Double digging in the KSU high tunnel
Submitted by mkbomford on Wed, 2008-02-20 15:25.
At the Kentucky State University Research and Demonstration Farm we grow organic cool season crops through the winter in an unheated high tunnel. Tomorrow we'll be serving freshly-harvested carrots, beets, lettuce, kale, and mustard greens to about 50 farmers who attend one of our regular workshops on sustainable agriculture. We'll also give them sweet potatoes that we have stored from our fall harvest and pasture-raised chicken that we use to cycle and spread nutrients and manage weeds.
High tunnels have great potential to allow year-round production through chilly winters like ours. They are low-cost structures, affordable to small and limited-resource farmers.
High tunnel growing has its problems, though:
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- Manufacturing the materials for a plastic-covered house requires energy. I estimate the embodied energy in our structure to be about 6 GJ per year, over the lifetime of the materials we used. We have opted for two layers of plastic, held apart by a 60 W blower fan that operates continuously. The air pocket between the layers improves the insulating capacity of the tunnel, but producing the electricity to run the blower fan consumes another 6 GJ, assuming the coal-fired power plant that generated the electricity was 30% efficient. For that kind of energy investment we could truck lettuce to Kentucky from California.
- High tunnels are cool and humid through the winter, creating ideal conditions for the fungus Sclerotinia sclerotiorum, which attacks many of our cool season crops we grow. Finding tactics to combat S. sclerotiorum that are compatible with organic standards has become a major research focus for us.
- Because it never rains in a high tunnel, salts that accumulate near the soil surface don't leach away. We don't use synthetic fertilizers that tend leave salt deposits, but we have used some fertilizer derived from feather meal. Animal byproducts tend to lead to more salt accumulation than plant-based composts.
We have been double-digging in an effort to encourage water movement through our soils, encourage salts to leach down through the soil profile, and improve our heavy clay soil.
Here is a video of Brian Geier double-digging one of the beds in our high tunnel:
The two and a half minute video shows about two hours of digging for Brian.
(That's me on the guitar and backup vocals in the soundtrack, singing with my friends Helena Triplett on banjo and Barbara Walker on washboard. Together we were the Raging Acorns.)
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