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NEW TECHNOLOGY PROVIDES FIRST-EVER SNAPSHOT OF FUMIGANTS’ IMPACT ON SOIL HEALTH

| Published 07.2022

June, 2022 – Soil fumigation is highly effective at managing soil pests that cause crop disease. However, it is regularly accused of doing more harm than good to overall soil biology. Advances in genetic sequencing technology can now provide a detailed snapshot of how fumigation actually changes bacterial and fungal populations in agricultural soil, and the close-up look is surprising many.

Regulators and even some scientists have alleged fumigation ‘sterilizes’ the soil, indiscriminately killing all microbes including the populations critical to soil structure and fertility, nutrient cycling and more. In fact, new data prove that belief is incorrect for the fumigants chloropicrin and 1,3-D (TELONE™).

Until very recently, determining a fumigant’s impact on soil was guesswork: 95% of soil organisms couldn’t be isolated and grown in the laboratory – and therefore couldn’t be quantified. Now, however, genetic sequencing technology can isolate and analyze ribosomal RNA, allowing a clear and complete description of a soil sample’s biological profile.

“We can finally stop guessing at what’s in our soil. For roughly $250 per sample, anyone who is interested can determine exactly what’s in their soil to a level of precision that was never possible before,” says Dr. John Washington, a plant pathologist and director of research and development at TriCal Group. “It’s a kind of genetic barcoding: the technology can identify every organism group and their relative amounts.”

Microbiome analysis shows that soil-applied chloropicrin and 1,3-D alter the soil biology in important but non-destructive ways. In fact, over the crop season, the soil’s total biome returns to much the way it was prior to fumigation, except for some fascinating changes. Each fumigant has distinct effects. For example, 2021 trials¹ showed Trichoderma, a well-known group of beneficial fungi, increased 20-100-fold in plots treated with chloropicrin. Population benefits lasted the entire season, and even extended into the next season in some settings, since Trichoderma overwinters in northern tree crop soils. The same trials showed Trichoderma did not increase in plots treated with 1,3-D alone, but did increase in plots treated with commercial formulations containing both chloropicrin and 1,3-D.

Beneficial root-colonizing bacteria Bacillus and Pseudomonas, which produce plant-active hormones, increase dramatically with both fumigants. Saprophytic bacteria and fungi, which live off non-living, decaying organic matter, also increase after fumigation. Saprophytes play major roles in Microbiome analysis shows that soil-applied chloropicrin and 1,3-D alter the soil biology in important but non-destructive ways. In fact, over the crop season, the soil’s total biome returns to much the way it was prior to fumigation, except for some fascinating changes.

TELONE™ is a Trademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow, used under license. TELONE™ is a federally Restricted Use Pesticide. Always read and follow label directions. 06012022 soil nutrient cycles, and also support soil structure, promote plant growth and are involved in natural, biological control of some soil-borne pathogens.

While these and other specific bacterial population findings are new, understanding of chloropicrin and 1,3-D’s soil health benefits is supported through research conducted by scientists from around the world. In late December 2021, University of Florida plant pathologists released a meta-analysis² – a comprehensive review of multiple research studies by other researchers – analyzing the impact of fumigants on non-target soil microorganisms. Their report concluded that, while fumigation can decrease biological abundance and diversity by 10 to 50% immediately after application, the effect is temporary: according to their findings, populations rebounded within 4-6 weeks following fumigation with chloropicrin/1,3-D mixtures.

In 2019, Phytobiomes Journal³ published research by Colorado and Oregon State researchers showing that fumigation with 1,3-D increased the population of Enterobacteriaceae, a family of bacteria that include species that specialize in nutrient cycling, while simultaneously decreasing the population of pathogenic fungi such as Pythium and Verticillium.The impact of beneficial microbes can be significant, with visible plant health noted inside of a single season and long-term benefits achieved over multiple applications of 1,3-D.

In 2017, applied and industrial microbiology journal AMB Express⁴ published results from a three-year soil microbe study conducted collaboratively by Dutch and Chinese researchers. The study described soil fumigation as offering a clear “legacy effect”: a strong and sustained increase in the relative abundance of the beneficial microorganisms, Actinobacteria and Saccharibacteria.

Fungal and bacterial diseases can have a major impact on crop marketability and profitability. For example, in potatoes, common scab (brown lesions on a potato’s skin) can reduce the value of the crop by as much as 20 to 50%⁵. Because crop production utilizes resources like water and fertilizer, significant disease-induced crop losses translate in effect to poor ecological stewardship, and bite deeply into both sustainability and a farm business’ total returns. Ultimately, better managing loss is exactly why growers turn to chloropicrin and 1,3-D, as they are the only tools available that decrease soil pests and diseases without compromising other aspects of soil health. “Research relating to chloropicrin and 1,3-D’s impacts on soil’s microbial populations is really interesting because it contradicts mainstream dogma and misunderstandings about the soil health effects of fumigants. Building from a more accurate understanding of what is actually happening in the soil, we’ll be positioned to make further gains in agronomy, sustainability and profitability. We’re now ready for much more productive and interesting conversations because we better understand the true dynamics of biological soil health and how to improve it further,” says Washington.

“It’s time to move past the long-held but completely wrong assumption that a soil fumigant is like a toxic bomb, sterilizing everything in its path. The new genetic sequencing technology shows that soil fumigation with chloropicrin or 1,3-D doesn’t destroy the soil biome; it actually supports it.”

¹J. Washington, 2022. Microbial shifts occur following application of Chloropicrin and 1,3-Dichloropropene across soils and crops from diverse regions. MBAO Conference, Orlando, FL Nov 2022
²Antonio Castellano-Hinojosa, Nathan S. Boyd, Sarah L. Strauss, Impact of fumigants on non-target soil microorganisms: a review, Journal of Hazardous Materials, Volume 427, 2022, 128149, ISSN 0304-3894, https://doi.org/10.1016/j.jhazmat.2021.128149.
³Yuan Zeng, Zaid Abdo, Amy Charkowski, Jane E. Stewart, Kenneth Frost. Responses of Bacterial and Fungal Community Structure to Different Rates of 1,3-Dichloropropene Fumigation. Phytobiomes Journal, 2019; 3 (3): 212 DOI: 10.1094/PBIOMES-11-18-0055-R
⁴Zhang, S., Liu, X., Jiang, Q. et al. Legacy effects of continuous chloropicrin-fumigation for 3-years on soil microbial community composition and metabolic activity. AMB Expr 7, 178 (2017). https://doi.org/10.1186/s13568-017-0475-1
⁵J. Washington, 2022. Microbial shifts occur following application of Chloropicrin and 1,3-Dichloropropene across soils and crops from diverse regions. MBAO Conference, Orlando, FL Nov 2022