Saturday, November 04, 2006

Organic Farming increases Global Warming

Glomalin: Hiding Place for a Third of the World's Stored Soil Carbon is a 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.

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.

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.

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.


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