Biofumigation for soil health in organic high tunnel and conventional field vegetable production systems

Biofumigation for soil health in organic high tunnel and conventional field vegetable production systems

Summary

This project tests biofumigation – a soil-borne disease management strategy using natural chemicals from brassicas – as a control for two broad-spectrum diseases that each pose a severe challenge to a different emerging vegetable production system in Kentucky. The fungus Sclerotinia sclerotiorum thrives in cool conditions, and attacks most of the crops grown in a system developed by Kentucky growers to produce organic vegetables year-round in solar heated high tunnels. Another fungus, Phytophthora capsici, spreads in warm weather and attacks many of the crops grown by the increasing number of farmers switching from tobacco to field vegetable production in our region. We hypothesize that biofumigation can be adapted to both the high tunnel and field vegetable system to manage these diseases while building soil organic matter and enhancing soil microbial activity. We are conducting a series of laboratory studies to identify promising biofumigant crops for each disease, followed by on-farm field trials adapting the biofumigation strategy to each system. This research responds to specific emerging disease threats and addresses two of the most important research topics identified by local growers in a survey distributed at a SARE-funded workshop.

Objectives/Performance Targets

• 1. Identify brassica varieties that inhibit survival and growth of S. sclerotiorum and P. capsici in lab-based bioassays.2. Determine the potential of brassica residue incorporation and solarization – alone and in combination – to reduce disease pressure from S. sclerotiorum and build biologically active soils in high tunnels used for year-round vegetable production.

  3. Determine the potential for brassica and non-brassica winter cover crops to reduce disease pressure from P. capsici and build biologically active soils in field vegetable production systems.

Accomplishments/Milestones

• Found glucosinolate concentration was highest in aboveground tissue of field-grown mustards (~70 umol/g), moderate in high tunnel-grown mustards (~40 umol/g), and lowest in greenhouse-grown mustards (~25 umol/g).Found ‘Pacific Gold’ mustard variety offered a superior combination of biomass production, cold tolerance, and glucosinolate production, relative to other mustards tested.

  Found that ‘Pacific Gold’ mustard performed best when planted in late April, with biomass produced at flowering falling steadily with later planting dates, up to late June.

• Repeated tests of burial depth and treatment period on soil temperature and sclerotial susceptibility to biofumigation and solarization in commercial high tunnels.Confirmed that solarization for one month was very effective, killing 100% of sclerotia 5 cm below the surface.

  Found that biofumigation with 1 kg of ‘Pacific Gold’ mustard per square meter did not reduce sclerotial survival.

  Found that ~0.16 g of fresh ‘Pacific Gold’ mustard tissue per mL of soil killed half of sclerotia after 24 hours of exposure.

  Measured extracellular enzyme activity of solarized and unsolarized soils after 2 and 6 weeks of solarization.

• Recorded no reports of P. capsici in Kentucky field vegetables in summer of 2008 (second consecutive drought year).Inoculated university research land with P. capsici, to provide suitable site for 2009 field study.

  Found that P. capsici is much more susceptible to biofumigation than S. sclerotiorum in lab assays, with complete inhibition of oospore germination at ‘Pacific Gold’ tissue concentrations above 0.12 g per mL of soil.

  Observed interaction between biofumigation with ‘Pacific Gold’ mustard and addition of Organica Plant Growth Activator. These soil amendments together increased cucumber seedling growth in the presence of P. capsici, but neither additive had an effect on its own.

Impacts and Contributions/Outcomes

• Solarization for organic control of white mold in high tunnels. Kentucky Fruit and Vegetable Conference and Trade Show, Lexington, KY, 01-08-08 (https://projects.sare.org/wp-content/uploads/Digger_201602_solarization.pdf).Sustainable Soil-Borne Disease Management:
  A Study of the Effects of Soil Solarization and Biofumigation on Sclerotinia sclerotiorum. Southern Sustainable Agriculture Working Group Meeting – Au Naturel Farm Field Trip, Smiths Grove, KY, 01-16-08 (http://organic.kysu.edu/SSAWGPoster.pdf).

  Organic Agriculture Roundtable. Women in Agriculture Conference, Lexington, KY, 10-31-08

  Effect of Glucosinolate Exposure on Sclerotinia sclerotiorum and Phytopthora capsici. Kentucky Academy of Science Meeting, Lexington, KY, 11-01-08 (http://organic.kysu.edu/BomfordKAS2008.pdf).

  Effect of Planting Date on Biomass Production by Brassica juncea var. ‘Pacific Gold’ Cover Crops. Kentucky Academy of Science Meeting Lexington, KY, 11-01-08 (http://organic.kysu.edu/Evaluation%20of%20Various%20Planting%20Dates%20of%20Brassica%20Juncea.pdf).

  A Simplified Procedure for Glucosinolate Quantification. Kentucky Academy of Science Meeting, Lexington, KY, 11-01-08 (http://organic.kysu.edu/GlucosinolateQuant.pdf).

  Vegetable Production in High Tunnels. Fairview Produce Auction, Christian County, KY, 12-10-08 (http://organic.kysu.edu/HighTunnelVeg.pdf).

  Fresh Tomatoes in January: Can B-ISA Make them Sustainable? Building-Integrated Sustainable Agriculture Summit, Berkeley, CA, 12-13-08 (http://organic.kysu.edu/B-ISA-HighTunnel.pdf).

• Grower cooperators and other growers with established high tunnels have started incorporating solarization periods and mustard plantings into high tunnel rotations.At least 5 farmers who have attended our workshops have been inspired to erect high tunnels.

• Organic.kysu.edu website, featuring information about this study, attracted 25,922 page views from 16,406 unique visitors in 2008.Updated webpage summarizes current study results (http://organic.kysu.edu/biofumigation3.shtml).

  13-minute streaming video summarizes objectives, methods and results of high tunnel study (http://organic.kysu.edu/SclerotiniaVideo.shtml).

  Video available through popular EnergyFarms blog (http://energyfarms.wordpress.com/2008/11/26/organic-disease-management-in-high-tunnels-a-little-piece-of-the-sustainable-agriculture-puzzle/).

• G.F. Antonious, M.K. Bomford & P.C. Vincelli. 2009. Screening brassica species for glucosinolate content. Journal of Environmental Science and Health 44: 311-316.

• Undergraduate student John Rodgers received hands-on training in research techniques through his involvement with this project.
  Project participants have received numerous requests for information about winter vegetable production in Kentucky.
  The number of certified organic farms in Kentucky doubled (from 52 to >100) in 2008.
  We expect recommendations generated by this research to enhance the sustainability of vegetable production systems by building soil health, reducing the need for external inputs, and allowing diverse crop rotations that include the many crops susceptible to P. capsici and S. sclerotiorum.
  We anticipate that new disease management tactics generated by this project will encourage Kentucky farmers to consider vegetable production as a high value alternative to tobacco.

Collaborators: