The elimination of a widely used soil fumigant has encouraged some agricultural scientists to pursue a world that knows no dirt, growing crops without soil.

The focal point of the movement is the California strawberry industry and its vigorous promotional arm, the California Strawberry Commission in Watsonville.  Strawberry production in California has been largely dependent on the use of a very effective soil fumigant that eliminated weeds, nematodes and diseases that attack strawberry plants and their fruit.

The fumigant, gaseous methyl bromide, was found as early as 1984 to contribute to depletion of the earth’s eight-mile-high ozone layer as it combined with other gasses to form CFCs. The ozone layer protects us all from harmful ultra violate rays emitted by the sun.

A full-scale, worldwide campaign to eliminate the use of methyl bromide began, and this year or next will reach its goal. It probably would have moved faster had it not been for sympathetic consideration for the mammoth contributions the strawberry crop makes to California’s economy.

Some impediments to methyl bromide’s elimination efforts came from the common sense arm of the scientific community.  It huddled behind the contention that seaweed in the world’s oceans creates more methyl bromide every day than California farmers could apply to the soil in years.  But the movement to phase out the chemical’s use was not to be denied.

The current issue of the University of California’s respected journal California Agriculture chronicles the progress and acceleration of the movement to eliminate use of the chemical for soil fumigation.  It also touches on the use of elements other than soil as the growth medium for strawberries.

The most likely candidate is coir, a material that can be created by combining cocoanut fibers, rice hulls, sterilized cow manure, almond hulls and perhaps some other inert materials in various ratios to form an almost soil-like matter. Young strawberry plants take to it like fish to water. Soil borne diseases and insects don’t seem to know how to exist in it.

Replacing soil is not that challenging for strawberry growers. Many have already adopted a practice of building knee-high mounded rows of soil as foundations for their plants. Workers travel firm walkways at ground level between the mounds to tend the plants and harvest the fruit. The beds are usually covered by plastic materials for weed and disease control, with the plants peeking through.

Total soil replacement is achieved also when plants are grown hydroponically, positioned so their roots extend downward into water, which circulates and carries enriching nutrients and compounds to prevent the growth of algae or other nuisance genetics.  In most cases hydroponic production is an indoor or greenhouse operation, which imposes certain limitations.

Before it was sentenced to oblivion, methyl bromide was used in a number of applications outside of the strawberry industry for weed and disease control.  Among crops that benefitted from its control of weeds and soil borne insects and disease were almonds, and wine grapes.

The chemical was applied by injection into the soil through tractor-pulled shanks, with the ground covered immediately afterward by tough plastic for a week or more, sealing the chemical in the soil. The plastic used was upgraded as concerns increased about the gas escaping to do its ozone layer damaging, but nothing provided a perfect seal.

It’s not clear how soilless agriculture matches up with sustainability, nor how practical it might be in large-scale applications or crops beyond strawberries, orchards for example. But once begun, research with it will take those issues into account in due time. In the meantime, don’t throw your dirt away.

 

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