This study evaluates the effects of varying potassium sulfate concentrations in the nutrient solution, as well as foliar applications of calcium nitrate and potassium silicate, on growth, physiological traits, nutrient status, and fruit quality of tomato (Lycopersicon esculentum Mill. Var. Isabella) grown in a greenhouse hydroponic system. A factorial experiment was designed with three potassium sulfate levels (0.5, 1.0, and 1.5 mM) and five foliar spray treatments (control, two levels each of calcium nitrate and potassium silicate). The results showed that combined application of 1.5 mM potassium sulfate with foliar calcium nitrate (0.25 g L−1) significantly enhanced plant height, leaf area, shoot and root biomass, as well as fruit yield, diameter, and vitamin C content, compared to other treatments. Application of potassium sulfate at 1.5 mM combined with foliar spraying of calcium nitrate at 0.25 g/L significantly enhanced overall plant growth. The fresh and dry weights of shoots increased by 4% and 12%, respectively, compared to the control. Additionally, the number of fruits per plant was significantly higher, resulting in a 35% increase in total fruit number per plant with this combined treatment. Calcium nitrate foliar sprays were more effective than potassium silicate in promoting most growth and physiological traits. Potassium treatments increased photosynthetic pigment concentration and nutrient uptake, while both calcium and silicon sprays improved plant vigor and fruit quality. The observed synergistic benefits are attributed to potassium role in stomatal regulation and assimilate transport, calcium contribution to cell integrity and photosynthesis, and silicon enhancement of water-use efficiency and leaf structure. Overall, the study demonstrates that managing the ratio and delivery of potassium, calcium, and silicon, through both nutrient solutions and foliar application, can significantly improve growth and nutrition of hydroponically cultivated tomatoes. These practical findings provide valuable guidance for optimizing tomato productivity and quality in soilless greenhouse agriculture.
