Anaerobic Soil Disinfestation; Its agroecological significance in California strawberry production

JOJI MURAMOTO

DEPT. OF ENVIRONMENTAL STUDIES

UNIVERSITY OF CALIFORNIA, SANTA CRUZ

Session 2: Organic agriculture and scale: Balancing environmental and consumer demandsFood, Agriculture and Human Impacts on the Environment: Japan, Asia and Beyond, November 6-7, 2017, UC Berkeley

Outline

California strawberries: conventional and organicAnaerobic soil disinfestation (ASD)Agroecological significance of ASD in CA

strawberries

California Strawberries $1.9 billon values in 2012 20-30% of world

production ~85% of US production 15,765 ha in 2014 by ~300

growers Av. yield: 70 tons/ha Year-round harvest

San Francisco

Los Angeles-20

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Santa Cruz, CA (1980-2010 Normal)

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Santa Cruz

Chemical fumigation• Methyl bromide + chloropicrin• Control soilborne disease and

weeds, increase yield• Core technology for the large-scale

mono-cultural strawberry production for the last 50 years

(Wilhelm and Koch, 1956)

Ozone Hole and Montreal Protocol

• Ozone layer: Earth’s “sun screen” – protects people, plants, and animals from ultraviolet radiation

• Skin cancer is the most common cancer in the US 1992: Methyl Bromide added to Montreal Protocol 2005: 100% phase out with limited exemptions in developed countries 2016: Expiration of Critical Use Exemption

Residential proximity to methyl bromide use during the second trimester was associated with markers of restricted fetal growth

“Although critical use exemptions for methyl bromide use are being phased out, the lack of fumigant alternatives may prolong its use in the state of California.”

Organic/Conventional Comparative On-Farm Strawberry Experiment at the Swanton Berry Farm 1987-1990 (Gliessman et al., 1996)

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Organic Strawberry Acreagein California 2000-2017

(California Strawberry Commission)

CSA/Farmers markets/Local natural food stores

Walmart/Whole Foods

Costco

11 % of total strawberry acreage in CA

Outbreak of Verticillium wilt at CASFS farm, UCSC in 2001 and 2002

Anaerobic Soil Disinfestation (ASD)

Four-step process1. Incorporate labile C-source2. Moisten the amended soil3. Cover by plastic mulch to limit oxygen

supply4. Maintain anaerobic decomposition

(Van Bruggen, 2014)

• Developed in the Netherlands and Japan independently ~2000 as a biological alternative to fumigation

• Principle: Acid fermentation in anaerobic soil

(Chiba prefecture, 2002)

Picture of paddy-upland mixed farming in Nara, Japan. Circa 1890.

Paddy-Upland Rotation: > 400 years of history in Japan (Tokunaga, 1997)

Pathogen

Temperature

C sourceType & Rate

Organic acids

Microbial shifts

Anaerobiosis

Water Depth and time

Crop genotype

Soil type /management history?

ASD Management Triangle (Shennan et al, 2014)

Anaerobic Soil Disinfestation (ASD) in California strawberries

1. Broadcast rice bran at 9 tons/acre

2. Incorporate bran3. List beds4. Cover w/ plastic mulch5. Drip irrigate total 1 to 2

ac-in over 3 wks6. Leave 3 wks and monitor

soil Eh (redox potential)

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5 6

ASD provides comparable fruit yield with fumigant

ASD-treated strawberry fields in California

•80% organic sites•20% conventional sites

•~20% of CA organic strawberry acreage•~2.5% of CA total strawberry acreage

Agroecological Evaluation of ASD

1. Optimize use of locally available resourcesPartial replacement of rice bran with cover crop

Use of cover crop as a partial C-source for ASD

ASD-Standard: rice bran 13 t/ac

ASD-CC: Sudan grass 1.4 tons-d.w./ac + rice bran 6 t/ac

Use of freshly mowed cover crop with reduced rate of rice bran created a stronger anaerobic condition than the standard ASD

Aerobic

Anaerobic

Agroecological Evaluation of ASD

1. Optimize use of locally available resourcesPartial replacement of rice bran with cover crop

2. Minimize losses of soil, nutrients, water and energyN2O emission, NO3-N leaching evaluation in progress

3. Optimize soil conditions for plant growth Tactical use of rice bran, wheat bran to supply nutrients

4. Promote genetic and species diversification Increased soil fungal diversity

Effect of treatments on number of fungal taxa and diversity of the community, determined by analysis of terminal restriction fragment length polymorphism data

of DNA from soils of strawberry field trials at the Watsonville site, 2011/12

(Shennan et al., 2017)OTU: Operational taxonomic unitShannon H: Shannon’s diversity index

Agroecological Evaluation of ASD

1. Optimize use of locally available resourcesPartial replacement of rice bran with cover crop

2. Minimize losses of soil, nutrients, water and energyN2O emission, NO3-N leaching evaluation in progress

3. Optimize soil conditions for plant growth Tactical use of rice bran, wheat bran to supply nutrients

4. Promote genetic and species diversification Increased soil fungal diversity

5. Favor beneficial interactions and synergies among agrobiodiversity components

Integration of crop rotation, genetic resistance, and ASD

Integrated Soil Health Management (ISHM)for Organic Production (Concept)

Soil health diagnosisTraditional/Molecular-base biological test

• Soil microbial community• Beneficial/pathogenic microbes• Diversity, keystone species

Physical, biochemical and chemical tests

Targets

• Crop• Yield• Market• Ecosystem services

Selecting practices• Variety • Crop rotation/cover crop • Soil amendment/fertilizer

• Compost, MSM, chitin….• ASD (C-source options)

Site-specific ISHM

Production

Location specificKnowledge intensive

Conclusions ASD: agroecological practice based on the principle of

acid fermentation in anaerobic soils Reducing external C-source and costs may be

accomplished by using cover crops/crop residues ASD increases soil fungal diversity Environmental impacts: N2O gas emission, NO3-N leaching

need further studies Future non-fumigant systems in CA and beyond will be

location specific and require integration of crop rotation, genetic resistance, and other tactics such as ASD

Thank you!Question?

joij@ucsc.edu