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a Institute of Soil Water and Environmental Science, Volcani Center, POB 6, Bet-Dagan, 50-250, Israel
b Aromatic, Medicinal and Spice Crops, ARO, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel
* Corresponding author (nativdud{at}agri.gov.il).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Abbreviations: DM, dry mass • EC, electrical conductivity • ROS, reactive oxygen species • SAR, sodium absorption ratio
Received for publication April 17, 2007.
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Perennial aromatic plants are cultivated as cash-crops for fresh or dry herb production, or as a source of essential oils and natural antioxidants. These summer crops require substantial amounts of water, up to 7000 to 9000 m3 ha–1 throughout the growing season, to satisfy their potential for intensive biomass production (Putievsky et al., 1990; Dudai, 2005). Hundreds of hectares of these crops are required to facilitate an economically viable industrial production system. Therefore, shortage of fresh water for irrigation in arid and semiarid regions restricts utilization of aromatic plants as industrial crops. Replacement of fresh water with treated effluent for irrigation of these plants could promote development of large-scale production systems for biomass, essential oil, and natural antioxidants in arid and semiarid zones.
Cultivation of aromatic plants for essential oils is suitable for irrigation with treated effluents because the heat applied during oil extraction eliminates human bacterial pathogens originating in the effluents and alleviates health concerns. Additionally, the essential oil, which is extracted mainly by steam distillation, will be free of inorganic ion contaminants such as heavy metals originating from the effluents, which may accumulate in the plant tissues and the soil.
Oregano and rosemary are two important aromatic crops. These perennial members of the Lamiaceae family, in addition to their essential oil yield production, are a good source for natural phenolic antioxidants (Putievsky et al.,1988; Ravid et al., 1997; Munné-Bosch and Alegre, 2001, 2004; Chun et al., 2005; Skerget et al., 2005). No information is currently available concerning the effect of irrigation with treated municipal effluent on growth and development of these crops, their essential oil yield or their antioxidant production.
Salinity and heavy metals contained in treated effluents may increase antioxidant activity and reactive oxygen species (ROS) production in plants. Increased antioxidant content and antioxidant activity were demonstrated in many plants in response to environmental stresses (Mittler, 2002). In rosemary, water stress induced changes in antioxidants which were suggested to be involved in prevention of plant tissues damage (Munné-Bosch and Alegre, 2000). Therefore, irrigation of antioxidant producer crops such as oregano and rosemary with treated effluent containing high levels of salts and heavy metals may induce stress on the plants, increase antioxidant phenolic compound production, and may lead to an economic advantage over regular water irrigation.
In the present study we aimed to evaluate the effect of irrigation with secondary treated effluent, containing high levels of salts, on plant morphology, fresh and dry herb yield, and essential oil and antioxidant phenolic-compound production in two aromatic crops, oregano and rosemary. The two cultivars used in the study, ‘Oren’ for oregano and ‘Zakuf’ for rosemary were developed for fresh herb production and the present study is first to test their potential for industrial production of essential oil and antioxidants. During a 3-yr project, yield components of the plants and composition of their essential oil and antioxidant phenolic compounds under irrigation with treated effluent were compared to cultivation with potable water.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Growing Conditions
The experiments were conducted at Akko Agricultural Experimental Station, located near the city of Acre (32°55'40'' N, 35°4'54'' E, sea level altitude) in northern Israel, during three consecutive years (2002, 2003, and 2004) in an open field, 0.1 ha in size. Soil at this site is a Vertisol, with 60% clay, 21% silt, and 19% sand. Precipitation varied from 585 to 728 mm yr–1, concentrated in the months of October through March, with an average annual evaporation of 1612 mm.
Rooted cuttings prepared by Hishtil nurseries (Afula, Israel) in May, were planted in the experimental plot, on 1 May 2002. A factorial design with two species and two water qualities was planted as a random design with 10 replicates. Each randomized block had four plots of two water qualities and two species. The plots were 10 m long beds, 193 cm wide (center to center). There were four rows of plants in each plot, five plants per running meter in each row, forming a total of 10 plants m–2. The plants were irrigated with potable water (control) or secondary-treated effluent.
Water Quality and Irrigation Treatments
The secondary-treated effluent used in the study were from domestic sewage of the towns Shomrat, Bustan, Kfar Masser, and Gadida. The effluent were treated at the Shomrat-Agamit Treatment Facility. Chemical composition of both sources of irrigation water was determined and is detailed in Table 1
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Routine Monitoring and Measurements
Throughout the experiment, pH, EC, Cl, N-NO3, N-NH4, Na, K, Cl, Ca+Mg, P, B, Mn, Cu, Zn, Al Cr, and Fe in the source water were analyzed once a month. The plants were harvested twice annually, and the quantity and quality of the yield were evaluated for each harvest. Yield components were evaluated on 29 Aug. and 2 Oct. 2002, 7 July and 26 Aug. 2003, and 28 Apr. and 13 July 2004. The harvests were performed with a hand reaping machine simulating the combine harvester. The plants were cut 10–20 cm above-ground, in accordance with conventional agronomic practice, and evaluated for fresh biomass, dry biomass, and percentage of dry weight (% DM) in the harvested material following oven desiccation at 64°C for 48 h. Quantity and quality of essential oils were also determined. Leaf dry weight was determined after separation from the stems, as a measure of marketable dry herb yield. The percent dry weight biomass of leaves was determined following 1 wk of desiccation at 40°C. Plant material was sampled for contents of inorganic elements on 15 Aug. 2004. For each replica biomass of three plants was combined, mixed, and ground together and a 0.5-g subsample was used for the analysis. The effect of the irrigation water quality on the morphological development of the plants was analyzed annually. Plant height, final leaf length, width, and area and the number and length of the internodes were evaluated on five plants within each plot.
Soil mineral content was analyzed in September 2004, before the beginning of the rainy season when water quality at the treated-water reservoir is poorest and potential effects on the soil are highest. Soil samples were taken separately from two soil layers, 0 to 60 and 60 to120 cm depth, 10 cm from the dripper. Soil from four sampling spots per plot, 8 cm wide each, were combined for the plot sample. Results presented are averages ± standard error, SE, n = 5.
Inorganic Chemical Analysis
Three different procedures were used for the extraction of various mineral elements from the plant tissue. For the analyses of Cl, dried plant samples were extracted with a dilute acid solution containing 0.1 M HNO3. Chlorine (Cl) was measured by potentiometric titration. For the analysis of N, P, K, Na, Ca, and Mg, the dry tissue was digested with H2SO4 (98%) and HClO4 (70–72%). The Na, K, Ca, and Mg were measured by atomic A/E (PerkinElmer 460; PerkinElmer, Waltham, MA), and P and N by color development. For the analysis of Zn, Mn, Cu, and B, the dry tissue was dry-ashed at 600°C and the ash dissolved with 32% HCl. Boron was analyzed with a Spectroflame Modula ICP 61E Trace analyzer (Thermo-electron Corp., Waltham, MA), and Zn, Mn, and Cu were measured by atomic A/E (Neves-Piestun and Bernstein, 2005).
The pH, EC, and the Cl, Na, Ca, Ca+Mg, and K concentrations in the soil were determined from extracts of saturated soil paste. The EC of the saturated soil paste extracts and the irrigation source water was measured with a conductivity meter, Na and K were analyzed by flame photometer and Mg+Ca by titration. In addition, B was analyzed with a Spectroflame Modula ICP and Ca, Fe, Cr, Cd, Pb, and Sr by atomic A/E (Neves Piestun and Bernstein, 2005). The N-NH4, N-NO3, P, and Cl were analyzed with an autoanalyzer (Lachat Instruments, Milwaukee, WI).
Analysis of Essential Oil Content and Composition
Essential oils were separated from the harvested fresh plant material by hydrodistillation. Samples of at least 250 g of fresh plant material were hydrodistilled for 1.5 h in a modified Clevenger apparatus. The essential oil was cooled and separated from the cohobated water.
Determination of essential oil composition was performed by GC–MS Analyses. Samples consisting of essential oil diluted in dichloromethane (1:100) were analyzed on an HP-GCD apparatus equipped with an Rtx-5SIL MS (30 m x 0.25 mm i.d. x 0.25 mm) fused-silica capillary column (Restek). Helium (at 1 mL min–1) was used as a carrier gas. Samples of essential oil were injected in the split injection mode at a ratio of 1:30. Samples of extracts were injected in both split and splitless injection modes. Injector temperature was 250°C and transfer line temperature was 280°C. Column conditions were 70°C for 2 min, 70 to 200°C at 4°C min–1 and 10 min at 200°C. The mass range was acquired by working in the EI mode (70 eV), in an m/z range of 45 to 450. The identification of the compounds was performed by comparing their relative retention indices and spectra with those of authentic standards or with those found in the literature (Adams, 2001), and supplemented with NIST 98 and QuadLib 1607 GC–MS libraries.
Antioxidant Activity and Phenols Analysis
Extraction of Phenolic Compounds
One-hundred milligrams of ground dried leaves was mixed with 10 mL of 80% methanol in a 15-mL tube. The tubes were shaken at 165 RPM overnight at room temperature. The extract was than transferred to an Eppendorf tube and spun for 5 min to remove particles, before it was used for the analysis. The remaining extract was kept in –20°C for further analysis.
Antioxidant Activity
Antioxidant activity was measured by a radical scavenging assay, using 1,1-diphenyl-2-picryldrazyl (DPPH). Radical scavenging was measured by monitoring the reduction of DPPH (Sigma, St. Louis, MO) in the presence of leaf tissue extract. Six milligrams of DPPH were mixed in 100 mL of 100% ethanol until it dissolved by vigorous mixing for 15 min. This reaction agent was made fresh for each new analysis. The purple color of a fresh nonreduced DPPH reagent, was adjusted to around optical density, OD = 1.0 at 517 nm. Ten microliters of the plant extract were placed in a dry, clean Eppendorf tube. Then, 990 µL of the DPPH reagent were added. The mixture was incubated in dark at room temperature for 1 h. The DPPH-plant mixture was read at 517 nm, using Agilent 8453 UV-Visible spectrophotometer (Agilent Technologies, Santa Clara, CA). The obtained absorbency values were subtracted from the original base line reading of the original purple color at OD517 = 1.0. Care was taken to read each sample in a range of OD517 of 0.3 to 0.6, to remain in the linear range and some samples had to be diluted before the assay to attain this range. A standard curve for chlorogenic acid (Sigma, St. Louis, MO) induced reduction of DPPH was performed under the same conditions as the plant extract. The antioxidant activity was then expressed as chlorogenic acid equivalent.
HPLC Analysis of Phenolic Compounds
HPLC (HP 1090 series II) was used for the separation and estimation of rosmarinic acid, carnosic acid, and carnosol. The method adapted from Cuvelier et al. (1996) was performed on a reversed phase C18 Purospher (Merck, Darmstadt, Germany) STAR RP-18 endcapped (25 cm by 4.6 mm, 5 µm pore size; Merck, Darmstadt, Germany) using a C18 guard column. Twenty microliters of the methanolic plant-tissue extract was injected. The mobile phase was programmed with a linear gradient from 90% A (840 mL of deionized water with 8.5 mL of acetic acid and 150 mL of acetonitrile), 10% B (methanol), to 100% B in 40 min, with a flow rate of 1.0 mL min–1, and 100% B to 45 min. The system was left to stabilize for 10 min between consecutive injections. The compounds were identified by comparison with the relative retention time of authentic samples. The absorbance at 284 nm of carnosic acid, carnosol and rosmarinic acid was determined based on a calibration curve of these compounds.
Total Phenolic Compounds Assay
Total phenolic compounds were determined according to a modified method from Chun et al. (2005). A sample of 50 µL of plant extract was added to a test vial and mixed with 7 mL water, and then 0.5 mL 1 M Folin–Ciocalteu reagent was added. After 3 min, 1 mL 5% Na2CO3 was added and the reaction mixture was allowed to stand for 30 min before the absorbance at 760 nm was measured. A standard curve was established for each assay using 0.2 to 4.0 of 0.15 mg mL–1 gallic acid in water.
Statistics
Results of yield biomass quantity and quality parameters, that is, fresh biomass, dry matter, percent DM, amount and percent of dry leaves in the harvested plant material, amount and percent of essential oils, as well as essential oils composition parameters, antioxidant activity, and content of inorganic and phenolic compounds in the plant tissues were expressed as means ± standard errors (SE), of five replicates. The statistical analysis was performed with JMP software (Version 5.0; SAS Institute Inc., 2002, Cary, NC) and SigmaStat (Jandel Scientific, San Rafael, CA) software packages. One-way and two-way analysis of variance (SAS general linear model procedures) were used to analyze the data at P = 0.05.
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RESULTS |
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Irrigation with treated effluent had no effect on overall plant development of oregano or rosemary. The morphological development of the plants was also not affected by the effluent. All the parameters evaluated, that is, plant height; internodes length and number; and leaf length, width, and area were similar in plants irrigated with potable water and the effluent (data not shown).
For all yield parameters similar results were obtained for the second and third experimental years of the project. During the first year, the plants were young and the yield was significantly lower than in following years (data not shown). Results presented are therefore averaged annual data for the second and third year.
Irrigation with the effluent did not affect growth and yield quantity of both aromatic plants (Table 2 ). Biomass production, which is an indicator of aromatic plants' yield for the fresh-herb market, did not differ compared to irrigation with potable water. The percent DM and percent of dry leaves weight from the total fresh weight, which determine yield for the dry-herb market were also not affected by water quality (Table 2). Similarly, production of essential-oil yield was not affected by irrigation with the marginal water, and the oil-yield was similar under irrigation with effluent and potable water, both in terms of production per area, as well as percent weight of the fresh biomass (Table 2).
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Irrigation with the treated effluent, as compared to potable water, did not alter the essential oil components, or their relative amounts, in both oregano and rosemary (Table 3 ).
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DISCUSSION |
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Several chemical characteristics of the effluent used in the project, that is, high bicarbonate, B content, and salinity, could have negative effects on plant growth and agronomic performance (Feigin et al., 1991). The lack of negative responses of the aromatic species in this study to 3-yr irrigation with effluent points at their resistance to the levels of the mineral elements present in the effluent, as is further discussed below.
Antioxidant Activity and Phenol Compounds Content
Reactive oxygen species are continuously produced in plants as byproducts of aerobic metabolism. Some are highly toxic and develop oxidative stress in plant cells. Therefore, plants develop various cellular enzymatic and nonenzymatic mechanisms for detoxification (Apel and Hirt, 2004). Environmental stresses including salinity and heavy metals increase ROS production and oxidative stress (Mittler, 2002). To reduce elevated ROS levels during oxidative stress conditions, some plants increase antioxidant activity through the generation of antioxidants. In these plants, stimulated generation of antioxidants signals the exposure to suboptimal conditions. Phenolic compounds are commonly found in plants and have multiple biological effects, including antioxidant activity (Kähkönen et al., 1999). Aromatic plants are especially rich in phenolic antioxidant compounds. The antioxidant activity of phenolic compounds in plants is mainly due to their redox properties and chemical structure, which can play an important role in neutralizing ROS such as free radicals, singlet and triplet oxygen, and peroxides (Zheng and Wang, 2001). Due to the carcinogenic potential of synthetic antioxidants, natural phenolic antioxidants are being promoted as food preservatives and diet supplements (Shetty, 1997; Botsoglou et al., 2002). Both oregano and rosemary are known as a good source of natural phenolic antioxidants (Del Bano et al., 2003; Chun et al., 2005; Almela et al., 2006). The antioxidant activity in oregano is attributed both to its essential oil and soluble phenolic fractions (Eguchi et al., 1996; Engleberger et al., 1988). Kikuzaki and Nakatani (1988) isolated five different phenolic compounds from leaves of oregano and among these rosmarinic acid was found to be present in highest concentrations. The phenolic monoterpenes, thymol and carvacrol are components of the essential oil in oregano and significantly contribute to its cellular antioxidant activity (Svoboda et al., 2006). In rosemary, water stress induced changes in antioxidant levels were suggested to prevent damage to the plants (Munné-Bosch and Alegre, 2000). Rosmarinic and carnosic acid were reported as major antioxidant active phenolic compounds in rosemary plants (Almela et al., 2006). Carnosic acid protects chloroplasts from oxidative stress in vivo by following a highly regulated compartmentation of oxidation products (Munné-Bosch and Alegre, 2001). Its concentration in rosemary leaves largely depends on seasonal and environmental factors, in addition to their genetic background (Hidalgo et al., 1998).
Our results demonstrated that antioxidant activity and phenol compounds content were not affected by 3-yr irrigation with the saline effluent (Fig. 1 and Table 4), and suggested that the levels of salinity and heavy metals in the effluent used for irrigation in this project were below the stress threshold level for these species. This is in agreement with no effects of the effluent on plant development, and yield quantity and quality (Tables 2–4
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Bicarbonate
High bicarbonate (HCO3–) concentration is typical of urban-treated sewage water. In Israel, bicarbonate concentrations are higher in the treated sewage water than in potable water by about 210 mg L–1 (Feigin et al., 1991) or more. A similar increase was found in the effluent used in this study (Table 1). To the best of our knowledge no information is currently available concerning levels of tolerance of oregano and rosemary to HCO3– and its effect on morphological development, yield quantity and quality of the plants. In the present study, HCO3– concentration in the treated sewage water was 640 to 690 mg L–1 and this concentration was apparently below the damage threshold. In a previous study involving effluent, similar HCO3– concentrations did not affect cut-flower production of roses (Bernstein et al., 2006). Total plant biomass production and oil yield of other aromatic species, that is, palmarosa [Cymbopogon martinii (Roxb.)]and East Indian lemongrass [C. flexuosus (Nees ex Steud.) W. Wats.] were reduced at 4.0 meq L–1 (240 mg L–1) of sodium carbonate in the irrigation water (Prasad et al., 2001).
Boron
We found no previous information about the effect of high B levels, in the range typical of the treated sewage water used in this project, on growth and production of oregano and rosemary. In most treated effluent in Israel, B content is higher than 0.5 mg L–1, which is the threshold for toxicity for many crops (Feigin et al., 1991; Maas, 1996). In the present study, the treated water contained 0.55 to 0.7 mg L–1 B (Table 1), about 0.5 mg L–1 higher than potable water. Apparently, these concentrations were below the threshold for damage in both plant species studied and hence did not effect the morphological development of the plant and yield quantity and quality. This suggests that these plants are relatively resistant to B. However, because B acumulates in plant tissues, damaging effects may occur, if irrigation with effluent exceeds 3 yr.
pH
The pH of treated effluents is usually higher than potable water from which they were derived, and ranges between 7.5 and 8.5 (Feigin et al., 1991). In the effluent used for our study, pH ranged from 7.5 to 8.1 which was about one unit higher than local potable water. Root damage of several plant species occurred at pH 7.6 (Zieslin and Abolitz, 1994). At high pH, availability of nutrients to the plant roots might change due to alterations in the solubility products of compounds in the fertigation and soil solutions, and changes in ion adsorption and release strengths of the soil complex. The pH levels of saturated soil pastes were similar in both water treatments, 7.55 for soil irrigated with potable water and 7.60 for soil irrigated with effluent at 0 to 60 cm depth. Therefore, the lack of response of the plants to the higher pH value of the effluent (up to 8.1) could result from the short duration of exposure to the high pH, occurring at the time of irrigation, as well as from plant resistance. We know of no study involving evaluation of pH effects on oregano and rosemary, however there are indications that other aromatic plants can tolerate high pH levels. For example, pot marjoram (Origanum onites L.) was abundant in soils with pH 7.99 (Gönüz et al., 1999), palmarosa and East Indian lemongrass grew successfully on moderately alkaline soils with pH up to 9.2 (Dagar et al., 2004), and no damage symptoms were reported for field mint (Mentha arvensis L.) growing in soil with pH of 8.2 (Gupta et al., 2002).
Salinity
High Na and Cl concentrations inhibit plant growth and development (Bernstein et al., 1995; Bernstein and Kafkafi, 2000). Respective concentrations of Cl and Na in the treated effluent reached 160 and 135 mg L–1 (EC value of 1.6 dS m–1) during the summer months, about twice as high as in potable water (Table 1); yet no signs of salinity damage were apparent on the plants (Table 2). Plant appearance, production, and oil quality did not differ after 3 yr exposure to the effluent as compared to potable water (Tables 3 and 4). This indicates that the threshold for salinity damage of both cultivars of rosemary and oregano used in this study, was higher than 1.6 dS m–1. Other aromatic plants demonstrated moderate tolerance to salinity. For example, mint species survived high salinity levels, with about 65% of the yield achieved even under 1 M NaCl (Dow et al., 1981; El-Keltawi and Croteau, 1987). Lemon balm (Melissa officinalis L.) was moderately tolerant to salinity, with optimal growth between 1 and 2 dS m,–1 and the threshold level for plant death was 6 dS m–1 salinity in the irrigation water (Ozturk et al., 2004). Growth and essential oil production of two rose geranium (Pelargonium graveolens L'Hér. ex Ait.) cultivars were not reduced under soil exchangeable sodium percentage (ESP) levels lower than 20.0 and 7.0, respectively (Prasad et al., 2006). Suppression of plant growth in three Cymbopogon grasses (Java citronella [C. winteranus Jowitt], East Indian lemongrass, and palmarosa) occurred at higher salinity levels than the level applied in this project (Ansari et al., 1998), and a salt tolerant line of palmarosa had a regeneration potential even under salt concentrations as high as 200 mmol L–1 (Patnaik and Debata, 1997).
N-NH4. Plants can take up N as NO3– or NH4+ (Mengel and Kirby, 1979). Due to the different physiological effect of these two ions on the plant, their concentrations in the root growing medium and their ratio, affect plant growth and performance (Goyal et al., 1982; Feigin et al., 1984; Marschner, 1986; Bar-Tal et al., 2001). In treated sewage water, most of the N is as N-NH4. In secondary treated effluent, N-NH4 concentration is usually in the range of 1.4 to 3.2 mmol L–1, and N-NO3 concentration is of 0 to 0.7 mmol L–1 (Feigin et al., 1991). In the present study, the effluent contained 1.3 to 2.2 mmol L–1 N-NH4 (23–40 mg L–1), and since ammonium nitrate was used as a fertilizer, the fertigation solution contained even higher levels of N-NH4. The resulting high percentages of N-NH4 did not reduce yield quality or quantity in any of the investigated species. This suggests that the level of N-NH4, common for most sewage waters following secondary purification is not restrictive for growth and production of oregano and rosemary. Under the experimental conditions, (i.e., growth in soil and irrigation twice weekly), due to nitrification processes in the soil, the plants were likely exposed to high N-NH4 concentrations present in the irrigation solution for limited duration only, following each irrigation event. It should therefore be considered that different plant responses might result from other irrigation schemes with effluent, or under different soil conditions.
Variability in plant response to the amount N and to the ratio between N forms exists within and between aromatic plant species. Java citronella responded well to applied N, with cultivars differing by up to 42% with respect to biomass production and up to 36% with respect to oil yield at the same N levels (Singh et al., 1980; Rao et al., 1983). Variation in biomass yield of a single cultivar of Java citronella with application of different types of urea has been demonstrated by Singh and Singh (1992). Nitrogen shortages and deficiency symptoms occur in many production areas in the United States and response to N has been widely examined (reviewed by Brown, 2003). In three mint species, oil production decreased with increased N application, being greatest with no applied N (Singh et al., 1989), but the oil quality did not vary appreciably with application of N fertilizer. Piccaglia et al. (1989) found that mineral fertilizers, N, K, and P induced only small changes in oil quality of sage (Salvia officinalis L.) and in sweet basil (Ocimum basilicum L.) ammonium fertilizer reduced essential oil content by 28% compared with nitrate fertilizer, and increased the sesquiterpenes percentage in the oil (Adler et al., 1989).
Potential of Oregano and Rosemary for Intensive Industrial Production Systems under Irrigation with Effluent
The understanding of how the plants respond to the agronomic growing conditions is a prerequisite for the prediction of essential oil and antioxidants yield, and for controlling oil quality. This is especially important since changes in the chemical composition affect the commercial value of the oil, with consequences to the grower's income (Dudai, 2005). Shortage of water in arid and semiarid regions throughout the world dictates utilization of marginal water, of low quality, for irrigation. Treated urban effluents, which may affect yield quantity and quality, are the most common alternative for agricultural irrigation. Therefore, in the present study, we evaluated the effects of irrigation with treated effluent on the quality and quantity of essential oil yield and selected antioxidant compounds in oregano and rosemary in assessing their potential as sources of plant aroma compounds and natural antioxidants.
The two cultivars used in this study were developed for high quality biomass production for the fresh herb production, and they were never tested for industrial production of essential oil and antioxidants. Our results for quantity and quality of the essential oil yield and phenolic antioxidants demonstrate the potential of these high biomass production cultivars for intensive high-quality industrial production systems. The essential oils produced by the two cultivars, 0.6 to 1.0% of the fresh biomass, are well within the acceptable range for an intensive oil and antioxidants industrial production (Table 2; Putievsky et al., 1998). The oil composition as well demonstrates a typical quality product (Table 3).
In addition to affects on the irrigated crops, much effort is currently made to study potential effects of effluent irrigation on chemical and physical properties of soils (Lado et al., 2005). In the present study, the secondary treated effluent used were of urban origin, contained only moderate levels of salts, and did not contain elevated levels of heavy metals. Heavy metal accumulation therefore did not appear in the soil or the plant tissues and salinity effects on the plants were moderate.
Aromatic crops require large volumes of irrigation water during a considerable part of the year. In the present study, 500 to 600 m3 to 1000 m2 yr–1 of water was applied to maintain optimal growing conditions. Limited water supply in arid and semiarid zones restricts aromatic crops cultivation on an industrial scale. Our results demonstrate that secondary treated municipal effluents are suitable for growth and quality production of oregano and rosemary and form the foundation for effluent-based industrial essential oil and antioxidants production in areas where water supply is limited. In addition, for large-scale production not otherwise possible due to lack of water, cultivation with effluents has an additive economical benefit to the farmers. Despite the cost of waste water treatment and distribution (Fine et al., 2006), annual crop costs are lower when irrigating with effluents because the price of effluent water in some areas is lower compared to potable water.
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ACKNOWLEDGMENTS |
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NOTES |
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