For 60 years, organic farmers have claimed they hold the secret to human sustainability. They claim modern high-tech farming “ruins soils,” and that, as they do, we must bar chemical fertilizers and synthetic pesticides from all our crop fields.
New research, however, shows the biggest factor in soil health is a recently discovered gooey protein called glomalin, produced naturally in soil by the mychorrizal fungi that live on the roots of most plants. Organic farming not only has no advantage in producing soil health, but organic farmers destroy the glomalin with their frequent plowing to control weeds.
Plowing Harms Soil Health
Plowing destroys the long slender hyphae (feeding tubes) of the fungi. That suggests no-till farming and low-till farming, which rely on herbicides to control weeds, may be better ways to sustainable human food production than organic farming. Less plowing means more fungi living on the plant roots, more glomalin, and healthier soils.
Glomalin clumps soil particles together, preventing erosion and keeping soil carbon from escaping into the air. The clumps also become miniature storehouses for moisture and plant nutrients. It is glomalin that gives soil its “tilth”–a subtle texture that permits farmers and gardeners to judge good soil as the particles flow through their fingers.
Glomalin wasn’t even discovered until 1996, by Dr. Sara Wright, a soil microbiologist at the government’s Sustainable Agricultural Systems Laboratory in Beltsville, Maryland. We are still learning its importance and functions. Without glomalin, Wright says, soil would be just loose dust and bits of organic matter, all too susceptible to wind and water erosion.
She says glomalin probably wasn’t discovered earlier because we thought humic acid was the source of soil tilth … and because it takes a heroic effort to unbind the sticky glomalin from the soil particles and carbon it’s attached to. (Wright uses a citrate bath plus heating to 250 degrees for at least an hour!)
Organic Farms Plowed Frequently
Organic farms are plowed frequently, to control weeds. Organic farmers refuse to use the chemical weed-killers that make low-till farming effective. (Weeds have always been man’s main competitors for food because they compete with crop plants for nutrients, water, and sunlight.)
Wright found 2.7 milligrams of glomalin per gram of soil in a grass buffer strip at Beltsville, only 0.7 mg/g in an annually plowed field nearby, and 1.7 mg/g after the third year of a no-till test. She’s found that glomalin levels increase steadily the longer the soils stay undisturbed, with as much as 15 mg/g in some undisturbed Mid-Atlantic grasslands. Herbicides were first developed in the 1970s, and some no-till fields have now been unplowed for nearly 30 years.
Glomalin is also encouraged by minimizing phosphorous applied to the soil, and that further penalizes organic farming. If organic farmers apply enough manure to supply adequate nitrogen for their crops, the manure will probably contain too much phosphorous for the mycorrhizal fungi to flourish.
Organic farmers do make extensive use of cover crops, which help improve glomalin levels. (The fungi need live plant roots to live on.) But Dan Towery of the Conservation Tillage Information Center points out that if conservation tillage already produces higher glomalin levels than plowed organic fields can sustain, using low-till with more cover crops should further increase chemical farming’s glomalin advantage.
A study currently underway is finding low glomalin levels in Costa Rican tropical forest soils. “We think it’s because of the higher temperatures and moisture” that break down glomalin, says Wright. This helps account for the historically low crop yields in most tropical agriculture.
No-till on the Rise
American farmers have already eliminated plowing on 37 percent of the nation’s 297 million acres of cropland. About one-third of the reduced-till acreage has been converted since herbicide-resistant biotech crops have improved low-till weed control.
The discovery of glomalin’s importance should stimulate new efforts to extend no-till farming, and to include more cover crops in the no-till systems (especially in the South with its longer growing seasons). Towery says he hopes it will encourage many farmers who currently use no-till intermittently (for example, no-tilling their soybeans but plowing their corn) to adopt a long-term “never-till” strategy that will maximize both soil health and erosion protection.
Glomalin may even help dampen the urge of city folks who’ve never grown crops to mandate low-yield organic farming.
Dennis T. Avery writes from Churchville, Virginia and is director of the Hudson Institute’s Center for Global Food Issues. http://www.cgfi.org/