richard swier

It would seem that plants can get all the carbon they need from the atmosphere. The photosynthesis equation goes like this:

6CO2 + 6H2O + light → C6H12O6 + 6O2.

Or put simply:

Carbon Dioxide + Water in the presence of Light = Carbohydrates and Oxygen.

So the place of carbon in the soil is about something else. Permiculture and conventional agriculture perhaps have different starting points and as well as different goals. By increasing organic matter/carbon in the soil, the permiculturist is improving soil fertility, soil structure, soil flora and fauna and increasing water holding capacity of the soil- etc , or in another words the permiculturist is primarily concerned with sustainability of the system: the long term health of the soil system, which will ensure the long term viability of his/her and future generations of future yield. Organic matter in the soil is the best way to achieve these goals. Conventional agriculture doesn't need healthy soil because it can achieves its goals on the basis of cheap inputs made possible by cheap fossil fuel. It is concerned with getting the highest yield for the the least amount of money invested. Check out this on you tube

http://www.youtube.com/watch?v=nhVWNwCRpKg from the 7.00 min mark

(Watch the whole programme because it is really excellent stuff! but from 7.00 shows how much oil goes into our food) Because fossil fuel is so relatively cheap ( for the moment) a fossil fuel based agricultural system is the best way (for the moment) to achieve a high yeild for little cost, while it is relatively more expensive to achieve those same goals organically. That's why organic food is more expensive. And that is why peak oil should be of concern to us all. As oil becomes more difficult and expensive to extract the price of energy will start to rise. The economics between the two systems may change dramatically. Especially as the soils farmed conventionally have been degraded by its methods and are totally reliant on cheap fossil fuel inputs to make them productive. Listen to Jeremy Grantham who is a commodity trader (ie he is very much a capitalist) yet he is extremely concerned about some of the unsustainable aspects of capitalism especially that of how we farm and treat the soil. He talks about a 'deal the farmer has made with the devil.'

http://downloads.bbc.co.uk/podcasts/radio/worldbiz/worldbiz_20130216-0050a.mp3 (listen from about two thirds of the way through to here the bit about soil it starts: 'everything else about it is brilliant'.

Done a little more research on the Pawlonia it seems like there is a bit of conflicting information about it. Some suggest that it is not a root nitrogen fixer after all. Some websites claim that its leaves fix nitrogen - something I have not come across before? This seems to be a characteristic of some tropical nitrogen fixing plants. Perhaps there is someone out there who can enlighten us? Anyhow, it seems like it is used extensively in China in Agroforestry situations to increase the yields of companion crops. That suggests potential suitability for forest garden type situations.

Dj, yes I agree I suppose we are all pioneers at the beginning. I guess it means we all potentially could make significant contributions/ and mistakes!!! in working out how to do it in our own particular set of circumstances. We are really lucky here in Devon UK as Martin Crawford has blazed a trail and shown how it can be done in the conditions we have in the UK. So it is easy for us here to see how well his designs works in practice and therefore feel confident to follow his recommendations. his two acre demonstration garden is about fifteen years old and is very impressive. Lots there on you tube if you want to get a feel for his garden. Furthermore I haver found that his various books are excellent resources in helping you to design a garden - highly recommended.

http://www.amazon.co.uk/Creating-a-Forest-Garden-ebook/dp/B003Z9JMYI/ref=sr_1_10?ie=UTF8&qid=1363083139&sr=8-10

There is a chapter in this book devoted to designing the nitrogen fixing plant aspect of a forest garden. The principles that he uses are described very clearly although they are expressed in the context of a cool temperate climate I imagine some of those principles will be universal. However for the detailed application of those principles in different circumstances adaptation will no doubt be necessary.

The main issues to consider with the designing nitrogen fixing in a forest garden situation, as I understand it are:
1 That most nitrogen fixers are quite light demanding - (elaeagnus is a rare exception)
2 if the cover of nitrogen fixing plants need to be 25 to 40 percent ( in a sunny situation) 50 to 80 percent (in shady situations). To get this kind of cover you need to fill much or most of you under-story/shrub layer with nitrogen fixers - you have to start sacrificing a lot of this very valuable space to nitrogen fixing plants when you might prefer to use that space for edible or other kinds of yields . Therefore it makes sense to get your nitrogen fixing done way up in the over story.
3 This conclusion is even more convincing when you also consider that: If you use nitrogen fixers in a sunny situation you need only half the area to be covered by nitrogen fixing plants compared to those in a shady situation.








Anyone wanting more detailed information on nitrogen fixing plants might benefit from this:

http://www.agroforestry.co.uk/publorders.html which is Martin Crawfords website where you could get a booklet called:

Nitrogen-fixing Plants for Temperate Climates
by Martin Crawford
2nd rev Edition, 1998. ISBN 1-874275-38-6. A4, 89 pages.
Plants which fix nitrogen (ie utilise nitrogen from the air) are some of the most useful plants in agriculture, horticulture, forestry and agroforestry. Their use can lead to much reduced fertiliser usage, lower losses of soil nitrogen through leaching, and improved soil fertility through increased soil organic matter.
Most people only know of the legumes as nitrogen-fixers; however, there are several other plants groups which do so, notably the so-called actinorhizal plants (including alders, Elaeagnus, sea buckthorn) which are mostly of temperate origin and better-suited to cool temperate climates.
This directory describes the different groups of plants which fix nitrogen, including the legumes, the actinorhizal plants, liverworts, and lichens. Most fixation occurs via a symbiotic relationship with bacteria in root nodules, and the nodulation status of temperate genera are listed, with notes on cross-compatibility between different strains of bacteria and different genera.
The nitrogen contributions which N-fixing plants can make are discussed, and an overview of the different uses given, including their use in forest and fruiting gardens as well as in forestry and agriculture. The main parts of the directory describe over 450 different species and their in-depth uses. This includes tables, organised by plant type, showing conditions required and uses of all species.


Not sure if this would be of any help to you in Colorado dj?

I won't be around for a while as I'm off to work on the forest garden - no internet access there. So keep up the good work

Hi - I was curious about what nitrogen fixing trees might grow in your part of the world, so that you might be able to mimic what can be done in more temperate climates with Alnus Cordata. Ie a really tall nitrogen fixing tree that allows you to plant lots of things under it. This looks like might work really well: Paulowia Elongata (i.e. not the the invasive P tomentasa ) if it did it would be a fantastic candidate. Although perhaps your cold snaps might be a problem. Information seems to suggest it tolerates climate extremes. I found this on a Florida gardening website.

http://forums.gardenweb.com/forums/load/flgard/msg0518271715347.html


climatic info here:

http://www.worldpaulownia.com/html/zones.html


'If you want a long-living nitrogen-fixing plant, try a Paulownia, aka Royal Empress, Tree. The fastest growing one,, is the fastest growing tree in the world and has leaves that make great organic matter to add to your soil, as they have much nitrogen in them.'




On the strength of this I've decided to see if we can experiment with it here in the UK too.

Hi David - I'm not sure what your situation is and what trees you are able to grow. What Martin Crawford does, is to plant a lot of Alnus Cordata (Italian alders) in his forest garden (they are really quick growing.) They grow, If I remember correctly to about 25 M tall) He begins to lop off the lower branches so that eventually the Alder canopy is way up above your edible trees so that they take up space up there rather than occupying the more valuable space at ground level and cast the least shade on your other trees. On our forest garden in Devon UK we have used Italian alders as our shelter belt so that we should get two yields from the the Alders. Shelter and nitrogen (from nitrogen fixing nodules plus leaf fall.) the only snag with this design is that the alders are quite late to leaf out, so perhaps Alders are not best used for shelter from your cold spring winds. However we are experimenting with planting ivy to grow up the alders to make them eventually more like deciduous trees.(Ivy is an excellent bee plant which would make for a third yield - Also the latest information suggests that Ivy does not harm or choke the host tree) I'd be interested to know what others think about this idea?

Check out eric Toensmeier's web site.

http://www.perennialsolutions.org/all-nitrogen-fixers-are-not-created-equal

He quotes Martin Crawford suggesting that between 25 to 40 percent ( in a sunny situation) 50 to 80 percent (in shady situations) should be nitrogen fixing plants in a forest garden

best wishes