Effect of various nitrogen sources on yield, antioxidant activity and active substances of Crocus sativus L.

To investigate the effect of different nitrogen sources on some quantitative and biochemical characteristics of saffron, an experiment was conducted based on a randomized complete block design with three replications in the University of Zanjan, Iran. The treatments were Azotobarvar-1bio-fertilizer (containing free-living nitrogen-fixing bacteria Azotobacter vinelandii) at two levels (0.1 and 0.2%), Nitrokara (containing symbiotic and free-living nitrogen-fixing bacteria Azorhizobium caulinodan) at two levels (1 and 2%), and a combination of both at four levels (1% Nitrokara + 0.1% Azotobarvar-1, 1% Nitrokara + 0.2% Azotobarvar-1, 2% Nitrokara + 0.1% Azotobarvar-1, 2% Nitrokara + 0.2% Azotobarvar-1) compared to control and one nitrogen level (40 kg ha^‑1) in the form of urea. The results showed that the highest number of flowers (49.94 m^‑2), the yield of stigma (312.02 mg m^‑2), and the maximum length of stigma (2.98 cm) was observed in 0.2% Azotobacter. The highest leaf nitrogen content and chlorophyll was obtained in 0.2% Azotobacter (2.117% and 2.112 mg g^‑1, respectively) and 40 kg ha^‑1 nitrogen (2.096 and 2.159, respectively). Also, 0.1% Azotobacter and 2% Azorhizobium treatments resulted in the highest dry weight of stigma (6.23 and 6.29, respectively). The highest antioxidant and total phenol of stigma were obtained in 1% Azorhizobium (62. 390% and 19.410 mg g^‑1, respectively) and the highest amount of flavonoids was observed in 0.1% Azotobacter (3.73 mg g^‑1). The highest crocin and safranal were obtained in 0.1% Azotobacter (177.200 and 57.460, respectively) and 1% Azorhizobium treatments (164.380 and 58.940, respectively). In conclusion, the results showed that high levels of different nitrogen sources had a positive impact on the quantity of stigma such that the highest yield was obtained in 0.2% Azotobacter. However, low levels of the bio-fertilizers, i.e., 0.1% Azotobacter and 1% Azorhizobium improved the antioxidant activity as well as active substances of saffron.