Optimizing Anaerobic/Biological Soil Disinfestation Amendment Composition Through Soil Fermentation Experiments

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Commodities

• Fruits: berries (strawberries)

Practices

• Pest Management: biological control, soil disinfestation, soil fermentation

Anaerobic (or biological) soil disinfestation (ASD) is a promising technique for control of soilborne plant pathogens, including fungal pathogens. Treated soil is amended with easily decomposable organic amendments, covered with plastic film, and saturated via irrigation for a brief time period to induce anaerobic conditions. ASD was developed as an alternative to chemical fumigation, which has severe ecological and human health hazards. Known mechanisms of ASD fungitoxicity include release of fungicidal volatile fatty acids (VFAs) and dissolved Fe²⁺ and Mn²⁺ because of anaerobic soil conditions, and changes to the soil microbial communities. However, little is known about how soil amendments (substrates) used in ASD, soil texture, and soil pH affect the balance of VFAs produced and the soil concentrations of dissolved Fe²⁺ and Mn²⁺, important components in suppressing soilborne fungal pathogens. In this proposed study, we will perform soil incubation studies on Fusarium oxysporum (Fo)-infested soils of varying soil texture to examine how substrate composition influences VFA and reduced metal balance. We will first perform soil incubation studies on soils of varying texture amended with varying levels of soybean protein isolate and dried molasses (to vary amendment protein to carbohydrate ratio), followed by greenhouse studies utilizing strawberries grown in soil infested with Fo and amended with a range of amendment types, and either limed or not limed (to alter soil pH during treatment). Data from this experiment will be used to identify the optimal amendments for not only Fo suppression, but also for strawberry plant health.

1. Evaluate the effects of ASD amendment substrate composition (protein-to-carbohydrate ratio) and lime application on Fo suppression and soil VFA, Fe²⁺ and Mn²⁺ balance in soils of varying texture.

Hypothesis: High-protein amendments and liming are expected to favor increased production of long-chain VFAs such as n-butyric and isovaleric acids compared to high-carbohydrate amendments and therefore enhance Fo suppression. Additionally, the efficacy of VFAs in suppressing Fo is expected to be lower in fine-textured than in course-textured soil due to greater levels of VFA adsorption by clay and silt particles. However, this is also expected to be counterbalanced by the release of greater concentrations of Fe²⁺ and Mn²⁺ into soil solution as silt and clay minerals are typically richer in Fe and Mn than sand minerals.

2. Evaluate VFA and reduced metal balance, plant health, and response of soil fungal populations (Fo, Trichoderma spp., mycorrhizal fungi) associated with different ASD amendments.

Hypothesis: High-protein/high-metal amendments such as spent brewer’s yeast and Azolla meal will both be expected to enhance production of long-chain VFAs such as n-butyric and isovaleric acid in addition to Fe²⁺ and Mn²⁺ compared to carbohydrate-based amendments such as wheat bran and dried molasses. Therefore, high-protein/high-metal amendments are expected to not only be more effective for suppressing Fo but also maximize benefits to plant health and beneficial soil fungi by supplying diverse biochemical substrate types as well as macro- and micronutrients.