[Soft_Landing]

I know a little about a lot, but I don't know much about soil.

I want to ask questions about soil in this thread, and I hope others can ask questions about soil here also. Hopefully some of our readers can answer some of our questions...

I think the question of soil is very interesting. On the simplest level, there is the question of sustainable food production. More broadly, the health of the soil is imperative for such 'solutions' to peak oil as bioethanol or biodiesel.

I understand plants get carbon from the air, and water from rain, but surely, plants must need other nutrients to flourish. If that is correct, what nutrients are they (they must include nitrogen, for example), and how do they typically get into the soil in the first place? I understand nitrogen needs to be 'fixed'. Anyone care to explain this part of the cycle?

Of particular interest to me in the sustainability of soil. What factors influence the health of soil? If you are moving minerals (or other) off site, how do they ever get back into the soil?

I want to get the soil loop closed in my mind. I'm sure there are people here who can throw in pieces of the puzzle. Ideally, everyone with soil questions can ask them here too...

[bart]

Great topic, Soft_Landing! You are right -- caring for soil will be a key concern as the cost of energy and natural gas go up, and we can no longer rely on synthetic fertilizers.

The questions fascinate me too. I've been reading about this off and on for about a year. Could I try to summarize what I've learned? I'm not an expert, so please excuse my inaccuracies, those of you who are professionals.

Soils are the magical and complex interface between the lithosphere and atmosphere, the basis of almost all life on the planet.

Soils are initially formed from the breakdown of rock. Soil can be formed on site, or can be transported to the site by wind or water. The particles of soil range from very small clay particles, to medium-sized silt particles, to the relatively large pieces of sand.

A critical component of soils is organic matter -- both the creatures that live in the soil and the decomposing bodies of dead plants and animals. Living in the soil are bacteria, fungi, insects, mammals, and other lesser known creatures. They form an incredibly complex ecology that is only partly understood. The soil biology is key for sustaining fertility and soil structure....

As you point out, the bulk of what plants need does not come through the soil, but through air (oxygen and carbon dioxide) and water.

The main soil nutrients are N-P-K, as listed on bags of store-bought fertilizer.
N - Nitrogen ultimately comes from the atmosphere. It is "fixed" into a form that plants can use by lightning, leguminous plants like beans that provide a home in their roots for N-fixing bacteria , other N-fixing micro-organisms , breakdown of organic matter)
P - Phosophorous (bones, rock, breakdown of organic matter)
K - Potassium (rocks, clay. breakdown of organic matter)


In addition plants need minor nutrients in smaller quantities (magnesium, calcium, sulfur, zinc, manganese, copper, boron and iron), as well as some trace nutrients.

Each of these nutrients has a different cycle. An important consideration is whether the nutrient is in a chemical form that can be taken up by plants. For example, plants use nitrate ions (NO3-) and ammonium ions (NH4+) but cannot use nitrogen (N2) in its gaseous form. Putting nitrogen into a form usable by plants is called "fixing" nitrogen.

As you point out, nutrients are constantly being taken off site in agriculture, as crops and animals are sold to consumers. They can be replaced in several ways:

1. Ground rock can be brought in from off-site.
2. Organic matter can be grown on site or brought in, to use as mulch (on top of the soil), as compost (having been decomposed, it is dug into the soil), or dug directly into the soil without being first decomposed.
3. Organic fertilizers and amendments, which typically provide nutrients in a concentrated form. For example, seaweed emulsion, bone meal, blood meal.
4. Animal manure from on-site or off-site animals.
5. Some crops (green manure, cover crops) are grown specifically for the health of the soil. Certain plants like comfrey and rye are particular good at bringing nutrients up to the topsoil from deep in the soil.
6. Synthetic fertilizers (like the N created by the Haber process, using natural gas).

The insight of organic farming is that organic matter (e.g., humus) in the soil performs many subtle and complex functions. For example, organic matter:
1. Improves soil structure
2. Increases water-holding ability
3. Keeps nutrients in soil. Helps make them accessible to plants.
4. Acts as a buffer against extreme conditions (e.g. low or high pH)
4. Serves as a matrix for soil biology.
6. Feeds the organisms in the soil

We've been able to ignore organic matter over the last century, because we've used petroleum and natural gas to create cheap and convenient synthetic fertilizers. With peak oil, we've got to relearn to care for our soils or we will go hungry.

References:

Soil Foodweb (Elaine Ingham)
http://www.soilfoodweb.com/sfi_html/index.html
Look around -- lots of great information, but it may be in unexpected places on the site. If you ever get a chance to hear her speak, it is well worth it.

http://soils.usda.gov/sqi/soil_quality/ ... index.html
Click on the "Soil Biology Primer" for an excellent introduction, with lots of photos (big file, if I remember). The primer can be ordered in print form from Elaine Ingham's site.

http://www.uctv.tv/gardening/
Online videos of in-depth lectures on gardening by University of California agriculture specialists. See the lecture titled "Soils for the Gardener".

http://zzyx.ucsc.edu/casfs/
Huge textbook on organic farming/gardening available online as PDF files. Created by University of California, Santa Cruz, for students in its agro-ecology program. The chapters on soils are Unit 2.1 (soil physical properties), Unit 2.2 (soil chemistry and fertility), Unit 2.3 (soil biology and ecology). The site seems to be down at the moment, but when it is up, you can click on the link for the textbook and you can download the files (large files).

I've found it surprisingly difficult to get good books on soils. The older textbooks on soil science are heavy on the chemicals and dismissive of organics and soil biology. Many of the books on organic gardening, on the other hand, are superficial.

Two good introductions, aimed at farmers but useful for others, are:
"From the Soil Up" by Donald L. Schriefer (Acres, U.S.A.)
"Building Soils for Better Crops" by Fred Magdoff and Harold van Es. Sustainable Agriculture Network (SAN).

Hope this is of use!
-bart

[Anonymous Coward]

Hope this is of use!
-bart

This is indeed of use. Many thanks, especially for the links.

[Soft_Landing]

Thanks for all that info, Bart. Wonderful.

A few comments:

As you point out, nutrients are constantly being taken off site in agriculture, as crops and animals are sold to consumers. They can be replaced in several ways:

1. Ground rock can be brought in from off-site.

This isn't really sustainable though, I guess.

5. Some crops (green manure, cover crops) are grown specifically for the health of the soil. Certain plants like comfrey and rye are particular good at bringing nutrients up to the topsoil from deep in the soil.

This seems like faster depletion too.

I'm going to start looking at soils seriously. I think I've been neglecting this interesting factor. Personally, it seems to me that cellulosic ethanol should be one of our most abundant sources of energy in the long run, but if I don't understand soils, how can I presume to be able to make a fair evaluation of cell. eth.? Thanks for the links.

Questions I am going to try to answer include...

What happens to plant growth if there is a lack of N/P/K/other trace elements?

Are the trace elements taken off site with produce, or do they work like catalysts in the soil? I think the latter possibility is just wishful thinking, but, maybe...

What's up with aeration of the soil/ tilling/ worms? Why is this good? Is it good?

What kind of things are bad for plants? Salt is bad, as far as I can tell. What do you do with soil that is too polluted to use? How do you 'clean' it?

I guess there's two seperate questions, really. What are the risks from using a soil too much (depletion)? And what are possibilities for damaging a soil with additives (pollution)?

Any and all answers/hunches/suggestions welcome.

[bart]

More great questions, Soft_Landing. I appreciate the chance to wrestle with them... Are there any people out there who can give us some help? In any case, here are my responses....

As you point out, nutrients are constantly being taken off site in agriculture, as crops and animals are sold to consumers. They can be replaced in several ways:

1. Ground rock can be brought in from off-site.

This isn't really sustainable though, I guess.

I haven't heard any suggestion that using ground rock would be unsustainable. In the literature I've read, it seems to be something you would do infrequently to fix a specific problem, rather than an ongoing practice (as applying fertilizers would be). I suspect the more immediate problem would be more the energy cost in bringing in rock dust (transporting heavy material).

5. Some crops (green manure, cover crops) are grown specifically for the health of the soil. Certain plants like comfrey and rye are particular good at bringing nutrients up to the topsoil from deep in the soil..

This seems like faster depletion too.

Again, I haven't heard any talk about this practice being unsustainable. I think the subsoil is so large in relation to the topsoil, that it isn't a problem. It seems that the benefit of cover crops / green manure is one of the few things that everybody in agriculture agrees is a Good Thing.

I'm going to start looking at soils seriously. I think I've been neglecting this interesting factor. Personally, it seems to me that cellulosic ethanol should be one of our most abundant sources of energy in the long run, but if I don't understand soils, how can I presume to be able to make a fair evaluation of cell. eth.?

Great point. You've probably seen the great discussions on cell. ethanol and bio-diesel on other threads.

What happens to plant growth if there is a lack of N/P/K/other trace elements?

I think what you're getting at is one of the central concepts in agricultural science:

Liebig's Law of the Minimum, often referred to simply as Liebig's Law or the Law of the Minimum, is a law developed in agricultural science formulated by Justus von Liebig. It states that growth is controlled not by the total of resources available, but by the scarcest resource. It was originally applied to plant or crop growth. It was found that increasing the amount of plentiful nutrients did not increase growth. Only by increasing the amount of the limiting nutrient (the one most scarce in relation to "need") was growth of a plant or crop improved. ( http://www.wordiq.com/definition/Liebig ... he_Minimum )

You wrote:

Are the trace elements taken off site with produce, or do they work like catalysts in the soil? I think the latter possibility is just wishful thinking, but, maybe...

I think the trace elements are needed by the plant and would be taken offsite with the produce. There are other things that act like catalysts in the soil. Maximizing these would be win-win, in that they make the process more efficient and remain onsite. Such factors would be soil structure, soil biology (bacteria, fungi, worms), good soil chemistry.

What's up with aeration of the soil/ tilling/ worms? Why is this good? Is it good?

I had a hard time figuring out why tilling the soil (plowing, digging the soil, etc.) was seen as necessary.

Apparently there are several reasons why this is done. First, weed control. Second, to incorporate organic matter (e.g. crop debris) into the soil. Third, to aerate the soil. What this actually does is to give the soil bacteria a heavy dose of oxygen (their limiting factor), enabling them to grow in numbers, eating organic matter (like humus), and releasing nitrogen and other nutrients needed by the plants.

The problems with tilling are several. It degrades the soil structure and is hard on the soil biology. It makes the soil more prone to erosion. By encouraging the bacteria to eat the humus, we are effectively "mining" the organic material in the soil -- getting N at the expense of the heath of the soil. Finally, and of great interest to industrial agriculture, tilling is expensive.

Tilling the soil is a hot topic nowadays -- the paradigm is shifting towards minimal or no tilling. Ironically, the impetus is coming from two opposing parties: industrial agriculture and the avant-garde organic gardeners (permaculture and Fukuoka's school, for example).

Worms are good guys to have around. They improve the structure of the soil, allowing greater circulation of air and water. They also improve the soil biology.

What kind of things are bad for plants? Salt is bad, as far as I can tell. What do you do with soil that is too polluted to use? How do you 'clean' it?

I wish I knew more about this. I know that salts accumulate as a result of irrigation and fertilization, and that they are a big problem in dry climates such as the Middle East and Southern California. On a small scale, flushing the soil with water can clear out salts. For example, plants in containers are especially prone to salt-build up, and a common recommendation is to flush them with water. On a large scale, I think this is a huge problem. In the Middle East, for example, such fields were abandoned.

I guess there's two seperate questions, really. What are the risks from using a soil too much (depletion)? And what are possibilities for damaging a soil with additives (pollution)?

"Using soil too much"
I think I would re-phrase this. The problem is farming unsustainably, by disregarding the soil and the soil biology. Farming sustainably improves the soil.

"Polluted soils"
I wish I knew more about this. The problem is that pollution is hard to detect, the effects are subtle and long-term, and the solutions are not easy.

Best of luck in your quest!

- bart

One reference I forgot to mention in the earlier post is ATTRA (National Sustainable Agriculture Information Service).
http://attra.ncat.org/publication.html
Many excellent online articles on sustainable farming topics. A real goldmine.

[backstop]

Alongside the sustainable use of aquifers, respect for the soil seems to me critical for any settled society, so I applaud the launch of this thread.

Sadly I know enough about soil only to know how little I know about it. A few points and observations may be relevant.

Soils began, as I understand it, by the specialized cellular-level symbiosis of plant and fungus (that we call lichens) breaking down rock (over a very long time).

Salination of soils due to irrigation can end their fertility. Desert results. Regular flushing is possible but costs huge amounts of water. Irrigated crops thus risk the loss of soil fertility and in many places are effectively mining out the aquifers. Salination has been taking land out of production faster than new irrigation projects can be brought online.

Beside those listed by Bart above, ploughing has a further critical demerit that is only just starting to be recognized, which is that it releases very significant quantities of CO2 per acre to the atmosphere.

Two points about the pollution of soils may seem tangential to the thread but I think are relevant:

Airborne NOx in the UK is directly correlated to the present global mass extinction event in a New Scientist article: (Scene set for next mass-extinction 27/3/04). Since the soil cannot thrive without a thriving ecology above it, NOx pollution should be recognized as a serious indirect threat alongside its well-recorded direct acidification impacts.

By the way, can anyone tell me whether putting cattle and pig slurries through anearobic decomposition (a 'methane digester') before using it on the land will reduce its emission of NOx ?

Airborne CO2 (now 33% above pre-industrial level and rising) has also been implicated in New Scientist (Peat-bogs harbour carbon time-bomb, 10/7/4) in the breakdown of peat soils to release carbon to watercourses, from where it is released as CO2 to the atmosphere. This effect began about 40 years ago, has been rising globally at 6% per year, and, if unchecked, will put up enough carbon dioxide to swamp the planet's natural carbon sinks by about 2035.

This is only one of the feedback loops that the greenhouse gasses are initiating. Its relevance to agricultural soils is that a stable climate is a prerequisite for the maintanance of soil productivity.

Can anyone quote me the price of a barrel of cellulose ethanol produced from organically grown crops ? Or the degree of soil fertility and biodiversity loss per square mile per decade of fossil-based biomass crops ? Or the impact on urban drift and local food production in developing countries of this novel cash crop ?

By comparison, developing traditional Coppice & Standards Woodland to produce energy carriers and yields, including firewood, charcoal, woodgas, methanol, electricity and heat, can not only bypass the critical problems of agro-energy crops but can also yield various significant benefits to the community and natural ecology.

hoping these notes are helpful,

regards,

Backstop

[Malone]

I'm not a soil scientist, but I play one sometimes for a large federal land management agency. When I first saw this thread, my thought was to say this is a really big subject, no way you're going to get much covered in a discussion like this. But Bart did a really good job of discussing the basics. One aspect of soils that I deal with mostly, which hasn't been discussed yet, is erosion. In addition to soil buildup and other pollution, you have to worry about keeping soil protected from the action of water and wind. Usually, that means covered with a good organic ground cover such as duff or living plants. Plant roots are also important for keeping soils anchored to any kind of a steep slope. Soil structure and aggradation is also an important protection against erosion, and current energy-dependent practices in agriculture often damage soil structure.

Compaction is also an important danger to soil. Bulk density of soil is the measure of how much mass of soil you have in a given volume. Lower bulk densities mean more pore space (also an indicator of structure) and therefore better water and air circulation. One factor you'll see in soil reports and surveys that is an indicator of this is available waterholding capacity (AWC). I just mention this so you'll know what it means when you see it. It's always relative and I can't say what measurements are good for your particular soil.

Another important quality you need to aquaint yourself with is cation exchange capacity. Most of the good minerals that a plant can use exist in the soil in the form of cations. Soils in the clay range have many negatively charged sites (this is way more complicated than it sounds) and these allow for the retention and exchange of these minerals.

One field of study I couldn't recommend highly enough is soil science. In my agency (the US Forest Service) we are seeing an extreme shortage of good people with a basic 4-year soil science degree. It isn't seen as a very popular major these days, even at the ag colleges. Seems everyone wants to go into genetics or the arcana of plant physiology and biochemistry. I think a young person getting a degree in soil science would always be able to find work. It would also be a great skill to have after fossil resources become more scarce.

[JackBob]

I know a little about a lot, but I don't know much about soil.

I want to ask questions about soil in this thread, and I hope others can ask questions about soil here also. Hopefully some of our readers can answer some of our questions...

The fine folks at:
http://www.bountifulgardens.org have done a lot of fine work in this regard. I have bought several of their spiral bound books. There is one called "One Circle" that addresses specifically the idea of totally sustainable agriculture in the minimum area etc. and that "we grow soils, not crops." I recommend them highly.

JackBob

[twxabfn]

I'm currently reading "How to Grow More Vegetables (Than You Ever Thought Possible On Less Land Than You Can Imagine)," which is a discussion of Ecology Action's GROW BIOINTENSIVE method for home gardening and mini-farming. It places great importance on soil health, humus, composting, and sustainability, and also has a pretty in-depth chapter on soil chemistry as well.

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

That's a link to Ecology Action's website. Happy reading.

-twxabfn

[Soft_Landing]

Home made fertilizer...

http://www.bidstrup.com/arc20040501.htm
snip

"They planted millet in three plots of typical Amazonian yellow clay soil from which all the Amazon jungle vegetation had been carefully removed. The first plot was the control plot - unaltered. The second plot was fertilized with standard agricultural fertilizers in the normal amounts. And the third plot had powdered charcoal added and mixed in, until it was a significant portion of the soil volume. The results were astounding. In the first plot, only a single plant grew, and it failed to mature and flower. In the second, a small crop grew, stunted, and producing very poorly. But in the third, the crop grew abundantly, chest high, and lush with seed. The scientists were able to determine that a community of bacteria grew in association with the plant roots, which freed mineral trapped in the charcoal, and made it available to the plant roots. "

How to build a compost pile, at runningonempty2:

http://groups.yahoo.com/group/RunningOnEmpty2/message/4520 (Join Required)

snip

The first step to overcoming peak oil is to start a Compost Pile. Yes, survival begins with EARTHWORMS, ROLLY POLLIES, and many other micro flora and fauna, all of whom will work diligently for you.

Composting is the basic necessary skill for gardening without fossil fuels. Here is an article I wrote for our local food cooperative website that explains how to do this...

related:

http://www.bettertimesinfo.org/alllinks.htm#COMPOST

Using human fecal matter as fertilizer:

http://www.weblife.org/humanure/default.html

snip

Who would'a thunk it? That's what a friend of mine said when he heard that the Humanure Handbook, 2nd edition, had received national book award recognition, including "Outstanding Book of the Year" and the book "Most Likely to Save the Planet." Who would'a thunk that a guy crapping in a bucket for a couple of decades could write and self-publish a book about it in 1995 that would, by 2003, be in at least 51 countries around the world? Don't people have anything better to read?

[Falconoffury]

So, poop will power the new world after the crash. Who would have thunk indeed. I need some farm land so I can start my poop pile.

[tokyo_to_motueka]

This is such a classic old thread! It deserves a new burst of life.

Article from the Independent (UK)

Rock dust grows extra-big vegetables (and might save us from global warming)
By Paul Kelbie, Scotland Correspondent

21 March 2005

For years scientists have been warning of an apocalyptic future facing the world. With the prospect of an earth made infertile from over-production and mass reliance on chemicals, coupled with an atmosphere polluted by greenhouse gases there seems little to celebrate. But belief is growing that an answer to some of the earth's problems are not only at hand, but under our feet.

Specialists have just met in Perth to discuss the secrets of rock dust, a quarrying by-product that is at the heart of government-sponsored scientific trials and which, it is claimed, could revitalise barren soil and reverse climate change.

The recognition of the healing powers of rock dust comes after a 20-year campaign by two former schoolteachers, Cameron and Moira Thomson. They have been battling to prove that rock dust can replace the minerals that have been lost to the earth over the past 10,000 years and, as a result, rejuvenate the land and halt climate change.

To prove their point, the couple have converted six acres of open, infertile land in the Grampian foothills near Pitlochry into a modern Eden. Using little more than rock dust mixed with compost, they have created rich, deep soils capable of producing cabbages the size of footballs, onions bigger than coconuts and gooseberries as big as plums.

"This is a simple answer which doesn't involve drastic life changes by anyone," Ms Thomson said. "People don't have to stop driving cars to do this, just spread some rock dust on their gardens. We could cover the earth with rock dust and start to absorb carbon in a more natural fashion which, along with reducing emissions and using a combination of other initiatives, will have a better and faster response."

Before the Thomsons began their "good life" experiment, erosion and leaching were so severe in the glen where they set up home that nothing had been grown there for almost 50 years. The basis of their theory is simple. By spreading a thin layer of the dust over the land, they are able to mimic the earth's glacial cycles which naturally fertilise the land.

Since the last ice age three million years ago, the earth has gone through 25 similar glaciations, each lasting about 90,000 years. "We are 10,000 years into an interglacial - a hiatus between ice ages - meaning modern soils are relatively barren and artificial fertilisers are needed," Mr Thomson said.

"By spreading the dust we are doing in minutes what the earth takes thousands of years to do - putting essential minerals in the rocks back into the earth."

Over the years the couple, who established the Sustainable Ecological Earth Regeneration (Seer) Centre charitable trust in 1997 to test their ideas, have slowly convinced others of their theory. They recently won a grant of almost £100,000 from the Scottish Executive to conduct Britain's first official rock dust trials.

The couple claim the technique may also play a significant role in the fight against climate change as calcium and magnesium in the dust converts carbon in the air into carbonates. Such is the interest in the theory that Nasa in the US is examining it in preparation for growing plants on other planets.

The couple say that the rock dust means that crops don't need water to produce harvests of magnificent vegetables. "It would be perfect for Third World countries that are usually unable to grow crops because the land is so dry," Ms Thomson said. "This could hold the solution for them."

"There is no doubt that, when rock dust is mixed with compost, it has a dramatic effect on crop yields," said Alistair Lamont, president of the Chartered Institution of Waste Management, who is impressed by the Seer experiment. "Future waste strategy is going to rely heavily on the diversion of biodegradable municipal waste from landfill, and one of the treatments involved is composting so we need to find a home for that compost.

"Agricultural land is something we need to work on and the benefits of rock dust in combination with compost can be seen at the Seer Centre at harvest time. We need to get farming to take on board the value of remineralisation and re-fertilisation.

Mr Lamont added that evidence showed that, since 1940, the mineral content of vegetables had fallen dramatically in this country. "We might be encouraged to eat a lot of vegetables but many don't contain the quantities of minerals that we need," he said.

(c) 2005 Independent News & Media (UK) Ltd.

This article was posted in the news area of PO.com and immediately got some negative comments. But TWilliam wrote an interesting comment defending the veracity of the article.

Rock dust is briefly mentioned in the above discussion between Soft_Landing and bart.

Would anyone care to offer their opinions as to weather rock dust + compost can play an important role post-peak and whether they see the Thomsons' claims as generally applicable?

[Petro]

takes alot of energy to make 'rock-dust'.

[tokyo_to_motueka]

takes alot of energy to make 'rock-dust'.

article says it's a "quarrying by-product".

and besides, would it be as much energy as manufacturing synthetic fertilisers from natural gas?

[Barbara]

What they call "biodynamyc agricolture" can save us all. It was estabilished by Rudolf Steiner in 1920, and in Italy it's 1% of production, like 5K hectares ("Demeter" brand).

[nth]

Hrm... didn't see anyone mention about micro nutrients like vitamins and other organic compounds.

Tilling soil increases amount of nitrogen and organic compounds available to plants, so they grow faster.

Reducing amount of organic compound reduces soils ability to balance the pH alkaline.

Elevated CO2 will make plants grow faster if it gets plenty of nutrients. Greedy polluters are funding research of this kind to say global warming is good for us.

Plants with more rhizosphere...roots area will be better for the soil. They will exude nutrients for bacteria.

N cycling. Plants have symbiotic relationship with bacteria who will make N available to the plants inexchange for C. You will see many of these plants in deserts or beaches where soil content is poor. These bacteria will only fix N when there is not enough N. So if you add fertilizer to these plants, the bacteria will not fix N.

[uNkNowN ElEmEnt]

Questions I am going to try to answer include...

What happens to plant growth if there is a lack of N/P/K/other trace elements?

The plants will tell you. their leaves won't be the right size, will be off colour or look permanently wilted.

Are the trace elements taken off site with produce, or do they work like catalysts in the soil? I think the latter possibility is just wishful thinking, but, maybe...

I once heard it takes 22 nutrients and minerals in the soil to produce 8 in a vegtable. (I think it was tomatoes we were discussing). While the produce does take nutrients out of the soil, using a good crop rotation and composting regime will make your soil sustainable.

What's up with aeration of the soil/ tilling/ worms? Why is this good? Is it good?

Tilling is not thought of as good by everyone. This school of thought thinks that by up ending and turning the soil you expose the nutrients that are under the first couple of inches to erosion and you loose what good you may have put into the soil.

The worm's poop is good for the soil and they loosen up the soil. This avoids compacting the soil which is critical in intesive gardening. This allows the roots to grow better and deeper if they aren't having to fight to loosen the soil up.

One thing that works well too is to cut the plants off at teh base and not pull up the roots when you harvest the crops. As the roots decomose they provide an addition to the humus layer and as they wither is leaves yet more looseness to the soil.

What kind of things are bad for plants? Salt is bad, as far as I can tell. What do you do with soil that is too polluted to use? How do you 'clean' it?

I don't know how many articles I've read that talk about reclaiming land. if its been doused in oil, salt or other chemicals you would probably ahve to plant it to alphalfa for several years before you could do anything with it.

I guess there's two seperate questions, really. What are the risks from using a soil too much (depletion)? And what are possibilities for damaging a soil with additives (pollution)?

The risks for both are loosing production and not being able to use the land at all.
When they talk about depletion, they mean using land unsustainably. Ie: not planting cover crops or green manure crops both of which (with a good crop rotation) can keep a well managed piece of land in use indefinitely.

Alternatively by using chemcial fertilizers you actually rob the soil of natural nutrients. If you have house plants they will live for a few years. then you will find (if you don't fertilize them) that eventually they will all die off as if they had gotten some disease or bug or something. This usually happens to a large number of them around the same time which would lead most people to think it was some kind of bug or something.

All soil naturally has nutrients and minerals in it, but plants will take them out and the soil will be barren. chemical fertilizers feed the plants but they don't feed the ground. they also can't supply all the nutrients crops need, so as the ground source is depleted it has to lie fallow for a period to recover these nutrients before it can be used again.

This is why managing your land and its needs will ensure sustainablity.

[bart]

Glad you woke up the thread, tokyo_to_motueka . When I get depressed about PO, I cheer myself up by thinking about soils and compost.

Thanks pstarr for the kind words. I agree with you that industrial-scale organic agriculture is not the final answer, though it is an improvement over regular industrial ag. The technology and techniques that large-scale organic ag develops will be helpful in a post-PO future, but in general "Local Agriculture!" is the new slogan rather than just "organic."

Permaculture and Steiner's bio-dynamic agriculture are fascinating alternatives. It's amazing that Steiner got so many things right, while agricultural science went more and more in the wrong direction. Many of his points are completely scientific and reasonable, while the more mystical elements (cow shit in a cow horn) are not harmful.

It seemed weird to me when I heard about rock dust, but the more I learned about it, the more sense it made. So I'd agree with the comments that TWilliam made at http://www.peakoil.com/article3194.html .

Using quarry fines (extremely fine dust that is a byproduct of stone quarrying) in a garden is not a new idea. I was doing it over a decade ago, and it indeed produces a huge increase in productivity, nutritional content and pest/disease resistance.

The process is known as soil remineralization, and as the article indicated, it is simply mimicking the natural process of revitalizing the soil that occurs during the advance and subsequent retreat of the glaciers during an ice age. The ice sheets grind millions of tons of rock into fine dust on their lumbering journeys from the mountains to the plains, where thick alluvial deposits of this material later serve as a base for rich, fertile soils once the glaciers recede.

So-called "trace minerals", increasingly absent from our foodstuffs, exist in healthy soil as a result of this process. A growing body of research is showing that the absence of these trace minerals (due to soil depletion) is a major factor in many diseases, not only in humans and animals, but plants as well. Soil remineralization provides a demonstrable improvement in the health and well-being of both gardens and of those that consume their produce.

Not to mention the stuff tastes even better!

David Holmgren (co-originator of Permaculture) is a big fan of rock dust -- see his recent book.

[nth]

Rock dusts are good, but nothing is better than organic nutrients and vitamins with the minerals already attached to organic molecules.

On a side note, tilling the land caused a lot of greenhouse gases. About a little less than 50% of current greenhouse gases are caused by agriculture. Not fossil fuel.