Do corm seeding rate and planting depth influence growth indicators of saffron (Crocus sativus L.)?

Saffron, the primary in the market now, is a food spice by far the world's most expensive. In order to study the effects of different corm seeding rates and sowing depth on physiological indices of saffron, an experiment was conducted as a factorial layout based on randomized complete block design with three replications at the research farm of the Ferdowsi University of Mashhad during 2015-2017 years. The experimental treatments were all combinations of different corms seeding rates in four levels (7, 8, 9, and 10 Mg ha(-1)) and sowing depth in three levels (10, 15, and 20 cm). The studied traits were the dry weight of mother and daughter corms, cumulative dry matter, and some growth indices such as leaf area index (LAI), crop growth rates (CGR), relative growth rate (RGR), and Leaf Area Ratio (LAR). The results showed 8 Mg ha(-1) corm seeding rate and 10 cm sowing depth increased total crop dry weight, CGR, and RGR in saffron. Based on obtained results at the beginning of the vegetative growth period, CGR declined for a short time. So that by continuing the vegetative growth, the plant reached on growth compensation point, and then CGR increased. From 180 days after the sowing date and in the late stages of vegetative growth, the growth rates trend decreased again. The results also showed that the LAR trend decreased from the early vegetative growth period, which can be explained by the faster growth of the daughter corms and other underground parts of the plant than the leaves during the early vegetative growth period. According to the results and the natural trend of mother corm breakup during the growing season, increasing density due to increasing competition between mother corms caused intensification in a weight reduction of mother corms in the late stages of the growing season. Also, in the first three months after sowing, daughter corms did not grow anymore, and the beginning of their growth coincided with the end of the saffron flowering period.