Evaluating the Effects of Municipal Waste Compost and Corm Weight on Qualitative Characteristic and Secondary Metabolites of Saffron (Crocus sativus L.)

Organic fertilizers are carbon-based compounds that increase the productivity and growth quality of plants. Municipal waste compost is an organic manure that improves the physical, chemical and biological properties of soil and adds organic matter and exerts a positive effect on elements absorption, quality and yield of saffron. In addition, in saffron cultivation, it is possible to produce considerable amounts of stigma by using of standard mother corms with a minimum weight of 8 g. Therefore, the aim of this research was to investigate the interaction effects of municipal waste compost and mother corm size on chemical properties of saffron.
This experiment was conducted with a factorial arrangement based on randomized complete block design with three replications at the Agricultural Research Station, University of Birjand during the growing season of 2014-2015. Treatments were four levels of municipal waste compost (0, 5, 10 and 20 t.ha-1) and three mother corm weights (0.1-4, 4.1-8 and 8.1-12 g). Flower of saffron was measured during autumn of 2015. Total phenol was determined using the Folin-Ciocalteu assay. Free radical scavenging activity of the samples was determined using DPPH method. Secondary metabolites of saffron (crocin, picrocrocin and safranal) were measured according to Iran’s national standard.
The results showed that the highest total phenol and antioxidant activity (10.0789 mg.100 gr-1 and 65.66%, respectively) was obtained in treatment 20 t. ha-1 compost and the lowest (10.0785 mg.100 gr-1 and 62.58%) was recorded in control. Results showed that addition of the compost rate significantly increased secondary metabolites (crocin, picrocrocin and safranal). So, corm weight had a significant effect on antioxidant activity and the main secondary metabolites and the highest characteristics were obtained for corm with 8.1-12 g. As, the effect of interaction of municipal waste compost and corm weight significantly affected the main secondary metabolites.
The results showed that fertilizer treatment and corm weight influenced chemical properties and the main second metabolites of saffron positively. It has been reported that plants cannot simultaneously allocate resources to growth and defence and that there is competition between proteins and phenolics in plants for the common precursors involved in their biosynthesis .These results led us to presume that saffron plants may utilise benefits from compost fertilizer for their protein synthesis and growth development. On the other hand, organic matter (e.g. compost) acts as precursors or activators of phytohormones and growth substances and secondary compounds in plants. The type of soil and the content of organic compounds in soil can have a decisive effect on increasing the content of organic compounds in soil and strengthening antioxidant activity.