Muck and Mystery
   Loitering With Intent
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October 24, 2006
Glomalin Critics

This is another post about strings used to get here. I repeated the search to see what would result but didn't find any actual "glomalin critics". I did find this older overview that had some information that was new to me.

In 1996, Dr. Sarah Wright and colleagues at the USDA's Agricultural Research Service isolated a glycoprotein called glomalin that literally "gums up" the soil rhizosphere (the interface between soil and plant roots) with carbon fixed from the atmosphere. The compound is produced by common soil fungi called mycorrhizae that frequent the roots of many crops.

When Wright removed glomalin from soil samples, the result was a lifeless mineral powder. The soil had lost its tilth - the substance that conveys texture and health. She had inadvertently discovered the fundamental factor of soil welfare, elusive for over 10,000 years. Humic acid, previously thought to be the main contributor to soil carbon, could muster only a tiny percentage of glomalin's carbon-storing capacity in the field.

Another extraordinary finding was that elevated carbon dioxide levels encouraged mychorrizae to work overtime. Working with a consortium of scientists from UC-Davis and Stanford, Wright simulated CO2 projections for the year 2100 and observed ramped up glomalin production, with thriving fungi.

I didn't know that Wright's team had done CO2 experiments with mycorrhizae. I take such studies with a dollop of salt since they usually aren't realistic; don't make changes gradually which often results in adaptation, don't make all the expected changes including temperature and moisture, and don't consider how the species composition of a site might change as conditions change - turbulence rather than feedback as a wise man once said.
Most importantly, the USDA research demonstrated glomalin's tendency to buildup in the soil. Intensively farmed fields consistently leveled off at 0.7 mg of glomalin per gram of soil, while undisturbed plots saw an increase from 1.3 to 1.7 within three years. In hindsight, the Dust Bowl of the 1930's wasn't a casualty of overfarming, but overplowing.

Conservation tillage maintains the supporting cast needed for soil stability, sparing mycorrhizae the stress of reestablishment every season. Aiming for at least 30% cover on the field, precision equipment gently seeds through crop residues, safeguarding soil against the elements and defending against drought.

Even before Wright's discovery, the National Soil and Water Conservation Society endorsed modern agriculture as the most sustainable in all history. According to the National Crop Residue Management Survey, 37% of corn and 57% of U.S. soybeans are now grown under some form of conservation tillage. Using herbicides and biotechnology, farmers can spray their fields with confidence, sparing produce, blighting weeds, and salvaging soil. Many more are following suit.

There are conditions, however. Members of the cabbage and spinach families are oblivious to the fungi's courtship. Growing these crops is essentially a fallow period because glomalin production stops altogether. Frequent rotation with more friendly crops is recommended.

Organic farming has two strikes against it in maintaining soil health. To satisfy nitrogen needs, crops require substantial amounts of manure. Yet manure supplies a glut of phosphorous, which shuts down glomalin production. Another complication is the near limitless supply of weed seeds bankrolled in the soil. Plowing digs up and activates seeds, causing self-induced weed outbreaks. Without herbicides, the fallback has to be the plow.

I knew about "ruderals", plants that are "non-mycorrhizal or only mycorrhizal if it suits their needs", having posted about them before, but hadn't fully grasped the consequences of growing them as a crop - that mycorrhizae are out of work and so glomalin production ceases entirely. With these crops, then, it doesn't really matter if the soil is plowed to death so far as mycorrhizae are concerned. It still matters in terms of outgassing - plowing releases copious amounts of CO2 and methane which pollutes the air and impoverishes the soil.
Mycorrhizae were noteworthy before glomalin's discovery, providing sanctuary and sustenance for a variety of soil microbes. Many of their dependents are agriculturally significant. One in particular is rhizobium, which harmlessly "infects" legumes (such as peas) to fix nitrogen from the air. Other specialized members can rapidly degrade herbicides like Roundup into carbon dioxide.

Previously labeled as an unknown and thrown away, glomalin's profound significance can only reinforce Wolfe's claim. A retiring of the plow is in order, not only to build tilth, but also to nurture the dynamic communities beneath our feet.

I hadn't known, or had forgotten, that mycorrhizae harbor and sustain soil microbes. It makes sense given their habits of transporting phosphorous, nitrogen and carbon around underground - the "dirt internet" so to speak. When mycorrhizae thrive, so does eveything else.

Lastly, I liked Cornell University ecologist David W. Wolfe's term "surface chauvinism", which encapsulates much of what I find wrong with popular views of agriculture.

Posted by back40 at 10:13 AM | Meta

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