Evaluation of the effect of different fertilizer sources on some characteristics of the corm and flower yield of saffron

 In recent years, in order to produce healthy products and reduce environmental problems, organic and biological fertilizers are used to increase soil fertility, meet nutritional needs and increase plant growth. Proper management of fertilizer consumption is one of the necessary tools to have a stable and profitable agro-ecological system in saffron. Due to the fact that few studies have been done on the combined use of biologic, organic and chemical fertilizers in saffron cultivation, therefore the present study was conducted to investigate the effect of biological fertilizers containing Azotobacter, Pseudomonas and Bacillus subtilis and different amounts of chemical and organic fertilizers on some characteristics of the corm and yield of saffron flower.

 Experiment was carried out as split-split plots based on a randomized complete block design with three replications at the Research Farm of Ardebil Agricultural Research Center during growing seasons of 2015-2016. Experimental treatments include: organic fertilizer at three levels, control, manure (25 t.ha-1) and vermicompost (10 t.ha-1) placed in the main plots. The second factor was chemical fertilizers in two levels including 100 and 200 kg.ha-1 nitrogen and phosphorus (NP) and the third factor is five levels of biological fertilizer including: no inoculation (control) and inoculation with Azotobacter, inoculation with Pseudomonas, inoculation with Bacillus subtilis and integrated inoculation (Azetobacter + Pseudomonas + Bacillus subtilis). The investigated traits were: leaf fresh weight, leaf dry weight, total corm, corm fresh weight, corm dry weight, corm diameter, number of flower and flower fresh weight. MSTATC software was used to conduct an analysis of variance (ANOVA) on all collected data. Significant differences between means correspond to a probability level of 0.05 according to the LSD test. Graphs were drawn using Excel software.

 The results showed that the application of chemical, organic and biological fertilizers caused a significant increase in the characteristics of dry weight of leaves, number and diameter of corms, fresh and dry weight of corms compared to the control. The integrated application of biological fertilizers increased the dry weight of saffron leaves by 76%, respectively, and also the dry weight of the corm by 81%, respectively, compared to the control. The results of analysis of variance showed that the simple effects of chemical and biological fertilizers were significant at the probability level of 1% on corm diameter. The results of mean comparison of chemical fertilizers showed that the 100% recommended chemical fertilizer treatment had the maximum stem diameter (21.78 mm), which had a significant difference with the 50% recommended fertilizer requirement treatment. Also, the results of the mean comparison of biological fertilizers showed that the combined application of biological fertilizers (Azotobacter, Pseudomonas and Bacillus subtilis) increased the corm diameter by 55% compared to the control (without inoculation). The yield of saffron flower also showed a significant increase under the influence of the applied treatments. The results of mean comparison of the chemical fertilizer treatment showed that the recommended chemical fertilizer treatment (200 kg.ha-1) compared to 50% of the fertilizer requirement (100 kg.ha-1) had the highest number of flowers with a significant difference.

 The results obtained in this research showed that the investigated traits of saffron corm were affected by the type and amount of fertilizers used. So that the simultaneous application of bio-fertilizers combined with organic and chemical fertilizers significantly affected the characteristics of saffron corms. The use of 200 kg.ha-1 chemical fertilizer along with bio-fertilizers was as effective on the measured traits as the use of 100 kg.ha-1 chemical fertilizer along with bio-fertilizers. Therefore, it can be said that the use of chemical fertilizers alone is not suitable and the combined use of chemical fertilizers with organic and biological fertilizers will increase the efficiency of chemical fertilizers and reduce the amount of chemical fertilizers used, which leads to a decrease environmental pollution.