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Use half-moon ditches to prevent soil erosion / Radio Scripts / Farm Radio International

Package 42, Script 8
October 1996
Word Count: 810

Use half-moon ditches to prevent soil erosion

You may live in a place where the land is dry and cracked. No trees, plants or crops grow there. Animals barely survive. You worry you will have to move to find better land for farming. You are not alone. Infertile land is spreading like a disease across many countries. We call this problem desertification. The land loses its cover of vegetation, the topsoil blows away, and only hard, cracked, land is left behind. But the problem can be fixed. Many countries are already fighting desertification and with your help it can be stopped. To find out what action is being taken where you live, consult a government representative, or a community organization. And listen to the following idea – a technique which may help you and your neighbours regenerate the land, grow crops, and make a profit again.

Half-moon ditches are easy to build, cost nothing, and keep water in the soil. These ditches, named after their half-moon shape, are ditches dug along the contour of a hillside.

This method of controlling soil erosion works well if the hillside slope is less than five per cent. It is easy to figure out if your slope is greater than five per cent. Take a stride straight downhill. Then measure the difference in height between where you started and where you ended. If it is about the width of three fingers then you know you have a five per cent slope. If the difference in height is greater than 3 fingers the slope is more than 5%.

Here is how to build a half-moon ditch

First you need to draw the half-moon shape in the soil. To do this, scrape a straight line horizontally across the hillside two strides (two metres) long. The two ends of the line should be at the same height on the hill. Then, stand at the middle of this line. From there walk straight downhill one stride and make a mark in the soil. Go back to one end of the horizontal line. Draw a curved line from the end of the line down to the mark, and then curve back up to the other end of the line. Now dig out some soil from inside the half-moon you have drawn until the hole is about two fists deep (10 centimetres). Pile the soil that you dig out of the hole along the downhill side of the curved half-moon to create a barrier that will stop and hold water. To make the soil barrier strong its base should be as wide as your forearm is long (50 centimetres). The top should be at least half that width. The soil barrier, called a bund, should be at least as high as your foot is long (30 centimetres).

Build the half-moon ditches during the last one and a half months of the rainy season. At this time the topsoil is moist and it will be easy to form and build the bunds. If you try to make the bund in the dry season, the soil will be too loose and may not stick together. You won't need any special equipment to build the half-moon ditches. It will probably take about four hours to build one ditch.

A half-moon ditch will help stop water from running off the land, which helps prevent soil erosion. Once the water is trapped by the barrier it soaks slowly into the ground.

Over time, soil full of nutrients moves down the slope and gets trapped in the half-moon ditch. Trees, shrubs, and grasses will take root in the rich soil.

As more grass and shrubs grow, they strengthen the barriers and slow down surface water run-off and evaporation. Eventually a whole line of dense vegetation also keeps livestock and people from crossing and damaging the bunds. Once the half-moon ditches are established, you can begin to plant food crops in them. Or you can plant trees for fuel.

Studies show that a four-year-old half-moon ditch will be almost completely covered with vegetation during the rainy season. Water stays in the soil, run-off erosion almost stops. Crops grow easily in the ditches.

The half-moon ditches are most effective if they are spread throughout the field. For the best erosion control, cover the entire field with half-moon ditches, spaced approximately 40 - 60 centimetres apart. And try to convince your neighbours to build some on their fields.

half-moon ditches are a simple way to help control the harmful effects of soil erosion which can lead to the spread of desert land. The ditches are easy to build and you won't have to buy anything to build them. half-moon ditches help you and your community take better care of the soil.

What is the United Nations Convention to Combat Desertification?

It is an agreement signed by countries around the world to share the responsibility of fighting the effects of desertification. Its goal is to help regenerate the soil in arid, semi-arid, and dry sub-humid regions. The Convention came about at the Earth Summit in Rio de Janeiro, Brazil, in 1992, where many developing countries, led by African countries, asked for the world's help in fighting desertification as quickly as possible.

In Paris in October 1994, 87 countries signed the United Nations Convention to Combat Desertification. Today more than 115 countries have signed the agreement. Once the governments of 50 countries have confirmed their participation the full course of action will begin. A plan for urgent action has been adopted to encourage immediate efforts in Africa because it is the part of the world which suffers the most from desertification.

What causes desertification?

Desertification is caused by changes in climate and by human activities. Drought sometimes makes soil dry up and crack, or makes the soil problems that already exist even worse. But there are four main ways that people make deserts: by overcultivating the soil, by allowing animals the overgraze the land which removes the covering of vegetation that protects it from erosion, by cutting down or burning trees, and by using improper watering methods which turn cropland salty.

What kind of action will be taken under the Convention?

One of the key elements of the Convention is what is called a "bottom-up approach". This means that people in small communities and their leaders will be consulted before decisions or actions are taken. The people in these communities will be involved in projects to stop desertification in their area. The Convention recognizes that people in affected communities, non-governmental organizations, experts, and governments must work together to fight desertification effectively and to find long-term solutions. That means farmers and scientists should share ideas about what the most appropriate farming techniques are. These ideas can be discussed with government and non-government organizations so that funds can be properly allocated.


  • This script was researched and written by Erik Nielsen, Toronto, Canada. It was reviewed by Jon Eakes, Interface Productions, P.O. Box 387, Station Delorimier, Montreal, PQ, Canada.
  • The publication of this script was made possible with the support of Desertification Office, Canadian International Development Agency, Ottawa, Canada.

Information Sources

  • 'Medias Lunas – Rejuvenate Bolivian Farmland', International Ag-Sieve, Vol. 2, No. 9, 1989, pages 1-2. Rodale Institute, 222 Main St., Emmaus, Pa., 18090 USA.
  • Agroforestry in Dryland Africa, D. Rocheleau et al., 1988. International Council for Research in Agroforestry, P.O. Box 30677, Nairobi, Kenya.