Technical Report on the International Workshop on Vetiver Bioengineering Technology for Erosion and Sediment Control and Civil Construction Stabilisation,

19 - 21 October, Nanchang, China.

Paul Truong

TVN Asia and Pacific Representative

This report concentrates on the technical aspects of the Conference; it is complementary to the very comprehensive general report prepared by Prof. Xu Liyu (10).

Invited Speakers: Dick Grimshaw and Paul Truong were invited by the Chinese Academy of Sciences and Diti Hengchaovanich by UNDP.

  2. Fifteen technical papers were presented although most of the papers concentrated on steep slope stabilisation, other aspects of VGT such as factors affecting vetiver establishment and growth were also presented. The following are highlights presented or discussed during the conference.
    1. Growth patterns and factors influencing vetiver growth in China.

Professor Xu presented a very comprehensive summary of factors affecting vetiver growth in China.

  • Latitude: from 10o N (Hainan) to 39oN (Tianjing). At Tianjing mean January temperature is 4oC, with winter minimum of -22oC. Growth starts at temperatures between 10 and 15oC, but best performance is in the range between 20 - 30oC (2-3 cm/day) higher temperatures at 40oC or higher affects growth (0.5 cm / day). Biomass production is affected more by soil fertility than temperature.

      1. VGT applications:
      1. Highway stabilisation

    There has been a great deal of highway stabilisation work done in Jiangxi and Fujian Provinces since 1997. The most impressive site was on a highway near Fuzhou planted by Mrs Zhang Jing.

    Several papers were presented on the application of VGT at various provinces in China, from the high altitude Yunan provinces, to the coastal Fujian provinces. Several major sites were visited during the post conference tour.

    A paper presented by Hong et al. (2) described in details the planning and results of this very difficult mountainous site on the Wuyi mountain range between Jiangxi and Jujian provinces. Despite very poor soil, with a small amount of manure and fertilisers, a very impressive 98% of establishment rate was achieved on this highly erodible site. Vetiver growth, both top and root was much better than the local grass Bamao, which is the traditional species used for road work stabilisation in this region.

    Results also indicate that vetiver growth was poorer at high altitude. Tiller number and plant height were reduced from 4.9 tillers and 57 cm to 3.3 tillers and 43 cm respectively when the altitude increased from 285 to 730 m above sea level. This was attributed to lower temperature, thick fog and less sunshine (shading) at higher altitude rather than altitude per se. This was supported by the observation in Yunan Plateau, where vetiver grew satisfactorily at an altitude of 1800m.

    It was noted that Fusarium wilt was observed in some young shoots, and soil temperature at 10cm deep was recorded at 17oC in October. It was also very interesting to see that vetiver was used to reinforce the traditional and very costly herringbone rock structure.

    Very successful and convincing results of VGT in road batter stabilisation. At this site, only the road itself is stabilised, but valuable farm land at the toe of the embankment is also protected from run off and sediment from the road. Excellent growth was obtained after 2 years.

    Although the soil along this lake side highway is extremely poor and highly erodible, vetiver was established quite easily and has successfully stabilised the very steep batters with growth exceeding 2 m after 2 years. This is in sharp contrast with the conventional treatment of concrete and rocks, which often failed. A good example of this was found along this highway where a massive slope of concrete protecting a very steep batter was broken up and moved down the slope.

    The need of appropriate fertiliser was also highlighted here. At one site where adequate fertiliser was applied, vetiver was at least 1.5 m tall and no erosion occurred. On the lower section of this batter where no fertiliser was used, growth was only 0.4 - 0.5 m and severe rilling was observed.

    At a few sites along this highway, after fixing some initial erosion, the contractor replanted the slope with another grass, a vetiver look-alike, but this local grass is poor and the ground was hardly covered after 2 years.

    The most impressive site was on a new World Bank financed Highway linking Fuzhou and Xiamen. This site was established by Mrs Zhang Jing, it covered about 5 ha in area with a vertical drop of 100m. The rows were well laid out on contour lines among concrete drainage channel. It was noted that double row planting was used here instead of the usual single row. When fully established this site will certainly be a showcase for VGT in southern China.

    In combination with VGT, the traditional rock and concrete structures were also used here, forming a very spectacular combination. It would be interesting to compare the cost difference between the two technologies.

    This ring road was built about three years ago and vetiver was planted by Dr Xia on both cut and fill slopes. Following the planting of contour hedges, Acacia mangium was planted in the inter row areas. Now the whole site both the cut and fill batters are completely stabilised and covered with both local species and A. mangium trees and grass. This was in sharp contrast to the untreated batter (opposite the trial site) where extensive rilling and gullying occurred.

      1. Old quarry rehabilitation
      2. A major concern in Guangzhou City was the rehabilitation of old quarries which are located within the city boundary. Two very large quarries are due to be decommissioned in a few years, so the local authority is very interested in using VGT for their rehabilitation.

        After showing the success of quarry rehabilitation works in Australia, the city environmental officer invited me to visit two working quarries and an old quarry, the latter has been successfully rehabilitated. On the flatter area, elephant grass was used successfully and economically for rehabilitation purpose. However, on steeper slopes, rock retaining walls were built to trap and retain the debris and sediment, at the enormous cost of US $15.30 per square metre of retained soil. With the cost of vetiver at $0.50 / m at most, the savings would be very substantial.

      3. Stream bank stabilisation
      4. The presentation on the use of VGT for stream bank stabilisation (7) attracted a lot of attention at the conference, as flood erosion is one of the major annual disasters in southern China, particularly in the Yantze watershed. As highway stabilisation with VGT is now well accepted in China, stream and channel stabilisation is probably the next target.
      5. Mine rehabilitation (6)
      6. Vetiver was found to be the best species on a trial established in a Zinc / Lead mine tailings in Guangdong (5). The tailings are high in Pb, Zn, Cu and Cd with total Pb and Zinc exceeds 3000 mg/kg and available Pb and Zinc at 100 mg/kg (well below the threshold level of these two elements).

        Although vetiver could be established directly on these tailings, due to the poor nutrient status of the tailings, additional of fertiliser and / or fresh garbage improved growth enormously.

      7. Sand dune stabilisation
      8. In the last 30 years (1950 - 1980) 660km2 (66,000 ha) of farm land in Jiangxi Province were lost to shifting sand dunes which move northward at the speed of 5m/year. Therefore, dune stabilisation is of high priority in the province (3).

        With the application of manure, vetiver was successfully established on the sand dunes with growth exceeding 110 cm after 7 months. The hedges have effectively slowed the sand movement by reducing wind velocity, which has in turn encouraged the establishment of volunteer grasses and herbs. The ground cover that provided by these species further improved the effectiveness of the vetiver hedges. Consequently, vetiver will be used to stabilise the sandy road batter along Poyang Lake next spring, due to its low cost and effectiveness.

      9. Effects of low temperature on vetiver growth.
      10. Don Miller found that vetiver grass in temperate zones (Gisbourne, New Zealand, latitude 38 degrees South) dies after 3 to 4 years, despite initial vigorous growth (4). Trials show that shading of the ground surface by the growing plant in summer can reduce soil temperature at 300mm depth by up to 60 C. Soil temperatures below about 190 C appear to restrict vetiver root growth. In addition a high concentration (over 200 per square meter) of cicada insects was found around the vetiver roots. The interaction of low soil temperature and insect attack appears to be causing plant death. Annual mowing of the vetiver grass in early summer allows a rapid rise in soil temperature and after three years, plant health is still good.
      11. Effects of plant growth retardant on vetiver growth and tillering
      12. As tall vetiver plants are not always appreciated under some applications such as golf courses and gardens, growth retardant application was trialed by Dr Xia Hanping to find the most effective type and concentrations for this application. In addition, growth retardants are known to encourage tillering which is a bonus for planting materials multiplication (9).

        Three hormones were trialed: B9 (daminozide), PP333 (paclobutrazol) and CCC (Chloro choline chloride) at two concentrations each. Results showed that all three promoted tillering from 11% - 53%, but only B9 retarded growth by 6% and delayed flowering for 10 days. On the other hand PP333 and CCC all promoted vetiver growth from 5 - 22% and they enhanced the number of flower head up to 31%. Results indicate that vetiver reacts quite differently from most crops in showing a high degree of tolerance.

      13. Planting materials production

    From his experience, Dr. Xia listed the following 12 important points for planting material production:

    1. Full sun as a C4 plant, vetiver growth is affected by shade.
    2. Fertile and well drained soil. Sandy loam is best. Clay soil is not suitable.
    3. Fertiliser application, P and or manure.
    4. Pruning before planting. Prune shoots to 20-30cm and roots to 5 -10 cm.
    5. Dipping roots. Dip roots in 2 - 25 ppm of 2,4,D hormones, dilute or slurry manure.
    6. Oblique planting. Plant vetiver at 60o angle, which is more convenient.
    7. Density: spacing 20 x 40 cm is recommended, higher density can affect tillering.
    8. Plant single tillers. Although single tiller planting has a higher mortality rate, it can produce higher tiller number over time than three tiller strips.
    9. Shallow planting, 3-4 cm depth is recommended.
    10. Avoid pruning. Cut once or twice per year. Best to prune it before harvesting.
    11. One year old plant is most appropriate for nursery production.
    12. Selling in clumps rather than tillers.
      1. Jiji grass - (Achnatheruum splendeus)

    There are 21 cultivars of jiji in central Asia of which 14 are in western and northwestern China. These are found on a wide range of soil types and climates (8).

    Distribution in China:

    Inner Mongolia, Gansu, Qinghai, Xingjiang, Shanxi, Ningxia and northeast China.

    Soil Type:

    Ecological characteristics

    Morphological characteristics:

    Research is being conducted by Prof. Xu and his student Mr Wang on its seed germination characteristics and growth under various conditions.

    1. General observation and comments
    1. Acknowledgment
    2. On behalf of TVN, I wish to thank the Chinese Academy of Science, UNDP the Xiangxi Highway Bureau and other organisations for their support and in particular Prof. Xu, Mr Fu Heng Sheng, Chief Engineer, Jiangxi Highway Bureau and Mr Harold Insley (Scott Wilson, Hong Kong) for their personal support.
    3. Further Readings

    The following papers were presented at the conference and can be found on the TVN Homepage <>

    1. Grimshaw, R. China and the VGT.
    2. Hong, C., Ming, W. and Peng, Y. Application of contour hedges techniques to the protection of highway embankment in Jiangxi Province of China.
    3. Hong, C., Feng, W., Yu, L., and Hu. G. Experiment of the application of vetiver to sand-fixing in subtropical deserts.
    4. Miller, D. Soil temperature and insect damage impacts on vetiver growth.
    5. Shu, W., Xia, H. and Zhang Z. Growth of vetiver and three other grasses on Lechang lead/zinc mine tailings: A field experiment.
    6. Truong, P. An overview of VGT in highway stabilisation and mine rehabilitation
    7. Truong, P. VGT for flood and stream bank erosion control.
    8. Wang, K. Jiji grass and its potential for soil erosion control.
    9. Xia, H. Effects of plant growth retardants on the growth of vetiver grass.
    10. Xu, L. Report International Conference on vetiver Bioengineering technology for erosion control and civil construction stabilisation held in Nangchang, China