Thursday, April 12, 2007

Vetiver Grass - Unique Roots

Paul Truong
TVNI, Brisbane, Australia

Most grasses have fibrous roots, which spread out from the underground part of the culm and hold the soil in a horizontal pattern. The vetiver roots, however, penetrate vertically into the soil, whether it is the main root, secondary root or their fibrous ramification. In vetiver the roots are biologically the most important and economically the most useful part. Also, owing to its vertical growth and weak tendency to branch the roots of vetiver rarely mix with the roots of other plants grown in vicinity, resulting in less competition to crop plants (Seshu Lavania, ICV3 2003).

Its root system is massive, deep, penetrating, tough, very fine and producing essential oil as well.

Massive roots: Through centuries of selection for essential oil production, vetiver has a very high Root:Shoot ratio around 1:1, one of the highest among grass species. This makes vetiver an ideal plant to build up organic matter in poor or degraded soils.

Extreme depth: Vetiver roots grow vertically, slow but steady, 3.3m in first year and acquiring a total length of over 7 meters after 36 months (Seshu Lavania, ICV3 2003). This feature provides vetiver with an extremely strong anchor to the soil, which is vital in erosion control of steep slopes such as road batters and riverbanks. At the same time it makes vetiver extremely drought tolerant as it can explore deep soil moisture. The combination of the large root mass and extraordinary depth makes vetiver an excellent candidate for carbon sequestration.

Penetrating: mature vetiver roots can penetrate compact soil profile such as hard pan, bitumen and mudstone

Toughness: Vetiver roots have a very high tensile strength, equivalent to 1/6 of design mild steel reinforcement, which strengthen weakly structured soil or uncompacted slopes. Vetiver roots are stronger than many tree roots.

Fineness: The fineness of vetiver roots has two important implications:
- Research showed that the tensile strength of vetiver roots increases with the reduction in root diameter, implying that stronger fine roots provide higher resistance than larger roots per unit cross section.

- Providing more root surface/soil/water interfaces for microbial population and activities, which are vital in the phytoremediation of both organic and inorganic pollutants.

Essential oil: Essential oil extracted from vetiver roots is highly valued for its fragrance in the perfume industry, insecticidal characteristics for termite control and increasingly for its pharmaceutical values. Vetiver oils are so complex that so far they have not been successfully synthesised.

In addition to these extraordinary morphological characteristics, vetiver roots also exhibit some very unique physiological features such as tolerance and accumulation of elevated levels of pollutants such as agrochemicals and heavy metals. But most surprisingly its ability to survive under extreme drought as well as water logged conditions or wetland, even under hydroponics conditions without aeration. So it is both a xerophyte and a hydrophyte, attributed to its aerenchymatous, fast growing root system.

Research in China showed that vetiver plant can switch from dry land to wetland mode in about three weeks, by developing special air cells (aerenchyma) in its roots to supply oxygen to the roots growing in the deep anaerobic soil or mud.

Root diameter distribution and tensile strength

(Hengchaovanich and Nilaweera,1996) (Cheng et al,2003)

Grass Mean diameter of roots (mm) Mean tensile strength (MPa)
Late Juncellus 0.38±0.43 24.50±4.2
Dallis grass 0.92±0.28 19.74±3.00
White Clover 0.91±0.11 24.64±3.36
Vetiver 0.66±0.32 85.10±31.2
Centipede grass 0.66±0.05 27.30±1.74
Bahia grass 0.73±0.07 19.23±3.59
Manila grass 0.77±0.67 17.55±2.85

Visit TVN picture Gallery for detailed images of vetiver roots:

Paul Truong

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