Quantitative and qualitative changes of ajowan (Carum copticum L. C.B. Clarke) essential oil in spring and summer cultivation under salinity stress

Ajowan (Carum copticum L. C.B. Clarke) is an annual plant of the Apiaceae family with medicinal, health and industrial uses. To investigate the effect of irrigation water salinity and planting date on some characteristics of this plant, a split-split plot experiment based on a randomized complete design with three replications was conducted in Isfahan, Iran. Two different planting dates (spring: March 23 and summer: June 21) and four different salinity levels (0.3 (control), 3, 6 and 9 dS/m), were assigned to main plots and subplots, respectively. The results showed that the highest plant height (93.2 cm) and biological yield (1367.7 g/m2) were obtained at 0.3 dS/m and summer planting date and maximum seed yield (230 g/m2) was observed at 0.3 dS/m and spring planting date. Increasing salinity levels decreased plant height, biological and seed yields. Interaction effects of salinity and planting season on essential oil percent and yield was not significant. The number of compounds identified in aerial parts of essential oil was 15 and 11 in summer and spring planting season, respectively. Based on the results, salinity had significant effect on essential oil yield, but no significant effect on essential oil percentage. Quality and quantity changes of essential oil components had no typical pattern. Spring was the most appropriate planting date in Isfahan climatic conditions for ajowan.