Mitigating Salt Stress in Cool-Season Turfgrasses Using Nano Silicon and Humic Acid: A Comparative Evaluation on Festuca arundinacea and Lolium perenne

Abstract Salinity stress is one of the major abiotic constraints limiting turfgrass growth, visual quality, and sustainability in landscape areas, particularly in regions where secondary-quality irrigation water is increasingly used. Developing effective and environmentally friendly management strategies to mitigate salinity-induced damage has therefore become a critical challenge for turfgrass systems. This study evaluated the effectiveness of nano silicon and humic acid in mitigating salinity stress in Festuca arundinacea ‘Bizem’ and Lolium perenne ‘Ringles’ grown under 6 dS m⁻¹ NaCl conditions. Salinity significantly reduced turfgrass quality, color, chlorophyll content, and growth parameters in both species. Nano silicon applications, especially at 200 cc da⁻¹ (NS200), markedly alleviated salinity-induced damage. Compared with the salt-stressed control, NS200 increased chlorophyll content by 51.4–62.6%, turfgrass quality scores by 25.1–31.2%, weekly clipping dry weight by 165.1-232.4 % across both species. In contrast, humic acid applied at 300 cc da⁻¹ showed limited improvements under the same salinity level. Overall, the results demonstrate that nano silicon, particularly at 200 cc da⁻¹, provides a more effective and consistent strategy than humic acid for improving physiological performance and visual quality of cool-season turfgrasses under moderate salinity stress.