BACKGROUND: Biostimulants are increasingly integrated into production systems with the goal of modifying physiological processes in plants to optimize productivity. Specifically, l‐α‐amino acid‐based biostimulants enhance plant productivity through improved photosynthesis and increased assimilation of essential nutrients such as nitrogen (N). This element is a major component of fertilizers, which usually are applied in excess. Thus, the inefficient use of N fertilizers has generated a serious environmental pollution issue. The use of biostimulants has the potential to address problems related to N fertilization. Therefore, the objective of this study is to analyze whether two biostimulants based on l‐α‐amino acid (Terra Sorb® radicular and Terramin® Pro) designed by Bioiberica, S.A.U company can compensate deficient N fertilization and test its effect on lettuce plants. Growth, photosynthetic, N accumulation, and N use efficiency (NUE) parameters were analyzed on lettuce leaves.RESULTS: Results showed that regardless of N fertilization, the use of both biostimulants, especially Terramin® Pro, increased biomass production. Moreover, both biostimulants enhanced photosynthetic, NO₃⁻ and total N accumulations as well as NUE parameters.CONCLUSION: Therefore, Terra Sorb® radicular and Terramin® Pro constitute a useful tool for crops development in N‐limiting areas, and in intensive agricultural areas without N deficiency allowing the reduction of N inputs without impairing crop yields and reducing environmental impact. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The present experiment addressed the effects of different iron (Fe) concentrations in the nutrient solution supplied as Fe-HBED, i.e., 0.02 (Fe0, control), 1.02 (Fe1), and 2.02 mmol L⁻¹ (Fe2) on lettuce (‘Nauplus’ and ‘Romana’) yield and compositional traits. This experiment was carried out in a greenhouse using an open soilless cultivation system, at the experimental farm of the University of Catania (Sicily, Italy: 37°24′31.5″ N, 15°03′32.8″ E, 6 m a.s.l.). The addition of Fe-HBED reduced the plants’ aboveground biomass (−18%, averaged over Fe1 and Fe2), but promoted their dry matter content (+16% in Fe2). The concentration of chlorophylls, carotenoids, anthocyanins, and antioxidants peaked at Fe2, along with the antioxidant capacity and concentration of stress indicators in leaves. The Fe content in leaves was promoted in the Fe-treated plants (+187% averaged over Fe1 and Fe2). ‘Romana’ showed the highest Fe accumulation (reaching 29.8 mg kg⁻¹ FW in Fe1), but ‘Nauplus’ proved a higher tolerance to the Fe-derived oxidative stress. The Fe2 treatment maximized leaf N, P, K, S, and Zn contents, while those of Ca, Mg, Mn, and B peaked at Fe1. Overall, our study revealed the effectiveness of Fe-HBED in increasing the Fe content and improving the nutritional quality of lettuce grown in soilless cultivation systems.