Nitrogen fixers?

It's time to add some nitrogen fixing shrubs/trees to my food forest design. I'm not sure how many to add. Is there a general rule of thumb about having a nitrogen fixer every ___ feet? Right now I know I only need one, since I'm concentrating on a fairly small area, but this will eventually take up quite a bit of space. I already have several existing fruit trees that will be incorporated at some point, and I thought that if I was gonna order plants I'd get several and put them in this year, even though I won't be doing anything else on that end of the yard right now.

Hi Cindybode! In my experience, nitrogen fixing plants can't be overdone. So have fun with it! If you want to find out more about Nitrogen fixation you can look here
http://www.visionlearning.com/library/module_viewer.php?mid=98

Rizobium bacteria, who knew?

Interesting. Who knew, indeed.

I'm not at all worried about overdoing it. I'm more concerned that I won't put enough in. I found a great looking false indigo at my local garden center the other day, so it's a start.

Some nitrogen fixers also have the benefit of producing fruit, such as the autumn olive, though it is invasive in areas. 

Cindo and all,

I am in the same boat with my plant guild.  I think the thing to do is look at your primaries (apple trees, large shrubs, etc.) and get to know them really well.  What kind of nitrogen do your primaries require?  All Malus species require a 6:10 primary to N2 fixer ratio.  38% of the plants in my guild need to be N2 fixers.  You could always put more in.  Some N2 fixers I have researched are:
peas, alfalfa, marigold, chives, red clover, black locust (the new love of my life), worms worms worms, some strawberry species, buckthorn, honeypod mesquite (beneficial insector as well), acacias, sweet fern, wild blue indigo, red alder. 

Do you have any you could recommend?

Marigold?  That isn't an n-fixer is it?

Jeff, do you have a source that refers to marigolds or strawberries as n-fixers? I'd be interested to read more.

Dave

Strawberry isn't.  I blew it.  Neither is marigold.  I was reading from my guild list, located next to my N2 fixer list.  Sorry y'all. 

That was just AWFUL, Steve!  IMAGINE, a mistake like that!

Neither Paul, nor Leah, nor Kelda nor I have EVER made a mistake like that!  NEVER!

   

(Wanna buy some swampland in Florida?)

Sue 

Why are all my plants dying?

My grandad always told me it takes a big man to admit his faults.

Do you really own swampland in Florida?

No.  That's an old joke:  if someone believes everything you tell them, sell them some underwater swamp land in Florida.  Even if you don't own any to sell.

Sue

Susan screwed it all up.  It's supposed to be "waterfront property in Florida" which is actually a foot or more underwater whenever the tide is high.  And loaded with gators.

Oh, yeah.  I forgot.

So, Steve, I've got some waterfront property for you! 

Sue

Gator stew, anyone? 

Good eats right there.

And back to the nitrogen fixers:
while I'd agree that you can't overdo it with nitrogen fixing, from what I've read in Edible Forest Garden, many food foresters Do overdo it with cramming too many plants into a space not big enough. So that's a cautionary note. You may lower productivity and stress the plants out (more pests), if the plantings are just too tight.

So, the full sizes of the plants are just something to read up on it. You can always go for an alfalfa understory though.

Alfalfa almost always comes up as one of the perfect plants.  Deep taproot, plus N-fixing, plus excellent biomass, and thrives on being harvested ...  but there is one glaring downside. 

It is freakishly picky about pH.  Unless your soil has a natural pH of 6.9 to 7.2, you're going to have to take on so much work, that, in the end, it will most likely turn out to be a big hassle. 

And in the puget sound area, expect your natural pH to usually be 5.8 to 6.5.

When you say "natural pH," do you mean untreated?  If we added a healthy amount of lime would that help? 

I was thinking red clover.  Also a deep taproot, N fixer, ground cover.  I don't think it is as pH picky either.

I have heard of people overcrowding as well, so I will map and plant carefully... but I was looking forward to doing the Sepp Holzer toss  

Lime will help you get the pH juuuuuust right .....  for a while.  Rain sorta rinses the lime away over time.

Rain, rain, rain .... what do we get?  Something like 60 inches a year?  But we did have a nice lawn all summer without having to water it at all!

Does this mean we need to limit what we plant to plants that thrive in acidic conditions? 

Yes.  Which is most stuff. 

I think that it is not a bad idea to have patches that you designate as artificially neutral soil and that annual liming will be required.

I agree.  Experimental zone 1.  Would a 5.9 pH be considered "slightly acidic" by most? 

Would red alder leaves and moldy sawdust make a good nitro- fixing mulch?

5.9 would be called "acidic".  6.5 would be "slightly acidic".

Red alder leaves:  I'm not sure:  does red alder duff have any alelopathic stuff?

I wouldn't call moldy sawdust nitrogen fixing.  Or, do you mean to say that it would be a good mulch for a nitrogen fixing plant?

I don't think red alder is allelopathic.

Sawdust requires nitrogen to break down. If it's mixed in with the soil, it will rob nitrogen from it and any surrounding plants.  If it is just laid on top of the soil, it will only take nitrogen where it touches the soil, it doesn't draw it out.

Sue

Personally,I think people are way too obssessed with nitrogen fixers;especially in zone 1-3.If the nitrogen fixers are not producing a usefull product and they are taking up space that otherwise could,thats too much(at least in closer zones).Why?...Well lets look at the big picture.In areas where compost is applied,there is probably more then enough nitrogen in that.Got pets?They shit and piss nitrogen(lots-as meat based foods create nitrogen rich waste).Live semi rural?I like to pee outside near plants I like.Humanure can add lots.Pet and human hair,dead skin cells!Humans and our activities generate lots of nitrogen in many unexpected ways.I'm not against nitrogen fixers in these zones,I just think we could stand to chill out and be less anal in our desighns.People have been managing nature and living in harmony with the earth for the last million years without even caring about such things and now we are supposed to be obsessed with the perfect desighn.In larger desighns in further away zones sure,but your average suburban yard?Who cares!

I have to agree a  to some extent with mt. goat. although you can't damage anything really with nitrogen fixing plants (although too much nitrogen can mess with blossoming and fruit/vegie production in some intances can't it?) if those nitrogen fixing plants are tilting the biodiversity out of whack or are planted in place of other productive and compatible plants to a large extent they could be rather impractical. especially if they require special care.

The only caution I would offer with adding lots of nitrogen-fixers (or lots of anything) piggybacks on the concern Kelda mentioned about crowding. If you have plants too tight in the PNW you may have more problems than just lower productivity. Many parts of the PNW have fungal issues like powdery mildew, brown rot, and peach leaf curl. One of the best way to prevent these is to increase airflow so those areas aren't so dank. In other words if you are in an area where the air seems to stagnate already creating a dense food forest might result in lots of fungal disease issues. In areas like this it may be important to use windbreaks to steer air in, create less dense plantings, and prune the trees for openness.

Dave

Yes, let's not forget that Bill Mollison lives in an area of high-intensity sunlight.  The spacing for plants in a food forest there has got to be different that in the PNW.

I was reading recently that some plants can get too much sunlight.  Their example was zucchini.  ZUCCHINI???  I thought that was a sunlight-lover?  Well, it is, but when it gets more than it needs, the leaves wilt. As soon as the sun shifts behind the trees or dusk approaches, the leaves return to normal.  Most people think the zucchini needs water, but it doesn't, it just had its limit of sunlight.

Sue

off topic but that is a tidbit I will be putting to use! I haven't had a good squash year in a while. I think if I get the opportunity I'll try planting them so that they get a spattering of afternoon shade. I thought that the whole problem was squash bugs but maybe they were just attacking the already stressed plants.

Now, that's a thought, isn't it?  I wonder if it is considered (by the plant) to be stress, or just a reaction?  Zucchini:  photo-phobic!  Who woulda thunk it?

I think it was in the same article on sensitivity to excess sunlight that the author mentioned the Native American 'Four Sisters' (most people think it's three, but it's really four) method of planting did provide a certain amount of shade to the squashes...

The corn grows up to the sun (it's planted first), and the beans are planted when the corn plants are at least a foot tall.  The squash are planted between the corn.  As the sun moves, the corn plants with the beans climbing up them provide some shade, the squash covers the ground and keeps the soil more moist and suppresses weeds.  The Fourth Sister is the Rocky Mountain Bee Plant (Cleome serrulata), which attracted pollinators to the other Three Sisters.

Sue

...only a few days left until the drawing for the ticket to the Bullocks workshop at the end of May...  thought I might make an entry on this subject...  Interesting stuff so far....

Wasn't it Stamet's who reported that Mico-rhyzo-fungi  (spelling??) actually are able to pass nutrients around in a forest eco-system?  Wasn't there some study somewhere that used Radio-labeled Nitrogen molecules that could be identified...  weren't they discovered to have been passed all around a forest area, the culprets being the fungi?

That being said, I have heard farmers report about how the one row of crops that they missed putting manure on one year failed to grow properly showing signs on Nitrogen deficiency--the Nitrogen from 1 foot away did not travel laterally in significant amounts to help the crops on the fringe that didn't get fed.

Another aside:
I stumbled onto an interesting used book in the book store that was published in the 1940's by the American Agronomy Association.  The book is called "Hunger Signs in Crops."  They present the results of years of study done with typically cultivated plants and are able to show what a plant that has been deprived of adequate Potassium looks like compared to a plant lacking adequate Nitrogen, Calcium, Boron, etc.  ...with color pictures.  This has been useful information to me--it has helped my understanding.  I've since done a google search for this book title and found that one can still find copies...

Regarding pH...  I recently read a paper published by a BioDynamic farmer in conjuction with a PhD level soil scientist at WSU that reports that the adding of a few ounces of BioDynamic preparations stirred into a barrel of water and sprayed in a pasture was able to significantly raise the pH of a test plot area compared to a control.  It did not raise the pH as high as the comparison plot spread with a couple of hundred pounds of lime (costing quite a bit of $$'s) naturally, but the elevation in pH on the BioDynamic plot was significant enough to raise the pH into a significantly more favorable zone (form 6.2 initially to 6.4 if I recall--the control stayed at 6.2, the limed plot rose to 6.7 as was predicted by the agronomist who calculated the amount of lime to add--if I remember correctly).  Another interesting thing about this study--the forage on the BioDynamic plot tested the highest in total gross protein production--something that would make the forage grown on this plot potentially more "valuable" nutritionally than the forage grown on the limed plot with the higher pH.  So what is going on here?  Conversation with the farmer and others resulted in the hypothosis that the "preparations" must some how "activate" the micro-organisms in the soil--the real regulators of soil conditions.  What's your guess??

Also...  if soils are "over wet" as they often are here in the Northwest, they will be deprived of Oxygen as the water fills the micro-pores in the soil taking up the available air space.  Any "composting" of organic matter that will be occurring in the soil will tend to be "anaerobic" and the end product will be more acid soil conditions.  Often times, soils that are tested for pH here in the winter time will naturally test lower in pH (more acidic) than the same soils tested later in the season when conditions are drier (higher pH).  It's more likely that drier soil will be able to breath better--better "aeration"/oxygen exchange and "aerobic" activity in the soil will increase--favorable aerobic micro-organisms are free to do their work.  Sometimes, I'm told, Nitrogen levels can sometimes test higher in the soil because these more active aerobic micro-organism will be breaking down organic matter more efficiently, thus making more Nitrogen available.
    I've learned that there is no one measure of anything that can be taken at face value without due consideration to other variables in the system.  Then there's the question of total Nitrogen vs. available Nitrogen in any given soil sample...  or Nitrogen in various forms: Ammonia, Nitrates, Etc.  Soil scientists will tell you that it can be a tricky business trying to understand whats really going on at any given moment.  I'm beginning to think that all that one can do is look for general trends...  Oh, yeah, and keep notes so you can compare observations over time...

Today's the 14th, the drawing for the ticket is on the 18th--only a few more days to go...  I may have to make another entry somewhere or another in the next few days...

Thanks,
  Dan

I'm not certain, but I'm pretty sure that that mycorrhizal stuff gets  dead when you turn the soil (plowing/tilling).  And if you are lucky there might be some spores in the soil so it could try again.  But it will take a while to make a comeback. 

Do you have a link for the biodynamic raising of the pH thing?

Overwet soils:  ahhhh, another grand benefit of a raised bed!

Paul,
    Why would you assume that Mycorrhizal fungi are killed with a simple turning of the soil??  Certainly, the fungi grow in established networks as can be observed--the little white or grey fuzz that sometimes appears--and these could be disrupted if/when the soil in disrupted, but Killed??

    The article about use of preparations was published in the BioDynamic Journal by the BioDynamic Agriculture Association--Google can help you find them and their catalogue of materials...  I read the article in hard copy.  I don't know if they've published it on the web or not.

    Raised beds, or not raised beds.  Funny you should mention this as the original "Raised bed" was not one that was piled up with nice 2x6's for borders.  The original name "Raised Bed" was used to describe a bed that had been double dug--the increased aeration of the soil would generally "raise" the top layer of the bed higher than it was prior to double digging and higher than the surrounding area.  So, all of the benefits of the original "raised bed" resulted from the improved tilth that is produced by double digging--improved drainage, more open spaces, less compaction that result.  Generally, if one goes to the trouble of double digging, one would also add organic matter/compost also which would contribute to improved structure, etc. as micro-organisms digest the stuff and secrete binding agents that help with soil texture.

      So...      to till or not to till...  to double dig or not to double did...    to "raised bed" or not to "raised bed"...    ??    These are all valid questions and I for one don't have such closely held beliefs that it must be a certain way as you seem to suggest, Paul.

    I'm out of time now...  I hope to comment more under the thread about tilling later on... 

Thank you,
    Dan

There is another type of raised bed that has nothing to do with double digging or fancy wood borders.  It is the simply piling up of dirt/soil/or just organic mater and planting in that.  Kinda like making a "hill" or "ridge" for growing some types of plants.

I live in an area of very sandy soil and sub-tropical climate, there is little point in double digging here in my experience.  Add a good six inches of compost or other organic matter and double dig it and in about 4 months it is no longer a raised bed and by the middle of the second planting season in it, it is a sunken bed.  If I simply pile the organic mater on top of the ground and plant in it, I can usually go two planting seasons at least before the bed has leveled itself.  Digging and turning the soil does disrupt the life within the soil though it might not kill it all.  I tend to only allow digging or turning of the soil when there is a strong reason to do it (perhaps to get rid of weeds or dig up root crops but I usually smother weeds and in a soft raised bed of organic matter most root crops don't need digging.)  I don't need a raised bed to deal with poor clay drainage, I need a raised bed to provide lots of moisture holding organic mater and to help the plants survive nematode attack a bit better.

But hay, this is supposed to be a thread about Nitrogen fixers which I am in search of good perennial sub-tropical nitrogen fixers that make good chop and drop mulch production.

paul wheaton wrote:
I'm not certain, but I'm pretty sure that that mycorrhizal stuff gets  dead when you turn the soil (plowing/tilling).  And if you are lucky there might be some spores in the soil so it could try again.  But it will take a while to make a comeback.   

I'm not sure turning the soil necessarily kills mycorrhizae either. If a bed is turned, but kept moist and shady, I think the mycorrhizae may reestablish itself. In fact, I would suspect that there are benefits to disturbing mycorrhizae at times (nutrient release?). I imagine the big problem comes when a field is plowed, dried out, and baked in the sun.

The authoritative reference for this answer would be Paul Stamets, of course. I bet he mentions it in Mycelium Running, but I haven't read it. Kourick might also cover it in Roots Demystified.

Dave

I am not certain about the mycorrhizae die, but at the very least it will be set back.  A lot. 

I do know that every time you till the soil, 30% of your organic matter is released into the air.    In other words, a lot of your OM is such a tiny particulate, that it may be sitting on the edge of being a gas. 

Soil structure is a valueable thing. 

OTOH:  if worms thoroughly aerate your soil, then you have all the perks of tillsed soil plus all the perks of mature mycorrhizae.

Certainly fungi have a primary role in forest eco-systems (breaking down leaf fall and such into forest floor duff and finally into soil) but aren't  the bacteria in the garden scape primarily responsible for making nutrients available to common vegetable plants??

We can't necessarily believe that it is fungi exclusively that are the active agents in creating favorable conditions for plants to grow--again fungi are mostly a forest thing.  Consider the ruminent animal with that extra stomach full of bacteria that literally digest cellulose and extract nutrition from it.  These bacteria are also secreted onto the pasture scape with the manure.  Not only does the manure add bits of undigested material that ads to the overall content of nourishing goodies in the soil, the manure also contibutes the bacteria that help break down these nutrients and help to make them available to plants that grow in the soil just as they make nutrients available to the animal organism.  It was this symbiotic cycle that was responsible for making the Great Plains one of the most fertile regions on the planet--thank you bacteria.

Dan

Of course bacteria are an important part, balance is all.
Keep in mind that many of the bacteria will also be disturbed by turning the soil since UV light often kills off what is turned to the surface and allowed to dry out.

"Till vs. No Till" certainly is a question that is hot these days.  I think that there is even a thread on this forum about this but since the subject has come up here...

    It is often tempting in life to latch onto an idea that seems to make sense (like no tilling) and then make the assumption that this is the ideal answer for all situations.  There may be some advantages that are missed in some situations if ones actions are limited by the use of only one way of thinking about something.

    I know of people who found that their vegetable production improved considerably when they finally did something mechanical to break up their soil.  They chose to use a Broadfork and not a roto-tiller.  There are advantages to use of a Broadfork compared to a motorized tiller (no gasoline involved, no loud noises, no vibration, no stinky exhaust) not the least of which is the fact that the Broadfork helps facilitate soil aeration without completely disturbing the layering of the soil.  By just making "slices" with the fork instead of subjecting the soil to the twirling tines of the tiller, a large proportion of the soil structuring is preserved while still benefitting from the positive effects of improved aeration.
    Plant roots and favorable micro-organisms actually need oxygen and if a clay soil becomes too compressed (water droplets from the rain or from overhead watering that "crash" down onto the surface of the soil are actually the biggest offenders that contribute to clay soil compaction) then there is a risk that the roots and organisms can "sufficate" and then the plants will not be at their best.
    In summary, I agree, tilling with a roto-tiller or indiscriminate plowing can be problematic--but there are some situations when mechanical activity can be helpful.
    Note: I also know of a very thoughtful fellow who  uses a tractor pulled "Rotovator" to just lightly blend the top two inches of a plot for the purpose of 1) smoothing out the large soil clumps to make a more regular planting surface and/or 2) mix in cover crop or grain seeds that he has broadcast by hand.  (Just leaving the seed on the surface can be a great invitation for birds to come and feast on the seed--stirring them in with a very shallow "Rotovation" is a method to keep the seed in the ground and away from the birds.)
    As I understand it, even when there is an indication to perform some mechanical treatment of the soil bed, this is something that does not need to be done often--like maybe only once in the fall when putting a bed to "sleep" for the winter in prep for spring planting...

    Many advocate heavy sheet mulching to cover a bed (which includes some watering) trusting that the worms will take over and churn through the mulch, breaking it down into lovely organic matter that then turns into rich humus--nice soil.  Certainly this is a lovely example of common sense soil building.  Sometimes, if one wants to plant a bed densely, one has to wonder, I should think, whether a heavy sheet mulch might restrict air movement into the soil thereby potentially limiting the benefits to be had with better soil aeration ??

    Back to the Nitrogen fixing idea--it seems to me that one goal is to ensure adequate organic matter in the soil that can then be acted upon by micro-organisms that will break this stuff down and turn it into valuable Nitrogen for the next round of growing to occur.  Nitrogen is not always stable in the soil--too much will just leach down during the winter rainy season here in the Northwest meaning that all of the work to get the Nitrogen there in the fall may be all for naught come spring time.  Timing can be important. 
    Other factors that would influence soil Nitrogen would be: pH, soil structure, and viability of soil micro-organisms (I'm probably missing a few things here...) all of which interact in complex ways to affect the overall Nitrogen levels in the soil and general nutrient availability.  "One answer" solutions may not work in all cases due to the many complex factors that influence soils in various locations.

    I understand that it is the presence of organic material in the soil in the form of slowly broken down material that can lend stability to Nutrient and Nitrogen availability.  Too much soil aeration such as in a hot climate with sandy soil would result in fast combustion of organic matter meaning that it might be harder to keep the nutrient levels high enough for growing some things in this type of soil.  In other cases, a soil might need help to develop enough "open" air space to facilitate the breakdown of organic matter in order to make it available for plant nutrition--is this case, perhaps mechanical action of some kind may prove to be beneficial...

What do you think??


Thanks,
  Dan

Oh I so agree that there is no single solution that will work for all situations.

Climate, soil type, space available, materials available, equipment available, crop planned, irrigation, season, starting point, purpose of the garden, and personal inclination will all affect the choice of garden or farming method.

I have sandy (doesn't hold the nutrients well) soil and a rainy hot season so the rains are stripping nutrients as some of the plants are needing it most.

Sounds like a job for a "Permaculture Design Consultant" or at least someone interested in the challenge of designing a small-scale sustainable food system...    I would hope that they wouldn't just tell you to make an Herb Spiral, a few Key-hole beds planted with Polycultures, and a food forest and then call it "Good"--there is more to good design than just these things.

Good luck!!

Dan