Shoot and root temperature effects on lettuce growth in a floating hydroponic system

'Ostinata' Butterhead lettuce (Lactuca sativa L.) was used to study lettuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond temperature on lettuce growth for 35 days. Pond water temperature setpoints 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 plant dry mass, and air temperature significantly affected growth over time. Maximum dry mass was produced at the 24/24 degrees C (air/pond temperature) treatment. Final dry mass at the 31/24 degrees C treatment did not differ significantly from the 24/24 degrees C treatment. The 24 degrees C pond treatment maintained market quality lettuce head production in 31 degrees C air. Using optimal pond temperature, lettuce production was deemed acceptable at a variety of air temperatures outside the normal range, and particularly at high air temperatures