Vegetative lines consists in planting vetiver grass lines following the contour lines, along stream banks and roadsides, in order to create a hedge. These hedges act like semi-permeable barriers, aimed to hinder surface erosion as they slown down run-off and retain sediments picked up by excess rainwater. This set-up improves water infiltration and helps to increase the ground moisture level. Their root systems also help stabilize the soil and prevent further soil erosion.
In order to achieve vegetative lines, vetiver bunches are dug up and separated into sprouts, cut to a length of 10 cm and then replanted 10-15 cm apart from each other along the contour lines, right before the rainy season starts. On slopes steeper than 10%, the hedges are located 5 m apart from each other on vertical distance, forming lines about 200 m long. The work starts at the top of the slope and continues downslope. Usually a double line of vetiver grass is recommended in order to create more efficient hedges.
Very similar to the intervention described above is the so called Vegetative lines with cactus. The latter is based on the same principle of the Vegetative lines with vetiver but it is suitable for drier environmental conditions (0 – 600mm). Like some other interventions, over time, this type of intervention can lead to the formation of terraces due to tillage and water erosion between the hedges.
Looking at the economic investment, the cost of the intervention is mostly influenced by the slope, and therefore the number of lines that need to be planted, availability of materials and labour. Nevertheless, maintenance plays a very important role in this type of intervention and its cost must be taken into account. It is often needed to fill the gaps along the hedges in order to keep their efficiency as barriers. Before the dry season, the height of vetiver grass bunches needs to be reduced and kept down to approximately 50 cm in order to prevent them from burning. It is also worth remembering that vetiver grass is not suitable for fodder because it is not appetizing, therefore the cut material is usually used for mulching.
Food and Agriculture Organization of the United Nations, 1991, Chritchley & Siegert, Water harvesting, http://www.fao.org/3/u3160e/u3160e00.htm. Reproduced with permission
WOCAT, 2012, Schwilch, Hessel & Verzandvoort, Desire for Greener Land, https://edepot.wur.nl/212528. Reproduced with permission.