Influence of Magnetized Irrigation Water and Variable NPK Levels on the Productivity and Technological Quality of Sugar Beet

Improving water productivity while maintaining technological quality is a major challenge for sugar beet production under increasing water scarcity. This study was conducted for only one year at one location during the 2023/2024 winter season near the Village Kafraljaraydh to evaluate the effects of irrigation water type (normal vs. magnetized), irrigation levels (100 and 75% ETc) combined into four irrigation treatments, and NPK fertilization levels (100, 80, 60, and 40% of the recommended dose) on growth, yield, quality, and water relations of sugar beet (Beta vulgaris L.) under field conditions in Egypt (2023/2024 season; strip-plot design; three replicates). Magnetized water treatment (MWT) enhanced vegetative growth, root development, and biomass accumulation, improving yield. The highest root yield (80.34 t ha−1) and sugar yield (16.62 t ha−1) were obtained under magnetized irrigation at 100% ETc; 80–100% NPK, representing a 3–6% increase over normal irrigation. Technological quality improved, with higher sucrose content, total soluble solids, apparent purity, and reduced impurity-related parameters (α-amino N, K, Na, and molasses sugar). Deficit irrigation reduced yield but had limited effects on quality. Water use efficiency was mainly driven by irrigation level, with higher values under 100% ETc, while MWT provided a moderate improvement. Reducing fertilization to 80% NPK maintained yield and improved quality under MWT. MWT improved crop performance and quality without increasing water use, supporting sugar beet production.