Integrating Azotobacter inoculation with nano-NPK foliar application: a sustainable strategy for enhancing growth, physiology, and sugar yield in sugar beet (Beta vulgaris L.).

Sugar beet is a key crop for the sugar industry, increasingly reliant on eco-friendly inputs to meet rising global demand. Plant growth-promoting rhizobacteria (PGPR) enhance plant growth via root associations, while nanotechnology offers solutions to limitations of traditional farming. However, while the individual benefits of PGPR and nano-fertilizers are well-documented, their combined application-specifically the integration of Azotobacter inoculation with foliar nano-NPK formulations-remains unexplored in sugar beet cultivation. Furthermore, no studies have investigated whether a multi-strain Azotobacter consortium (A. chroococcum + A. vinelandii) combined with complete nano-NPK can synergistically enhance sugar beet productivity beyond the effects of either treatment alone. Therefore, this study aimed to evaluate the synergistic effects of integrating Azotobacter inoculation with foliar nano-NPK application on growth, physiological performance, biochemical traits, and sugar yield in sugar beet, and to determine whether this combined approach outperforms individual or partial applications. To address this knowledge gap, a two-year field study using a split-plot design was conducted, with Azotobacter inoculation assigned to main plots and five nano-NPK formulations to subplots. Agronomic, physiological, and biochemical traits were evaluated at harvest. The combination of Azotobacter and complete nano-NPK (N + P+K) achieved superior results across all measured parameters. Notably, total chlorophyll content increased by approximately 122.8%, carotenoids by 82.6%, leaf area index by 95%, and sugar yield showed the most dramatic improvement, increasing by 94% (from 3.03 to 5.87 t ha⁻¹). Root yield also increased substantially by 65% (from 21.21 to 35.02 t ha⁻¹), accompanied by enhanced nutrient concentrations in leaves. This study is the first to demonstrate strong synergy between a dual-strain Azotobacter consortium and complete nano-NPK application, significantly improving nutrient use efficiency, physiological performance, and yield. The strategy provides an effective, sustainable approach with the potential to reduce dependence on conventional fertilizers in sugar beet production.