The Effect of Simultaneous Application of Organic Fertilizers and Potassium Sulfate on Yield and Characteristics of Saffron Flowers and Stigmas (Crocus sativus L.)

Saffron (Crocus sativus L.) is a perennial plant of the Iridaceae family and is cultivated in Iran, Morocco, India, Greece, Italy, and Spain. Iran is considered the main producer of saffron, with the most optimum climate for saffron. Today, the dramatic increase in food production in the world requires high amounts of chemical fertilizers. However, some of the adverse effects of chemical fertilizer overuse in conventional farming practices have been well reported. In this regard, manure can be a good alternative, which can guarantee both agricultural production and nature protection. Potassium is one of the most important nutrients for plant growth after nitrogen. In spice plants, potassium indirectly improves nitrogen utilization and protein formation, flower size, flower yield, oil content, color, etc. in spice plants. This study investigated the effect of different animal manures in combination with different levels of potassium sulfate on saffron flower criteria.

The factorial experiment was carried out based on a randomized complete block design with three replications at the agricultural lands of Jovein County, during the three cropping years of 2015-16, 2016-17, and 2017-18. The first factor includes three types of organic manure: laying poultry manure (5 and 10 ton.ha-1), broiler poultry manure (5 and 10 t.ha-1) and cow manure (20 and 40 ton.ha-1) and control (without the use of organic manure) and the second factor includes different amounts of potassium sulfate fertilizer (0, 100 and 150 kg.ha-1). The basis for determining the consumption of each organic fertilizer was applied based on the recommended nitrogen and soil test. Saffron was cultivated in September 2015 in the length of 3 m and width of 1 m plots. Flower yield was determined randomly from 40 × 50 cm-2 quadrates. Data analysis and figure drawing were performed using SAS 9.1 and MS-Excel software.

The results of analysis of variance in two years showed that the effect of animal manure and potassium sulfate and their interaction were significant on the number of flowers, total flower weight, stigma dry weight, and style dry weight. Also, potassium sulfate and manure's main effects and interaction were significant on the dry weight of flowers without stigma and style in the second year. However, the main effects of potassium sulfate and manure significantly affected on the dry weight of flowers without stigma and style, but their interaction was not significant in the third year. The highest number of flowers was obtained in the treatment of 150 kg.ha-1 potassium sulfate and 40 ton.ha-1 cow manure in the second year, and it was obtained in the treatment of 150 kg.ha-1 potassium sulfate ten ton.ha-1 laying poultry manure in the third year. The highest total flower weight belonged to the treatment of 150 kg.ha-1 potassium sulfate and 10 ton.ha-1 was laying poultry manure in second and three years. The highest stigmas dry weight was observed in 100 kg.ha-1 potassium sulfate and 40 ton.ha-1 cow manure treatment in the second year, and the highest amount of this trait was related to the treatment of 100 kg.ha-1 potassium sulfate and ten ton.ha-1 broiler poultry manure in the third year. The results of this experiment indicate that the application of animal manures and potassium sulfate combination has positive effects on improving the yield of saffron flowers and eco-friendliness. It seems that the combination of animal manures and chemical fertilizers can reduce the use of chemical fertilizers.

The results of this study showed that the best treatment for most traits was 150 kg.ha-1 potassium sulfate and 40 ton.ha-1 cow manure interaction treatment in the second and third years, and then the 150 kg.ha-1 potassium sulfate and ten ton.ha-1 laying poultry manure treatment could be mentioned as the superior treatment. In general, according to the findings of this study, it seems that the simultaneous application of optimal amounts of ecological inputs and chemical fertilizers of potassium sulfate can reduce the destructive effects caused by excessive use of chemical fertilizers on this valuable medicinal plant while improving the properties of saffron flowers.