apply when I had moisture.

"The benefits from inoculation depend on survival
of introduced rhizobia in the soil. They
must survive long enough after sowing to nodulate
the host, and it would be desirable for the
rhizobia to persist between cropping seasons.
Soil moisture content and temperature are factors
that strongly influence survival of rhizobia."

Here is a link that might be useful: Survival of rhizobia

Why don't you try kvass? Sounds like a perfect situation to test it's effectivesness.

Here is a link that might be useful: One of the best recipes

Nova, it is highly recommended to inoculate with the appropriate rhizobia when first planting cultivated legumes in a piece of ground. That is because those super-specific species aren't highly likely to be in a random location. However, I strongly suspect that for clover, a very widespread wild/feral plant, the rhizobia in question are likely present at least in small numbers in the vast majority of soils and climates that clover would favor. The addition of fertilizers and irrigation that would stimulate the growth of clover will ultimately increase the populations of the rhizobia automatically.

You might consider diluting molasses with water and sprinkling it around to feed the rhizobia already in place. Some have success feeding with corn gluten too.

Dicot, I think that is a good idea. The same as adding it to a compost pile. That would feed not only the clover rizobia but also other soil microbes necessary for soil health. But I think I'm going to throw in some of the right rizobia for good measure. I found some new strains that claim they are faster growing.

novascapes - how do you think they survived before humans? They can go dormant during bad times.

Don't waste time an money trying to introduce certain soil microbes. Water the pasture or lawn adequately and they will return.

You need more then just adequate water, you need to proper environment. A soil well endowed with organic matter will provide the environment necessary for them to live and grow in. Innoculation then would not be necessary.

Yep, even if one has to cut down and chip an entire forest to "endow" one's soil with OM, one should do it, without thought of one's soil type, latitude, or climate. Maybe I should try that for my north florida sand. Of course, hairy indigo ( a legume) is well established there, complete with its needed rhizobia, thriving in less than 1% OM in the soil and extremely dry winter conditions.

Nova, did you come to a conclusion on this issue?

Mixed cover crops is the most sustainable solution: lots of legumes and brassicas in the same seed mix. "Roots in the ground all year round" is my soil flora and fauna recipe. Plants put 60% to 80% of their photosynthat int the root zone for a reason: to attract the animal-life that protects and feeds them. Regards. Peter.

"Nova, did you come to a conclusion on this issue?"

After speaking to head of the micro biology dept. at TAMU I found out what I needed. There is not doubt that during drought a lot of microbes will be killed off. But the fact that there is still some green here and there in the pasture indicated there is still life. Even though looking at the ground it seems there is no moisture at all there is some. Usually enough to sustain life to enough microbes so when the rain comes back so do they. He also said that experments have shown that the addition of microbes increases N production with legumes.
The other thing is that the presence of nodules on my clover is an indication microbes are there. The color is an indicator of the N production. This a nutrient requirement. Usually Phosphorus. (The soil microbes digest the organic material and the phosphorous is turned into a mineral. The mineral is the dissolved by water as is then available to the plant.) But also was to early in the season to tell.
So basically I'm good to go.
The best part, through my researching on how to grow microbes I learned a heck of a lot about the role they play in the soil.

"He also said that experments have shown that the addition of microbes increases N production with legumes"

I presume that 'microbes' in the above sentence is referring specifically to relevant species of rhizobia? And that these are studies regarding pasture legumes specifically?

It seems to me that severe drought cause a multitude of effects simultaneously. Microbial, insect, plant, etc basically all life reduces to very little activity. Why single out reduced rhizobia activity as being the main problem? Isn't the main problem the lack of moisture? For sure pasture is much more vulnerable to drought than natural cover. That is why at my florida pasture I am growing rows of bushes to ameliorate drought and dry wind effects.

Very interesting thread here. I would like to assist with some comments..

@ lazygardens :: bacteria going dormant.. while that is true for many, it is not true for all. And in my line of work, from observation, many pathogenic bacteria survive and many beneficials do not sporulate, and so do NOT revitalize when water is added.

@novascapes :: kvass.. it is the croatian word, also, for yeast, which makes bread rise. The reason certain localities are retained is because new strains are invented by innovation and passing of bacteria, just like dog breeding. In Russia, ladies who make homemade bread always share and keep their sourdough. A pinch is always saved from a good bread and re-used, next time.

@kimmsr :: innoculation is necessary for many beneficials. Stresses will reduce bacteria. The idea of repeated innoculations is to create biofilm.. which is a cluster or colony, that becomes more hardy, and more capable of surviving a shock.

@pnbrown :: Yes, remember, a healthy plant with lots of leaves means lots of photosynthesis, and lots of that means that carbon fixation is occurring in higher amounts, meaning more sugar is being sent down to the soil to feed the bacteria. Sugar is basically a humate, and a product of photosynthesis. same reason to not eat sweets when you have a bacterial infection. It is food for bacteria.

My question is: Does anyone know of any rhizobia bacteria that are not just for legumes? i mean, certainly there must be a benefit of rhizobial bacteria, say, for grasses, or a tree?

a sverko

Frankia type bacterias will fixate nitrogen in some genus and a few species within some genus of plants...none are really important for vegetable crops.

Some "blue-green algae" (actually bacteria, cyanobacteria) do the same...rice is pretty much the only crop that benefits from this one...sugar cane a little bit.

There is genetic work being done to help plants who normally don't benefit (or benefit much) from N-fixating bacterias to take advantage of certain strains, though.

if you are involved with research, have a search for cyanobacteria growing experiments, using UTC.. i dont think anyone has done one.

i have considered it.. not using anabaena (which is water-based), but fischerella (needs soil), nostoc (both soil and water), or spirulina, or one of the related bacterias..

These are some of the bacteria I am aware of that will fix nitrogen besides the Rhizobia:
Azospirillum
Paenibacillus
Klebsiella
Azotobacter
Pseudomonas

Some are independent.
Most will form loose associations with grass and trees.

Here is a link that might be useful: Garden For Nutrition