Synergistic effect of nano-chelated iron fertilizer and vermicompost tea on the stigma yield and phytochemicals of Crocus sativus L. in an alkaline soil

Saffron ( Crocus sativus L.) is considered the most valuable spice in the world, and its cultivation requires specific soil conditions to maximize yield and quality. While saffron can grow in calcareous soils, the high pH levels typically associated with these soils can limit optimal production. Limited studies have demonstrated that applying nano-chelated iron fertilizer (NCIF) and solid vermicompost individually can enhance saffron growth and yield. However, the combined effects of NCIF and liquid vermicompost tea (VCT) in alkaline conditions remain unexplored in saffron or other plants. This study investigated the individual and combined impacts of NCIF soil drenching (0, 4, and 8 kg ha − 1 ) and VCT foliar applications (0, 10, and 20%) on stigma yield and phytochemicals in various parts of saffron plants grown in an alkaline soil. VCT and NCIF, particularly in combination, significantly reduced electrolyte leakage, while enhancing total chlorophyll content, flower yield, and stigma biomass and length. The integrated application of 20% VCT and 8 kg ha − 1 NCIF yielded the highest concentrations of safranal, crocin, picrocrocin, and total flavonoid content, alongside superior DPPH scavenging activity, and reducing power in stigma. Similar improvements in phenolic content and antioxidant properties, along with enhanced iron-chelating activity, were observed in the petals and leaves. These novel findings underscore the synergistic effect of NCIF and VCT to improve saffron stigma yield, quality, and antioxidant properties under challenging soil conditions.