In this master’s thesis, the effects of nutrient solution heating and biostimulant Amalgerol® Essence application on the morphological and biochemical characteristics of lettuce (Lactuca sativa) were examined during spring hydroponic production using an NFT (Nutrient Flow Technique) system. Four cultivation methods for two cultivars were compared: with and without heating of the nutrient solution, and with and without a biostimulant. At technological maturity, total and marketable plant weight, rosette diameter and height, and stem height were measured. Laboratory analyses included dry matter content in leaves, nitrate levels, total phenolic content, and photosynthetic pigment content; anthocyanin content was also determined in the red-leaf cultivar. The highest yield in the green-leaf cultivar was achieved with the heated nutrient solution without a biostimulant (4.43 ± 0.09 kg/m²). In the red-leaf cultivar, the yield was similar with the heated nutrient solution both with a biostimulant (3.29 ± 0.043 kg/m²) and without (3.30 ± 0.062 kg/m²). In the heated solution, plants developed larger and taller rosettes with longer stems, while the biostimulant resulted in more compact growth. Dry matter content and nitrate content were significantly higher in the unheated solution, although the addition of the biostimulant had no significant effect. Temperature and biostimulant application did not significantly influence total phenolics, anthocyanins, or photosynthetic pigments. However, there was a significant difference between the cultivars in total phenolics and photosynthetic pigments.
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