Common knowledge or conventional wisdom is just that, something that is generally accepted as fact, until it isn’t. We can look throughout history and find plenty of things that were generally accepted until new discoveries challenged and disproved those things. For decades, the living, microscopic portion of our soils has been somewhat of a mystery. If the organism wouldn’t grow in a petri dish, it was difficult to know if it was present and if its’ populations were increasing or decreasing. Modern techniques have provided far greater insight into the microbial world that lives unseen in our soils. We can now extract genetic information from a teaspoon of soil and determine which organisms are present through their genetic fingerprints.
Now on to soil fumigation: the process of applying a liquid below the soil surface which subsequently transitions to the gas phase and the vapors move through the soil profile. These vapors are present from days to weeks based on the chemistry and application technique. Depending on the fumigant used, the vapors can be toxic to soil borne pathogens, nematodes, and weed seeds. This is why soil fumigants were originally put into use, to control soil borne diseases. Based on this information, it is easy to jump to the conclusion that soil fumigation would have devastating impacts on soil microbial communities. In fact, we often hear that soil fumigants sterilize the soil. Reducing populations of certain organisms such as Fusarium or Rhizoctonia are advantageous, but there are multitudes of organisms that are beneficial to plant growth and soil function, and it has been assumed that these have been equally reduced like the pathogens.
Enter modern techniques. A group of scientists at the University of Florida have been investigating the impact of soil fumigation on microbial communities and recently published some of their findings (https://www.sciencedirect.com/science/article/abs/pii/S0048969724007988?via%3Dihub)1. This group looked at soil microbial communities in a plasticulture tomato production system before and after fumigation with several different fumigant treatments as well as beds that were left untreated. First off, even the most effective soil fumigants don’t sterilize soils. There are a multitude of organisms that were found shortly after fumigation. They also found that fumigant treatments with greater than 60% chloropicrin consistently increased tomato yield, which is why producers use these products. The use of fumigants resulted in significant changes in the soil microbial communities and fumigants reduced the microbial diversity of soils, but these changes are temporary and those soils reverted to their original state by the next growing season. Some of these changes in microbial complexity could hinder some of the major functions of microbes in the soil such as nitrogen metabolism and carbon fixation. So, these findings do not come as a huge surprise to anyone who is familiar with soil fumigants and how they function.
But you know how we mentioned common knowledge earlier, well here’s the challenge to that. Most readers of this article are probably familiar with beneficial organisms that are naturally present in the soil or can be purchased and applied, often referred to as “bug in a jug” products. Some of the most common products available contain various species of Bacillus bacteria or Trichoderma fungi. These researchers found that the abundance of Trichoderma was increased after treating the soil with chloropicrin, even more than the untreated. Yes, you read that correctly. The abundance of Trichoderma was greater after treatment with chloropicrin compared to doing nothing and that change persisted until the end of harvest. A similar pattern was observed for Bacillus and Paenibacillus species, both of which serve beneficial roles in the soil.
Soil fumigants play a critical role in many production systems and are a necessity to manage major yield limiting pests. However, are these the only uses for soil fumigants? Based on this University of Florida research, could we use chloropicrin, a soil fumigant, to increase the abundance of naturally occurring beneficials like Trichoderma? Could a soil fumigant be used in the role of a bio-stimulant? That would certainly be a challenge to conventional wisdom.
Feel free to contact us to discuss these ideas further and to learn more about what chloropicrin could do in your field.
- Ref: Castellano-Hinojosa A, Karlsen-Ayala E, Boyd NS, Strauss SL (2024) Impact of repeated fumigant applications on soil properties, crop yield, and microbial communities in a plastic-mulched tomato production system. Science of the Total Environment 919: 170659; doi: https://doi.org/10.1016/j.sciotenv.2024.170659 ↩︎
