Report 7 (of 7): Vetiver, a Grassy Solution - Mexico

Introduction

Every year, worldwide, 75 billion tonnes of top soil is removed, by the weather, from farmland. The state of Oaxaca in south-east Mexico is an important centre of biological diversity because of its position as a land bridge between two parts of a continent. Its big central valleys and mountains have been home to one of the ancient Indian civilisations and the origins of agriculture.

Most of the people in the state rely on farming for their livelihood but soil erosion and the loss of soil fertility are major problems affecting the communities in Oaxaca. It is one of the poorest states in Mexico with very high rates of malnutrition and migration by farmers to the United States because the land has become so degraded that there is no longer sufficient farmland to cultivate. It has been estimated that up to 70% of the territory of Oaxaca (an area the size of Portugal) suffers moderate or severe erosion.

As traditional farming practices breakdown or are replaced, the rate of soil erosion is increasing rapidly. Forests are being cut down, unsuitable slopes are being cultivated and land is being overgrazed without appropriate methods to conserve soil. Most of the region is becoming a man-made desert. Many areas lack sufficient water to produce good crops due to uncontrolled run off which also carries away the earth.

Vetiver Grass

Vetiver grass originally comes from India where it is known as Khus. It is now used in more than 50 countries for soil and water conservation, land restoration and low cost road maintenance. The system of soil and moisture conservation is based upon stabilising the soil with vegetative contour barriers of vetiver grass.

Vetiver Grass Systems

In the wet tropics, vetiver hedges can be established in five months. In arid areas, it usually takes about three seasons. Once established, the vetiver hedges completely stop the erosion of the top layer of soil. Rather than concentrating run-off water into streams and therefore making it more erosive, the hedges slow the run-off, spread it out and filter out the silt while letting the water seep through the entire length of the hedge. Silt trapped behind the grass barrier spreads back across the field. Vetiver grass grows through the silt, forming a natural terrace over the years.

The system is cheap and sustainable. The farmer can do all the planning and maintenance without any assistance and so the only cost is his own labour. There is no need for expensive equipment or labourious maintenance. The grass reproduces by division of the plant and not by its seed. The plant is divided into slips and put into the ground like seedlings. Once the roots are established, the plants develop quickly and can grow to more than two metres high after just a few months.

Vetiver grass systems cost less than one tenth of other engineered soil conservation systems which have arbitrary limits for growing food crops, with 12% being the maximum ‘safe’ slope on which they can be used. Using vetiver grass and the system of contour planting and planning between the stabilising hedges, food crops have been produced safely on 100% slopes, that is, slopes with angles of 45 degrees. Therefore, vast areas of land which have previously been considered unstable, can now be safely used for the production of crops providing the hedges are maintained. It is also used for restoring very degraded and eroded land.

Planting Vetiver Grass

Vetiver grass will flourish over a range of ecological conditions although it grows better under humid conditions with annual rainfall above 700 mm. It also grows in all types of tropical and subtropical soils.

Vetiver grass should be planted about 15 centimetres apart in a single furrow along the contour lines of a slope, along the edge of a terrace, along the top of a paddy field, or along the side of a river or dam. The grass quickly grows together to form a dense hedge which can measure up to 2 metres high. The base is about one metre wide, with a strong, dense and mainly vertical root system which can penetrate up to 3 metres deep.

When planted in a thin line on the contour of a slope, it is the clustered mass of the vetiver stems which act together with collected debris in the soil to produce an impenetrable barrier. The stiff dense leaves of a vetiver hedge stop the flow of water on the slope, capturing the soil and absorbing the water through its deep root system. This barrier halts the surge of water which would otherwise sweep away the topsoil during a tropical downpour. A vetiver hedge therefore, slows down and spreads out rainfall, allowing it to filter through gradually without taking soil and silt with it.

Characteristics of Vetiver Grass

The roots produce a strong aromatic oil which makes the grass resistant to most pests. The grass is palatable to livestock and it does not spread like a weed because it is practically sterile. After three years, a vetiver hedge will require no further maintenance but regular cutting will make it grow stronger. The leaves can be used as a mulch to help retain soil moisture, for thatching and for handicrafts.

SASO - Suelos Agua y Semillas de Oaxaca

In 1995, a small local group called Suelos Agua y Semillas de Oaxaca (SASO) found a source of vetiver grass near Oaxaca. SASO became an NGO called LASOS, A.C. in 1997, and with the help of the Comisión Oaxaqueña de Defensa Ecologica, started a programme for erosion control and soil restoration involving local farmers, communities, government and non-government organisations and researchers.

Originally, SASO began the project with 40 plants and there are now more than 50 nurseries growing Vetiver grass throughout the state. Vetiver grass has been grown successfully in all the major soil and climate conditions of Oaxaca. Hedgerows are already beginning to form natural terraces and groups of women are cultivating vegetable gardens between the hedges.

The Advantages of Vetiver Grass

• It can reduce erosion with a hedge which is just one plant wide.

• It can survive on many different soil types.

• It can grow in a wide range of climates and temperatures, and survive all the forces of nature except freezing.

• It is cheap, easy to establish and the hedges are easy to maintain.

• It is not difficult to remove if it is no longer wanted.

• It is largely free of insects, diseases and pests and does not host any pathogens that attack crops.

• It has a deep penetrating root system.

WARNING!

There are two types of vetiver grass - one has fertile seeds and one does not. It is important to use the one without fertile seeds to ensure that the grass does not spread uncontrollably and become a menace to adjacent crops. For this reason and to avoid a potential hazard, it is recommended that the sterile type of vetiver (vetiverea zizanoides) is used for erosion control and soil conservation.

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Intermediate Technology would like to thank the National Research Council, the Vetiver Network and SASO for providing the original material on Vetiver Grass.

TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.