Carbon sources for anaerobic soil disinfestation in southern California strawberry

Authors: DAUGOVISH, OLEG - University Of California Agriculture And Natural Resources (UCANR); VALDES-BERRIZ, MARIPAULA - University Of California Agriculture And Natural Resources (UCANR); MURAMOTO, JOJI - University Of California Agriculture And Natural Resources (UCANR); SHENNAN, CAROL - University Of California; ZAVATTA, MARGHERITA - University Of California Agriculture And Natural Resources (UCANR); Henry, Peter

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2023
Publication Date: 6/19/2023
Citation: Daugovish, O., Valdes-Berriz, M., Muramoto, J., Shennan, C., Zavatta, M., Henry, P.M. 2023. Carbon sources for anaerobic soil disinfestation in southern California strawberry. Agronomy. 13(6). Article 1635. https://doi.org/10.3390/agronomy13061635.
DOI: https://doi.org/10.3390/agronomy13061635

Interpretive Summary: Anaerobic soil disinfestation is an organic-approved method for reducing weeds and pathogen abundance in soil. This method works by stimulating anaerobic conditions in soil through the addition of a carbon source, water, and an oxygen-impermeable tarp. California strawberry growers frequently use rice bran as their carbon source, but this material is becoming increasingly expensive. This work tested two lower-priced carbon sources for efficacy in strawberry production: dried distiller’s grain and wheat middlings (a by-product of milling). Field trials were conducted in two years near Santa Paula, California. Dried distiller’s grain significantly reducted M. phaseolina viability both years; wheat middlings reduced viability of this pathogen in a single year. Both carbon sources increased yield compared with the control and reduced germination of Cyperus esculentus (yellow nutsedge). These promising results suggest that dried distiller’s grain and wheat middlings are viable and cheaper alternatives to rice bran for anaerobic soil disinfestation.

Technical Abstract: Anaerobic soil disinfestation (ASD) has been adopted in over 900 ha in California strawberry production as an alternative to chemical fumigation. Rice bran, the predominant carbon source for ASD, has become increasingly expensive. In 2021-22 and 2022-23 field studies, we evaluated 20-30% lower-priced wheat middlings (Midds) and dried distillers grain (DDG) at 6 and 7 t/acre as alternative carbon sources to rice bran. The study was placed at Santa Paula, California in September of each season in preparation for strawberry planting in October. Soil and air temperatures were 18-26 °C during that time. After incorporation of carbon sources into the top 30 cm of bed soil, beds were reshaped, irrigation drip lines installed and covered with totally impermeable film (TIF) to prevent gas exchange. Beds were irrigated to saturate the bed soil within 48 hours after TIF installation. Anaerobic conditions were measured with soil redox potential (Eh) sensors placed at 15 cm depth in all plots. Both DDG and Midds plots maintained Eh at -180 to 0 mV during the two ASD weeks, while untreated soil was aerobic at 200 to 400 mV. Permeable bags with inocula of Macrophomina phaseolina, a lethal soil borne pathogen of strawberry, and tubers of Cyperus esculentus were placed 15 cm deep in the soil at ASD initiation and retrieved two weeks later for analyses. Two weeks after that, holes were cut to aerate beds and ‘Victor’ or ‘Fronteras’ bare-root strawberry were transplanted into them. ASD with DDG reduced viable microsclerotia of M. phaseolina 49% in the first season and 75 to 85% with both carbon sources in the second season. Both ASD treatments reduced tuber germination of C. esculentus 86-90% compared to untreated soil in one of two years. Additionally, Midds and DDG provided greater sufficiency of plant-available nitrogen and phosphorus compared to untreated soil with synthetic pre-plant fertilizer and improved fruit yields 40 and 30%, respectively. ASD with these carbon sources can suppress soil pathogens and weeds and help sustain organic strawberry production in California.