Effect of the Nitrate-Urea Ratio, Nickel Levels, and Light Intensity on the Development of Lactuca sativa L. under Hydroponic Conditions

Resumen

Objective: To determine the effects of the nitrate/urea ratio, nickel concentrations in the nutrient solution, and different light intensities on the development of lettuce cultivated in a hydroponic system. Design: The experiment was conducted using a completely randomized design with a 2 × 3 × 3 three-factor arrangement, comprising 18 treatments and five replicates. The evaluated factors were the nitrate/urea ratio, nickel concentration, and light intensity. Results: The 80/20 nitrate/urea ratio promoted the greatest root volume, leaf fresh weight, leaf and root dry weight, and larger leaf area, thus indicating higher efficiency in nitrogen assimilation when part of the supply was provided as urea. Nickel at a concentration of 1 mg L^-1 tended to enhance growth compared with the absence of nickel. Likewise, a light intensity of 400 μmol m^-2 s^-1 increased root volume, dry biomass, and leaf greenness. Study limitations/implications: Further research is needed to evaluate other mineral sources and different specific spectral compositions for production under controlled environments, as these represent a promising opportunity to improve the development and quality of hydroponic lettuce. Findings/conclusions: Nickel exerted moderately positive effects at a concentration of 1 mg L^-1, and its combination with the nitrogen source ratio of 80/20 under a light intensity of 400 μmol m^-2 s^-1 resulted in greater root volume, dry biomass, and leaf greenness (SPAD). Therefore, this treatment can be considered a viable alternative for improving lettuce development in hydroponic systems.