Mitigating on-farm toxins using fungi: a case study on two farms.

This grant encompasses two different projects: (1) remediation of organophosphates in an organic-transitional farm and (2) evaluation of and remediation of toxins on a fire affected ranch.

Part 1: Reduction of Herbicides and Pesticides by Fungi on Organic-Transitional Vegetable Farm

Initial soil testing

The first step in the process was to identify what pesticide residues may be present. Historical pesticide use was determined by pulling the spray records of the previous 2019 year from the records of the regional Ag Commissioner. According to these records the previous years applications included several broad spectrum herbicides.

These included paraquat dichloride (Gramoxone herbicide), acetamiprid (Assail insecticide), sethoxydim (Poast herbicide) and saflufenacil (Treevix herbicide). In addition, by personal conversation with the previous farm manager it was discovered that additional herbicide application occurred, not included in the spray records.  It was learned that annual applications of glyphosate (Roundup herbicide) and glufosinate  (Liberty herbicide) had also been applied to the orchard in the previous year.

To determine which pesticides residues had persisted into the 2020 year, a sample plot was selected to test for the full panel of know pesticide applications.  Samples were taken to the depth of 5”, in three sample locations, then homogenized prior to being submitted for laboratory testing. Labs were unable to test for paraquat dichloride due to its volatility, likewise was glufosinate was not an available test. In addition for testing for glyphosate, samples were also tested for aminomethylphosphonic acid (AMPA) one of the primary degradation products of the glyphosate. Of the materials tested for, only glyphosate and AMPA were present.

The section of field dedicated to the study was separated into 6 different 10’ X 25’ plots. Each plot was sampled in three separate locations at the depth of 5”, the sample sites were flagged for resampling at a later date, and the samples from each respective plot were homogenized and submitted to the lab for glyphosate and AMPA analysis.

For the purpose of this study 3 of the plots received a fungal inoculation, and seeded with cover crop, and 3 plots served as controls. Each 10’ X 25’ plot was assigned a number 1-6, and treatments were assigned at random.

For each Fungal Treatment Plot received 0.5 cubic yard (14 cubic feet) of rice straw/rice hull oyster mushroom spawn (mushroom impregnated substrate). This mushroom spawn was rototilled into the top several inches of soil, and seeded with cover crop

(vetch, clover, faba, wheat).

The Control Plots received one of the three following treatments respectively:  application of 0.5 cu.ft. of uninnoculated rice straw/hulls and seeded with cover crop  (termed “mulched” for the purposes of this study), cover crop only, and no treatment/no  irrigation/no mulch. Overhead irrigation was applied to all of the plots over the duration of the study sufficient to sustain cover crop, with the exception of the “no treatment” plot which was not rototilled, left as bare soil, and no irrigation was applied.

After the period of 60 days, the cover crop began to flower; the point in time at which cover crops are typically mowed/tilled-in. At this time the soil was resampled. The original 3 sample sites per plot were identified, sampled to the depth of 5” and homogenized prior to be submitted to the lab for analysis.

Part 2: Reduction of Fire Borne Toxin on Fire-affected Ranch 

The second project is emerges from the “Camp Fire” which ravaged Northern California in November of 2018, totally leveling the town of Paradise.  As we continue to see fire-storm’s impact on the urban-agrairian gradient of California, it is important to understand the impact of these fires on soils. 

The Camp Fire Resource Monitoring and Research Symposium on June 4th at Chico State University Chico, brought together researchers and extension agents who have been examining impacts and contamination in the wake of the Camp Fire and lessons learned from the Santa Rosa and Carr fire. Jackson Webster and Sandrine Matiasek of CSU Chico have been sampling creeks throughout Butte County. Their preliminary research indicates that fire baked soils are hydrophobic and surface flow is precipitating persistent organic toxins and heavy metals into the waterways. The resounding narrative from the symposium is that very little is known about rates of contamination in soils (and virtually no testing for dioxins is being done). 

TurkeyTail Farm was one of the farms destroyed during the 2018 Camp Fire. The charred remains of the barns and water system were removed by debris removal contractors, but several areas went unaddressed by this service. Areas that had vehicles and sheds have not been tested for heavy metals and there was no testing for persistent organic pollutants like dioxin, benzene and polycyclic aromatic hydrocarbons. One of the purposes of this study is to get baseline information on the toxins present after forest and structural fires and to build on research already being performed.

The damage to the property was extensive. The property was seated on a steep hill with dense vegetation that had burned at very high temperatures. The RV itself was completely incinerated, leaving just the scorched frame. In addition, the frame was stuck behind two burnt shipping containers with no other access points for debris removal. Over a year after the fire event all the ashen debris remained in place.

 A composite sampling of 5 different sites in the ash footprint of the RV were collected and tested for heavy metals, benzenes, dioxins, and PAHs. Heavy metals and dioxins were detected.

For the purpose of this project Oyster Mushroom (Pleurotus ostreatus) mushroom  “spawn bags” were used. “Spawn bag” is the mushroom farming industry term for straw/woodchip filled bags with the fungus growing in it.  This mushroom spawn was incorporated in to the debris by hand and top dressed with a layer of Jute Landscape Fabric and straw that had been sterilized in calcium hydroxide. These layers served for moisture protection, but also as an indicator of active mycelial growth.

Oyster mushroom (Pleurotus ostreatus) mycelium grown on rice straw served as a source of fungal inoculum (termed spawn). To grow oyster mushroom spawn, rice straw is pasteurized in a 180 degree Fahrenheit water, drained, then allowed to cool. The straw  is inoculated at the rate of 1 part myceliated wood chip spawn to 10 parts pasteurized straw, and then placed in clean bags to incubate for two weeks. After a period of two weeks the fungus completely colonizes to straw and is ready to apply to the field.

To approximately 1 cubic yard of mushroom spawn was used to inoculate each 20’ X 20‘ plot. To maximize soil-mushroom contact, the 20’ X 20’ plots were rototilled lightly to loosen the soil surface, the mushroom spawn was shredded across the plot, and tilled again to integrate mushroom matter and maximize mycelial contact. The plot was then covered with oyster mushroom impregnated jute landscape fabric for moisture retention and additional mycelial mass. Finally the plot was mulched with additional rices straw to protect mushroom spawn and retain moisture. Overhead irrigation was applied as needed to sustain the fungus

Fungus was permitted to grow for a duration of ~6 months, during which it was monitored for active mycelial growth and mushroom emergence. After this period the soil was resampled for contaminates for comparison to baseline levels.