23 - Soils - Rainwater Harvesting with Vetiver
23 • Rainwater Harvesting with Vetiver
The idea is to improve your crops by getting more rainwater to stay in the soil instead of running off. This is done by growing vetiver hedges which at the same time reduce soil erosion. Water running down a sloped field carries much topsoil. It is retained by the vetiver grass (A, in thepicture) and most of the topsoil is deposited there (B). Some water runs through the hedges (C). The deep roots - 2 or 3 m - hold the plant firmly to the ground (D). The roots also open up the ground, so that more of the rainwater penetrates into the ground - it is “harvested”.
Most farmers in the developing world are totally dependent on rainwater. Most of Southern Africa has one rainyseason where it is possible to grow crops, and a dry season where only the few with irrigation can produce. Vetiver hedges enables farmers to harvest rainwater so they can grow vegetables/ crops for a longer period. This works two ways: • Rainwater running on the ground is stopped or slowed down. • The big root system opens up the soil and enables more water to penetrate into the ground. Thevetiver hedges must be planted in contours (same level) with 10 metres between hedges. They will efficiently stop soil
erosion, which in a country like Zimbabwe has been calculated to annually remove 50 tons of soil per hectare per year. This not only creates problems in neighbouring Mozambique (floods) but with this soil many nutrients are lost, which could have been used by the crops. The extrawater in the soil will extend the growing season or make it possible to grow crops that need more water. The system can even be used in very dry areas by planting vetiver hedges in the dry river beds. It will be possible to grow crops behind the hedges in the period after the short rainy period. The vetiver grass will survive periods of flooding. Start making the system in a small area, so you findout the best ways of growing vetiver under your conditions, and so you can see that it works.
Vetiver grass. Description of A-D in the text
How to make a vetiver nursery: A vetiver nursery is best made in a humid area, that is too wet for normal farming. It can also be made on a small scale by using wastewater from the kitchen, bath, etc (see section 41 about waste watercleaning). Vetiver is very easy to grow and can grow under nearly all conditions. If you have little water for watering it is best to grow the plants first in plastic bags. If there is enough water, plastic bags are not needed and they can be planted directly in the ground.
40 Green World Actions
If you do not know anyone who has vetiver plants, find suppliers at “The V e t i v e r Ne twork”www. vetiver.org. Or contact the GAIA-Movement. Plant with 15-20 cm between the grass tillers
Planting contour rows in dry areas
• • • • • Plant them in the beginning of the rainy season. Prepare the contour lines for the hedges by using an A-frame. If possible, avoid planting them in the shade. Make a small ditch 10-20 cm deep - this will give the plants some more moisture. If you do not usepolybags, dip the roots in mud slurry (mud mixed with water) so they do not dry out while you are planting. Cover them with wet sacks, and plant the same day. Planting distance should be no more than 15 cm. Plant 3 tillers in each hole. Plant so the pale greenish area at the bottom of the leaf base is just covered.
A vetiver nursery
Start by getting some vetiver plants. If you have totransport them, keep them out of the sun and with the roots in water. • Cut the leaves at 20 cm and the roots at 10 - 15 cm. • Mix cow dung (or compost or clay) into a bucket of water. • Place the vetiver with the roots in the bucket. • After 4-5 days in the shade small new roots are seen. • Separate the tillers and plant in polybags (plastic bag with small holes used in nurseries). • The better soil...
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