Agronomic, Biochemical, and Physiological Responses to Magnesium (Mg) Application in Tomato (<i>Solanum lycopersicum</i> L.) under Greenhouse Conditions

Magnesium fertilization positively impacts various physiological processes in plants, leading to increased yield and fruit quality. In the present study, we determined the effects of the foliar application of magnesium on the yield, fruit quality, fruit biochemical content, and enzyme activity of tomato plants. The study was performed in a plastic greenhouse. The study evaluated magnesium sulfate application through drip irrigation at a single dose of 0.005 kg m² and foliar application at rates of 0%, 0.25%, 0.5%, and 0.75%. As a consequence, the highest average fruit weight was obtained with the foliar application of 0.50% Mg. In terms of the fruit color’s a* value, the best results were again obtained with the application of 0.50% Mg. Mg applications proportionally increased the leaf chlorophyll content. Similarly, the highest leaf Mg content, the leaf relative water content, the fruits’ malic acid content, and the best fruit juice pH value were determined with the application of 0.75%. On the other hand, the application of 0.25% Mg produced the best results on the leaves’ K, Ca, and Na content, as well as in the fruits’ ascorbic acid content. Significant differences were not found in terms of the effects of the treatments on antioxidant activity, total protein amount, and enzyme activity. The application of 0.50% Mg contributed to the fruit color; 0.75% Mg application contributed to the chlorophyll, pH, and malic acid content; and the application of 0.25% Mg contributed to an increase in ascorbic acid. In conclusion, for greenhouse tomato production, a foliar application of 0.50% Mg is recommended to achieve larger, red-colored fruits. A 0.75% Mg application is suggested for increasing the chlorophyll content, lowering fruit juice pH, and enhancing malic acid content in fruits. A 0.25% Mg application is recommended to increase ascorbic acid content in fruits.