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OK, I'm going to make things really complex, since some how I did not get
Keith's post, and interpose my comments with Jack's. More needs to be said.
In a message dated 8/27/97 5:28:39 PM, you wrote:
>>1. Are the non-native species of legumes that we use in
>>permaculture actually fixing much nitrogen, seeing very few of
>>us would be inoculating our seeds?
>Depends... some, as the medics, are great nitrogen-fixers and also great at
>finding the needed mycorhyzal (sp?) cohorts, at least here. Look to how the
>plants grow in depleted deep sandy soils for a hint as to whether they have
>found the bacteria.
ELFIN PERMACULTURE REPLY: Some legumes fix nitrogen and some don't. I read
somewhere that MOST do not, but I don't remember the source. Fortunately,
most crop legumes (all that I know about) fix nitrogen. The rate varies, as
Jack suggests. At least as important as the species of fixer, however, is
soil condition, including mycorhhizal fungi, which promote fixation, certain
trace minterals, and of course pH. High levels of available N depress
fixation, generally. Moreover, at least some legumes, such as white Dutch
clover (T repens) increase the rate if fixation when cut or grazed! What a
deal! The more you use the more you get. Probably due to mycorhhizal
action, soil organic mater promotes fixation. Personally, I have not yet
selected crops purely because of their rate of fixation, there being so many
other factors to consider. A really good design option is to use n-fixing
trees as shelter belt and fence posts, particularly if they have other
browse, forage, feed, food, fuel and timber options. Not to mention shade,
transpirational cooling, wildlife habitat, ad infinitum. Sorry--got carried
away--we are at the stage of selecting such trees now for our design at
Barking Frogs Farm.
Don't neglect non-leguminous nitrogen fixers, which can do a really
impressive job. I've never seed anything nodulate like some alders on land
that owns us up in Massachusetts. Phenomenal! No N shortage in that swamp!
Here at Barking Frogs Farm, our biggest N fixer is azolla in our waterways.
Most of you know that this is an aquatic fern that symbiotically associates
with a N fixing cyanobacteria (misleadingly called blue-green algae).
>>2. At what point does the nitrogen fixed into nodules become
>>available? Do we have to wait for the plant to die? or are nodules
>>'sloughed off' during the life of the plant?
JACKS REPLY: >Most of the nitrogen fixed by a legume -- from 40 to 90 percent
or so --
>ends up in the leaves (since leaf production is the major use of the
>nitrogen by the plant), so the tops are most important. Tops which are cut
>release from 40% (cut and let lie) to 60% (cut and dig in) of their
>nitrogen the first year, on average, and one might expect something
>analogous for the nitrogen in the roots.
ELFIN's REPLY: Well as a general think Jack is right. However some
associations "leak" significant amounts N directly into the soil and so
benefit companions directly. Again, I suspect that this is amplified by
mycorhhizae, though this is not by any evidence, but because it is the
pattern. Not even a guess, just a suspicion. Good Master's Thesis for
someone. Good permaculturists don't worry about short term cycling, anyway,
we are in for the long haul. If you take most of the crop off and never
return anything, you aren't in for the long haul. Completely closed cycles
are a myth, granted, but completely open cycles are a suicide note. So add
the fixers that suit the total design and move that soil fertility up by
seady increments. Rapid changes in soil are an invitation to soil-borne
Fukuoka worked out a lot of this. I'd substitute another legume very, very
carefully as he took `15 years to work out his system and I may not live
another 15 years. (I'd like to, of course.)
>>3. Is there much point in planting legumes in rich soil
>>specifically for nitrogen fixing purposes?
JACK'S REPLY>In accord with what you've written (nitrogen-fixing is suspended
>nitrogen is adequate), no. Much more effective under conditions of high
>nitrogen is either 1) cropping, or 2) catch-cropping. Cropping is good
>sense, usually the soil is improved just for the purposes of cropping and
>receiving a yield. If season or other conditions are inappropriate, "catch
>crops" are used to capture nitrogen and any other available nutrients. For
>these purposes a catch crop is wanted that has high nutritional
>requirements for the mineral element in question. In the case of nitrogen,
>it's hard to beat the grasses -- annual rye, oats or wheat (crops), corn,
>etc. Dry matter production by grasses can easily double that of a good
>legume. I like the idea of a mix, such as of a grass and a leafy green such
>On the other hand, the Land Institute in Kansas, USA has found in
>establishing prairie plant mixes that the more legume species that are
>included in an initial seeding, the greater will be the number of ALL
>species (whether legume, grass, broadleaf, etc.) which become established
>on a permanent basis. So nitrogen is not always the main or only issue.
>As for planting under trees, tap-rooted plants are best since fruit trees
>tend to concentrate feeder roots on or near the surface. Mustard is good
>here, too, comfrey, etc., but most grasses have phenomenal root systems and
>will compete strongly with fruit trees. Pasture mixes of non-competitive
>grass/legume mixes can be gotten from such supply houses as Peaceful Valley
ELFIN'S REPLY: Well Jack clearly tried to steer us back into permaculture
here. If you plant something mainly for one reason, it isn't permaculture.
Stack those functions, fella! There are more considerations than we can
think about, but we should think about as many as we can. In Massachusetts,
in highly organic soil that was naturally well mineralized (too rocky to plow
and apparently never grazed), I'd get three pickings, massive pickings, of
Commodore green beans in a 90-frost free day growing season. This is a 65
day bean. Clumps of nodules got to the size of a child's fist. I fertilized
the beans with wood ash for the trace mineral and pH bump. One light
dressing, no ammendments, following corn that bore up to 6 ears per stalk,
three large ones routinely. I've followed the same pattern in other soils
with maybe 1/5 the yield if I was lucky. Generally I rotated 1/4 legumes on
an area basis and 1/2 of the garden was corn, alternated each year and 1/4
other vegetables. We added manure, fed livestock probably tons of weeds, ate
like kings and had the market on premium green peas in our pocket. (We got
20 percent higher than retail--supermarket prices--for snow peas at a local
chinese restaurant solely on the basis of quality) Even the peas were
I'm a big guy and pretty strong. I'd take it poorly if people decided not to
feed me because I'm big and strong anyway.
For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since
1982), Elfin Permaculture workshops, lectures, Permaculture Design Courses,
consulting and permaculture designs (since 1981), and now correspondence
courses via email. Next starts in Oct. 1997. Internships available.
Copyright, 1997, Dan & Cynthia Hemenway, P.O. Box 52, Sparr FL 32192 USA
The organizing principle of the Universe is silliness.