nutrients content and yield in selected cultivars of leaf lettuce ( Lactuca sativa l . var . crispa )

Five cultivars of leaf lettuce (Lactuca sativa L. var. crispa) – Bergamo, Dubáček, Frisby, Lollo Rossa and Redin – were evaluated in two-year experiments carried out at the Faculty of Horticulture in Lednice (Mendel University of Agriculture and Forestry in Brno). Experiments were conducted in two trial years, 1998 and 1999; the lettuce was cultivated in three seasons: spring, summer and autumn. After the harvest, contents of following nutrients were evaluated: vitamin C, minerals (K, Na, Ca, Mg), fibre, dry matter and nitrates. The weight of leaf rosette was also recorded. The contents of selected substances and weights of leaf rosette were ranged as follows: vitamin C (65 to 302 mg/kg), potassium (2,394 to 6,477 mg/kg), sodium (39 to 223 mg/kg), calcium (200 to 755 mg/kg), magnesium (110 to 413 mg/kg), fibre (4.98 to 12.22 g/kg), dry matter (59 to 140 g/kg), nitrates (293 to 3,817 mg/kg) and the weight of leaf rosette (164 to 502 g). A significant influence of cultivar was found in the case of K, Na, and Ca content, as well as in dry matter and weight of leaf rosette. The growing season affected significantly all the evaluated substances, except for fibre. The year of cultivation affected all the evaluated parameters but Ca. It appears from the results that the contents of monitored substances were significantly influenced by cultivar as well as by growing season and year.