Effect of different levels of irrigation and harvesting time on some agronomical characteristics and oil production of Carum copticum L

Introduction Ajowan (Carum copticum L.) is an annual plant and herbaceous belonging to the Apiaceae family (Majnoon Hosseini and Davazdah emami, 2007). The main component of ajowan essential oil is Thymol. Other main components of seed oil include α-pinene, β-pinene, p-cymene, γ-terpinene, p-cymine and limonene (Majnoon Hosseini and Davazdah emami, 2007). Irrigation scheduling based on developmental stage or deficit irrigation is the technique of applying water on a timely and accurate basis to the crop, and is the key to conserving water and improving irrigation performance and sustainability of irrigated agriculture (Omidbaigi, 2009). Water stress substantially alters plant metabolism, decreasing plant growth, yield and photosynthesis but in some medicinal plants increase active substances such as essential oil (Bettaieb et al., 2009; Rebey, 2012). Heidari et al (2012) indicated that seed yield and essential oil yield affected by water stress and during maturation stages and found great differences in the essential oil percentage. Rezaei- Chiyaneh (2011) reported that number of umbels per plant, number of seeds per umbels, 1000-seed weight, biological yield, seed yield and essential oil yield significantly decreased with increasing irrigation intervals, but essential oil percentage increased.
Despite considerable studies on the effect of drought stress on field crops the information on the behavior of the aromatic and medicinal plants has not been well investigated under water deficiency. Therefore, the main objective of the present study was to find out the effect of water deficit and harvesting time on the performance of plant and change in oil Ajowan in during stage of maturity. And so, it can be determine the optimal irrigation level and harvest time to maximize the seed yield and essential oil content.
Materials and methodsField experiment was conducted at the farm located in West Azerbaijan province- city Nagadeh, Iran (latitude of 36, 57' and longitude of 45, 24’ at an altitude of 1328 m above mean sea level) during growing reason of 2010-2011. Treatments included irrigation (Irrigation after 60, 90, 120, 150 and 180 mm evaporation from class A pan) as main plots and harvesting time (milky, dough and maturity stages) as subplots were arranged as split plot based on randomized complete block design with three replications.
Mean annual temperature and rainfall were 12.40 ˚C and 323 mm, respectively. The soil was clay- loam. Each plot size was 3.2 m× 4m involving 8 rows with 40 cm between rows and a distance of 25 cm between plants in the row on April 4, 2011. Basic fertilization was applied at the time of soil preparation at rates of 100 kg/ha N and 150 kg/ha p2o5. Weed control was performed manually. Also a block distance the main plot 1.5 meter and three-meter distance between the two blocks were considered to have an effect on both the moisture adjacent plots.
The essential oil was isolated from 3o g of the fruits by conventional hydro-distillation for 3 h according to the method described in British Pharmacopeia. The essential oil content was calculated as a percentage.
SPSS software was used for statistical analysis. To compare the means of Duncan's multiple range test at 5% probability level was used.
Result and discussionResults of ANOVA showed the significant effect of irrigation on the plant height, number of umbels per plant, number of seeds per umbels, 1000-seed weight, biological yield, seed yield, essential oil percentage and essential oil yield. All the mentioned traits significantly decreased with increasing irrigation intervals from 60 to 180 mm evaporation. The highest yield of seed (1074 kg.ha-1) and essential oil yield (39.63 kg.ha-1) were achieved by irrigation after 60 mm evaporation. The effects of harvest date on the number of umbrella per plant, 1000-seed weight, biological yield, grain yield, essential oil percentage and essential oil yield were significant. The highest seed yield (931 kg.ha-1), essential oil percentage (4.35%) and essential oil yield (40.13 kg.ha-1) were obtained in dough stage. Telci et al (2009) compared the variation of fennel fruit essential oil composition during maturation stages and found great differences in the oil composition.
ConclusionIncreasing irrigation intervals from 60 to 180 mm evaporation resulted in decreasing plant height, umbels per plant, seeds perumbel, seeds per umbelet, 1000-seed weight, biological yield, seed yield and essential oil yield. Since irrigation after 90 mm evaporation of the irrigation after 60 mm evaporation of grain produced no significant difference and stage of dough showed higher performance. Therefore, it is recommended that to maximize essential oil production and achieve acceptable performance of Ajowan plant, it would be grown under moderate water deficit stress and be harvested at hard dough stage.