Soil fumigation has been an important tool in New Zealand crop production for decades because it is highly effective at managing soil pests that cause crop disease. However, it is often criticized by some for being detrimental to soil health.
There is a persistent myth that soil fumigants harm the microbiological diversity and abundance of beneficial microbes in the soil despite extensive evidence to the contrary. In light of a global focus on agricultural sustainability, it is essential to understand the real impacts of soil fumigants on soil health, using science-based criteria and best technology available.
Major advances in automated, genetic sequencing technology combined with commercially available services, such as Biome Makers (www.biomemakers.com) can now provide a detailed and comprehensive analysis of the types and abundance of microorganisms in the soil.
“In my capacity as a research and development director in the Trical Group, based in Florida, USA, I have enthusiastically embraced these new and powerful tools that allow us to study and characterize the soil microbiology genome in soils treated with our soil fumigant products globally,” says Dr. John Washington, a plant pathologist and microbiologist.
“It’s a kind of genetic barcoding: the technology can identify every organism group and their relative amounts. We can compare treated versus non-treated soils, soil fumigants versus fumigant alternatives, and the dynamics of soil microbiology and how it changes over time following any agricultural input. These tools are key in allowing the scientific and agricultural community to more fully understand the soil biology component of soil health in an objective and scientific manner, looking for positive or negative effects of our inputs and whether or not we can manipulate the soil biome to enhance crop production. Concurrently it allows us to get past the old myths and gross misinterpretation of soil fumigant impacts, for example, and focus on specific and real effects.”
“For example,” Washington says, “microbiome analysis shows that soil-applied chloropicrin and 1,3-D alter the soil biology in important but non-destructive ways. Across different crops and locations including apples and blueberry in Michigan, and ornamental and vegetable crops in Florida, our research is clearly showing that Trichoderma, a well-known group of beneficial fungi, increased 20-100 fold following soil fumigation. Population benefits lasted the entire season, and even extended into the next season in some settings, where significantly higher populations of Trichoderma persisted over the winter in northern tree crop soils. Additionally, the beneficial root-colonizing bacteria Bacillus and Pseudomonas, which produce plant-active hormones, increased dramatically following soil fumigation. This likely explains why we see major increases in healthy root growth in crops where soils were fumigated prior to planting. And one of the most surprising findings is that no evidence was found that diversity or abundance of soil microorganisms suffered when soil samples collected 30-90 days after treatment were analyzed.”
Washington says that this evidence is being corroborated in studies being conducted by university researchers at the University of Florida who are addressing concerns about agricultural sustainability of soil fumigation.
“Not all of these conclusions are novel,” says Washington, “even in the older literature where these new analysis tools were not used, the impacts of soil fumigation on soil microbiology were largely positive, albeit temporary.”
In late December 2021, University of Florida plant pathologists released a meta-analysis – 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.
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%. 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.
Washington is now working with Leicester’s Soil Solutions in New Zealand, who is coordinating the soil biome research in apple and melon and blueberries. “We are initiating these studies with these growers in mid-May and this will provide us with specific and comprehensive data in New Zealand crops, something we plan to present locally when the results are complete,” says Washington.
“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.”