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market-farming - Re: [Market-farming] Lettuce in April

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  • From: "Bill Shoemaker" <wshoemak AT inil.com>
  • To: "Market Farming" <market-farming AT lists.ibiblio.org>
  • Subject: Re: [Market-farming] Lettuce in April
  • Date: Thu, 24 Apr 2003 08:09:04 -0500


> If I recall
>correctly, several catalogs carrying row covers mention that row covers of
>the same density as mine have about an 80-90% light transmission
capability.
>The 4 degree temperature differential you mention would most likely apply
>during overnight lows in the 30's but I question that during the daytime
>when the sun would be shining directly onto black plastic without the row
>cover. There is one good way to find out. Place thermometers on the
>plastic both under and outside of the row covers and compare.

Marlin

I did that kind of work back in the 80's and 90's. We found that
overnight lows were indeed higher under the covers but only by 1-2 degrees,
most nights. But during the day, the high temps under the spun-bonded
tunnels tended to be 8-11 degrees higher at their peaks if the sun was
shining. If it was mostly cloudy, there would still be a warm up but it
would be less, usually around 4-5 degrees. Black plastic will warm the air
around the plant but because the air isn't "captured" like it is in a
tunnel, the heat doesn't accumulate so peak temperatures don't get as high
as they do inside covers. And you're right about the shading effect at
around 80-90 % of full sunlight. It depends on the grade of the spun-bonded
material you use for a tunnel and how much debris has become lodged in it.

Bill Shoemaker
Sr Research Specialist, Food Crops
Univ of Illinois - St Charles Hort Research Center





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