Comparative evaluation of bulk and nano-formulated calcium, phosphorus, and potassium fertilizers in improving salinity tolerance of faba bean

BACKGROUND: Engineered nanoparticles (ENPs) have attracted considerable attention because of their potential role in enhancing crop tolerance to abiotic stresses, particularly salinity. Salinity is one of the major environmental constraints limiting crop productivity worldwide, as it adversely affects plant growth, physiological performance, nutrient uptake, and ionic balance. RESULTS: In this context, the present study evaluated the effects of foliar application of calcium-phosphate-potassium (CaPK) fertilizers in both bulk and nanoparticle (CaPK-NP) forms on the growth, physiological performance, and gene expression analysis of faba bean (Vicia faba L.) under saline field conditions during two growing seasons (2021-2022). To achieve this objective, foliar sprays of bulk CaPK and CaPK-NPs were applied at concentrations of 8 and 16 mL L⁻¹. Key growth traits, photosynthetic performance, antioxidant activity, ion balance, and the expression of selected ion transporter genes namely SOS1, VHA2, VFK1, and KUP7 were assessed to better understand the mechanisms underlying salt stress mitigation. The results showed that the 8 mL L⁻¹ bulk CaPK treatment consistently improved growth, photosynthetic pigments, antioxidant responses, nutrient uptake, and the Na⁺/K⁺ balance compared with untreated plants. Furthermore, gene expression analysis demonstrated the upregulation of ion transport-related genes, suggesting improved ionic homeostasis under saline conditions. Notably, the application of 16 mL L⁻¹ bulk CaPK resulted in the greatest enhancement of yield parameters. Although CaPK-NPs also improved several measured parameters, bulk CaPK frequently produced comparable or even greater enhancements under the experimental conditions. CONCLUSIONS: These findings suggest that foliar CaPK application may contribute to improved salinity tolerance in faba bean. However, further multi-location studies and long-term environmental assessments are still required before making broader agricultural recommendations.