A field experiment was conducted at Gelbana district, Sahl El-Tina (latitude of 30.57º N and longitude of 32.20º E), North Sinai Governorate, Egypt, in 2021/2022 and 2022/2023 to find out the optimal level of nitrogen fertilization and some combinations of Spirulina platensis extract and potassium silicate on growth, yield, and quality of sugar beet. This work included 21 treatments of three nitrogen levels and seven foliar combinations of Spirulina extract and potassium silicate. A complete block design in a split-plot arrangement with three replicates was used. Results indicated that fertilizing beets with 288.0 kg N ha^-1 increased proline content, root diameter, fresh weight, root impurities, and sugar lost to molasses. Enriching beets with 230.4 and/or 288.0 kg N ha^-1 gave the highest leaf area index, photosynthetic pigments, sucrose, extracted sugar percentages, quality index, root and sugar yields ha^-1 in both seasons. Spraying beet tops with (3.60 g L^-1 ha^-1 Spirulina extract combined with a fixed dose of potassium silicate) resulted in a significant increase in leaf area index, photosynthetic pigments, root diameter, fresh weight, α-amino-N content, yields of root and sugar ha^-1. However, proline, potassium, and sodium content decreased compared to other single doses of algal extract. Application of 230.4 kg N ha^-1 and spraying beet tops with a combination of (3.60 g L^-1 algal extract and 7.20 cm³ L^-1 potassium silicate) led to a significant increase in sucrose %, quality index, root and sugar yields ha^-1 with a reduction in sodium and potassium contents