by Zhao Zhaoqing (Highway Association of Zhejiang Province), Hong Xiumin (Highway Administrative Bureau of Zhejiang Province), Xu Jianqiang (Highway Administrative Section of Jingning County)
Several years ago when the author Zhao Zhaoqing was in Madagascar had opportunity to see vetiver grass, but knew very little about its function, application, etc. In the recent years a lot of information was granted by China Vetiver Network and a leading group was formed by directors of Provincial Highway Administrative Bureau, Highway Association, Communication Bureau, etc. And a project was launched to introduce vetiver to highway protection, including the selection of healthy seedlings, the establishment of propagation base, and the applications of using vetiver for highway stabilization. The application showed that vetiver had miracle function in embankment protection. Although the embankments suffered from two strong typhoon attacks, the highways were not effected. It was confirmed that vetiver is an ideal plant for embankment protection. To spread the technology more rapidly a vetiver company was established and registered as Zhejiang Vetiver Engineering Development Company Limited. It is the first company in China involving vetiver and established by highway institutions, in addition to that many companies were established in Guangdong and Fujian Provinces by private sectors engaging in land greening and soil conservation.
Located on the east part of China, Zhejiang Province has continental area over 100 000 km2 and 40 000 000 population, dominated by hills and mountains. In the recent years in Zhejiang Province the highway construction has been implemented very rapidly towards its goal of establishing " 2 longitudinal, 2 latitudinal, and 5 connection highways" of which some were constructed and some are in constructions. Beside, reconstruction of low-grade roads have been also in process. It is inevitable to clear original vegetation when building roadbed, roadstead, etc., causing soil erosion, slope unstability, and environmental problem. In turn, the deteriorated environment often causes transportation problem through soil erosion, slope collapse, landslides, etc. and threatened traffic safety. The situation becomes more serious in mountainous area. For example, for the section of Li-Jin road of 80 km there happened 30 collapse for altogether 40 000 m3 of soils and rocks during the period of 1998 - 1999. Besides, there were 3 sections which were sunk or washed away and 1 landslide. It cost 3.5 million Yuan to repair.
Traditionally , engineers use concrete or rock wall or framework to fix the excavated slopes and road embankments, but it causes a lot and at the same time leads to further environmental problem because passengers do not want to see the white concrete during travelling, instead of green vegetation. Following economic development people pay more attention to the quality of environment. As a result, highway engineers started to use bio-engineering method to protect the roads and the slops along the roads. The Highway Association of Zhejiang Province launched a project in Lishui City of Zhejiang Province in 1999 to use vetiver to protect national highway NO. 330 and Province Highway No 52, where the slope was very unstable and often caused road blocks.
The Li-Jin section of national highway NO. 330 started to build in 1996 and finished in 1997. The location was mountainous with light loamy soil. The original vegetation was destroyed along the road during construction. Some place became barren hill. Besides, new erosion gully happened every where on the highway embankment. Because the road construction broke the original slope balance, the slope became more unstable. Collapse took place for several times. More serious, large scale land slides happened for several times at the section of 5K+450, which caused traffic blocks. To clear the blocks the highway administration had to spend large amount of labor and expenditure by building new wall or stakes from time to time.
A section with most serious erosion problem was selected to plant vetiver grass on Li-Jin line of national highway NO. 330, which includes: 5K + 450 (cut), 10K + 400 (fill), 12K+100 (fill), 12K + 600 (cut). The total area was 11100 m2 (table 1). There were 2-3 tillers per clump during planting spacing (100 -150 cm) x 10 cm.
Table 1. General condition of vetiver applications
Location 5K + 450 (cut) 10K + 400 (fill) 12K+100 (fill) 12K + 600 (cut)
slope condition cut fill fill cut
planting date (April, 2000) 24 22 23 23
sloping 1:2 1:1.5 1:1.5 1:1.5
planting area (m2) 3000 600 2500 5000
* the weather was fine during planting dates. The soils were light loam with medium amount of stone
2.1 Vetiver growth behavior
Observations were implemented around every month since planting to measure and record the height, tillering, roots, etc.
Observation on 12 May, i.e. 20 days after planting, vetiver plant was 9.1 cm high in average. It had a maximum of 23 cm high, 5 tillers per clump, 13 cm deep of root. About 90% of the plants stared the growth of roots, and 70% plant turned into green.
Observation on 12 June, i.e. 50 days after planting, the plant was 149.4 cm high and had 17 tillers/per clump and root was 80 cm deep in average. It had a maximum figures of 200 cm high, 21 tillers /clump.
Observation on 18 August, about 4 months after planting, the roots were well developed with 132 cm deep and 3.5 mm in diameter of main root.
2.2 Soil erosion control
Observation on 12 November indicated that at the section of 12K + 100 (fill) there was dense root system from ground surface to 80 cm below surface. Observation on 22 May 2000, one year and one month later since planting, the root was 180 cm deep. On 25 August each clump had a root system for 60 cm in diameter with 230 cm deep. The grass was 250 cm high. The embankments were well fixed by root system while the stems controlled water erosion and sediment movement.
At the section 10K + 500, raining caused embankment sinking with numerous gullies in 1998 before vetiver planting, and therefore caused road unstable. To prevent further erosion, concrete wall was constructed at the foot of the slope (fill), but the problem still remained to be solved because the slope was still open to sky and subject to further erosion. Few months later since vetiver planted on 22 April 1999 erosion was controlled and slope was fixed with very few fine gullies.
Based on the experience in 1999, another 7900 m2 was planted with vetiver grass in 2000. So, altogether 222 800 tillers were used at the most dangerous sections along the national highway.
The application was at the section of 40K of newly constructed highway and vetiver was planted on from 29 May to 1 June, 2000. Situated on the high mountains, the total planted area was 6278 M2. The soil was sandy with little organic matter. Plants could not grow well and suffered from frequent draught and water logging, and great daily temperature difference. Just after vetiver planting there was high temperature as high as 38.3C and heavy rain (461.8 mm in June). In July, there was a continuous high temperature of 38.4C for 9 days with rainfall of 201.5 mm. In August, there was a continuous high temperature of 36.9C for 7 days with rain fall of 251.5 mm.
On 23 August, around 80 days since planting a strong typhoon attacked the area with rainfall of 70 mm on 23, and 45 mm on 24. Although soil was saturated by water the highway was little effected, and the embankment was appropriately fixed without gullies, slides, or sinking. Observation showed that the survival rate was 98%. The grass reached 130 cm high. There were 3-6 tillers/ per clump and the roots were 80 cm deep. However, the embankment without vetiver produced a lot of sediments accompanied by collapse. the transportation was effected.