A Sustainable Technology Approach to Lettuce (Lactuca sativa L.) Grown Under Greenhouse Condition Through Foliar Application of Various Biostimulants

Biostimulants play a crucial role in producing high-quality products with increased yields while also positively impacting sustainable agriculture by reducing reliance on chemical fertilizers and promoting soil fertility. In this context, an experiment was developed to evaluate the influence of several commercial foliar fertilizers and biostimulants (Cropmax, FullGreen, Nutrigizer, and Rerum) on the yield and quality parameters of lettuce cultivated in a greenhouse system. The tested products have different formulations, with all containing macronutrients and microelements. Cropmax and Rerum also include amino acids, while Nutrigizer 60 2E contains humic acids. The experiment was arranged in a randomized block design and comprised five treatments, with a control and four biostimulants, Cropmax, FullGreen, Nutrigizer, and Rerum, each replicated five times. Foliar treatments were applied four times to the butterhead lettuce variety ‘Analena’, suitable for spring to autumn production. All foliar treatments resulted in an increase in leaf biomass compared to that for the control variant. Notably, foliar fertilization with Rerum increased the yield by 2.19 times compared to that in the control. Quality indices—dry matter, ascorbic acid, and sugar contents—also improved after treatments. The foliar treatments also significantly enhanced key quality indices, with the Rerum variant showing the most pronounced increases in dry matter (24.11%), ascorbic acid (69.75%), and sugar content (26.38%) compared to those for the control. These results demonstrate that foliar application of biostimulants, particularly Rerum, is an effective sustainable technology strategy for significantly enhancing both the yield and nutritional quality of greenhouse-grown lettuce.