Building soil faster than nature

From http://www.growbiointensive.org/grow_main.html

"Build the soil up to 60 times faster than in nature, if properly used"

I read "How to Grow More Vegetables" a while back and I'm not sure if they give more detail about how this is possible. I'm very skeptical of this claim, although I still have a ton to learn about soil and plants. Does anyone have any better idea what is meant by the vague quote here. Are they referring to just building up the organic part of the soil 60 times faster or are they talking about the whole soil including the inorganic mineral component? Would increasing the amount of organic matter and soil life increase the rate of break down of parent material? From what I know it seems that a realistic goal of a sustainable agricultural system would be to build soil at the same rate as nature. Is it really possible to build soil faster than nature without bringing in outside inputs? Of course we can build soil faster than nature with bringing in outside inputs, which could be sustainable, but I don't think that's relevant to the research being done at Ecology Action.

Also, has Ecology Action published scientific research papers on what they are doing. I'd be very interested to see mineral and organic content measured in their soils over a 30 year time period.

Have you checked their free publications to download?

http://www.growbiointensive.org/publications_main.html

My guess is, this is not based on research but just a guess, that plant roots and the chemicals they exude, and perhaps humic acid, would work to break down parent material faster in a Biointensive setting than might happen under other circumstances, especially compared to the "dead" soil of chemical agriculture.  But keep in mind the vital part of soil is not so much in the mineral component as in the humus.

I looked at that page earlier, but didn't notice the different tabs, so maybe some of the information is on there. Thanks

As far as i know, you can, but you will need a lot of human energy and a lot of natural resources. I have a book but don't have with with me now.
What i'm really happy about this book is, that i've read it at the same time i was reading square foot gardening. Forget about native soil SFG said. No go. But also bio-intesive is not close to me anymore, as i can work with native soil in much more gentle way.

I trust nature. I can build soil life and everything in this aspect with the help of natural, local vegetation in just one year. That's enough imo. I think we shouldn't be focused on perfect soil. Imo we loose to much of it's native qualities.

The question here, imo, should be, do we really need to build soil up 60 times faster, if you can assist nature doing it's things and build soil enough to grow what you want in just one year.

Biointensive has always seemed like too much work to me.    I would rather dig once to remove rocks and build a hugel bed, but I can't imagine double digging every year!

The Keyline Plan also claims to build soil much faster than in nature. They are at opposite ends of the extensive/intensive spectrum, and so their similarities are very telling.

Both contrive to keep soil moist, aerated, fed, and warm much more deeply and consistently than nature would. Keeping soil well-fed is accomplished in very different ways: biointensive methods call for crop residues to be produced as abundantly as possible, composted ex-situ,
and dug deeply into the soil, while the keyline plan calls for flushes of root growth and dieoff, with optional shallow discing-in of some crop residue. Keyline is open to limited use of superphosphate in the first year, and perhaps less of the C and N grown are volatilized.

Differences in aeration strategy are also very important, with Yeomans striving to mix soil layers as little as possible, and Jeavons, as much as possible.

The information at the first link says they ran experiments and their results are documented after 8 years.  So instant is being implied, but there is nothing instant about it.

Also they do this by turning 60% of what is planted back into the soil - so basically it looks like intensive composting to me.

I would have to read it all in more detail, but from what I gleaned it involves lots of work and time - no surprise.

jamie mcbride says they return 60 0/0 of what is grown to the soil. If you do that sort of thing iforming soils woudl be quicker, maybe if you are poorer with less land you have to eat seventy percent of the vegetable matter that grows.  .
    There is a system for growing more in less space  in which you make raised beds and add a lot of manure to the soil, the french market gardening system or the chinese one and in the old days there must have been a lot of horse manure outside Paris say, if transporte was, as it was, horse drawn and in china you use humanure plentifull near cities were vegetables traditionally are grown. If you use a system like these with lots of manure you will have lots more vegetables and lots more vegetable matter to return to the soil. so bettering it would be quicker.
sepp HolZer if you whatch his videos is always looking after his soil, spoils it rotten and is a hard worker it seems, his soil would get better faster and it might look as if it was easier than it was if you forget that he is a person who lavishes care on it and can organise some expensive activities maybe including buying goodies for hhe soil,borrowing and paying back money to do so till he was richenough to just use his own money.
    I only let the natural vegetation change the soil and the clay has quickly changed its texture to something much easier to dig in two years as i remeber it it was already different  but not everywhere but if i want to grow vegetables on it things dont go so well, i suspect it lacks nutrients so i have a better soil but not good enough using the natural plants. Not good enough to be a market gardener so it all depends how much tender lovign care you can give the soil. Can you keep ducks so there are ducks  to manure it, If you lived there on your land you would have a potetially wiht worms to  breakit down, biggish quanity of humanure to feed to the soil if the farm was not big . How much can you give to the soil? agri rose macaskie.

rose macaskie wrote:
jamie mcbride says they return 60 0/0 of what is grown to the soil. If you do that sort of thing forming soils would be quicker, maybe if you are poorer with less land you have to eat seventy percent of the vegetable matter that grows. 

I'm not sure about that, at all. A poor family and their rabbits may need to eat seventy percent, but I think adding a tame animal to the mix just replaces some fraction of the work of detritovores.

A lot of poor subsistence farmers grow things like rice, maize, garbanzo beans, sorghum, etc. The dry mass of the inedible portion of those plants can be a lot higher than the dry mass of the edible portion. If anything, biointensive methods would allow many poor farmers to eat a higher proportion of the vegetable matter they grow, since Jeavons suggests devoting significant space to things like sweet potatoes (edible greens, as well as tubers), potatoes, and leeks, which don't produce a lot of inedible plant matter.

Also, some fraction even of the plant material that a poor farmer does eat, ends up being returned to the soil.

The whole idea behind this method was to allow a minimum space to feed a person completely. If anything, its irrigation requirements might be what makes it unsuitable for poor farmers.

  TalKing of irrigation methods as joel hollingsworthtsays watering maybe the most expensive part of biointensive farming and thinking of how plank says you don't need more than enough good soil for just your needs, as in you don't need a very thick layer of topsoil.  One of the things that drove me to write about this sort of thing, before I started writing here when i just started to learn a whole lot more, was that in Spain they are very careless of their soil, reducing fires being more important than good soil, so they do for vegetation and i thought that that is silly in a hot country they need good soils more because they absorb and retain more water.
  It seems that the english have been ruining their soils to through modern farming methods during my life.
  Organic matter absorbes a lot of water as a towel in a sink would absorbe more than a sieve full of sand for one. For another  humus in the scientific sense as humic and fulvic acids and humins absorbs even, more they  behave like gelatine and absorb many times their  own weight in water and all this without getting water logged as clay does. When things are water logged they are not getting enough air and suffocate. Good soil holds a lot of water but does pass what it cannot hold and so has air in it too so water for your crops is a prime reason for having good soils, they will go on providing for plants in a drought in the wet season and the water in them will last longer at the onset of a dry season if your country has such a thin,g.
  Wheats' growing season coincides with Spains' wet season,  it can be grown without irrigation. Plants whose growing paterns coincide with the weather paterns are  the plants a country should grow. A good soil would assure that the wheat did not suffer from any  blips in the weather, water shortages if there were two weeks without rain in the growing season.

In the most famouse soils in the world the good top soil is not six inches deep but two yards deep or two metres. In the the Ucran even up to six meters. They are called after the ucranian word for black soil, chernozen, chernozemic soils, they formed on grass lands. That is terra pretta soils or chernoyen soils of rumania and ucran, russia through to siberia and they are also found in the canadian prairies, texas, a bit in north east china. Apparently they can form on any soils from sandy to clay ones!

The other consideration, when thinking of the advantages of lots of top soil, is carbon fixing because you want to stop global warming and to claim carbon credits. Cabon is fixed in the topsoil, the good soil. we have fixed more carbon if this soil is deep. agri rose macaskie.

i agree with those that use hugel beds and swales and keyline and mulch. These are some techniques i have used with great success.

we have some really old worn out soil that had been farmed by a celery farmer for years before we had the property. We had just let a lot of it go to rest for many years as we didn't need to use it. The last few years we have been building areas up with hugel beds and we couldn't believe our gardens there this year, they were fantastic. Esp the tomatoes and potatoes, the first year on a new hugel bed were out of this world.

didn't have to water even with the drought, very tasty and filled the freezer with tomatoes..potatoes aren't dug yet but the growth was incredible and not a bug

i use a lot of sheet composting/sheet mulching on our property and that really improves the growth of plants as well. I have made swales on our slopes where plants seemed to need some extra moisture, and filled the swales with mulch, and the trees there thrive..

Yeah I read that book by seeds of change gardening for the future of the world. They talked about Jean Jeavons

If you ask me the 60 times faster thing is a load of BS.

What they should say is "with added inputs you can build soil 60 times faster than in nature". But they clearly don't want to admit that. I think it's myth promotion at it's worst.

Argh.

Like someone said, what do they mean by building soil? It's more like soil conversion.

Masanobu Fukuoka talked about this, he said something along the lines that farmers claim to be building soil, caring for soil, but they are really just bending the soil to their wills, making it easier for tasks such as tilling and cultivation.

IMO, just because you have cultivated your soil to the point that it is easy to dig in, does not mean at all that you have built soil, or even that you have improved it.

Subverting nature to the whim of mankind, tisk tisk.

Emile Spore wrote:
If you ask me the 60 times faster thing is a load of BS.

What they should say is "with added inputs you can build soil 60 times faster than in nature". But they clearly don't want to admit that. I think it's myth promotion at it's worst.

Argh.

Like someone said, what do they mean by building soil? It's more like soil conversion.

Yes, they really should clarify about the outside inputs. I could claim to build soil 100 times faster than nature by bringing in even more outside inputs and depleting the surrounding soil 100 times faster where the inputs are gathered. I'm not against outside inputs, but I feel a lot of books either claim you don't need them, or they don't consider the sustainability of outside inputs. I think sustainable rotten wood and forest floor litter gathering from a surrounding forest for the use in hugel beds or some other practice is an excellent idea. Surely you'd be building soil faster than nature, because you are taking outside minerals and organic mater and concentrating it in the garden beds. This isn't using magic like many systems appear to, but rather just hard work and intelligence.

I think there needs to be a lot of clarification around the terms soil building/forming, soil conversion, soil improvement, etc. When I think of soil building/forming, I think of the natural process where the factors involved are parent material, climate, topography, biological factors, and time. To claim to build soil faster than nature is to claim to improve on the soil forming factors in an area. And that's what I'm still trying to find the answer to. Is it possible to improve on the soil forming factors in an area above the rate of soil forming for the natural ecosystem in that area?

barefooter wrote:
... Is it possible to improve on the soil forming factors in an area above the rate of soil forming for the natural ecosystem in that area?

I think it is, but am not making claims as to 10X or 60X. Bill Mollison has said a lot about building soil much faster than the standard textbook figures.

Seeding lots of legumes can make a big difference - in nature, the poorest soils tend to have plant ecosystems that favor legumes, but the seed bank may be limited. By intentionally adding legumes, the change is much faster. Introducing shrubs or trees to grassy areas to break up the deeper soil layers and move nutrients up speeds things up. Doing swales or keyline work is going to make the system more productive when water is scarce during parts of the year. Stack some of these strategies up, and yield can improve rapidly compared to nature.. . fungi start getting active, phosphorous gets pulled into the system.

In some areas, adding an ounce of molybdenum to an acre of land can dramatically improve plant growth (especially legumes).... that could come from a mineral supplement, or from larger amounts of seaweed or fish meal fertilizer ... but that can be a relatively long lasting soil amendment that moves the entire ecosystem up a few notches. 

Emile Spore wrote:What they should say is "with added inputs you can build soil 60 times faster than in nature". But they clearly don't want to admit that.

They grudgingly admit that their earlier experiments relied on unsustainably-high inputs of compost.

Interestingly, they address this by bulking up their compost with soil dug out of the garden.

That sounds a little dishonest on its face, but the more I think about it, it is also probably a way of cutting down on volatilization of nutrients.

In situ composting (which I like a lot better) can keep more nutrients in the soil because there are places among the minerals to store them in, and because minerals on the surface don't evaporate the way organic matter does, and perhaps by several other mechanisms that can be replicated just by adding topsoil to the compost pile.

I think that adding minerals when building a hot pile would allow for a lower C:N ratio in the initial mix, because what really matters is the ratio of N sinks (C being the prototypical N sink) to N sources. This should allow one to build a compost pile without intentionally drying out any greens to form browns.

To make a long story short, I'm not 100% confident that their claims are reliable, but I also think it is worth learning from their work, and (contrary to their strict warnings that Biointensive[sup]TM[/sup] loses its magic if you don't follow all methods exactly) adapting the most-workable parts of it wherever they seem appropriate.

I am skeptical of the value of incorporation of organic matter into the soil in general. I have been warned by more than one author and farmer "don't force feed the soil". I have witnessed the horror personally of "soil indigestion" and the rampant and hostile weeds it produces. The argument is that the soil becomes acclimated to being force fed, so it requires the same work be done again and again. I would be fine with incorporation for breaking new garden beds, but I doubt I will ever make that a perennial endeavor.

I think that it is true that we can "build soil faster than nature". But they are making that fatal flaw that Fukuoka warns us about. We believe that we grow the plant, we build the soil, but it is nature. To me the fact is that we have harmed nature on a grand scale and it's natural abilities to build soil have also been harmed, but we can harness the abilities of nature to build soil than what was taking place before we started working on the problem.

Soil gets moved very slowly in nature, but we can move it and by moving it properly, we will slow and reverse erosion and that will help to build topsoil faster. Nature does this by blowing down trees that leave behind craters which water collects in.

We can also bring back the large fauna that build soil and through proper management perhaps we can build soil even faster than the buffalo did.

I don't want to stop anyone from using organic matter in the form of inputs, I think it's a bit impractical not to, one would often have to live a life of poverty and be lucky to be rewarded for their efforts if they didn't. But I personally have come to find that Organic farmers are often bigger story tellers than fishermen.

We need solutions that will work for everybody, not just you and me and the choir.

If everybody in the world decided all the sudden that they wanted to be organic farmers, suffice to say there would be a lot of issues to work out and people wouldn't be handing out free horse shit anymore.

Emile Spore wrote:We need solutions that will work for everybody

Hm...I'd settle for modes of inquiry that would find a unique solution for each person who applies them.

Point taken, on force-feeding soil. I'm certain I have a lot to learn, there!

I also agree that thinking as if we are outside of nature is problematic on just about every level, from ontology all the way down to tactics and reactions. Anyone with their head on straight won't talk about soil-building that's faster than nature, but rather faster than neglect, or unusual in nature.

Joel Hollingsworth wrote:
Hm...I'd settle for modes of inquiry that would find a unique solution for each person who applies them.

I agree.  Everyone has a different situation and different resources, abilities, etc.  To not advocate possible solutions because they might not work for everyone is, I think, extremely counterproductive.  And an argument against permaculture I see all the time - it won't work for everyone (therefore is useless). 

Regarding keyline, keyline plowing seems to require power equipment, which is extremely expensive and so out of the reach of anyone who doesn't have thousands of spare $$. 

Both Biointensive and Keyline seem to have helped a number of people.  They might not be able to help everyone, but, I think there are probably other options! (for instance, permaculture    )

so I take it that there is a philosophical question regarding using outside resources. I can understand that from a truly best case scenario, however that is not the reality that we live in, in my opinion. I make a portion of my financial gain each year exploiting the waste streams form "the real world". It grieves me to see so much material being discarded from those who differ in life style. Yes it does cost me and the world as a sustaining system extra resources for me to "harvest" from another's waste stream, but I use it to build our portion of the world. So is moving a part of a whole to use it in a positive way, worth the use of resources that are part of the whole, to use this as an asset rather than a liability. I do not know if the whole of our culture will ever change from it's comsumer driven wastefullness just due to human nature, but why not take from their waste to better at lease some of the whole? Part of me likes the biodynamic idea of the earth and universe as a living whole rather than a segmented parts. Can we truly say that taking material from one location to another is all bad? If I take sustenance from my garden, but defecate in to another area is that not the same?
kent

machinemaker wrote:
so I take it that there is a philosophical question regarding using outside resources. I can understand that from a truly best case scenario, however that is not the reality that we live in, in my opinion. I make a portion of my financial gain each year exploiting the waste streams form "the real world".

My curiosity about soil building is more theoretical than practical for todays world. When I have my own land, I will of course be bringing in as much free material from unused waste streams as I can to enrich the soil. I agree that we should try to adapt to the current predicament while still dreaming about what the future looks like rather than getting too caught up in ideologies. Basically using the waste products of highly unsustainable practices while still thinking about where the inputs might come from when the waste stream dries up.

Are there any websites or past discussions (even on other websites) that disagree with Jeavon's numbers and "facts" ? I mean like any studies or atleast comparison beds over a long period of time to see if there are differences ?

a little humor here..

what nature where..?

if you are talking about a bottomland after a huge flood, not a chance..mama nature can bring in everyones soil from upland and dump it directly on top of your bottomland..so..i guess you could say that depends on which mama nature you are talking about..

she'll also bring donw a bunch of trees and sewage and put it in the soil at the same time..

Ahipa wrote:
Are there any websites or past discussions (even on other websites) that disagree with Jeavon's numbers and "facts" ? I mean like any studies or atleast comparison beds over a long period of time to see if there are differences ?

I've been briefly searching for criticism, but this is about the most strongly worded I've found:

"There are plenty of books on small-scale organic intensive gardening available these days; everyone has their favorites. John Jeavons’ How To Grow More Vegetables is among the most popular, though there are also plenty of people who swear at it rather than by it. Most of these latter seem to like Steve Solomon’s Gardening When It Counts, so having both of these on your shelf may be a good idea. "

http://thearchdruidreport.blogspot.com/

But as far as good comparison studies, I can't find any.  It would be great if someone had the kind of spare time and energy to do these kinds of studies, it would be very useful to compare the productivity of various methods.

Steve Solomon, from Gardening When it Counts:

The intensivists say that putting vegetable rows far apart is a waste of garden space and that gardeners do it only in foolish imitation of farmers, who have to do it so that machinery can work the field. This assertion is not correct. The reason people traditionally spread out their plants (and why farm machinery was designed to match this practice) was so that the vegetables could go through rainless weeks without damage or moisture stress...Once ultra-crowded plants have formed a crop canopy...moisture loss is so rapid during sunny weather that to prevent moisture stress, you will need to give the beds at least half an inch (1.25 centimeters) of water every other day in hot spells. If the soil doesn't retain much moisture, you'll apply less water, but you'll apply it every day. I've seen sandy intensive beds need irrigation twice daily in really hot weather. This requirement tightly shackles gardeners to their gardens.

He includes a table with biointensive spacings as well as his 3 different recommendations for spacings, discussing how to choose among them based on climate, soil type, and availability of irrigation water.

Here's a comment from the Wikipedia entry for Biointensive, which is basically verbatim from Jeavons' book, as I recall:

"Because some of these techniques result in intensive productivity, the system must be practiced as a whole in order to prevent soil exhaustion. Although the goal of the biointensive method is sustainability, if the techniques concerning productivity are practiced without the techniques concerning sustainable fertility, the fertility of the soil may be used up even more quickly than with normal unsustainable methods. The most important element for sustainable fertility is the growing of sixty percent compost crops, composting, and when possible safe and legal human waste recycling."

So it is evident that if one is not scrupulous about maintaining fertility, the soil can be used up faster WITH Biointensive methods than without.  I think here is one of the most important difference between permaculture and Biointensive.  With permaculture, fertility of the soil is more likely to be retained almost passively by the gardener, with the plants and critters doing most of the work as the gardener provides mulch through pruning, whereas with Biointensive, the gardener herself is doing much more of the work actively maintaining the soil by making compost.

Aw yes Ludi, you remind me of the other problem. They love to talk about composting as a soil building technique. To me this seems to be the opposite of the truth! Composting wastes a ton of organic matter,  from off gassing and drainage. From what I have read, they don't mention where you should get your composting materials, just that you should compost. So you are going to be using your 60% cover crops to compost? A lot of work for less return to me haha!

Joel Hollingsworth wrote:
Steve Solomon, from Gardening When it Counts:

He includes a table with biointensive spacings as well as his 3 different recommendations for spacings, discussing how to choose among them based on climate, soil type, and availability of irrigation water.

I remember him saying that but its specfically a water issue; I wish he talked more about it because I know while living in California he was trying to make a bio-intensive farm.

Most people have no problem heavily irrigating their land esp. if it is just a backyard.

But has anyone seen such yields themselves?

Emile Spore wrote:
From what I have read, they don't mention where you should get your composting materials, just that you should compost.

You're supposed to grow them in the largest section of cultivated area.  60% carbon crops, 30 % calorie crops, and 10% vegetable crops.

http://www.growbiointensive.org/grow_main.html

  One big thing i learnt off my american in Spainish, farming book, written by north american agricultural experts with a prelude by Hugh Hammond Bennet that great american natural farmer or some such, was to think of the roots leaving a lot of vegetable matter under the soil. Now when things grow i think, as a miser does, with greedy satisfaction of the roots filling the soil.  agri rose macaskie.

Ludi, so you are saying that they are composting their carbon crops? To me this is utter folly, quite the opposite of building soil.

So to delve deeper into the realms of agricultural health, philosophy and dare I say practicality, why is it that we want to have vegetable/calorie gardens?
I would rather make a go at creating forage pastures and savanna for man and beast, comfrey, dandelion, salsify, sunchoke, cow parsnip, chestnut I hope will satisfy my calorie crop need. Obviously I can get all the vegetation from wild plants. If need be, I can hit land hard with animals, if need be, add bedding and scatter oats or speltz or plant corn and squash.

If there are a few vegetables I can't live without, it's garlic, peppers and sweet potatoes. I will go into sweet potatoes for a second. Despite claims to the contrary, they are incredibly easy to grow almost anywhere, even in clay, as long as it's not too wet, you just might not get a huge root yield. But in my experience the leaves always yield awesome! They are my favorite cultivated green. They are also all the varmints favorite, I wonder why. According to Charles Walters they extract the most amount of minerals of any vegetable, over 70!

I guess the argument against what I extol is lack of space. Sunchokes and chestnuts yield awesome with minor care. So does the right varieties of corn. So does Rice. I am not alone in the thought that we can produce enough food on a small plot of land, without cultivating the soil. We shall see I suppose.


OH OH, it's also important to remember that closer spacing sometimes actually reduces crop yield overall.

Years ago I read a book called Malabar Farm by Lous Bromfield. He was an author who had spent years in France and was appalled by what he found when he returned to the States. He built up a highly successful farm out of totally abused and worn out land using almost entirely organic  techniques. He felt it was more important to get SOMETHING growing on land where virtually nothing would grow but weeds , and if that meant artificial fertiliser INITIALLY, so that he could then get something to turn into the soil to give it something to chew on (sheet composting) then so be it. He was a very early advocate for organic farming and very influential in his day.
Unfortunately I think the book  is out of print, I have been trying to replace my copy for years. The farm is now a State Park. His bio is on Wikipedia

Emile, yes, one of the goals of Biointensive is to produce human food in the least amount of space possible (they apparently have got it down to 4000 square feet per person).  I recommend the book "One Circle" for anyone interested in more details about small-space diets.  The primary caloric basis for these vegan diets is root crops such as potatoes.  Grain is  absent  because it takes too much space.

Ludi wrote:

Emile, yes, one of the goals of Biointensive is to produce human food in the least amount of space possible (they apparently have got it down to 4000 square feet per person).  I recommend the book "One Circle" for anyone interested in more details about small-space diets.  The primary caloric basis for these vegan diets is root crops such as potatoes.  Grain is  absent  because it takes too much space.

More pertinent questions. Where do they grow the seeds to plant their carbon cover crops? Grain is absent, what about the cover crops, are they not grain? Corn and rice can yield more per acre than potatoes, most grains can out yield by nutrient value most other root crops, at least the ones that humans deem useful as a staple. Some of them can be grown together. 

Cover crops don't seem like an efficient use of space to me, I would rather use them as temporary or semi long term pasture for animals, or food crops for animals to harvest in field and deposit their manure in the field.

Potatoes and vegetables might be a balanced diet for some, but not for me, most would consider this a meager existence in the frozen north!

Emile Spore wrote:
More pertinent questions. Where do they grow the seeds to plant their carbon cover crops? Grain is absent, what about the cover crops, are they not grain?

Grains don't form a significant portion of the diet in the "One Circle" diets.  In the Ecology Action studies, potatoes and other root crops seemed to be able to provide the most calories in the smallest amount of space.

The "One Circle" diets are very meagre and not something most of us would want to eat, but again,the goal of these diets is to provide a (nearly) nutritionally complete diet in the smallest amount of space. 

Emily spore you ask about cover crops and i am not quite sure what you mean but if i have got it right heres an answer.
      I suppose all crops cover the land, grain ones for example but the name cover crops comes from the crops planted when the land is left fallow a year , or in between crops, like you might havrvest in july and not plant wheat say till autumn or spring. Cover crops would cover the land when you werent growing anything in it and serve as a green fertiliser. That is you grow clover that fixes nitrogen on its roots and plough it in when you come to planting your grain crop so as well as providing cover to th eground between crops i it provides nourishment to the soil.
You leave land fallow because soil can get exausted after growing a crop, crops take up nitrogen potasium and phosphrus and other things like iron calcium, so if you leave the soil a bit it can redisolve from the rocks minerals the minerals the plants have taken out of it replenish itself with minerals the plants use  and so wil be more fertile so much so that here in spain they always leave the land fallow for a year if they are growing crops not in pasture land.
  I have just read about leaving land fallow in texas looking up carbon crops and it says they do it there in order for the land to accumulate enough humidity to grow a crop again. They have tried growing cow peas on the land as a cover crop and they did not make an apreciable difference to the moisture in the soil when grain planting time came along, they only reduced the moisture a tinybit. Texas would have a moisture problem it is a long way south.
      You can collect yuor own seed, i tried collecting clover seed this year and it was easy to collect.agri rose macaskie.

where are these cover crops being grown? Where is land being depleted to create them? What about prairie and pasture instead of crops that require a year of fallow to grow?

I might not understand the question...

A cover crop is grown overlapping with (underplanted) or following the food producing crop within the same footprint.  A mixture of grasses, legumes, and root crops are common.  The goal is that despite intense cropping and harvest there is always something growing in the soil to avoid leaching of soluble nutrients and to maximize production of biomass on every piece of ground.

There are many settings where a forage system is not viable either due to population density, seasonal drought, or lack of sufficient land tenure.  Developing approaches for producing lots of human food in small spaces, without pollution, that can be done with hand tools seems like a reasonable goal.

"In the GROW BIOINTENSIVE system, soil fertility is maintained by allotting 60% of what is grown to compost crops."

It is unclear if this 60% is in addition to the 60-30-10 ratio recommended for survival production of human calories...  As the system depends of compost and doesn't use a fallow period, I'd expect this 60% is a 'carbon donor' to maximize production in the remaining 40%.

http://www.growbiointensive.org/grow_main.html

It seems these folks are not thinking about pleasure in their program.

In "One Circle" the smallest amount of land devoted to producing human food is about 1000 square feet.  In Biointensive, the smallest amount of land used to produce food and compost ingredients is 4000 square feet.  So if you were a small woman who could grow her One Circle diet on 1000 square feet, you would have 3000 square feet in which to grow compost ingredients.

Emile, again, the point of Biointensive and One Circle is to grow food using the smallest amount of land possible.  Prairie and pasture take up a lot of space and are not available to people in, say, a city or town.

Someone with prairie and pasture available would probably not want to bother with Biointensive/One Circle methods. 

The question is, you have to have seeds to plant cover crops and these have to be grown somewhere, so where are they being grown and harvested? A portion of the cover crops could be let to go to seed, but I would like to see the people who put this to practice, since harvesting those seeds without machinery and expensive equipment is very time consuming and laborious, even more so than growing and processing grains!

Emile Spore wrote:
The question is, you have to have seeds to plant cover crops and these have to be grown somewhere, so where are they being grown and harvested?

Maybe ask them?

http://growbiointensive.org/contact.html

Personally I think it would be fairly easy to grow some sunflowers to eat and some for seed to plant for compost ingredients.