DAILY AND SEASONAL VARIATION OF NITRATE CONTENTS IN LETTUCE CULTIVARS IN HYDROPONIC SYSTEM IN SOUTHERN BRAZIL
Lettuce presents a great ability of nitrate accumulation, especially in hydroponics in which the ion availability is high. Nonetheless, nitrate accumulation depends primarily on genotype and light intensity. The aim of this work was to quantify the nitrate contents in lettuce cultivars according to the harvest time and crop-season in hydroponic system. Three experiments were conducted in three crop-seasons: spring of 2008, autumn and winter of 2009, in Pelotas RS, south of Brazil. Four cultivars were studied: Green Garden (GG), Red Garden (RG), Great Lakes Iceberg (GLI) and Vera Sunny (VS) lettuce types, at four harvest times (8:00, 14:00, 18:00 and 23:00 hr). In spring, the lowest average nitrate accumulation was found at 18:00 and 23:00 hr (2058 and 2244 mg kg-1) and in GLI leaves (1825 mg kg-1). In autumn, the lowest average accumulation was observed at 8:00 hr (1378 against 1620 mg kg-1 obtained as average of the other harvest times) and for RG and GLI cultivars (1360 and 1448 mg kg-1). In winter, GG and RG presented similar nitrate accumulation (mean of 2182 mg kg-1) and for both cultivars the lowest nitrate accumulation was observed at 8:00 hr (1545 against the average of 2394 mg kg-1 of the other harvest times). GLI presented lower nitrate accumulation than VS (1915 and 2679 mg kg-1, respectively) and the harvest at 14:00 hr led to a lower accumulation than at 18:00 hr (2054 against 2454 mg kg-1, respectively). The lowest nitrate accumulation average was obtained in autumn (1559 against 2526 and 2189 mg kg-1 obtained in spring and winter, respectively). In general, we can recommend Great Lakes Iceberg cultivar. We also recommend an early morning harvest in winter and autumn and a late afternoon harvest in spring crop-season in order to get lower nitrate accumulation in hydroponic lettuce.
Peil, R.M.N., da Fonseca, L.A., Strassburger, A.S., Strassburger, K.F. and Medeiros, C.A.B. (2012). DAILY AND SEASONAL VARIATION OF NITRATE CONTENTS IN LETTUCE CULTIVARS IN HYDROPONIC SYSTEM IN SOUTHERN BRAZIL. Acta Hortic. 952, 651-657
Lactuca sativa, nitrate accumulation, harvest time