4.2 Root zone warming treatments
Flat heating plates were placed on a growth chamber table and alternately operated for 15 minutes/ and ceased heating for 15 minutes for 10 hours/day. No heating was applied for the subsequent 14 h. Each cycle of RZW was 24 h composed of 10 h with intermittent warming, and 14 h without. Disposable aluminum trays (30X40 cm) containing 7-10 mm height of tap water were placed over the heaters and 800 ml pots with six week old tomato plants were placed in the aluminum trays. The plants were fertilized with slow release fertilizer (1 g each, Osmocote, Everris International BV, Heerlen, The Netherlands) containing N (18%), P2O5 (9%), K2O (10%), MgO (2%), Fe (0.3%), Mn (0.04%), Cu (0.037%), Zn (0/011%), B (0.1%), Mo (0.015%) and water was added daily to the pots. Temperature at 5 cm depth of the mock and treated pots reached 21±1 and 28±1ºC during the warming period while the canopy temperatures were 18-21ºC during the entire experiment. This experimental design aimed at mimicking real agricultural conditions, where natural daytime soil heating in different settings can result in root zone warming while the plant canopy remains at lower temperatures (Elad et al., 2016a). Incubation took place in an illuminated, air conditioned growth chamber with 21±1ºC and 2200 Lux light intensity, 12h daylight.