At the 2013 GroSci conference this summer, full name: The International Symposium on Growing Media and Soilless Cultivation, I had a chance to tour the growing operations of some of the major players in the international floriculture world. The Dutch are definitely not messing around when it comes to floriculture, in fact The Netherlands is the world’s largest exporter of ornamental plants and cut flowers.
At Deliflor Chrysanten, the world’s largest Chrysanthemum breeder, we learned about some of the challenges of growing in field soil under glass. Many greenhouses have cement floors and use soilless media to produce plants in pots, but some leave the soil exposed and use it for cultivation. With continuous cultivation of the same or similar crop on a single patch of soil comes a build up of pathogens, especially fungal pathogens that specialize in infecting that particular crop. Many of these fungal pathogens like Verticillium spp. can form resting structures in the soil that persist for long periods of time. What are your options as a grower in this type of production system?
1) Move the greenhouse to a different patch of soil (OK, not really an option because of the heavy up front investment in the greenhouse and land. High tunnels are designed to be moved…greenhouses, get out of town!)
2) Spray/ fumigate the soils with synthetic chemical fungicides (Effective, but carries an environmental burden)
3) Steam sterilize the soils in situ (Current method of choice, less toxic than fungicides, but carries a high fossil fuel cost and therefore a different kind of environmental burden)
4) Biological soil disinfestation
What is biological soil disinfestation? It is a technique developed separately in Japan and The Netherlands as a biologically based crop disease management strategy. The basic principle is that a carbon based substrate is added to the soil, then the soil is covered with an impermeable layer. Oxygen levels rapidly decrease in the soil as soil microbes consume the feast provided by the added organic matter. Anaerobic microorganisms become active in the soil in the absence of oxygen and contribute to the build up of compounds in the soil that are toxic to the resting structures of fungal plant pathogens (most likely organic acids). The tarp is removed and the soil is allowed to stabilize for a few days before planting while aerobic microbes become active again and the toxic compounds are degraded.
We heard from Henk Meints of Thatchtec who has been carrying out research and development for specialized blends of organic matter for use in soil resetting.
A special thanks to Paula van Ommen for allowing me to use her beautiful photos of these farm tours.