Effect of Potting Mixture on Plant Growth , Yield and Oil Quality of Vetiver ( Vetiveria zizanioides L )

Vetiver is an economically important plant used in ayurvedic medicine and for extraction of some essential oils. The present study was undertaken to determine the effect of potting mixture on plant growth, root yield, oil content and oil quality of Vetiver. Plants grown in top soil : sand mixture (at 1:2) showed higher plant growth, oil content and quality as compared to other treatments.


INTRODUCTION
Vetiver, (Vetiveria zizanioides) (Poaceae), is an important medicinal and aromatic plant.Economically most important part of the Vetiver plant is root.It is used for the treatment of arthritis, rheumatism, lumbago, sprain etc. Vetiver roots are used for extraction of essential oil which has a profoundly relaxing effect on the nervous system, relieving tension and stress (Maffei 2002).
One of the main problems in Vetiver production is the root damages caused during harvesting that reduce the harvestable yield.During manual harvesting 40% of the roots remain in the soil after harvesting (Maffei 2002).The damaged roots also affect the oil quality.Plant growth, root yield, oil yield and quality depend on various factors such as growing media, climatic conditions, quality and age of the roots.Hence a demand exists to determine a suitable growing media to increase the harvestable root yield while improving oil yield and oil quality.
Shoot and root dry weight, number of tillers and number of leaves were recorded at 9 month after planting.The data were analyzed using ANOVA with Statistical Analysis System (SAS).Roots were air dried for 3 weeks for the extraction of oil through steam distillation.Extracted Vetiver oils were analyzed for Khusimol, β-Vetivenene, β-Vetivone and α-Vetivone using Gas Chromatography Internal normalization method .

RESULTS
Significantly higher (P≤ 0.05) root dry weight (521g) was recorded in plants grown in potting mixture of top soil: sand: coir dust (1:2:2) followed by potting mixture of top soil: sand (1:2) (482g) (Figure 1).It is reported that in South India, the average fresh root yield is around 4 -5 t/ha with a maximum of 7.6 t/ha (Chadha 1995).In Sri Lanka the local demand mainly supplied through the harvest from the wild.
Plants grown in potting mixture with paddy husk found unsuitable for Vetiveria root production because of the lower yield and adhered husk particles to the roots.Higher amount of sand and coir dust can retain adequate moisture and ability to provide better aeration for the root growth and development of Vetiveria.This may be one of the reason for better growth and yield performances occur at the top soil: sand: coir dust (1:2:2) than other treatments.
The quality of oil depends upon the age of the root and the length of distillation period (Maffei 2002).If the roots stay in ground for over two years, the yield of oil diminishes considerably as the root system tend to become woody and lose in essential oil content and the oil becomes very viscous with a dark colour but of high quality (Chadha 1995).Because of these reasons root samples taken from 9 months after planting was used for the oil extraction.
Plants grown in mixtures containing top soil: sand: coir dust (1:2:2) and top soil: sand (1:2) showed the highest growth and yield with higher oil content and quality than other treatments.Vetiveria grown in mixtures containing coir dust particles had coir dust adhered to the roots and made cleaning a labour intensive process.Coir dust also affected badly on oil distillation process and reduced the purity of the oil.Because of these practical difficulties observed in the top soil: sand: coir dust (1:2:2) potting mixture, top soil: sand (1:2) mixture is considered as the most promising potting mixture for Vetiver root production.

Table 1 : Percentages of oil and its components in Vetiver grown in different potting mixtures
(T -Top soil, S -Sand, C-Coir dust, P-Paddy husk, W-Saw dust)