Effect of Superabsorbent Application under Different Irrigation Regimes on Photosynthetic Pigments in Cuminum cyminum and its Relation with Seed and Essential Oil Yield

Cumin, sometimes spelled cummin (Cuminum cyminum L.; Apiaceae), also known as Zeera is native from the East Mediterranean to India. Its seeds are used in the cuisines of many different cultures, and it is also used as a medicinal plant, serving as a digestant, as well as being used to treat anemia and the common cold. Cumin is a drought tolerant plant, has a short growth season of 100 – 120 days, with optimum growth temperature ranges between 25°C and 30 °C. Drought is one of the most important environmental factors that influences seed yield of crop plants in arid and semi-arid regions,through physiological response of plant. To reduce drought stress damages, some synthetic materials like hydroplus superabsorbent polymers, highly hydrophilic due to low cross-links in their structure, can be used to save soil moisture. Thus, superabsorbent polymer may have great potential in restoration and reclamation of soil and storing water available for plant growth and production.
To evaluate accumulation of photosynthetic pigments and seed yield of cumin, a factorial experiment was conducted based on randomized complete blocks design with three replications at the Research Farm of Urmia University (latitude 37.53° N, 45.08° E, and 1320 m above sea level).- The soil texture of experimental site was clay loam (28% silt, 32% clay, 40% sand) with 22.5% field capacity, 1.54 g/cm3 soil density, and pH 7.6. Treatments were four irrigation regimes (irrigation after 50, 100, 150 and 200 mm of evaporation from class A pan) and different amounts of superabsorbent polymer (0, 60, 120, 180, 240 and 300 kg/ha). To measure the chlorophyll content (Chlorophyll a, b, and total chlorophyll), 0.25 g of grounded leaves were adjusted to 25 ml by distilled water, and 0.5 ml of this solute was mixed with 4.5 ml acetone 80%. The upper zone of centrifuged solution was taken for spectrophotometery at 645nm and 663 nm wavelengths. To measure the yield of cumin seeds, 2 m2 of each plot was harvested and immediately were dried in the shade and at a temperature of 25 ° C. Essential oil, 25 g of powdered seeds in a one-liter flask, was extracted (W/W) by the Clevenger method (Hydro distillation) for 3 hours.
Analysis of variance showed the significant interaction between the superabsorbent polymer and irrigation on the amount of leaf chlorophyll a, chlorophyll b, total chlorophyll, seed yield, percentage and yield of essential oil. This implies a different physiological response of cumin plant in terms of adding different amounts of superabsorbent and irrigation. Means comparison indicated that the highest concentration of chlorophyll a (0.266 mg/l) and total chlorophyll (0.518 mg/l) were obtained from plants irrigated after 50 mm of evaporation without polymer application. The maximum (0.259 mg/l) and minimum (0.028 mg/l) leaf chlorophyll b belonged to irrigation after 200 mm of evaporation using 60 and 240 kg/ha polymer, respectively. The highest yield of seed (1226 kg/ha) and essential oil (36.5 kg/ha) were obtained from well-watered plants (irrigation after 50 mm of evaporation) and 60 kg/ha of polymer. Increasing irrigation intervals from 50 to 200 (50, 100, 150 and 200) mm of evaporation, need 120, 180 and 120 kg/ha polymer correspondingly for production of optimal yield of cumin. Essential oil of cumin plants was gradually and significantly enhanced by increasing irrigation distance, up to 150 mm of evaporation from pan, (with this particle)follow down by severe stress. Like seed yield the lowest yield of essential oil (0.9 kg/ha) belonged to plants irrigated after 50 mm of evaporation using 120 kg/ha superabsorbent (less than irrigation after 200 mm of evaporation). In general, in the case of well-watered plants, irrigation after 50 mm of evaporation with a small amount of superabsorbent (60 kg/ha) produced maximum seed yield and oil. However, if there is no access to water and increasing irrigation intervals twice (irrigation after 100 mm of evaporation from pan) for maximum performance requires the use of 120 kg/ha polymersince the essential oil of irrigation after 200 mm of evaporation is very low. But, if we use higher amounts of superabsorbent (300 kg/ha) more than double the yield of essential oil was obtained from this irrigation level.
A significant interaction between irrigation and superabsorbent, recommended a certain amount of polymer used as the optimum level for each irrigation regime so that the proper yield of essential oil was affected by optimal superabsorbent quantities of chlorophyll, seed yield and essential oil content. In conclusion, the suitable amounts of superabsorbent polymer were different for each irrigation regime,thereforeit is recommendedless than 120 kg/ha for control (non-stress condition) and moderate drought stress- and - 300 kg/ha for severe stress to produce essential oil of cumin plants, respectively.