effects of humic acid application and mother corm weight on yield and growth of saffron (crocus sativus l.)

introduction saffron as a food, spicy and medicinal plant has more than 62000 ha under cultivation with about 250 tons annual dry stigma production in iran, which includes about 90% of its world production. therefore, this plant has a specific value in agricultural export products of iran (fallahi et al., 2014). due to the important role of saffron in iran’s agroecosystems, the improvement of its agronomic practices is essential. nutritional management and mother corms size are two of the main factors affecting growth and yield of saffron. humic acid is an eco-friendly fertilizer that improves the physical, chemical and biological properties of soil. this nutritional source has hormonal compounds and exerts a positive effect on elements absorption, quality and yield of plants. 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. because, large corms have a positive effect on stigma yield especially in the first growth cycle and the weight of replacement corms and consequently saffron flowering in the other growth cycles (nassiri mahallati et al., 2008). therefore, the aim of this research was to investigate the interaction effects of mother corm size and different rates of humic acid on growth and yield of saffron. materials and methods this experiment was carried out as factorial based on randomized completely block design with three replications in research farm of ferdowsi university of mashhad, iran, during two growing season (2009-2011). experimental factors were consisted of mother corm weight (4-5, 6-8 and 9-10 g) and application of humic acid (0, 20, 40, 60, 80 and 100 kg.ha-1). mother corm planting was in early october, 2009 with 10×20 cm corms distances and planting depth of 10cm. humic acid (dissolved in water) was used along with the first autumnal irrigation in two season growth. flower and stigma yield of saffron were measured during autumn of 2009 and 2010. in addition, three corm clones were selected randomly in each plot and then all replacement corms were removed after leaf withering in may, 2011. corm measured indices were included of number of replacement corms per clone, total corms weight per clone, scale weight per clone, mean replacement corms weight and number of buds per replacement corm. finally, data analysis was done using sas 9.1 and means were compared by duncan’s multiple range test at 5% level of probability. results and discussion results showed that planting of larger mother corms improved the growth indices of replacement corms and saffron yield. the total weight of replacement corms per colon (91%), number of flowers per square (84%), flower yield (66%) and stigma dry yield (154%) were higher for the larger mother corm (9-10 g) than small mother corm (4-5 g). this result is similar to findings of nassiri mahallati et al. (2008) which concluded that planting of more than 9 g mother corms improved the growth and yield of saffron. selection of appropriate corms is the main factor in saffron cultivation, because the flowering capacity of the plant depends heavily on the weight of planted corms. planting of small corms is not affordable because they usually do not produce flower in the first growth season (kumar et al., 2009; mohammad-abadi et al., 2011). moreover, application of different levels of humic acid had a positive effect on the growth and yield indices in saffron. in the highest level of humic acid application (100 kg.ha-1), the amounts of mean number of bud per corm (10%), mean diameter of corm (19%), mean weight of corm (70%), number of flowers per square (38%), flower yield (39%) and stigma dry yield (183%) were higher than control. the positive effects of humic acid on the growth of plants is related to many factors such as increased water and nutrient absorption, increasing the availability of elements, development of plant root system, higher chlorophyll content and change in enzymes activity in the plant (sabzevari et al., 2010). conclusion generally, the findings of current study revealed that the use of large mother corms (more than 9 g) in combination with humic acid application had positive effects on replacement corms growth and stigma yield of saffron. acknowledgments we wish to thank vice president for research and technology, ferdowsi university of mashhad, iran for the financial support of the project (grant number 214b, august 30, 2009).