Effect of Root-Zone Heating on the Yield and Some Quality Parameters of Hydroponically Grown Tomato

The cost of heating the greenhouses in the North of Spain is one of the main costs that growers had to afford. The main objective of this trial was to evaluate the effect of root-zone heating at 20 C at two contrasted air regimes on tomato production and quality. Tomatoes were grown hydroponically in two separate greenhouses from January to June (2009). Two treatments were conducted: (i) air was heated to 18/12 degrees C day/night (+AH) and (ii) air was not heated (-AH). Moreover, in each of these greenhouses two treatments were established regarding the root-zone: (i) root-zone was heated to 20 degrees C continuously (+RH) and (ii) root-zone was not heated (-RH). During the air heating period mean minimal night temperatures were 12.1 degrees C in +AH and 10.6 degrees C in -AH, but the lowest minimal night temperature were 11.1 degrees C in +AH and 3.3 degrees C in -AH. The mean day temperatures were 20.3 degrees C in +AH and 19.3 degrees C in -AH. The production of tomatoes was significantly higher in +AH with respect to -AH. The cumulative total production values were (kg m(-2)) 17.3+/-1.2 in +AH-RH, 16.2+/-1.0 in +AH+RH, 134.3+/-1.0 in -AH-RH and 14.2+/-1.7 in -AH+RH. Regarding the root-zone heating treatments, there were no significant differences in the total production of fruits between +RH and -RH in any of the air heating treatments. Fifteen days after the end of the air heating there were significant differences in the sizes of the harvested fruits. In +AH, the root-zone heating lead to smaller fruit size. In contrast, in -AH, the root-zone heating induced higher fruit size. Regarding tomato quality, treatments did not affect the fruit parameters.