Can natural fortification increase Fe and Zn content in organically grown tomatoes?

Natural fortification can be used to increase the mineral content of the edible part of plants. In horticultural crops, foliar fertilization is used extensively, being a way to provide nutrients through leaves (a faster way compared to soil applications). Moreover, Fe and Zn are two important nutrients for plant growth and development, despite the low kinetic mobility. As such, considering the importance of Fe and Zn in plants and the fact that tomato is one of the most consumed horticultural crops worldwide, this study aimed to verify if in the middle of a biofortification process (after two foliar applications) Fe and Zn content in tomatoes of Solanum lycopersicum (beef heart variety - also known as Coeur de Boeuf) organically grown can improve. The experimental field was selected and followed the protocols for tomato growth in accordance with the organic production mode. Two foliar applications were carried out during the production cycle, with a mix of two products of Fe and Zn (Zitrilon – 15% and Maxiblend) with two concentrations (treatment 1 or low mix and treatment 2 or high mix). Through X-ray fluorescence using a XRF analyzer under He atmosphere, leaves of tomatoes submitted to the biofortification process showed an increase of 76.9% of Fe content and double Zn content, in treatment 2. However, treatment 1 only showed increases in Zn content (by 75.5% compared to control). Regarding tomatoes fruits, treatment 2 showed an increase of 7% of Zn content, relative to control content. Naturally enriched tomatoes with Fe and Zn showed minor changes in colorimetric parameters (Chroma and Hue) and no significant differences in L parameter (brightness / luminosity), regarding control. Additionally, biofortification did not affect tomatoes height and diameter at this stage of development, varying between 75.7 – 84.3 mm and 76.7 – 93.3 mm, respectively. In conclusion, two foliar sprays of Fe and Zn can improve tomatoes and leaves content under organic production practices without triggering toxicity to the plants and not affecting tomatoes height and diameter, and only presented some minor changes in color parameters (CieLab scale).