Steaming the Beds: Organic Farming Research for More Effective Agricultural Practices
Since 2023
The Scientific Method has been chosen to assess the impacts of "steaming" raised organic tomato beds in high tunnels because it offers a flexible framework that can be adapted to various research contexts and findings during the course of the experiment:
Observation: For nearly 30 years, Hillandale Farm has been growing organic tomatoes in raised beds that are infected by the Verticillium Wilt. Every year, this wilt begins debilitating the plants' vascular system by colonizing the V. fungi in the xylem tissue of the plant until it begins to block the transport of water and nutrients. This slow weakening process can reduce the robustness of plants, cause stunting, reduce the size and yield of fruit, and will ultimately kill the host. In some years, mortality has risen to ~50%, greatly impacting the financial sustainability of the Hillandale Farm organic growing operation.
Hypothesis: By using IPM and cultural practices, Hillandale Farm (HF) embarked on a long and arduous journey to raise tomato plants organically, adhering strictly to USDA NOP standards, in soils infected by the Verticillium dahliae. This decision was made after being advised by the URI Extension Service in 1997 that any such attempt would be futile in soils contaminated by this wilt. Practices like grafting desirable fruit bearing hybrid plants onto robust rootstock, modifying irrigation management regimes, introducing beneficial fungi and bacteria to soil, and other means of intervention were employed over 25+ years with some degree of success; however, mortality rates remained relatively high on average, which prompted the consideration of steaming beds before planting every year. After some debate around the anticipated collateral damage to the soil microbiome, HF decided to experiment by steaming 2-3 beds in each high tunnel over the past 3 years (2023 - 2025), comparing & contrasting the treated beds to the untreated ones.
Prediction: The first 6-8" of soil horizon in beds treated with a steamer - provided by the RI Southern Conservation District - would have most of the bacteria and fungi, both beneficial and pathological, eradicated by the steam. Beneficial microbes would be successfully reintroduced to the organic soils after steaming using the proprietary HF compost every year, resulting in a win-win situation. It was further predicted that the ensuing yields would be boosted due to either the eradication of the Verticillium fungi or a reduction in their colonies, slowing the onset of the plant disease and plant mortality rate. It is also anticipated that the treated beds will show a decrease in the diversity and overall concentration of microbial aggregates (colonies of good bacteria and fungi) in the soil, something that will be analysed under a microscope and hopefully reportable in the fall of 2025. And, lastly, due to the recolonization of the V. Dahliae after steaming beds, the competent resteaming of beds annually or biannually will be necessary in order to maintain plant health and higher yields of tomatoes on a per plant and annum basis.
Experimentation: The Control in each high tunnel were the untreated beds (not steamed), and the experimental group were the steamed beds. All beds, controlled and treated, received the same compost, organic liquid fertilizers, and other miscellaneous organic inputs.
Data Analysis: The data being collected from the experiment is ongoing and represented mostly by observation of plants in terms of robustness, the presence of disease symptoms, the mortality rate, and ultimately by overall yield. While the study is non-conclusive, observations and yields of plants between treated beds and untreated ones are markedly different:
Conclusion:
Observation: For nearly 30 years, Hillandale Farm has been growing organic tomatoes in raised beds that are infected by the Verticillium Wilt. Every year, this wilt begins debilitating the plants' vascular system by colonizing the V. fungi in the xylem tissue of the plant until it begins to block the transport of water and nutrients. This slow weakening process can reduce the robustness of plants, cause stunting, reduce the size and yield of fruit, and will ultimately kill the host. In some years, mortality has risen to ~50%, greatly impacting the financial sustainability of the Hillandale Farm organic growing operation.
Hypothesis: By using IPM and cultural practices, Hillandale Farm (HF) embarked on a long and arduous journey to raise tomato plants organically, adhering strictly to USDA NOP standards, in soils infected by the Verticillium dahliae. This decision was made after being advised by the URI Extension Service in 1997 that any such attempt would be futile in soils contaminated by this wilt. Practices like grafting desirable fruit bearing hybrid plants onto robust rootstock, modifying irrigation management regimes, introducing beneficial fungi and bacteria to soil, and other means of intervention were employed over 25+ years with some degree of success; however, mortality rates remained relatively high on average, which prompted the consideration of steaming beds before planting every year. After some debate around the anticipated collateral damage to the soil microbiome, HF decided to experiment by steaming 2-3 beds in each high tunnel over the past 3 years (2023 - 2025), comparing & contrasting the treated beds to the untreated ones.
Prediction: The first 6-8" of soil horizon in beds treated with a steamer - provided by the RI Southern Conservation District - would have most of the bacteria and fungi, both beneficial and pathological, eradicated by the steam. Beneficial microbes would be successfully reintroduced to the organic soils after steaming using the proprietary HF compost every year, resulting in a win-win situation. It was further predicted that the ensuing yields would be boosted due to either the eradication of the Verticillium fungi or a reduction in their colonies, slowing the onset of the plant disease and plant mortality rate. It is also anticipated that the treated beds will show a decrease in the diversity and overall concentration of microbial aggregates (colonies of good bacteria and fungi) in the soil, something that will be analysed under a microscope and hopefully reportable in the fall of 2025. And, lastly, due to the recolonization of the V. Dahliae after steaming beds, the competent resteaming of beds annually or biannually will be necessary in order to maintain plant health and higher yields of tomatoes on a per plant and annum basis.
Experimentation: The Control in each high tunnel were the untreated beds (not steamed), and the experimental group were the steamed beds. All beds, controlled and treated, received the same compost, organic liquid fertilizers, and other miscellaneous organic inputs.
Data Analysis: The data being collected from the experiment is ongoing and represented mostly by observation of plants in terms of robustness, the presence of disease symptoms, the mortality rate, and ultimately by overall yield. While the study is non-conclusive, observations and yields of plants between treated beds and untreated ones are markedly different:
- Grafted plants unaffected by Verticillium are typically grown over a 8-9 month period and have had an historical average yield of 40+ pounds of tomatoes.
- In treated beds, HF is witnessing more robust grafted plants that either successfully stave off the fungus infection or show a substantially slower infection rate, thus prolonging the vegetative life and yield of tomatoes, which is either consistent with the historical average harvest of 40+ or within ~10 lb of reaching it.
- Grafted plants in untreated beds are showing early signs of infection, lacking robustness, stunted, and generally dying off after yielding < 15 lb. of tomatoes.
- The flavor and overall character (form, size and locular structure) of the fruit does not appear to be significantly different between plants in treated and untreated beds, although more testing and tasting will occur during the summer of 2025 with additional reporting thereafter.
- Microscopic analysis of the soil microbiome is planned for the fall of 2025 during a learning expedition with Johnson & Wales University and will be reported later in the year.
Conclusion:
- Steaming beds either slows the onset of the disease or reduces the presence of verticillium to the extent that certain plant phenotypes can live out a normal life cycle with higher yields expected of grafted plants, barring of course any nutrient deficiencies or pest infestations.
- Steaming does not appear to completely eradicate the Verticillium dahliae but instead reduces their presence in the soil, effectively providing a more even "playing field" and balanced soil microbiome.
- The design of the steamer and its entire apparatus matters in terms of the efficacy of the steaming treatment (temp. depth, area), as some beds seem to be less responsive in terms of plant health. Likewise, the operator of the steamer needs the proper training to remove or at least reduce the margin for human error in order to maximize the results of treatment.
- Since soils act like a "living bridge" and are responsible for the decomposition and mineralization of organic matter, their health determines the long term productivity of plants as well as the nutrient density and other healthy attributes (polyphenols, carotenes, amino acids, etc.) in the fruits, vegetables, and proteins grown in and above them. Hence, until more analysis occurs, it's too early to report on the effects of steaming on the overall health of the soil microbiome and associated health benefits.
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