Effect of biological fertilizers on the yield and some morphological characteristics of saffron (Crocus sativus L.)

Applying chemical fertilizers has traditionally been employed to enhance saffron cultivation yields. However, their excessive usage has not only failed to increase yields significantly but has also resulted in soil element depletion and environmental pollution. In the context of sustainable agriculture, the use of biofertilizers presents an alternative approach. Biofertilizers play a crucial role in reducing the dependency on chemical fertilizers by aiding in the mobilization of mineral elements within the soil, ultimately leading to heightened yield levels. Therefore, due to the importance of increasing the yield of saffron as a strategic export and medicinal plant, an experiment was conducted in a randomized complete block design format with three replications in the research farm of the Semnan Natural Resources Department during the year 2022. Iron-zinc (FeZn), potassium (K), phosphorus (P) biofertilizers, and their combination together with the control (total of 8 treatments) were experimental treatments and applied as fertigation in the middle of February 2022. The studied traits included flowering period, number of flowers, fresh and dry flower weight, fresh and dry weight of stigma, height and diameter of stigma tip, number and length of leaves, and leaf chlorophyll content. The field soil was analyzed before the experiment, and it was a saline calcareous soil with alkaline pH and high levels of nutritional elements, which does not need chemical fertilizers for saffron cultivation. Mean comparisons showed that biofertilizers caused a significant increase (p < 0.05) in all traits except length and number of leaves, height, and stigma diameter compared to the control. This research showed that the combined application of K and FeZn biofertilizers had the best results. So that the highest values of the number of flowers (175 number.plot-1), fresh weight of flowers (72.61 g.plot-1), dry weight of flowers (7.92 g.plot-1), length of flowering period (21 days), chlorophyll a content (0.728 mg.g-1 of leaf fresh weight), total chlorophyll content (5.97 mg.g-1 leaf fresh weight), stigma fresh weight (4.28 g.plot-1) and stigma dry weight (0.804 g.plot-1) were recorded in the  K+FeZn treatment. Overall, the cultivation of saffron with biofertilizers improved most of the quantitative and qualitative traits of saffron by affecting the uptake of nutrients, and the combined use of biofertilizers can significantly increase saffron yield through synergistic effects.