[permaculture] Double-dug?

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Sun Dec 13 02:31:10 EST 2009

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.
Long straight handled version:
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."
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
(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.
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.
(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
Klauw of Hark 8t
8 medium tines
Klauw of Hark 6t
6 long tines
Tuinhark 8t
8 medium tines, 167 cm overall length
Tuinhark 6t
6 medium tines   167 cm
Tuinhark 5t
5 long tines  167 cm. length
Tuinhark 4t
4 long tines
Fijnhark 10 t
10 medium tines
Amerikaanse Hark 10 t
American style rake
10 medium tines

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

Garden Rake, 4 prongs, fine toothed
Width : 5.2 in (13 cm)
Handle Length : 59 in. (150 cm)
Price : $83.00
Product Code : 6007

American Rake, 10 tined
Width : 12 X 3.1 in (42 X 8 cm)
Handle Length : 66.9 in. (170 cm)
Price : $118.00
Product Code : 6070
This company offers an amazing selection of good tools for biointensive 
gardeners and double diggers, much to choose from:
# P.O.Box 235
White Hall, VA 22987
# 877-353-7783
# contact at waycooltools.com
# 434-823-4600

> 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
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.
And this great blog article with extensive links on double digging
using the Chadwick/Jeavons French Intensive biointensive method:
Double Digging
"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:
Ecology Action http://www.growbiointensive.org/biointensive/Ecology.html
See also Bountiful Gardens http://www.bountifulgardens.org/
Other links: 
Biointensive Gardening Technique
Bountiful Gardens
Ecology Action Biointensive Gardening
Books by John Jeavons
Soil Quality resources, webforum archives, materials from various lists:
souscayrous' biological farming & permaculture collection
Hazelip, Bonfils and more
Soils In Biological Agriculture
Remineralize the Earth
Additional Soil Quality Links and Literature
Compost Tea, Soil Foodweb, Soil Quality Discussion:
Archive 1
Archive 2
Archive 3
Archive 4
Archive 5
Gardening Hand Tool Sourcelist
(needs revising)
Soil and Health Library
Glomalin: Hiding Place for a Third of the World's Stored Soil Carbon

Glomalin, extracted from
undisturbed Nebraska soil and
then freeze-dried.

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.

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 

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.

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 
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

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 
Technician Kristine Nichols
checks the progress of corn
plants growing in containers
specially designed for
glomalin production.

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.

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 

"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 

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 

"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 

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 

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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