Glyphosate and GM crops are harming no-till soils

Magazine dedicated to promoting GM crops and glyphosate herbicides in no-till systems recommends reducing the use of these products

No-Till Farmer is a magazine aimed at farmers who grow GM glyphosate-tolerant corn and soybeans using herbicides instead of ploughing to control weeds. In a revealing sign of the times, the magazine has published an article detailing the serious problems of soil and plant health caused by the application of glyphosate on these GM crops in no-till systems.

The article gives the lie to the regular promotion of no-till farming with GM crops as environmentally friendly – generally on the claimed grounds that by avoiding ploughing it mitigates climate change by reducing the number of tractor passes in fields, thus reducing fossil fuel use, and stores carbon in the soil rather than releasing it into the atmosphere. While the new article focuses on other aspects of no-till farming with GM crops, it makes clear that these systems create a host of negative impacts for farmers and the environment alike.

The paywalled article, written by No-Till Farmer’s senior editor John Dobberstein, draws on the expertise of Robert Kremer, a retired research microbiologist with the USDA-Agricultural Research Service and adjunct professor at the University of Missouri, as well as other researchers.

Noting that “there may be trouble on the horizon for glyphosate”, Dobberstein says that when measured by pounds applied per square mile, the use of glyphosate has increased from less than 1 million pounds in 1974 to 28 million pounds in 1995, and 80 million pounds in 2010. Between 1974 and 2014, 30 billion pounds of glyphosate were applied to US agricultural lands, according to federal data.

Glyphosate lingers in soil

Referring to claims that glyphosate is typically neutralized and degraded by soil microbes after a period of time, Dobberstein notes that in the last 5 years, evidence seems to be mounting through research studies that the herbicide is lingering in the soil environment longer than anticipated and initiating a host of non-target effects.

According to Dobberstein, impacts include absorption by non-target crops through roots, suppression of beneficial mycorrhizal fungi (which enable plants to acquire more nutrients from the surrounding soil and confer protection against diseases), increase in potentially pathogenic microorganisms, reduction in earthworm activity, and chemical residues in soil and water. It could also have negative effects on respiration for soil-dwelling organisms and nutrient immobilization for plants and microorganisms.

Dobberstein adds that Cornell University researchers have found that beneficial Pseudomonas in the soil — bacteria which produce plant-stimulating hormones to promote plant growth and antifungals to defeat problematic fungi such as Pythium and Fusarium — decreased when the glyphosate seeped into the surface soil layer by leaching or release from glyphosate-treated plants. Fusarium produces toxins that can seriously harm livestock or humans that eat crops infected with it.

Kremer told attendees at the National No-Tillage Conference earlier this year, “This is all supported by research. I’m not just making this up. With that amount of glyphosate out there, it’s beginning to raise some eyebrows and people are wondering what else might be happening with this amount of chemical in the environment.”

Glyphosate-Fusarium link

One of the main concerns of researchers, Dobberstein writes, is how glyphosate affects soil biological processes and the soil rhizosphere – the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. Kremer says that glyphosate is released through the roots of plants and that can suppress the antagonistic microbes that we need to keep pathogens down in soil: “Maybe one of the reasons we see more Fusarium on the roots is because these pseudomonads will suppress Fusarium.”

The Cornell researchers’ findings showed glyphosate doesn’t affect different members of the Pseudomonas species in the same way. For example, when Pseudomonas protegens, a bacterium used as a biocontrol agent for cereal crops, and Pseudomonas fluorescens, used as a fungus biocontrol for fruit trees, were exposed to varying glyphosate concentrations, the researchers noted no negative effects.

But in two species of Pseudomonas putida, used in soil fungus control for corn and other crops, the growth of the bacteria was suppressed, according to Ludmilla Aristilde, assistant professor of biological and environmental engineering at Cornell’s Atkinson Center for a Sustainable Future.

Aristilde told No-Till Farmer: “If a farmer is using Pseudomonas fluorescens as a biocontrol, then it is probably okay to use glyphosate. But if the farmer uses Pseudomonas putida to control fungal pathogens in the soil, then glyphosate is more likely to prevent the bacteria from doing its job.”

Dobberstein cites research by Kremer in which residual glyphosate was detected in soils two years after the original application. Kremer explains that there was a correlation between the residual soil glyphosate and the colonization of the roots with the Fusarium. In soils not treated with Roundup, there were lower levels of Fusarium.

Two years later they conducted similar testing for residual glyphosate in a field and found over 1,000 parts per billion of glyphosate in the soil — the highest level that the lab could test for.

Kremer says, “The main point is that this chemical is hanging around in silt loam soils, and at the part-per-million level, that’s a couple pounds per acre. And where is that glyphosate in the soil? It’s probably in the upper couple inches, so it’s very much magnified at the soil surface, and that could maybe add up to 4 to 5 pounds per acre.”

Kremer cited reports from Argentina and Brazil where farmers are concerned about Roundup herbicide suppressing mycorrhizae in soils. He comments that growers there are taking native grasslands loaded with mycorrhizae and planting them with Roundup Ready crops, potentially leading to reduced mycorrhizal colonization of crops grown in these soils.

He explains that glyphosate can affect the germination of the mycorrhizal spores and that affects the infection of the roots. He adds that data show that the mycorrhizal colonization is lower with Roundup and that some of these structures in the root that are necessary for phosphorous and water uptake are also reduced.

Effects on beneficial organisms

Kremer adds that glyphosate and GM crops can also negatively affect other beneficial soil organisms, such as small insects and earthworms, which no-tillers have worked hard to bring back.

Kremer says, “This is a concern because these organisms interact with each other helping to decompose organic substances, build up soil organic matter and mineralize nitrogen, phosphorous, sulfur and potassium.”

“We’re all in one big family there, so you can kind of understand if these very small inferior organisms are becoming affected, what does it take before mammals higher in the food chain are affected as well?”

Effects on plants

Glyphosate lingering in the soil can also negatively affect Roundup Ready soybean or corn plants that take in the chemical, Kremer says.

Glyphosate kills weeds by disrupting their protein synthesis, causing them to die. But there’s a secondary mechanism, Kremer says, that causes that plant to become susceptible to opportunistic soil microbes that attack the plant’s roots and eventually kill it.

Kremer explains that glyphosate is systemic and ends up being present throughout the plant, including in soybean pods and seeds. About 30 to 40% of the herbicide reaches the root system of the resistant crops, which includes actively growing root tips. Some of the glyphosate is released out into the soil and enters the environment.

Kremer adds glyphosate may also be re-absorbed by the plant back through the roots after the initial application. Researchers have seen root tip damage and stunted root growth in some soybean plants when glyphosate was re-absorbed by the same plant, he says.

Kremer carried out a study involving green beans planted in either sterilized or unsterilized soil, with the former treatment designed to eliminate all the microbes in the soil. A control plot was included without any Roundup treatment.

The plants in non-sterile soil died more quickly after glyphosate treatment as they began to release nutrients through the roots, stimulating the opportunistic pathogens to attack the root and begin to kill it, Kremer says.

Between 1997 and 2007, researchers on a testing project consistently found Fusarium colonization in the roots of glyphosate-tolerant soybeans. The presence of Fusarium, Kremer says, is an indicator of microbial imbalance in the rhizosphere and shows potential for pathogenicity.

In 2003 and 2004, Kremer and fellow researchers found increased Fusarium colonization in the roots of glyphosate-tolerant corn compared to corn acres where non-glyphosate herbicides were used, as well as with glyphosate-tolerant soybeans when compared to no glyphosate being applied.

Kremer also told No-Till Farmer about another case – a no-till field where a farmer killed fescue with glyphosate and immediately planted soybeans the next day.

Kremer compared roots in soybeans where fescue was killed with ground where the grass wasn’t killed and found similar results: root colonization by fungus where Roundup was applied, while on the other ground there was very little fungus on the roots. This led him to believe residual glyphosate caused the Fusarium colonization.

“As the grass is dying it’s building up fungi on the root systems, and as these living soybean seedlings are being established, the fungi is transferring from the dying vegetation onto the living roots,” he says. “This has been shown many times where they do a lot of no-tilling of cereal grains in the Pacific Northwest. The same thing was happening to that crop as well.”

He showed results from a study in 2009 that examined the impact of glyphosate on beneficial microorganisms that fix nitrogen. They noted reductions in root nodulation and nitrogen fixation in field-grown soybeans that had 0.75 pounds per acre of glyphosate applied.