Resumen

PREMUZIC, Z; PALMUCCI, HE; TAMBORENEA, J  y  NAKAMA, M. Chlorination: phytotoxicity and effects on the production and quality of Lactuca sativa var. Mantecosa grown in a closed, soil-less system. Phyton (B. Aires) [online]. 2007, vol.76, pp.103-117. ISSN 1851-5657.

The addition of chlorine constitutes an economical disinfection method for closed, soil-less systems. Three quantities of sodium hypochlorite (0.55, 5.5 and 11 ppm) were applied to closed, soil-less greenhouse- grown lettuce (Lactuca sativa), to study the effect on its production (fresh weight and dry matter) and some commercial and nutritional quality factors (phytotoxicity, Vitamin C, nitrates). Sodium hypochlorite was weekly added within the nutrient solution, and the chemical properties (pH, EC and chlorides) of the recycled solution were measured. Damage to leaves was evaluated 15 days before harvest. Chlorination produced different effects regarding both production and quality. All treatments presented plants with excellent commercial weight, although quantities of 0.55 and 5.5 ppm presented a 17% greater weight. However, this improvement was statistically not significant. Three different groups were observed for the phytotoxicity effects: the 11 ppm dose showed 42% of damage to leaves, while leaf damage was 22% for the 0.55 and 5.5 ppm quantities, and 15% for the control. The addition of sodium hypochlorite did not affect (significantly) Vitamin C and dry matter production. All treatments presented nitrate contents exceeding the allowed values; this fact was related with the nitrate composition of the nutrient solution. The chemical properties of the nutrient solution were adequate for the species. This study suggests the 0.55 and 5.5 ppm quantities as a positive option regarding plant weight. Further research should be developed to adjust fertilization, and to diminish the phytotoxicity symptoms.

Palabras clave : Chlorination; Lactuca sativa; Nitrates; Phytotoxicity; Vitamin C.

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