Influence of organic and chemical fertilization on growth and flowering of saffron under two irrigation regimes

The combined effect of water and nutrient availability is one of the most important factors in corm growth and flowering of saffron. In addition, it seems that applying water in amounts more than conventional amounts in semi-arid areas can be more useful in saffron cultivation. Accordingly, the effects of irrigation regimes [two and four weeks intervals equal to application of 3600 (conventional irrigation treatment) and 7200 m3.ha-1 (extensive-irrigation treatment) during saffron growth], as well as organic (30 ton.ha-1 cow manure based on soil and manure analysis results) and chemical fertilizers (220, 150 and 100 kg.ha-1 urea, super-phosphate and potassium sulfate, respectively) with a control treatment (no-fertilizer) are studied on some physiological growth indices, corm production and flowering of saffron in this experiment. The experiment was conducted as factorial based on a randomized completely block design with three replications in Sarayan county, Iran, during 2014-2016. Vegetative growth indices were studied during the first growth cycle, while flowering indices were measured during the second growth season. Total biomass has an increasing trend during saffron growth cycle in all treatments. This index was higher in cow manure treatment in both levels of water availability, during the last two growth months. Crop growth rate (CGR) was slow (below 3.9 g.m-2.day-1), rapid (3.9-12 g.m-2.day-1) and intermediate (5.5 g.m-2.day-1) in the early (the first 90 days of growth), middle (90-150 days after growth) and late (150-180 days of growth) growth periods. The highest CGR (12 g.m-2.day-1) was obtained in cow manure treatment and 145 days after the first autumnal irrigation. In all treatments, leaf weight ratio (leaf to total plant weight ratio) has a decreasing trend from two months after the first irrigation until the end of the growth cycle and it is slightly higher in fertilization treatments. Cow manure application increased the corm production and total corms weight per plant by 15 and 13%, respectively, compared with the control treatment. The highest mean weight of replacement corms (6.4 g) was shown in combined treatment of cow manure and two weeks' irrigation intervals. The highest values of flower number (98 flower per m2), flower yield (24.3 g.m-2), style yield (0.56 g.m-2) and dry petal yield (3.7 g.m-2) were obtained in plants that had been treated with cow manure and received water in intervals of 4 weeks. In cow manure fertilizer and control treatments, the highest flower and stigma yield were obtained in irrigation intervals of 4 weeks, while in chemical fertilizer treatment, the highest flower and stigma yield were obtained in 2 week irrigation intervals. Therefore, it seems that application of cow manure combined with consumption of 3600 m3.ha-1 is suitable during the first growth cycle of saffron during which corm density and transpiration area are low.