In the experiment, which took place from May to July 2021 at the laboratory field of the Biotechnical Faculty, University of Ljubljana, and in which soil samples were analyzed until December 2022, water consumption for irrigation was evaluated in three cropping systems: soil cultivation in covered and uncovered soil and in a hydroponic system. The experiment was conducted in a greenhouse, with 4 replicates. Soil moisture probes were used to determine water use for irrigation and water distribution in the soil profile, measuring the percent water content in the soil and the level of nutrient solution in the tank. Soil and plant samples were collected during the experimental period to monitor nitrate nitrogen content, and nitrate content was later analyzed by extraction in an automated spectrophotometric instrument. We also measured lettuce plant biomass and dry matter content in plant samples. The greatest increase in plant biomass was found in the hydroponic system. Lettuce grown on bare soil had the highest dry matter content (5.3%), and hydroponically grown lettuce had the lowest (5.0%). Lettuce grown on film required the least amount of water for 1 kg of product (4.37 L/kg fresh weight and 86.7 L/kg dry weight, respectively), lettuce grown on bare soil required 8.35 L/kg fresh weight and 157 L/kg dry weight, respectively, and lettuce grown hydroponically required 23.7 L/kg fresh weight and 474 L/kg dry weight, respectively. The lowest nitrate content was found in technologically mature lettuce grown on bare soil (317.47 NO3¯ mg/kg fresh weight), on soil with film 1.012.31 NO3¯ mg/kg fresh weight and in hydroponic system 1.123.93 NO3¯ (mg/kg fresh weight. The content of nitrate nitrogen in the plants and in the soil decreased during the growing season.
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