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  • From: "Lawrence F. London, Jr." <venaurafarm@bellsouth.net>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] Double-dug?
  • Date: Sun, 13 Dec 2009 02:31:10 -0500

Lawrence F. London, Jr. wrote:
Jeff wrote:
Just curious, can someone give me an explanation or a how to on double digging a plot for biointensive plantings?

The essence of it is that you invest a lot of effort and materials up front, inverting the soil, fragmenting the crumb structure, with associated temporary disruption of soil life and soil structure, oxidation of organic matter and release of co2 through exposure of humus to air. You remove much of the soil in the bed, add organic matter and mineral based soil amendments to it, homogenize these materials then return the amended, enriched soil mix to the bed. This is done in

increments of one (typical short (42" to 48") English D-handled) digging spade blade width wide and one spade blade length deep for the width of

One of these:

Wooden D-handled digging spade:
28" length for most people, 32" for tall people or get the long straight handled version, see below.
http://www.bulldogtools.co.uk/img/products/thumbnails/5610012820_500x263.jpg
http://www.bulldogtools.co.uk/index.php?mod=3&id=7&rid=1
Long straight handled version:
http://www.bulldogtools.co.uk/index.php?mod=3&id=12&rid=1
This is the big dog on the block when it comes to traditional English hand gardening tools; these were available at the beginning of the modern organic gardening and farming movement in the 1960's:
Bulldog - Quality Garden, Contractor and Agricultural Tools
Rollins Bulldog Tools
"Bulldog Tools have been made at Clarington Forge in Wigan, England, for over 200 years. Generations of Farmers, Contractors and Professional Landscapers stand testimony to a quality of product upon which their livelihoods depend. The skill and craftsmanship that were the key to the company's success in those early days are still maintained and are available to this day."
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You will also need:
1) a D-handled garden spade (less angle between handle and blade)
2) a D-handled digging fork
3) a D-handled spade fork
All of these can be seen at the Bulldog site
4) You will need an eye hoe, preferably the Japanese farmer hoe with short handle and a few other tools, available from Hida Tool:
Hida Tool
http://www.hidatool.com/shop/shop.html
(this is the most useful eye hoe to get, the other is lighter in weight)
Kusakichi Brand #524 Farmer Hoe
item# blade length overall size price
N-7524 7inch x 5inch 41inch $49.20
This is an amazing tool, used to clean silt and OM from between beds to put back on beds - ridge making hoe - or move dirt or make beds
Kusakichi Brand #553 Ridge Hoe
item# blade length overall size price
N-7553 15inch x 6inch 48inch $69.60
Kusakichi Brand #531 Farmer Rake
item# blade length overall size price
N-7531 8 5/8inch x 5 3/4inch 41 1/4inch $59.00
This is a three wide-tined hoe, great for weeding and tilthing,
disturbs soil structure less.
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Sneeboer tools are excellent. Great if you can find a source for them in the USA. The tools to get from them are the variois sizes and configurations of their SEEDING RAKES; they are indispensible!
They also have a great garden spade and an exceptional Dutch-style spade fork, a one of a kind tool, as are the seeding rakes (you will find it difficult to do without several sizes of this useful tool.
SNEEBOER & ZN
http://www.sneeboer.com/
Products
http://www.sneeboer.com/index2.php?page=19
(an amazing array of quality tools)
These are the seeding rakes:
-The best seeding rakes for preparing a seedbed for new plantings are
-the ones with 6 and 8 medium length tines - the others are less
-useful for this aplication.
Sloothark 4t
4 long tines & 185 cm length
http://www.sneeboer.com/index2.php?page=19&articleID=114
Klauw of Hark 8t
8 medium tines
http://www.sneeboer.com/popup.htm?beheer/ass/img/org_product115-1.gif
http://www.sneeboer.com/index2.php?page=19&articleID=115
Klauw of Hark 6t
6 long tines
Tuinhark 8t
8 medium tines, 167 cm overall length
http://www.sneeboer.com/index2.php?page=19&articleID=117
Tuinhark 6t
http://www.sneeboer.com/beheer/ass/img/org_product118-1.jpg
6 medium tines 167 cm
http://www.sneeboer.com/index2.php?page=19&articleID=118
Tuinhark 5t
http://www.sneeboer.com/beheer/ass/img/org_product119-2.jpg
5 long tines 167 cm. length
http://www.sneeboer.com/index2.php?page=19&articleID=119
Tuinhark 4t
4 long tines
http://www.sneeboer.com/beheer/ass/img/org_product120-2.jpg
http://www.sneeboer.com/beheer/ass/img/org_product120-1.jpg
http://www.sneeboer.com/index2.php?page=19&articleID=120
Fijnhark 10 t
http://www.sneeboer.com/beheer/ass/img/org_product207-2.jpg
10 medium tines
http://www.sneeboer.com/index2.php?page=19&articleID=207
Amerikaanse Hark 10 t
American style rake
10 medium tines
http://www.sneeboer.com/beheer/ass/img/org_product208-2.jpg
http://www.sneeboer.com/index2.php?page=19&articleID=208

http://www.sneeboerusa.com/
Sneeboer USA
c/o Cole Gardens
430 Loudon Road
Concord, NH 03301
phone 603-229-0655
fax 603-229-0657
doug@sneeboerusa.com

Garden Rake, 4 prongs, fine toothed
http://www.sneeboerusa.com/Images/Large/6007.jpg
http://www.sneeboerusa.com/Images/6007.jpg
Width : 5.2 in (13 cm)
Handle Length : 59 in. (150 cm)
Price : $83.00
Product Code : 6007

American Rake, 10 tined
http://www.sneeboerusa.com/Images/Large/6070.jpg
http://www.sneeboerusa.com/Images/6070.jpg
Width : 12 X 3.1 in (42 X 8 cm)
Handle Length : 66.9 in. (170 cm)
Price : $118.00
Product Code : 6070
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http://www.the-organic-gardener.com/images/garden-tool-english-spade.jpg
http://www.vegetablegardener.com/assets/uploads/posts/2873/kg17-double-digging-01_lg.jpg
http://www.gardeningknowhow.com/images/double-digging.jpg
http://hubpages.com/hub/HubMob-Topic-Of-The-Week-Green-Thumb-Hubbers-Landscaping--gardening-and-loving-your-yard_1
http://shop.waycooltools.com/images/1192658156236-807030603.jpeg
This company offers an amazing selection of good tools for biointensive gardeners and double diggers, much to choose from:
WayCoolTools.com
# P.O.Box 235
White Hall, VA 22987
# 877-353-7783
# contact@waycooltools.com
# 434-823-4600
http://shop.waycooltools.com/category.sc?categoryId=3

the bed (38-50" wide depending on the gardener's height).

After this process is completed you need never again turn your soil,
except to a depth no greater than is necessary to control newly emerging weeds, break crust and create a fine, loose seedbed. You now have biointensive no-till, permanent raised beds.

This technology has been around for centuries and it works.
There is a very big net gain for soil, its inhabitants and the environment.

See John Jeavons books, Alan Chadwick's literature and lectures (links on my website) and Aquatias' "Intensive Culture of Vegetables, French System".

Double digging is as essential and indispensible to gardening anywhere in the world, where the climate does not mandate other methods, as grain is to bread.

I'll work up a complete description of the method with variations next.

Here's more; this is good material from the BBC:

Gardening Guides
Digging your garden
http://www.bbc.co.uk/gardening/basics/techniques/soil_digging1.shtml
Double digging

Double digging is useful when drainage needs to be improved, or if the ground has not been previously cultivated. This is a time-consuming process but is worth the hard work and will result in good soil.

* The soil is worked to a depth of two spades, rather than one, and it’s essential to keep the two layers of soil (subsoil and topsoil) separate. In order to do this, the lower half of the trench can be dug over in situ.
* Remove the soil from the upper and lower spits of the first trench and from the upper spit of the second, placing it aside on the ground in three separate, clearly marked piles.
* The soil can then be transferred from the lower spit of the second trench to the base of the first trench, and from the upper spit of the third trench to the top of the first. This ensures that the topsoil and subsoil remain separate.
* Continue digging trenches in the same way, until you reach the end of the bed where soil saved from the first trench can be used to fill the appropriate layers in the final trench.
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And this great blog article with extensive links on double digging
using the Chadwick/Jeavons French Intensive biointensive method:
Double Digging
http://constructal.blogspot.com/2006/04/double-digging.html
"In 2004 we also volunteered at the Center for Sustainability to help double dig some of their garden plots. Double digging is the first step in the bio-intensive gardening technique, which we were unfamiliar with. So I did a little bit of research on the technique and this year I am going to try it on our garden plot. This technique was developed by Alan Chadwick and furthered and promoted by John Jeavons of Ecology Action. It aims at maximizing the yield from the available area AND maintain the soil quality at the same time through sustainable organic methods of gardening. The center for sustainability has a very good webpage about this technique. Some other links I found are at the bottom of this post."
Center For Sustainability http://www.engr.psu.edu/cfs/
and there, on double digging:
http://www.engr.psu.edu/cfs/projects/biointensive.aspx
Ecology Action http://www.growbiointensive.org/biointensive/Ecology.html
See also Bountiful Gardens http://www.bountifulgardens.org/
Other links: http://constructal.blogspot.com/2006/04/double-digging.html#Links
Biointensive Gardening Technique
http://www.engr.psu.edu/cfs/projects/biointensive.aspx
Bountiful Gardens
http://www.bountifulgardens.org/growbiointensive.html
Ecology Action Biointensive Gardening
http://www.growbiointensive.org/biointensive/GROW-BIOINTENSIVE.html
Books by John Jeavons
http://www.growbiointensive.org/biointensive/book.html
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Soil Quality resources, webforum archives, materials from various lists:
souscayrous' biological farming & permaculture collection
Hazelip, Bonfils and more
http://www.ibiblio.org/ecolandtech/souscayrous
Soils In Biological Agriculture
http://www.ibiblio.org/ecolandtech/permaculture/mailarchives/discussion-threads/soil-quality/
Remineralize the Earth
http://www.ibiblio.org/ecolandtech/orgfarm/remineralization/remineralization.selected-writings
Additional Soil Quality Links and Literature
http://www.ibiblio.org/ecolandtech/soil-links+lit.html
Compost Tea, Soil Foodweb, Soil Quality Discussion:
Archive 1
http://www.ibiblio.org/ecolandtech/SoilWiki/message-archives/composttea+soilfoodweb+soilquality/1/maillist.html
Archive 2
http://www.ibiblio.org/ecolandtech/SoilWiki/message-archives/composttea+soilfoodweb+soilquality/2/maillist.html
Archive 3
http://www.ibiblio.org/ecolandtech/SoilWiki/message-archives/composttea+soilfoodweb+soilquality/3/maillist.html
Archive 4
http://www.ibiblio.org/ecolandtech/SoilWiki/message-archives/composttea+soilfoodweb+soilquality/4/maillist.html
Archive 5
http://www.ibiblio.org/ecolandtech/SoilWiki/message-archives/composttea+soilfoodweb+soilquality/5/maillist.html
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Gardening Hand Tool Sourcelist
(needs revising)
http://www.ibiblio.org/ecolandtech/documents/gardening-hand-tools.faq
Soil and Health Library
http://www.soilandhealth.org/index.html
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Glomalin: Hiding Place for a Third of the World's Stored Soil Carbon
http://www.ars.usda.gov/is/AR/archive/sep02/soil0902.htm

Glomalin, extracted from
undisturbed Nebraska soil and
then freeze-dried.
(K9969-2)

A sticky protein seems to be the unsung hero of soil carbon storage.

Until its discovery in 1996 by ARS soil scientist Sara F. Wright, this soil "super glue" was mistaken for an unidentifiable constituent of soil organic matter. Rather, it permeates organic matter, binding it to silt, sand, and clay particles. Not only does glomalin contain 30 to 40 percent carbon, but it also forms clumps of soil granules called aggregates. These add structure to soil and keep other stored soil carbon from escaping.

As a glycoprotein, glomalin stores carbon in both its protein and carbohydrate (glucose or sugar) subunits. Wright, who is with the Sustainable Agricultural Systems Laboratory in Beltsville, Maryland, thinks the glomalin molecule is a clump of small glycoproteins with iron and other ions attached. She found that glomalin contains from 1 to 9 percent tightly bound iron.
A microscopic view of an arbuscular mycorrhizal fungus: Click here for full photo caption.
A microscopic view of an
arbuscular mycorrhizal fungus
growing on a corn root. The
round bodies are spores, and
the threadlike filaments are
hyphae. The substance coating
them is glomalin, revealed by
a green dye tagged to an
antibody against glomalin.
(K9968-1)

Glomalin is causing a complete reexamination of what makes up soil organic matter. It is increasingly being included in studies of carbon storage and soil quality. In fact, the U.S. Department of Energy, as part of its interest in carbon storage as an offset to rising atmospheric carbon dioxide (CO2) levels, partially funded a recent study by lab technician Kristine A. Nichols, a colleague of Wright's. Nichols reported on the study as part of her doctoral dissertation in soil science at the University of Maryland.

That study showed that glomalin accounts for 27 percent of the carbon in soil and is a major component of soil organic matter. Nichols, Wright, and E. Kudjo Dzantor, a soil scientist at the University of Maryland-College Park, found that glomalin weighs 2 to 24 times more than humic acid, a product of decaying plants that up to now was thought to be the main contributor to soil carbon. But humic acid contributes only about 8 percent of the carbon. Another team recently used carbon dating to estimate that glomalin lasts 7 to 42 years, depending on conditions.


For the study, the scientists compared different chemical extraction techniques using eight different soils from Colorado, Georgia, Maryland, and Nebraska. They found that current assays greatly underestimate the amount of glomalin present in soils. By comparing weights of extracted organic matter fractions (glomalin, humic acid, fulvic acid, and particulate organic matter), Nichols found four times more glomalin than humic acid. She also found that the extraction method she and Wright use underestimates glomalin in certain soils where it is more tightly bound than usual.
Soil scientist examines a soil aggregate coated with glomalin: Click here for full photo caption.
In her Beltsville laboratory,
soil scientist Sara Wright
examines a soil aggregate
coated with glomalin, a soil
protein she identified in 1996.
(K9972-1)

In a companion study, Nichols, Wright, and Dzantor teamed up with ARS chemist Walter F. Schmidt to examine organic matter extracted from the same soils under a nuclear magnetic resonance (NMR) imager. They found that glomalin's structure differs from that of humic acid—or any other organic matter component—and has unique structural units.

In a current study in Costa Rica, partly funded by the National Science Foundation, Wright is using glomalin levels and root growth to measure the amount of carbon stored in soils beneath tropical forests. She is finding lower levels of glomalin than expected and a much shorter lifespan. "We think it's because of the higher temperatures and moisture in tropical soils," she explains. These factors break down glomalin.

Forests, croplands, and grasslands around the world are thought to be valuable for offsetting carbon dioxide emissions from industry and vehicles. In fact, some private markets have already started offering carbon credits for sale by owners of such land. Industry could buy the credits as offsets for their emissions. The expectation is that these credits would be traded just as pollution credits are currently traded worldwide.
Soil scientist and technician examine extracted soil organic matter constituents: Click here for full photo caption.
Soil scientist Sara Wright
(foreground) and technician
Kristine Nichols use nuclear
magnetic resonance to examine
the molecular structure of
extracted soil organic matter
constituents.
(K9971-1)

How Does Glomalin Work?

It is glomalin that gives soil its tilth—a subtle texture that enables experienced farmers and gardeners to judge great soil by feeling the smooth granules as they flow through their fingers.

Arbuscular mycorrhizal fungi, found living on plant roots around the world, appear to be the only producers of glomalin. Wright named glomalin after Glomales, the taxonomic order that arbuscular mycorrhizal fungi belong to. The fungi use carbon from the plant to grow and make glomalin. In return, the fungi's hairlike filaments, called hyphae, extend the reach of plant roots. Hyphae function as pipes to funnel more water and nutrients—particularly phosphorus—to the plants.

"We've seen glomalin on the outside of the hyphae, and we believe this is how the hyphae seal themselves so they can carry water and nutrients. It may also be what gives them the rigidity they need to span the air spaces between soil particles," says Wright.
Technician checks progress of corn plants: Click here for full photo caption.
Technician Kristine Nichols
checks the progress of corn
plants growing in containers
specially designed for
glomalin production.
(K9973-1)

As a plant grows, the fungi move down the root and form new hyphae to colonize the growing roots. When hyphae higher up on the roots stop transporting nutrients, their protective glomalin sloughs off into the soil. There it attaches to particles of minerals (sand, silt, and clay) and organic matter, forming clumps. This type of soil structure is stable enough to resist wind and water erosion, but porous enough to let air, water, and roots move through it. It also harbors more beneficial microbes, holds more water, and helps the soil surface resist crusting.

Scientists think hyphae have a lifespan of days to weeks. The much longer lifespan of glomalin suggests that the current technique of weighing hyphae samples to estimate fungal carbon storage grossly underestimates the amount of soil carbon stored. In fact, Wright and colleagues found that glomalin contributes much more nitrogen and carbon to the soil than do hyphae or other soil microbes.

Two rows of dried soil samples: Click here for full photo caption.
Dried samples of undisturbed
soil (top row) and material
left after extractable organic
matter has been removed
(bottom row). Although minerals
are the most abundant components
of soil, organic matter gives
it life and health. Soil
samples from left to right
are from Maryland, Nebraska,
Georgia, and Colorado.
(K9974-1)


Rising CO2 Boosts Glomalin, Too

In an earlier study, Wright and scientists from the University of California at Riverside and Stanford University showed that higher CO2 levels in the atmosphere stimulate the fungi to produce more glomalin.

They did a 3-year study on semiarid shrub land and a 6-year study on grasslands in San Diego County, California, using outdoor chambers with controlled CO2 levels. When CO2 reached 670 parts per million (ppm)—the level predicted by mid to late century—hyphae grew three times as long and produced five times as much glomalin as fungi on plants growing with today's ambient level of 370 ppm.

Longer hyphae help plants reach more water and nutrients, which could help plants face drought in a warmer climate. The increase in glomalin production helps soil build defenses against degradation and erosion and boosts its productivity.

Wright says all these benefits can also come from good tillage and soil management techniques, instead of from higher atmospheric CO2.

"You're in the driver's seat when you use techniques proven to do the same thing as the higher CO2 that might be causing global warming. You can still raise glomalin levels, improve soil structure, and increase carbon storage without the risks of the unknowns in global climate change," she says.

Putting Glomalin to Work

Wright found that glomalin is very manageable. She is studying glomalin levels under different farming and ranching practices. Levels were maintained or raised by no-till, cover crops, reduced phosphorus inputs, and the sparing use of crops that don't have arbuscular mycorrhizal fungi on their roots. Those include members of the Brassicaceae family, like cabbage and cauliflower, and the mustard family, like canola and crambe.

"When you grow those crops, it's like a fallow period, because glomalin production stops," says Wright. "You need to rotate them with crops that have glomalin-producing fungi."

In a 4-year study at the Henry A. Wallace Beltsville (Maryland) Agricultural Research Center, Wright found that glomalin levels rose each year after no-till was started. No-till refers to a modern conservation practice that uses equipment to plant seeds with no prior plowing. This practice was developed to protect soil from erosion by keeping fields covered with crop residue.

Glomalin went from 1.3 milligrams per gram of soil (mg/g) after the first year to 1.7 mg/g after the third. A nearby field that was plowed and planted each year had only 0.7 mg/g. In comparison, the soil under a 15-year-old buffer strip of grass had 2.7 mg/g.

Wright found glomalin levels up to 15 mg/g elsewhere in the Mid-Atlantic region. But she found the highest levels—more than 100 mg/g—in Hawaiian soils, with Japanese soils a close second. "We don't know why we found the highest levels in Hawaii's tropical soils. We usually find lower levels in other tropical areas, because it breaks down faster at higher temperature and moisture levels," Wright says. "We can only guess that the Hawaiian soils lack some organism that is breaking down glomalin in other tropical soils—or that high soil levels of iron are protecting glomalin."

It's Persistent and It's Everywhere!

The toughness of the molecule was one of the things that struck Wright most in her discovery of glomalin. She says it's the reason glomalin eluded scientific detection for so long.

"It requires an unusual effort to dislodge glomalin for study: a bath in citrate combined with heating at 250 °F for at least an hour," Wright says. "No other soil glue found to date required anything as drastic as this."

"We've learned that the sodium hydroxide used to separate out humic acid in soil misses most of the glomalin. So, most of it was thrown away with the insoluble humus and minerals in soil," she says. "The little bit of glomalin left in the humic acid was thought to be nothing more than unknown foreign substances that contaminated the experiments."

Once Wright found a way to capture glomalin, her next big surprise was how much of it there was in some soils and how widespread it was. She tested samples of soils from around the world and found glomalin in all.

"Anything present in these amounts has to be considered in any studies of plant-soil interactions," Wright says. "There may be implications beyond the carbon storage and soil quality issues—such as whether the large amounts of iron in glomalin mean that it could be protecting plants from pathogens."

Her recent work with Nichols has shown that glomalin levels are even higher in some soils than previously estimated.

"Glomalin is unique among soil components for its strength and stability," Wright says. Other soil components that contain carbon and nitrogen, as glomalin does, don't last very long. Microbes quickly break them down into byproducts. And proteins from plants are degraded very quickly in soil.

"We need to learn a lot more about this molecule, though, if we are to manage glomalin wisely. Our next step is to identify the chemical makeup of each of its parts, including the protein core, the sugar carbohydrates, and the attached iron and other possible ions." Nichols is starting to work on just that.

"Once we know what sugars and proteins are there," says Nichols, we will use NMR and other techniques to create a three-dimensional image of the molecule. We can then find the most likely sites to look for iron or other attached ions.

"Researchers have studied organic matter for a long time and know its benefits to soil. But we're just starting to learn which components of organic matter are responsible for these benefits. That's the exciting part of glomalin research. We've found a major component that we think definitely has a strong role in the benefits attributed to organic matter—things like soil stability, nutrient accessibility, and nutrient cycling."

As carbon gets assigned a dollar value in a carbon commodity market, it may give literal meaning to the expression that good soil is black gold. And glomalin could be viewed as its golden seal.—By Don Comis, Agricultural Research Service Information Staff.

This research is part of Soil Resource Management, an ARS National Program (#202) described on the World Wide Web at http://www.nps.ars.usda.gov.

Sara F. Wright and Kristine A. Nichols are with the USDA-ARS Sustainable Agricultural Systems Laboratory, Bldg. 001, 10300 Baltimore Ave., Beltsville, MD 20705; phone (301) 504-8156 [Wright], (301) 504-6977 [Nichols], fax (301) 504-8370.


"Glomalin: Hiding Place for a Third of the World's Stored Soil Carbon" was published in the September 2002 issue of Agricultural Research magazine.





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