The Effect of Different Levels of Sheep Manure and Sulfur on Biochemical Traits and Active Ingredients of Saffron (Crocus sativus L.)

Introduction: Saffron (Crocus sativus L.) is the most precious agricultural product and one of the most valuable spices and medicinal plants with many applications in the food and pharmaceutical industries. Iran is the largest producer and exporter of saffron in the world, and more than 90 percent of the world's annual saffron production is produced in Iran. Recently, concerns about the ability to maintain soil fertility and ecological stability have been raised as an important issue regarding chemical fertilizers. Animal fertilizers do not have unilateral effects, but on the one hand, they help provide nutrients, and on the other hand, they improve soil structure. Also, providing plants with the elements they need plays an important role in increasing the quality of food produced and improving the health of society. Sulfur also has the potential to reduce soil pH, at least on a small scale around soil particles, due to its capacity to oxidize and produce sulfuric acid. Therefore, it can be effective, especially in the rhizosphere region, in dissolving insoluble nutrient compounds and releasing essential elements. Therefore, using elemental sulfur as an acidifying agent is useful in increasing the ability to absorb nutrients in calcareous soils. Therefore, considering the importance of saffron as a vital economic and medicinal product of the country, the objective of this project was to simultaneously study the effect of sheep manure and sulfur on the active ingredients and biochemical traits of saffron, so that steps could be taken towards sustainable production and increasing the quality of this important medicinal plant.
 
Materials and Methods: This study was conducted to investigate the effect of sheep manure and sulfur on biochemical traits and active ingredients of saffron during 2018-2019 and 2019-2020 in the Sarayan region in a factorial manner and a randomized complete block design with three replications. Experimental treatments included sheep manure at four levels (0, 20, 40, and 60 t. ha^-1) and sulfur at three levels (0, 200, and 400 kg. ha^-1). The planting operation began in September 2018. Each plot consisted of four lines, with a distance of 25 cm between two planting lines and a distance of 5 cm between the corms on each line, and 40 corms were planted on each line. Simultaneously with the start of flowering in the second year (late November 2019), saffron flowers were harvested from the entire surface of the plots in the early morning hours, taking into account the marginal effect (half a meter away from each side of the plot). The different parts of the flower were dried naturally in the shade. After drying, the saffron stigmas harvested each day were mixed and used for testing and were prepared for measuring biochemical traits. To determine the free radical scavenging rate of saffron stigma, the radical scavenging capacity was measured using 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging method, to measure the total phenol content of saffron stigma, the gallic acid method and Folin-Ciocalchio reagent were used, the anthocyanin of stigma was measured using the differential pH method, to measure the qualitative compounds present in flower stigma, the Iranian national standard method was used, and the chlorophyll a, b, total chlorophyll and carotenoid amounts were measured using the Arnon method. Statistical analysis of the data was performed using SAS 9.4 software. Data comparison was also performed using the protected Duncan’s multiple range test at a probability of 5%.
 
Results and Discussion: The results demonstrated that sheep manure and sulfur had a significant impact on the biochemical characteristics of stigma (antioxidant, phenol, and anthocyanin), effective substances of stigma (picrocrocin, crocin, and safranal), and biochemical characteristics of leaves (chlorophyll a, b, total, and carotenoid) of saffron. The treatment of 60 t. ha^-1 of sheep manure has the highest amounts of antioxidants (30.46%), phenol (62.52 mg. 100 g dry weight^-1), anthocyanin (33.41 mg. 100 g dry weight^-1), picrocrocin (33.00 absorption of 1% aqueous solution at 257 nm), crocin (285.667 absorption of 1% aqueous solution at 440 nm), safranal (34.56 absorption of 1% aqueous solution at 330 nm) and chlorophyll b (0.048 mg. g fresh weight^-1). With a consumption of 400 kg. ha^-1 of sulfur, antioxidant 12.31%, phenol 0.35%, anthocyanin 31.56%, picrocrocin 30.95%, crocin 48.48%, safranal 11.23%, chlorophyll a 16.80%, Chlorophyll b 8.33%, and carotenoid 16.14% increase compared to the control. Also, the highest amount of phenol (62.73 mg. 100 g dry weight^-1), anthocyanin (29.63 mg. 100 g dry weight^-1), crocin (287.33 absorption of one percent aqueous solution at 440 nm), safranal (38.81 absorption of one percent aqueous solution at 330 nm), total chlorophyll (1.026 mg. g fresh weight^-1) and carotenoid (1.026 mg. g fresh weight^-1) at the level of 60 t. ha^-1 of sheep manure and 400 kg. ha^-1 sulfur was obtained.
 
Conclusion: The findings of this experiment indicated that sheep manure and sulfur positively influenced the biochemical traits and active components of saffron.