Optimization of cow manure levels and corm weight in saffron (Crocus sativus L.) by Central Composite Design

In this work, effects of cow manure and corm weight on flower yield, stigma yield, style weight and qualitative criteria of saffron using central composite design was done. This experiment was conducted with 13 treatments and two replications at the Research Field of Ferdowsi University of Mashhad during the growing season of 2015-2016 and 2016-2017. The treatments were allocated based on low and high levels of cow manure (0 and 40 t.ha-1, respectively) and corm weight (7 and 20 t.ha-1, respectively). Flower number, fresh weight of flower, dry weight of stigma, dry weight of style, stigma yield and crocin (coloring agent), picrocrocin (a specific bitter taste) and safranal (the main cause of odor) contents were calculated as dependent variables and changes of these variables were evaluated by a regression model. The quality of the fitted model was judged using the determination coefficient (R2). The results showed that the effect of linear component was significant (p≤0.01) on all studied characteristics. Effect of square component was significant (p≤0.01) on all studied criteria except for crocin content. Interaction effect of full quadratic was not significant on none of these traits. The range of R2 was calculated from 79.28 to 94.30. The highest simulated and observed values of flower number (93 and 81.36 flowers.m-2, respectively) and stigma yield (0.523 and 0.46 g.m-2, respectively) observed in 40 t cow manure per ha and 13.5 t corms per ha.