Nano and chelated iron fertilization influences marketable yield, phytochemical properties, and antioxidant capacity of tomatoes

Iron (Fe) is one of the limiting micronutrients essential for crop productivity. The goal of our study was to evaluate the effects of different sources and rates of Fe fertilization on the marketable yield, physical and chemical properties, and phytochemical quality of fresh market tomatoes (Solanum Lycopersicum L., cv. Sunbrite). A factorial experiment under a drip-irrigated plasticulture system was conducted in a completely randomized design with two sources of Fe (nano vs. chelated) and four rates of application (0, 10, 20, and 40 mg/L) with four replications. Results indicated that relative chlorophyll concentration in the leaf (SPAD index) increased significantly (by 24 to 27%) with 10 and 20 mg/L of both nano- and chelated Fe fertilization compared to the control. Increasing Fe fertilization decreased the leaf SPAD readings. The total fruit yield of tomato was 1.6 to 1.8 times higher under the chelated- and nano Fe fertilization and the increase in yield was significantly higher under the chelated Fe fertilization, when compared to the control. In contrast, the tomato harvest index was highest under 10 and 20 mg/L of nano Fe than under other Fe treatments. While the chelated Fe fertilized tomatoes had significantly higher concentrations of vitamin C (34%), ß-carotene (6%), total carotene (25%), flavonoid (17%), and polyphenol (66%), the nano Fe, in contrast, increased ß-carotene, total carotene, and polyphenol concentrations by 25, 33, 51, and 7%, respectively, compared to the control. The 20 mg/L chelated Fe significantly increased the vitamin C, total carotene, flavonoid, polyphenol concentration, and antioxidant capacity more than any other Fe treatments. Based on the principal components analyses, vitamin C, lycopene, and anthocyanin were identified as the core indicators of the tomato nutrition quality index (NQ(Index)). The NQ(Index) ranged from 47 to 54, falling within the medium level of nutritional quality (40 to <70). In conclusion, the chelated Fe, when applied at 20 mg/L, was the most appropriate rate based on highly correlated connectivity for the phytochemicals syntheses associated with the improved tomato antioxidant capacity.