Investigating the Effect of Corm Weight, Arbuscular Mycorrhizal Fungi and Azotobacter on the Growth and Yield of Saffron (Crocus sativus L.)

Introduction: Saffron (Crocus sativus L.) is the most expensive agricultural product and one of the most valuable medicinal and spice plants that have many uses in the food and medicine industry. Iran is the largest producer and exporter of saffron in the world, and more than 90% of the world's annual saffron production is produced in Iran. A balanced supply of nutrients based on proper fertilizer management is one of the most effective factors in the sustainability of saffron production, especially in dry and semi-arid areas, so that up to 80% of the formation and yield changes of the saffron flower are determined under the influence of the variables governing the soil, especially the amount of organic matter. Soil fertility management is a proper strategy for increasing soil organic matter, strengthening microbial communities, enhancing agricultural input efficiency and eventually improving plant quantitative and qualitative yields. To attain this goal, the fertilization management program should be designed to increase nutrient use efficiency. Optimal nutrient delivery, controlled-release fertilizers, integrated fertilization management, the use of organic nutrient resources, and beneficial symbiotic microorganisms with plant roots are all examples of methods that helps achieving nutrient use efficiency. Chemical fertilizers are the most often used fertilizers in saffron fields, and their excess can jeopardize farmed soil and water quality, and reduce the yield of saffron. As a result, biological fertilizers have attracted more interest for being more safe, low-cost, and have fewer negative environmental effects. Therefore, the present study was conducted to investigate the effect of the weight corm, mycorrhizal fungi, and Azotobacter biofertilizer on the growth and yield of saffron, so that by selecting the best amount of biofertilizers and the appropriate corm weight of the saffron corm.
 
Materials and Methods: In order to investigate the effect of corm weight, mycorrhizal fungi and Azotobacter biofertilizer on growth and yield of saffron, an experiment was conducted in the 2022-2023 year as factorial based in randomized complete block design at the Birjand Agricultural Faculty. The experimental factors included three levels of corm weight (0.1 to 4, 4.1 to 8 and 8.1 to 12 g), two levels of bacterial biofertilizer (application and non-application of Azotobaror-1 fertilizer containing Pantoea agglomerans strain O4 bacteria) and two levels of mycorrhizal biofertilizer (containing arbuscular mycorrhizal fungi strains Glomus mosseae, Glomus intraradices and Glomus etunicatum and a control without mycorrhiza). Bacterial treatments were applied in the first year of planting by inoculating saffron corms by preparing a suspension of the above bacteria mixed with distilled water in two times. The first time was done before planting by dipping the corms and the second time was done with irrigation 40 days after planting and also in the first irrigation of the second year according to the instructions of Zistfanavar Sabz Company. Mycorrhiza treatments were done at a rate of 10 grams for each corm by adding it to the planting hole at the time of planting according to the instructions of Danesh bonyan Zist Sepidan Hayat Paya Company.
 
Results and Discussion: The results of the interaction effects of corm weight, mycorrhiza fungus, and Azotobacter bacteria on saffron vegetative traits in the first year of the experiment showed that the highest number of leaves per plant (9.33), average leaf dry weight (0.16 g), leaf length (37.00 cm), total weight of corm with scales (23.68 g), number of corms (5), average weight of main cormlet (21.15 g), and average weight of secondary cormlets (3.42 g) were obtained from corms weighing 8.1-12 g and the use of mycorrhiza fungus and Azotobacter bacteria. In the second year of the experiment, the highest number of flowers per square meter (83.96), flower yield (66.37 g.m^-2), fresh stigma yield (32.2 g.m^-2), and dry stigma yield (58.0 g.m^-2) were obtained from 8.1-12 g corm and the use of mycorrhiza fungi and Azotobacter bacteria.
 
Conclusion: Overall, the results of this study indicated that growth and yield of saffron were improved with the simultaneous use of higher weight corm (8.1-12 g) and the use of mycorrhiza fungi and Azotobacter bacteria. Therefore, the use of biofertilizers and the development of mycorrhizal hyphae in agricultural soil, can improve saffron cultivation areas in sustainable agriculture and reduce the losses caused by the excessive use of chemical fertilizers.