Climate and management factors influence saffron yield in different environments

The economic yield of saffron (Crocus sativus L.) has a wide range in different parts of the world, and it is not clear why this considerable difference exists. In this research saffron yield and yield components of 13 fields with varied geographic and climatic conditions were studied to determine which factor(s) are more important. Among the studied factors, temperature, field age, soil texture, bulk density, soil and water pH, irrigation events, and growth period had the greatest effect on saffron yield. The highest dry stigma weight, as economic yield, was obtained in three regions of Birjand (27 kg ha−1), Sarayan (24 kg ha−1), and Golshan (23.5 kg ha−1), followed by Neyshabur (18 kg ha−1) and Kashmar (17.5 kg ha−1), which had lower temperatures, coarse soil, balanced soil, and water pH, and longer growth periods. The average yields were increased until the sixth or seventh year (20.8 kg ha−1) and then decreased, however, it seems to be economic before the 10th year. Lower temperatures in early fall were important to stimulate flowering and increase yield in that year, and warm and sunny days in the spring are important for next year yields. We found that the optimal temperature for the first irrigation is ∼16°C and for flowering is ∼5°C–10°C. High-yield fields did not have higher irrigation water volumes but more irrigation events (6.3), resulting in less water volume per irrigation. No direct relationship was observed between manure consumption and yield; however, processed manure increases yield by improving the soil structure and moisture retention ability. Fields with a complete chemical fertilizer composition had higher yields. It was concluded higher yields are achieved in saffron fields where regions are higher in altitude (at least 1300 m) and lower temperature in early autumn with complete fertilizer composition (especially sulfur and iron). There was no evidence of high salinity sensitivity of saffron.