Climate change is forcing the search for innovative solutions to effectively reduce its harmful effects on food production. In addition, increasingly stringent regulations are being introduced in the European Union (the European Green Deal), mandating reductions in mineral fertilizer doses, which can reduce crop yields. One innovative technology could be soil fertilization and foliar application of Si-based fertilizers. A two-year field experiment (2023 and 2024), in commercial crop conditions in Kraski (52°2'42\" N, 18°54'6\" E), in Central Poland, studied the effect of differentiated soil fertilization and the foliar application of Si-based products on the yield and quality of maize grain at two levels of nitrogen/phosphorus/potassium (NPK) fertilization (100% and 50%). The soil fertilizer SiGSsup® (Si—200 g kg^-1, Ca—181 g kg^-1, Mg—46 g kg^-1, and Mn—45 g kg^-1) was applied to the soil at doses of 100, 300, and 500 kg ha^-1, alone or with Barrier Si-Casup® (Si—336 g dm^-3; Ca—207 g dm^-3) foliar fertilizer (1 dm³ ha^-1). The number of combinations assessed is 16. The effects were compared against the control treatment. The experiment evaluated plant physiological parameters, grain and dry matter yield, grain moisture content and quality (protein, fat, and starch content), and grain yield components. The highest grain yields were obtained with soil fertilization at a dose of 500 kg ha^-1 (giving an increase of 17.5%), at a dose of 300 kg ha^-1 plus foliar application (+16.4%), and at a dose of 500 kg ha^-1 plus foliar application (+17.8%). The increase in grain yield in treatments with a half-rate of NPK was of a similar magnitude (on average, +11.9%) to the full rate (+12.6%) compared to the control treatments. Doubling the NPK rate contributed to an increase in grain yield of 7.8%. The applied fertilization had a significant and beneficial effect on the protein and fat content of the grain, while it reduced the starch content.