Assessment of the Impacts of Humic Acid Application and Mycorrhizal Fungi Inoculation on Flowering and Stigma Quality of Saffron under Two Irrigation Regimes

Abstract

The shift toward sustainable medicinal plant production underscores the importance of biological inputs. This study evaluated the effects of humic acid application, mycorrhizal inoculation, and two irrigation regimes on reproductive growth and quality of saffron (Crocus sativus L.). The experiment was conducted as a split-split plot based on a randomized complete block design (RCBD) with three replications, where irrigation intervals (20 and 40 days) were the main plot, humic acid (0 and 5 kg.ha⁻¹) was the sub-plot, and mycorrhizal inoculation (noninoculated, Glomus mossea, and G. intraradices) was the sub-sub plot. The studied traits were the number of flowers, flowering rate, flower yield, petal yield, style yield, and stigma yield, as well as stigma quality parameters (crocin, picrocrocin, and safranal content). Results indicated that the triple interaction of experimental factors was significant on all studied traits. The shortest irrigation interval (20 days) combined with humic acid application and G. mossea inoculation significantly increased fresh flower yield (79.63 g.m⁻²), dry stigma yield (0.88 g.m⁻²), style yield (0.22 g.m²), and petal yield (9.88 g.m ²). Crocin content was highest (274.5, absorbance of 1% aqueous solution at 440 nm) under 40-day irrigation intervals with humic acid and G. mossea inoculation, while safranal (35.80, absorbance at 330 nm) and picrocrocin (124.5, absorbance at 257 nm) improved under 20-day irrigation intervals with humic acid and G. mossea. Conversely, extended irrigation intervals (40 days) without humic acid and without mycorrhizal inoculation resulted in the lowest crocin and safranal content. Overall, the findings demonstrate that combining humic acid with G. mossea inoculation under frequent irrigation optimizes both the quantity and quality of saffron. It was concluded that although the use of organic inputs is beneficial, the results of their single application may differ from those of their combined application. On the other hand, the interaction among two or more of these inputs can also vary depending on conditions, including water availability and the type of mycorrhizal species.