Potassium substitution by sodium in sugar beet (Beta vulgaris) nutrition on K-fixing soils

Alluvial soils with illite and vermiculite clay minerals are highly potassium (K)-fixing. Such soils have been reported to require a huge amount of K fertilization for optimum plant growth. For halophytic plants such as sugar beet, sodium (Na) can be an alternative to K under such conditions. This study was conducted to investigate the possible substitution of K by Na fertilization with reference to K-fixing soils. Three soils, i.e., Kleinlinden (subsoil), Giessen (alluvial), and Trebur (alluvial), differing in K-fixing capacities, were selected, and sugar beet plants were grown in Ahr pots with 15 kg soil pot⁻¹. Three treatments (no K and Na, K equal to K-fixing capacity of soil, and Na equivalent to regular K fertilization) were applied. In a second experiment, containers (90 cm x 40 cm x 40 cm) were used with 170 kg Kleinlinden soil each, and one sugar beet plant per container was grown. In both experiments, plants were grown till beet maturity, and beets were analyzed for sucrose concentration and other quality parameters such as α-amino nitrogen to calculate white-sugar yield with the New Brunswick formula. The results showed that growth and quality of sugar beet were not affected by Na application, and ultimately there was no decrease in white-sugar yield. Moreover, the soils with more K-fixing capacity were more suitable for K substitution by Na. It is concluded that Na can substitute K in sugar beet nutrition to a high degree and soils with high K-fixing capacity have more potential for this substitution.