Crop and pan coefficients for saffron in a semi-arid region of Iran

Saffron (Crocus sativus L.) is an important prennial crop planted in Iran. The growing period of saffron is mostly winter and spring, which makes it a popular crop in areas with limited water supply. Crop coefficients, Kc (the ratio of crop potential evapotranspiration (ETcp) to reference crop evapotranspiration (ETo) of saffron are needed to calculate water requirements. ETo was estimated by the FAO Penman procedure. The values of ETcp and ETo were 486 and 991 mm for the first year (1998–1999), and 670 and 975 mm for the second year (1999–2000), respectively. Higher ETcp for the second year was due to the higher number of corms per unit area. The values of Kc varied through the growing season from 0.22–0.24 to 0.94–1.05, and 0.68–0.78 at the beginning, middle and end of the crop's cycle for both years. The pan coefficient varied from 0.23 to 1.10 for the first growing season and from 0.32 to 1.12 for the second growing season. The highest pan coefficient occurred in winter.