Total Essential Oil Yield Research Articles

INORGANIC AND ORGANIC FERTILIZATION IN BIOMASS AND ESSENTIAL OIL PRODUCTION OF MATRICARIA RECUTITA L.

In the production of aromatic plants, fertilization is one of the factors that affect the biomass yield and the composition of secondary metabolites of an economic importance. The aim of this study was to compare the effect of fertilizer sources (FS) and harvest days (HD) on the flower yield, as well as, diameter, plant height, biomass production and accumulation of essential oil of chamomile (Matricaria recutita L.). Plants were grown in a hydroponic system with two types of substrate, one from volcanic rock, locally called “tezontle” and another from a mixture of soil, compost and perlite (50:20:30). The source of inorganic fertilizer was the Steiner solution at 75% nutrient concentration. While organic fertilizers consisted of application of humic acids and an organic fertilizer with biosynthetic amino acids. The results showed that inorganic fertilizer and harvest days have a positive influence (P≤0.05) in the morphological variables evaluated, but there are no differences in total yield of essential oil. This depends on the fresh flowers per treatment, while, α-bisabolol yield was increased by the humic acids application.

Yield and Quality Parameters of Thymus x citriodorus (Pers.) Schreb. (synonym T. fragrantissimus, T. serpyllum citratus and T. serpyllum citriodorum) Cultivated under Ankara Ecological Conditions

Lemon thyme (Thymus x citriodorus (Pers.) Schreb) is widely grown as ornamental aims in Turkey and has no natural distrubition. It's a hybrid of Thymus vulgaris L. and Thymus pulegioides L. Compared with other Thyme species, Thymus citriodorus has a herbaceous oblique structure and rhizome formation. By means of this research, T. citriodorus was firstly cultivated in a field experiment and its yield and quality parameters recorded in semiarid conditions. Field trials were conducted in the Central Research Institute for Field Crops, Ankara, at complete randomized block design with four replications during the years of 2009 and 2010. Total yield of green herb, drug herb and drug leaf were 3769–4707kg/da, 1193–1475kg/da and 742.3–844.2kg/da, respectively. The average content and total yield of essential oil were detected 1.430–1.308% and 16.93–19.42 L/da. In comparison to other lemon odor sources such as Melissa officinalis L. (0.01–0.03%) and Cymbopogon citratus [DC] Staph. (0.2–0.5%), its essential oil content (1.3–1.4%) was found rather satisfactory. Though most Thymus species are thymol containing, the main component of Thymus citriodorus essential oil was determined as ‘geraniol’ with lesser amount of lemon scented citral (geranial + neral) (from twenty-one constituents).

Physiomorphological response of rose-scented geranium ( Pelargonium spp.) to irrigation frequency

The effect of irrigation frequency on leaf physiomorphological processes of rose-scented geranium ( Pelargonium capitatum × P. radens cv. Rose) was investigated in a glasshouse study at the Hatfield Experimental Farm of the University of Pretoria, Pretoria, South Africa, from November 2005 to October 2006. Daily, and every 2nd, 3rd, 4th , and 5th day irrigation were applied as treatments. Leaf samples for electron-microscopic observations were taken one week prior to harvesting, whereafter all plants were re-watered. For each of the irrigation frequency treatments, 50% of the plants were then exposed to a one-week irrigation withholding period (brief stress treatment) prior to harvesting. During this period, physiological properties were recorded on a daily basis to identify or monitor change. Higher irrigation frequency and a brief water stress period increased essential oil yield. Lower irrigation frequency tended to increase the citronellol to geraniol (C:G) ratio to unacceptably high levels (C:G > 3). Upon re-watering, stomatal conductance (G s) and transpiration rate (R t) were significantly lower for the lower irrigation frequency treatments, compared to the higher irrigation frequency treatments, while no noticeable differences were observed in water potential (ψ w) and relative water content (RWC). At the end of the one-week stress period, G s, R t, ψ w and RWC were lower for the plants that were more frequently irrigated compared to the less frequently irrigated treatments. Water stress reduced leaf size, and apparently increased trichome density, whereas the total number of trichomes per leaf remained more or less the same, indicating that total essential oil yield is mainly affected by leaf number (and not by leaf size or trichome number). Stomatal closure was the main water stress avoiding/adaptation mechanism. These results demonstrate that rose-scented geranium plants can make physiomorphological adaptations to save water. However, such a water saving strategy was counter-productive, since it resulted in lower essential oil yield and lower water-use efficiency.

Response of palmarosa {Cymbopogon martinii (Roxb.) Wats. var. motia Burk.} to foliar application of magnesium and micronutrients

A field investigation was carried out on red sandy soil in the semi-arid tropical climate of south India to investigate the response of industrially important, multi-harvest, aromatic crop palmarosa {Cymbopogon martinii (Roxb.) Wats. var. motia Burk., family: Poaceae} to foliar application (2.5g/L single application for each harvest at 700L nutrient solution per hectare) of magnesium (Mg), manganese (Mn), iron (Fe), zinc (Zn), boron (B) and their residual effect on the succeeding harvest. During the experimental period, palmarosa crop afforded four harvests, 49.5–70.6t/ha total biomass yield (fresh weight), 211.4–384.2kg/ha total essential oil yield and Rs. 232,540–422,620/ha (US$ 4844.6–8804.6/ha) gross returns. Fifth harvest (no nutrients were applied) performed to examine the residual effect of Mg and micronutrients applied to the previous four harvests revealed the absence of residual effect pointing to the need for application of nutrients to individual harvests. Foliar application of Mg and micronutrients significantly increased the yield attributes (plant height, tiller number/plant, leaf number/plant), biomass yield, essential oil yield and gross returns of palmarosa. Mg and micronutrients enhanced the total biomass yields by 37.0–42.6% and the total essential oil yields by 44.6–81.7% in comparison to the control (water spray).All the treatments produced good quality essential oils with 1.5–3.2% linalool, 79.7–85.8% geraniol and 4.5–10.3% geranyl acetate. Mg and B additions declined linalool (%) in the second and fourth harvests and increased geraniol (%) in the first harvest. Mg and micronutrients application improved geraniol (%) in the second harvest. Except Zn, all the other nutrients decreased geranyl acetate (%) in the second harvest, but in the third and fourth harvests Mn and B increased geranyl acetate (%).

Arthropod communities related to different mixtures of oil ( Glycine max L. Merr.) and essential oil ( Artemisia annua L.) crops

Plants can host many herbivores and their natural enemies during their growth cycles. For this reason, changes in the relative abundance of crop and weed plants in a monocropping system as well as different crop plants in an intercropping system may produce great bottom up impacts in the specific and functional structure of spontaneous communities of arthropods. The hypothesis of this study was that the combination of two contrasting species, soybean ( Glycine max, Fabaceae, N 2 fixing plant) and annual wormwood ( Artemisia annua, Asteraceae, VOCs plant), would be related to different spontaneous communities of arthropods depending on the proportion of each species, and this would favor crop biodiversity without compromising crop production. The objectives of the study were: (a) to analyze the differences of spontaneous communities of arthropods related to different soybean (S)–annual wormwood (W) mixtures, using standard crop management for S production in Argentina, (b) to determine S and W total biomass and W essential oil content and yield and, (c) to analyze the relationship between arthropod communities and crop productivity. Factorial field experiments with 3 replications were done during 2006 and 2007. S density was kept constant (40 plants m −2) and different W densities (plants m −2) were added. Treatments were pure S, S + 2W, S + 4W, S + 8W and pure W (8 plants m −2). Arthropods were sampled at soybean full flowering and were classified in functional groups as herbivores and non-herbivores. S and W total and relative biomass and W essential oil content and yield from leaves and inflorescences were estimated in reproductive stage. Arthropod morphospecies abundance and richness were determined for each treatment. Data were analyzed using uni (ANOVA) and multivariate (CCA) techniques. Arthropods belonging to 7 orders presented a total richness of 48 morphospecies in 2006 and 36 in 2007, while total abundance was 379 in 2006 and 318 in 2007. The proportion of non-herbivores was higher than the proportion of herbivores. Different arthropod communities were observed according to each treatment. No differences were found among treatments in S + W and S total biomass production, while W total biomass and essential oil yield were both different among treatments. Relative biomass production of S and W was the main explanatory variable related to the contrast of arthropod communities between pure annual wormwood (W) and the rest of the treatments. Annual wormwood could be used as an accompanying essential oil crop or left as a weed in the densities tested in this work, favoring biodiversity and, eventually, pest management without compromising soybean crop yield.

Comparative analysis of essential oil composition and oil containing glands in Ocimum sanctum L. (Holy basil) under ambient and supplemental level of UV-B through gas chromatography–mass spectrometry and scanning electron microscopy

Field grown plants of holy basil (Ocimum sanctum L.) were treated with biologically effective supplemental ultraviolet-B (sUV-B) radiation (ambient +1.8 kJ m−2 day−1) to evaluate its effect on specialized oil glands and quantity and quality of the essential oil. The total yield of essential oil increased significantly by 42.0% after sUV-B treatment. Gas chromatography–mass spectrometry analysis showed that most important flavor compounds β-caryophyllene, germacrene-D, ethyl linoleolate, β-elemene and camphenol increased significantly after sUV-B treatment. Moreover, the level of main compound eugenol was not affected significantly. Scanning electron microscopy analysis showed turgidity of oil glands after sUV-B exposure and it was well correlated with the higher yield of essential oil. The result is of specific interest because if other parameters remain constant, sUV-B may affect the production of the essential oil in Ocimum sanctum L.

Modulation of wild marigold (Tagetes minuta L.) phenophases towards the varying temperature regimes – a field study

Field experiments were conducted during 2007 and 2008 at experimental farm of Institute of Himalayan Bioresource Technology, (CSIR) Palampur (HP), India to study the performance of wild marigold (Tagetes minuta) under changing temperature regimes over the crop growth period. The established agroclimatic indices for temperature studied elsewhere in the domain viz., relative temperature disparity (RTD), growing degree days (GDD), heliothermal units (HTU) and photothermal units (PTU) were computed for different varied dates of sowing the crop. Distinct changes in weather parameters concomitant to different sowing time consequently caused significant variation in the performance of the crop. The results indicated that the early sown crop had longest crop span (224 days) than the late sown crop (102 days), from sowing to harvesting. The mean GDD accumulation from sowing to harvest ranged from 1378 to 2518°C days HTU from 6781 to 15706°C days hour and PTU from 17400 to 33052°C days hour. Total biomass, and content and yield of essential oil were correlated with different heat units calculated during the crop growth seasons. All the agroclimatic indices had positive correlations with biomass, oil content and oil yield. Thus, these indices seem to be effective in taking into account and expressing the effect of varying ambient temperature on the duration between the phenological events for comparing the crop response to the ambient temperature between different phenological stages.

Volatile Fraction of Lavender and Bitter Fennel Infusion Extracts

The relative proportions of chemical classes (hydrocarbons, oxides, alcohols/ethers, aldehydes/ketones, acids/esters/lactones) in the essential oil of lavender (Lavendula angustifolia Mill., family Lamiaceae) and bitter fennel (Foeniculum vulgare Mill. subsp. vulgare var. vulgare (Mill.) Thellung, family Apiaceae) and in the volatile fraction of infusion extracts were examined and showed remarkable differences. The volatile compounds of infusions were isolated by hydrodistillation and solid phase extraction (SPE). Their qualitative and semiquantitative compositions were compared with the essential oil isolated by hydrodistillation directly from the plant material and analyzed by GC-MS. Furthermore, quantification of the major constituents of lavender oil and of the volatile fraction obtained by hydrodistillation of the infusion was performed. Comparison of the total essential oil yield quantified by hydrodistillation of the lavender infusion (0.7% v/w, corresponding to plant material) with the essential oil yield of the blossoms (5.1% v/w) revealed that only 13.9% of the initial oil could be extracted by infusion. The main constituents of the volatile fraction of the lavender infusion were (hydrodistillation/SPE): linalool (39.3%/28.2%), 1,8 cineole (24.8%/18.9%), cis-linalool oxide (furanoid) (5.8%/8.0%), trans-linalool oxide (furanoid) (4.1%/7.1%), camphor (5.3%/4.0%) and alpha-terpineol (4.0%/3.0%). The major constituents of lavender essential oil were linalool (28.8%), 1,8-cineole (18.05%), linalyl acetate (13.9%) and alpha-terpineol (4.0%). Most intriguing, in the volatile fraction of lavender infusion a significant proportional decrease of linalyl acetate and an increase of linalool oxides was recognized. The essential oil yield of fennel fruits was 12.5% v/w, whereas 1.8% v/w volatile fraction (corresponding to plant material) was obtained by hydrodistillation of the fennel infusion, which is equivalent to 14.5% of the initial fennel essential oil. The main constituents of the volatile fraction of the fennel infusion were (hydrodistillation/SPE): trans-anethole (56.4%/54.8%), fenchone (36.2%/39.5%) and estragole (2.5%/2.2%), which were also the major compounds of the genuine bitter fennel essential oil. In infusions, the proportion of ethers vs. ketones was shifted significantly towards a higher proportion of the latter compared with the essential oil obtained from the fruits.

Investigation of the Volatile Fraction of Rosemary Infusion Extracts

The relative proportions of chemical classes (hydrocarbons, oxides, alcohols, ketones, esters) in the essential oil of rosemary (Rosmarinus officinalis L., Lamicaeae) and in the volatile fraction of the infusion extracts were examined and showed remarkable differences.The volatile compounds of the infusion were isolated by two different methods, hydrodistillation and solid phase extraction (SPE). The main constituents of the volatile fraction of the infusion were (hydrodistillation/SPE): 1,8-cineole (42.4%/44.7%), camphor (31.4%/31.8%), α-terpineol (8.6%/8.1%) and borneol (8.3%/7.8%). The qualitative and quantitative composition of the volatile compounds of the infusion was compared to the essential oil isolated by hydrodistillation directly from the leaves. The major constituents of the essential oil of the leaves were 1,8-cineole (41.6%), camphor (17.0%), α-pinene (9.9%), α-terpineol (4.9%) and borneol (4.8%). Comparison of the total essential oil yield quantified by hydrodistillation of the infusion (0.36% v/w) with the essential oil yield of the leaves (1.84% v/w) revealed that only 19.6% of the initial oil could be extracted by infusion.

Static and dynamic superheated water extraction of essential oil components from Thymus vulgaris L.

Superheated water extraction (SWE) performed in both static and dynamic condition (S-SWE and D-SWE, respectively) was applied for the extraction of essential oil from Thymus vulgaris L. The influence of extraction pressure, temperature, time, and flow rate on the total yield of essential oil and the influence of extraction temperature on the extraction of some chosen components are discussed in the paper. The SWE extracts are related to PLE extracts with n-hexane and essential oil obtained by steam distillation. The superheated water extraction in dynamic condition seems to be a feasible option for the extraction of essential oil components from T. vulgaris L.

EFFECT OF FOLIAR SPRAY WITH BA (Benzyladenine) AND B-9 (Daminozide) ON ESSENTIAL OIL PRODUCTION AND CHEMICAL COMPOSITION OF Majorana hortensis, MOENCH PLANT

This research was conducted at the Agriculture Experimental Station, Faculty of Agriculture, CairoUniversity, Giza in two successive seasons of 2005-2007 and 2006-2008. The aim of this research was to study the effect of foliar spray with BA and B-9 on essential oil production and chemical composition of marjoram plant. The plants were sprayed with BA at the rates of 50, 100 and 150 ppm, while B-9 at the rates of 500, 1000 and 2000 ppm in addition to control treatment which sprayed with distilled water. The obtained results can be summarized as follows: BA at the rates of 50, 100 and 150 ppm or B-9 at the rates of 500, 1000 and 2000 ppm increased all recorded parameters as compared to control treatment with significant differences in most cases during the two seasons. In the first season, the highest value of essential oil percentage was produced with B-9 at 1000 ppm, while the highest values of essential oil yield were obtained with BA at 50, 150 ppm and with B-9 at 1000 ppm treatments. In the second season the highest values of essential oil percentage and essential oil yield were produced with BA at 50 and 100 ppm, respectively. The major essential oil components were linalyl acetate and terpinen-4-ol. The highest percentage of linalyl acetate was detected in the oil of the plants sprayed with B-9 at 1000 ppm in the two seasons, while in the first season, the highest percentage of terpinen-4-ol was found in oil of the plants sprayed with B-9 at 500 ppm as well as the highest percentage of terpinen-4-ol in the second season was produced from control treatment followed by B-9 at 500 ppm. In the first season, the highest values of chlorophyll a, b and carotenoids were produced with BA at 50 ppm, B-9 at 2000 and 500 ppm, respectively. While in the second season, the highest values of chlorophyll a, b and carotenoids were obtained from B-9 at 2000 ppm, BA at 150 ppm and BA at 150 ppm, respectively. The highest values of total carbohydrates percentage were resulted in B-9 at 2000 ppm in the two seasons. In the first season, the highest total seasonal yield of essential oil was obtained from B-9 at 1000 ppm, while in the second season, the highest value was produced from BA at 100 ppm. Generally in combined statistical analysis B-9 at 1000 ppm was the most effective treatment in increasing total seasonal yield of essential oil. The lowest values of all recorded parameters were produced from the control plants in the two seasons. Different cuts as general mean had a significant effect on all recorded parameters in the two seasons. The highest values of essential oil percentage, chlorophyll a, b and carotenoids were produced from the third cut in the two seasons. Also, the highest values of total carbohydrates percentage were produced from the second cut and third cut in the first and second seasons, respectively. The highest values of essential oil yield were obtained from the third cut and fourth cut in the first and second seasons, respectively. The interaction between the growth regulators (BA or B-9) and the cuts increased all recorded parameters as compared with the control in any cut during the two seasons with significant differences in most cases.

Rose-scented geranium ( Pelargonium capitatum × P. radens) growth and essential oil yield response to different soil water depletion regimes

Effective irrigation management in arid and semi-arid regions, like South Africa, could increase crop yield and thereby improve productivity of scarce fresh water resources. Experiments were conducted at the Hatfield Experimental Farm of the University of Pretoria, South Africa, from 2004 to 2006, to investigate the effect of soil water depletion regimes on rose-scented geranium ( Pelargonium capitatum × P. radens cv. Rose) essential oil yield, essential oil composition and water-use efficiency in an open field and a rain shelter. Four maximum allowable soil water depletion levels (MAD), 20, 40, 60 and 80% of the plant available soil water (ASW) in the top 0.8 m root zone, were applied as treatments. Plant roots extracted most soil water from the top 0.4 m soil layer. Increasing the soil water depletion level to 60% and higher resulted in a significant reduction in herbage mass and essential oil yield. Water stress apparently increased the essential oil concentration (percentage oil on fresh herbage mass basis), but its contribution to total essential oil yield (kg/ha oil) was limited. Irrigation treatments did not affect essential oil composition. An increase in maximum allowable depletion level generally resulted in a decrease in leaf area and an increase in leaf to stem fresh mass ratio. Up to 28% of irrigation water could be saved by increasing maximum allowable depletion level of ASW from 20 to 40%, without a significant reduction in essential oil yield.

Effect of nitrogen and potassium fertilizer on growth, herbage and oil yield of irrigated palmarosa (Cymbopogon martinii [roxb.] wats. var. motia burk) in a semi-arid tropical climate

Palmarosa (Cymbopogon martinii [Roxb.] Wats. Var. Burk., family, Poaceae) is grown as a perennial crop for production of high value essential oil, which finds application in high-grade perfumery and cosmetic products. A field investigation was carried out for 2 years (2002–2004) at the Central Institute of Medicinal and Aromatic Plants, Resource Centre, Bangalore, on a red sandy loam soil in the semi-arid tropical climate, to study the influence of different levels of nitrogen (0, 100 and 200 kg N ha−1 year−1) and potassium (0, 61.5 and 123.0 kg K ha−1 year−1) on growth, herbage, essential oil yield, oil content and quality of palmarosa (Cymbopogon martinii [Roxb.] Wats. var. Burk., family, Poaceae) grown under irrigated condition. During the period of investigations, palmarosa gave eight harvests in two years with 42.3–74.1 t ha−1 in total (total of eight harvests) herbage yield, and 218.3–382.1 kg ha−1 total essential oil yield. Application of nitrogen at 200 kg ha−1 year−1 increased the total herbage yield by 104.5% and total essential oil yield by 102.6% over control (no application of nitrogen). Addition of potassium (K) at 123 kg ha−1 year−1 enhanced the total herbage yield by 21.8% and total essential oil yield by 23.7% in comparison to no K application. The quality of the essential oil with 75–84% geraniol and 7.8–13.3% geranyl acetate was found to be good and readily accepted in the market.

High Irrigation Frequency and Brief Water Stress Before Harvest Enhances Essential Oil Yield of Rose-scented Geranium (Pelargonium capitatum × P. radens)

Pot experiments were conducted to investigate the effects of irrigation frequency and withholding irrigation during the week before harvesting on rose-scented geranium herbage yield and essential oil yield and composition. A factorial experiment with three irrigation frequencies (twice a day, once a day, and every second day) and two growth media (silica sand and sandy clay soil) were conducted in a tunnel. One week before harvest, irrigation was withheld for half of the pots in each treatment combination. In a glasshouse, sandy clay soil was used as growing medium, and five irrigation frequencies (everyday, everyday with 1-week irrigation withholding period, every second day, every third day, and every fourth day irrigation to pot capacity) were applied as treatments. Results showed that essential oil content (percent oil on fresh herbage weight basis) increased as the irrigation frequency decreased. Both herbage yield and essential oil yield positively responded to frequent irrigation. Thus, higher herbage and essential oil yields were obtained from the highest irrigation frequency. A 1-week stress period significantly increased total essential oil yield as well as oil content per fresh herbage weight. The results highlighted that conditions of high soil water availability followed by brief water stress just before harvesting would maximize rose-scented geranium essential oil yield. Citronellol and citronellyl formate tended to increase with an increase in the stress level, but the reverse was true for geraniol and geranyl formate. Other major essential oil components were unaffected by water stress.

Studying the Effect of Nitrogen and Potassium Fertilizer on Growth and Essential Oil Content of Cymbopogon citratus and Vetiveria zizanioides

To study the effects of nitrogen and potassium fertilizers, a field experiment was conducted in watershed area of Kulhal, DehraDun at 20 % slope. Experiment consisted of four doses (0, 25, 50 and 75 Kg ha−1) of nitrogen and potassium and sixteen possible combinations were laid out in Randomized Block Design in two replications. Observations recorded after two years of plantation revealed that height, total biomass production and essential oil content was maximum in Lemon grass under the treatment of 50 Kg nitrogen per hectare. Total biomass and essential oil yield in case of Khus grass were maximum with the application of 75Kg of potassium per hectare. Results clearly indicated that application of fertilizers in Vetiveria zizanioides and Cymbopogon citratus can boost up the growth and oil yield.

Chemical composition of the essential oil from leaves of Lippia citriodora H.B.K. (Verbenaceae) at two developmental stages

The chemical composition of the essential oil extracted from fresh leaves of Lippia citriodora (Verbenaceae) was analyzed by GC-FID and GC–MS in May, when growth rates are maximal, and in September, in full bloom. In both samples the main constituents were geranial, neral and limonene constituting 66.3% of the total essential oil yield in May and increasing to 69% in September. Their individual percentage values, however, changed considerably for geranial and neral decreasing from 38.7 to 26.8% and from 24.5 to 21.8%, respectively, and for limonene increasing from 5.8 to 17.7%. All other components remained more or less unchanged both qualitatively and quantitatively. FT-IR spectrometry was also applied for the qualitative determination of the main components.

Biomass yield, essential oil yield and essential oil composition of rose-scented geranium ( Pelargonium species) as influenced by row spacings and intercropping with cornmint ( Menthaarvensis L.f. piperascens Malinv. ex Holmes)

Rose-scented geranium ( Pelargonium species, family, Geraniaceae) is a vegetatively propagated (through rooted stem cuttings), initially slow growing, high value aromatic crop. Cornmint ( Mentha arvensis L. f. piperascens Malinvaud ex Holmes, family, Lamiaceae) is also a vegetatively propagated (through rhizomes, runners or stolons and terminal stem cuttings), high demand aromatic–cum–medicinal crop. Essential oils isolated through steam distillation of shoot biomass of these two crops are extensively used in fragrance, flavor, and pharmaceutical industries and in aromatherapy. A field experiment was carried out during the vegetation periods of 1996–1998 in semi-arid tropical climate to investigate the influence of different row spacings (60×30, 75×30, 90×30 and 120×30 cm) and intercropping cornmint cv. Shivalik on the biomass yield, essential oil yield and essential oil composition of rose-scented geranium cv. Bourbon. The row spacing of 60×30 cm (60 cm between rows and 30 cm between plants within the rows) was superior to other row spacings and produced 57.4 t/ha total (total of four harvests) biomass yield (132.4% higher than 120×30 cm spacing) and 52.7 kg/ha total essential oil yield (98.9% greater than 120×30 cm spacing). Intercropping of cornmint did not affect biomass yield and essential oil yield of rose-scented geranium and yielded 5.6 t/ha of biomass and 21.3 kg/ha of essential oil of cornmint as bonus yields over and above that of rose-scented geranium. However, biomass yield and essential oil yield of intercropped cornmint suffered reductions of 53.4 and 59.1%, respectively, compared with monocropped cornmint. Intercropping controlled weed growth and decreased total (total of three harvests) biomass yield of weeds by 40.0% in rose-scented geranium intercropped with cornmint. The chemical composition of essential oils of both the crops was not influenced either by row spacings or by intercropping. The quality of essential oils of both the crops was good and was readily accepted in the market.

Biomass and essential oil yields of rainfed palmarosa ( Cymbopogonmartinii (Roxb.) Wats. var. motia Burk.) supplied with different levels of organic manure and fertilizer nitrogen in semi-arid tropical climate

A field investigation was carried out for 2 years (1994–1996) on a red sandy loam soil in the semi-arid tropical climate of South India, to study the influence of different levels of farm yard manure (FYM) (0 and 15 t/ha per year) and fertilizer nitrogen (0, 40, 80 kg N/ha per year) on the biomass and essential oil yields of palmarosa ( Cymbopogon martinii (Roxb.) Wats. var. motia Burk., family, Poaceae) grown under rainfed condition. During the period of investigation, palmarosa gave seven harvests in 2 years with 23.6–37.2 t/ha total (total of seven harvests) biomass yield, and 99.2–159.1 kg/ha total essential oil yield per hectare. Application of FYM at 15 t/ha per year increased the total biomass yield by 10.7% and total essential oil yield by 10.3% over control (no application of FYM). Addition of nitrogen (N) at 80 kg/ha per year enhanced the total biomass yield by 57.6% and total essential oil yield by 60.3% in comparison to no N application. The quality of the essential oil with 1.7% (E)-β-ocimene, 2.5% linalool, 73.1% geraniol, 15.8% geranyl acetate and 2.0% β-caryophyllene was found to be good and was readily accepted in the market.

Biomass and essential oil yields of cornmint ( Mentha arvensis L. f. piperascens Malinvaud ex Holmes) planted in different months in semi-arid tropical climate

A field experiment was conducted in the farm of Mr Jayanthilal Sachdev, a progressive farmer on a red clay loam soil in the semi-arid tropical climate of South India, to study the influence of planting cornmint ( Mentha arvensis L. f. piperascens Malinvaud ex Holmes, family: Lamiaceae) in different months on its biomass and essential oil yields. In this climate, cornmint was harvested six–seven times in a period of 17–18 months. August (rainy), November (autumn), and December (winter) planted crop produced significantly superior total biomass and essential oil yields compared to September and January planted cornmint. The results indicated the feasibility of intercropping cornmint with tomato (6.3 t/ha) during the first harvest period. The quality of the essential oil with 73.0% menthol, 9.6% menthone, 4.0% isomenthone, and 4.0% menthyl acetate was found to be good and readily accepted in the market. This investigation in a farmer’s field with 42.5–63.5 t/ha total biomass yield and 196.3–271.5 kg/ha total essential oil yield, clearly demonstrated the economic feasibility of cultivating cornmint in semi-arid tropical climate. It has also shown the possibility of planting the crop during different seasons and growing it as a biennial.

Effects of osmotic stress on the essential oil content and composition of peppermint

The essential oil content and composition of hydroponically-grown peppermint ( Mentha x piperita L.) plants (29- and 36-day-old cuttings) were each affected by growth solution potential (ψ s) and duration of exposure to mild and moderate osmotic stress. After one week of treatment, the essential oil content of leaves increased from 44.0 to 61.1 ul μl g −1 leaf dry wt as ψ s decreased from −0.05 to −0.6 MPa, and no differences in shoot biomass, leaf area, or total oil production by leaves were evident in plants grown at these treatment levels. The same levels of ψ s applied for two weeks resulted in larger differences in plant growth and leaf oil content. When plants were subjected to increasing levels of osmotic stress, leaf essential oil content increased linearly from 44.0 to 70.8 μl g −1 dry wt, but shoot biomass and leaf area each decreased exponentially. Total essential oil yield of plants subjected to two weeks of treatment was significantly reduced as stress increased. The major constituents of essential oil, menthone and menthol, together accounted for ca 80% of the total monoterpenes, and this proportion was unaffected by treatment. Few consistent trends in oil composition among stress treatments were evident, although the relative proportion of sesquiterpenes increased with osmotic stress.