Crop Comments: Glyphosate Residue Persists Longer Than Expected

My first contact with herbicide residue injuring field crops came in the 1970s, as an agronomy Extension agent. A farmer had me examine his alfalfa seeding that had a weird mortality pattern. He had planted corn two years earlier, fallowed the piece in question the next year, planting a legume seeding the third year. He showed me a strip at the edge of the field where the alfalfa had sprouted, then promptly died.

After he’d planted corn the first year he had a commercial spray applicator apply 4#/acre of active ingredient atrazine with a “sticker” on what he thought was a 10-acre piece. The applicator came with a tank preblend of weedkiller for 10 acres. However, the field was only about 9.5 acres because of vegetation encroachment over the edges. The applicator ran out the rest of the blend on that 0.5-acre border.

That overlap band had very little growing on it. I called Professor Russell Hahn, Cornell Extension weed scientist, describing the situation to him. He said that in most soil types atrazine has a half-life of about 10 months, which would mean that this herbicide viability might be degraded to 40% after a year. We determined that after another year the herbicide’s activity would be degraded by another 60%, ending up at 16% of its original potency. Multiplying that by the 4#/acre original dosage meant the field had 0.64#/acre atrazine activity after 24 months. Now double that number in the spray-overlapped area: that strip had 1.28#/acre of atrazine activity – enough to kill his alfalfa crop.

In July 2009, Extension researchers reported crop losses in North Carolina being linked to certain broad leaf herbicides containing picloram. People with gardens and organic farms who relied on horse manure or compost for fertilizer noticed their plants were dying. The herbicides, used by hay producers to grow weedfree hay, were applied there. That hay crop was ingested by horses and cattle.

“Based on the published reports it appears that these herbicides pass through the animal basically intact,” said Jeanine Davis, Ph.D., associate professor and Extension specialist at NCSU. “After being excreted in the urine and manure they still act like herbicides.”

The most widely used herbicide in farming history has set records for in-soil longevity. I recently interviewed two scientists who demonstrated that a natural food component could successfully combat harmful effects of the most heavily used and insidious herbicide ever adopted by farmers: glyphosate.

The scientists were Dieter Harle and Don Huber. They used liquid residue from sauerkraut production to break down glyphosate residues. In sauerkraut production, the lactic acid formed from cabbage is the result of natural fermentation.

Glyphosate kills weeds by chelating vital trace minerals that weeds need to survive. (“Protected” crops have been genetically engineered to survive the herbicide.) Glyphosate residues remain in soils for years. The most common agricultural trace element being functionally immobilized is manganese (Mn).

(Note: The sauerkraut juice research was originally inspired by failure of organically produced cabbage; a 36-month chemical purging period wasn’t enough to deaden the herbicide’s sting.)

In a paper titled “Saga of Soggy Sauerkraut,” published in the Journal of the American Society for Horticultural Science, Michael J. McNeill, Ph.D., teamed up with Harle and Huber.

They determined what caused water- logged organic sauerkraut, losses of which surpassed $1,000,000. (The glyphosate had been applied at least 36 months – the organic rules’ mandated minimum – before the organic cabbage was planted.) The scientists proved the soggy sauerkraut was caused by a glyphosate-induced Mn deficiency. Lactic acid formed from un-waterlogged cabbage came out fighting.

Lactobacillus plantarum microbes appear naturally on the surface of cabbage leaves and the surrounding environment. A common bacterium in plants and soil, L. plantarum initiates spontaneous fermentation when cabbage is salted. These beneficial bacteria, present on the raw vegetables, convert cabbage’s sugars into lactic acid, creating sauerkraut’s sour flavor while preserving it.

The scientists discovered that raw sauerkraut juice (RSKJ) degrades glyphosate. Their studies showed that microbes in the juice, particularly L. plantarum, produce enzymes that break down this herbicide. This process was confirmed in laboratory tests and field trials in which application of sauerkraut juice reduced glyphosate levels by approximately 85% in soil, releasing bound nutrients and thus improving crop yields.

This research, built on earlier findings about microbes degrading pesticides, spotlighted specific microbes known for their ability to detoxify. This demonstrated natural bioremediation through using fermented products. RSKJ was fermented but still raw, and it successfully deactivated glyphosate.

McNeill contends that since 1972, when glyphosate was first commercialized in the U.S. on a small scale, these herbicide residues have increasingly permeated the nation’s soils. Glyphosate residues have been much longer lasting than what growers and scientists expected. USDA’s organic standards mandate that land being transitioned into organic production must not receive any commercial fertilizer, synthetic pesticides nor genetically modified seed for a minimum of 36 months. However, crops genetically modified to survive applications of glyphosate retain this rather small molecule in their tissues. Then they pass it on to whatever (or whomever) ingests it or just leave it as corn (or soybean) trash in the fields following harvest.

McNeill demonstrated glyphosate can remain active in soil over 20 years – so crops grown on some certified organic land still can test positive for this herbicide’s residue. Prior to 1972, he believes, the nation’s cropland acreages were inherently healthier, even though many other ag chemicals were already in use then. He asserts that over the intervening 50-plus years glyphosate subtly degraded the health of soils, crops, livestock and ultimately people.

In their experiments, McNeill, Huber and Harle showed that treating the soil with 15 gal/acre of RSKJ increased the availability of Mn and other trace minerals in the irrigated silt loams and sandy loams being studied. They determined that available Mn and other traces in the soil were initially low, presumably due to chelation by glyphosate. Six months after the treatment with RSKJ, all of these traces were slightly more biologically available.

The research showed that RSKJ application improves shell corn yields by an average of 12.9 bu./acre; corn silage yields were improved by 2.28 tons/acre.

McNeill said, “In modern times, to work more land farmers have abandoned mechanical cultivation in favor of herbicides. These chemical weedkillers are chelators. Long story short, these cause imbalances in plant nutrition, which, in turn, cause more disease and insect pressure. So growers started using more fungicide, more insecticide, more chelators, more poison being dumped onto the ground. All these chemical inputs appeared to work … until they didn’t.”

These scientists preach the need to break this cycle. Chelators cause imbalances in plant nutrition, which cause more disease and insect pressure. So growers embraced the vicious chemical cycle mentioned above. Each successive input attempted to repair damage caused by the previous one.

This approach didn’t work: sick soils became the norm, resulting in sick crops, resulting in sick animals, including people. That’s the bad news.

The great news shared by Huber, Harle and McNeill is that a natural product, RSKJ, is beginning to break this cycle, thus accelerating the return of healthy soils – and with them more productive crops.

by Paris Reidhead