oa Agrochemophysica - Plastic tunnels : a study of air temperature

Volume 12, Issue 1
  • ISSN : 0302-7112



Air temperature was measured at five different heights in a plastic tunnel using shielded resistance thermometers. During the day, changes in air temperature with height above ground of about 15,0 �C m-1 can occur (lapse conditions) whereas in the night, �1,5 �C m-1 is possible (inversion conditions).Rapid cooling in the tunnel occurs after sunset (5,5 �C h-1 inside the tunnel compared to 3,5 �C h -1 outside) as a result of the plastic cover being highly transparent to long wave radiation. This rapid cooling causes condensation of water on the inside of the cover. The plastic cover with its water film being virtually opaque to long wave radiation and being a good radiator, provides a means of considerably reducing the cooling rate. As a result of the reduced cooling, the inside air temperature is less than that outside between about 16h30 (sunset) and 18h00 (the attainment of an inside relative humidity greater than 85 %). The maximum inside air temperatures were, on average, 4,2 �C greater than the outside maxima. The inside minima were 1,3 �C greater than the outside minima. For the days on which frost occurred outside the tunnel, the average inside air temperature was 1,4 �C. Outside the tunnel, the air temperature was less than 0 �C on ten occasions whereas the inside air temperature was never less than 0,5 �C.

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