Healthy soil and sustainable growing

[<mdnagel@verizon.net>]

Another way/reason that petrochemical farming is going to die out...


-Mark Nagel
Everett, WA


Source: 
http://findarticles.com/p/articles/mi_m3741/is_9_50/ai_92589768/print?tag=artBody;col1

Glomalin hiding place for a third of the world's stored soil carbon
Don Comis

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.

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 
(C[O.sub.2]) 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.

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.

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.

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.

Rising C[O.sub.2] Boosts Glomalin, Too

In an earlier study, Wright and scientists from the University of California 
at Riverside and Stanford University showed that higher C[O.sub.2] 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 C[O.sub.2] levels. When C[O.sub.2] 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 C[O.sub.2].

"You're in the driver's seat when you use techniques proven to do the same 
thing as the higher C[O.sub.2] 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[degrees]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.

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, e-mail wrights@ba.ars.usda.gov, nicholsk@ba.ars.usda.gov.

COPYRIGHT 2002 U.S. Government Printing Office
COPYRIGHT 2002 Gale Group