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NEWS & CURRENT AFFAIRS

The Nairobian

Want to stop flooding fields? Try this grass

Smart Harvest

By George Mbakahya | May 16, 2020

**Vetiver grass growing on a rehabilitated gully in Rift Valley. For good results, the vetiver grass is planted in single or multiple rows on the contour to form a protective barrier across the slope.** [Fred Kibor, Standard]

Increasingly, the country is experiencing severe floods. General flood control measures have involved building costly drainage channels and embankments that are broken at peak flows. At farm level, the thinking should shift to slowing water from reaching rivers, and drainage channels to reduce peak flows before they cause damage.

This is where planting of vetiver grass becomes handy. Vetiver can be used strategically to reduce the amount of water in the soil, thereby allowing soils to absorb more water during the rainy season. The plants’ stiff stems reduce the flow, so the water is less likely to reach devastating peak flows that can cause destruction.

This technology is appropriate because the other soil conservation methods such as contour banks, earthen bunds and concrete structures are expensive, temporary and hard to implement.

The advantages

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Vetiver is a live system which develops with the deposition of sediment and it can be introduced on farms with minimum or no changes to the existing farm layout.
Its root system is dense, fibrous and strong to trap and hold the soil, thus protecting against erosion. The strong and deeply rooted characteristic, extending to 10-13 feet within 24 months, allows the vetiver to resist flood waters and survive deep water flow.

Its deep roots can also provide important and much needed stabilisation to slopes at risk of slippage. These roots do not interfere with the crop yields because they grow straight down with few lateral surface roots.

Vetiver is drought-tolerant and bush-fire resistant. It can be a great source of mulch biomass that can be utilised in the farm for retention of moisture and rebuilding the top soil. Apart from binding the soil, vetiver grass does not compete for nutrients and water with other crops.

It is affordable

It can be planted along the edge of existing terraces to reinforce the banks against collapse. The oil in vetiver roots also appears to be a deterrent to burrowing rats. For good results, the vetiver grass is planted in a single or multiple rows on the contour to form a protective barrier across the slope. When it rains, the grass barrier slows the runoff water thus allowing deposit of sediment.

Planting

Vetiver grass does not set from seed. To propagate the grass, large clumps are split up to give around five to six slips which are planted with animal or compost manure. On a high slope area, the grass should be

planted on the ridge of hillside ditch or bench terrace. This is because, the terraces are easily eroded by flowing rain water.

To prevent damage as mentioned and to prolong maintain humidity to the soil, plant vetiver grass at the ridge of the hillside ditch or the outer side of the ridge of bench terrace.

For the irregular gentle slope areas which experience fewer problems in soil loss due to flooding, planting vetiver grass to maintain soil humidity can be done by circular planting around the tree or semi-circular planting where the grass is planted around 1.5-2.0 metres far from the base of trees in semi-circular alignment facing uphill to check the water flow and for trapping the soil sediment.

On medium slope area, contour cultivation should be done to prevent overflow of water. In non-slope areas, there are no problems in soil loss, however, flooding can still occur, so, planting of vetiver grass to keep humidity to the soil as much as possible is a good method.

For the rain-fed cropland, planting of vetiver grass will confine water within the area allowing minimum flow.