SHOOT AND ROOT TEMPERATURE EFFECTS ON LETTUCE GROWTH IN A FLOATING HYDROPONIC SYSTEM

'Ostinata' Butterhead lettuce (Lactuca sativa L.) was used to study le ttuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond te mperature on lettuce growth for 35 days. Pond water temperature setpoi nts of 17, 24, and 31 degrees C were used at air temperatures of 17/12 , 24/19, and 31/26 degrees C (day/night). Pond temperature affected pl ant dry mass, and air temperature significantly affected growth over t ime. Maximum dry mass was produced at the 24/24 degrees C (air/pond te mperature) treatment. Final dry mass at the 31/24 degrees C treatment did not differ significantly from the 24/24 degrees C treatment. The 2 4 degrees C pond treatment maintained market quality lettuce head prod uction in 31 degrees C air. Using optimal pond temperature, lettuce pr oduction was deemed acceptable at a variety of air temperatures outsid e the normal range, and particularly at high air temperatures.