Discovered in 1996 by Sara F. Wright, which she named after the Glomales order of fungi, 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.
This is an excerpt from the Wild Ones Journal
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What is it?
Glomalin molecules contain thirty to forty percent carbon, stored in both its protein and sugar subunits, along with nine percent tightly bound iron. It permeates organic matter, binding it to silt, sand, and clay particles, forming clumps, stabilizing the soil, adding to soil structure, or tilth, keeping other stored soil carbon from escaping.
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.
Glomalin accounts for twenty-seven percent of the carbon in soil, and is a major component of soil organic matter. It weighs twenty-five percent more than humic acid, a product of decaying plants that up to now was thought to be the main contributor to soil carbon. And glomalin lasts seven to forty-two years in the soil, depending on conditions.
How does Glomalin Work?
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 to make glomalin. In return, the fungi’s hair-like 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. When hyphae stop transporting water, their protective glomalin sloughs off into the soil, where it helps soil build defenses against degradation and erosion, and boosts its productivity.
Wright says that all these benefits can come from good tillage and soil management techniques. 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 four-year study, 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.
“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.
By Maryann Whitman
Modified from the USDA-produced Agricultural Research magazine, September 2002. This research is part of Soil Resource Management, an ARS National Program (#202).