Biomass yield, essential oil yield and essential oil composition of rose-scented geranium (Pelargonium species) as influenced by row spacings and intercropping with cornmint (Mentha arvensis L.f. piperascens Malinv. ex Holmes)
Introduction
The essential oil of rose-scented geranium (Pelargonium species, family, Geraniaceae) extracted by steam distilling the above ground freshly harvested shoot biomass and aroma chemical rhodinol separated through fractional distillation of the volatile oil, are widely used in the fragrance industry, aromatherapy and sparingly used in the flavor industry. Rose-scented geranium oil has a strong, rose-like odor with minty top note accompanied by a slight grassy background. The aromatic oil is extensively used in various types of rose fragrances where petal and foliage effects are desired; in scenting of soaps due to its stability in slightly alkaline medium and in cosmetic products. In aromatherapy the volatile oil is used for menopausal problems, skin disorders, nervous tension and anxiety.
The essential oil of menthol mint or cornmint (Mentha arvensis L.f. piperascens Malinvaud ex Holmes, family, Lamiaceae) isolated by steam distilling the above ground freshly harvested or partially dried flowering or vegetative shoot phytomass and menthol crystals isolated through chilling and centrifuging the fragrant oil are extensively used in flavor, fragrance and pharmaceutical industries. Cornmint oil has a characteristic strong minty odor. It is used in prescriptions for cold remedies, cough drops, dentifrices, mouth washes; in scenting cigarettes; flavoring tobacco, chewing pan (rolled betel leaf containing menthol, lime paste, betel nut and other products), bakery products and in cosmetic products. In aromatherapy, the essential oil is prized for its cooling effect on the skin; for pain relieving properties; for treating digestive problems, migraine, heartburn, aching feet, travel sickness, sinus and catarrh problems.
India is a net importer of rose-scented geranium oil as demand far exceeds its production, therefore, excellent potential exists for extending its cultivation. Rose-scented geranium is propagated vegetatively through rooted terminal stem cuttings. The transplanted cuttings have a characteristic initial slow growth and are susceptible to weed competition during this lag phase leading to yield losses (Rajeswara Rao and Bhattacharya, 1997). To utilize the uncovered inter row space, applied inputs such as irrigation water and fertilizers, to check weed growth and to enhance crop productivity, attempts were made to grow short duration legumes like cowpea (Vigna unguiculata (L.) Walp.), blackgram (Vigna mungo (L.) Hepper) (Prakasa Rao et al., 1984, Prakasa Rao et al., 1986) or greengram (Vigna radiata (L.) Wilez.), clusterbean (Cyamopsis tetragonoloba (L.) Taub.) (Rajeswara Rao et al., 2000) or butterbeans (Phaseolus luteus L.) (Narayana et al., 1986) and spices like garlic (Allium sativum L.) (Muni Ram and Kumar, 1998) as intercrops in rose-scented geranium. Similarly, for controlling soil erosion and for reaping higher returns, rose-scented geranium was intercropped in trees such as lemon-scented gum (Eucalyptus citriodora Hook.) (Singh et al., 1998b), bluegum (Eucalyptus globulus Labill.) (Dhyani et al., 1995) or wattle (Acacia mearnsii L.) (Agarwal et al., 1995).
India and China are the important producers and exporters of cornmint oil, menthol crystals, dementholised oil and mint terpenes (Rajeswara Rao, 1999). Cornmint is also propagated vegetatively through rhizomes, runners or stolons and terminal stem cuttings. Intercropping cornmint with tomato (Lycopersicon esculentum Mill.) (Rajeswara Rao, 1999), or greengram (Muni Ram et al., 1998) or radish (Raphanus sativus L.), okra (Abelmoschus esculentus Moench.), and cowpea (Singh et al., 1998a) improved land use efficiency and economic returns. Growing menthol mint as an intercrop in sugarcane (Saccharum officinarum L.) (Kothari et al., 1987, Randhawa et al., 1989) or citronella (Cymbopogon winterianus Jowitt.) (Singh and Ram, 1991) or poplar (Populus deltoides Bartram ex Marshall) (Singh et al., 1990) was also recommended for higher productivity and returns.
Rose-scented geranium and cornmint can be planted during the winter season in the semi-arid tropical climate of India and they need frequent, light irrigations for their optimum growth. The former is a deep rooted crop and the latter is a shallow rooted crop. Cornmint takes 4 months and rose-scented geranium 5 months to come to maturity for their first harvest. The compatibility of these two crops as companion crops in an intercropping system was not explored earlier.
Though, different spacings ranging from 30×30 to 120×30 cm were recommended for rose-scented geranium in various agro–climatic locations, these recommendations were based on general cultivation practices, rather than experimental evidences (Rajeswara Rao, 2000a). However, Prakasa Rao et al. (1988) found 60×45 cm spacing to be optimum for obtaining high yields of rose-scented geranium in Bangalore plains, India.
This field experiment was, therefore, conducted to investigate the influence of row spacings and intercropping cornmint on biomass yield, essential oil yield and essential oil composition of rose-scented geranium in semi-arid tropical climate.
Section snippets
Material and methods
The field study was carried out during the vegetation periods of 1996–1998 at the Central Institute of Medicinal and Aromatic Plants, Field Station, Hyderabad, India. The experimental location experiences semi-arid tropical climate. The soil of the experimental field was a red sandy loam (alfic ustochrept) with pH 7.4 (1:2.5 soil to solution ratio), EC 0.42 dS/m, organic C 0.3%, total N 0.03%, available P 10 μg/g soil and exchangeable K 128 μg/g soil. The experiment was laid out in randomized
Plant height
In 60 and 75 cm row spacings, lack of sufficient inter and intra-row space and possible competition for sunlight resulted in significantly taller plants compared with 90 and 120 cm row spacings (Table 1). The plants were 17.7% lengthier in 60 than 120 cm row spacing.
Intercropping had no effect on plant height of rose-scented geranium. The plant height of citronella another aromatic crop was also not affected when intercropped with cornmint (Singh and Ram, 1991). A similar observation was made
Conclusions
This field investigation demonstrated that:
- a
60×30 cm (60 cm between the rows and 30 cm between the plants within the rows) spacing is optimum for rose-scented geranium for harvesting high biomass and essential oil yields and good quality essential oil;
- b
cornmint is a compatible intercrop in rose-scented geranium as it did not influence the growth, biomass and essential oil yields, quality of rose-scented geranium oil and produced additional yield of good quality cornmint oil in intercropping
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