Relationship between fertilization and planting depths on antioxidant activity in saffron (Crocus sativus L.)

As saffron is planted in autumn, freezing stress can damage the cell membrane, reducing the corm's growth. These effects justify the necessity of studying agronomic strategies to promote plant tolerance to freezing stress. This study evaluated the impact of fertilization and planting depth on some antioxidant activities in saffron by using split plots in a randomized complete block design with three replications in 2020 and 2021. The fertilization includes 1- Nitrogen, potassium, and phosphate fertilizers based on soil test (NPK), 2- Biofertilizers (BIO) (nitrogen-fixing bacteria, phosphates, and potassium soluble bacteria), 3- Chemical fertilizers (CHE) (calcium, microelements, potassium and amino acids) and 4- Combined method (BIO- CHE) and planting depth (10 and 15 cm). Catalase activity levels were found to be higher using nitrogen, potassium, and phosphate fertilizers in 2020 and biofertilizer at a depth of 15 cm in 2021. In comparison to nitrogen, potassium, and phosphate fertilizers, with planting at a depth of 10 cm, this was an increase of 96%. Superoxide dismutase enzyme activity was highest in 2020 from nitrogen, potassium, and phosphate fertilizers and in 2021 from chemical fertilizers. When compared with nitrogen, potassium, and phosphate fertilizers and a planting depth of 10 cm, the increase was 38.7%. Chemical fertilizers resulted in a higher dry weight of corm in 2020, while in 2021, the combined method and 10 cm planting depth produced the highest dry weight. In 2020, corm dry weight correlated significantly with leaf catalase, leaf polyphenol oxidase, and superoxide dismutase activities in the mother corm, while inversely correlated with leaf proline and mother corm polyphenol oxidase activities. As a general recommendation, use chemical fertilizers and plant 15 cm deep to reduce winter freeze stress.