Soil Conservation in Rwanda

1Why this matters

Drive through almost any district in Rwanda and you will see hillsides cut into wide steps, lines of grass along the slopes, and trees standing in the middle of fields. These are not decorations. They are Rwanda's answer to soil erosion, built by farmers, cooperatives and whole villages during umuganda. Soil conservation means protecting soil from erosion and keeping it fertile.

2Methods that slow down water on slopes

• Radical (bench) terraces: the slope is dug into a series of level steps. Water soaks into each flat bench instead of running downhill. They are costly in labour but very effective on steep slopes.
• Progressive terraces: strips of grass or hedges are planted along the contour; soil washed from above builds up behind them, so over several years the slope turns into terraces by itself.
• Contour ploughing: ploughing and planting in rows across the slope, along the contour lines, so each ridge traps water.
• Anti-erosion ditches: trenches dug across the slope to catch runoff and let it soak in or lead it away safely.
• Grass strips of napier or similar grasses along the contour, which also give fodder for cattle.

3Methods that cover and feed the soil

• Afforestation and agroforestry: planting trees on steep land, and trees such as grevillea among crops; roots bind soil and leaves break the force of rain.
• Mulching: covering soil with dry grass or crop remains to protect it from raindrops and keep it moist.
• Cover crops such as beans and sweet potatoes that keep the ground covered.
• Crop rotation and intercropping to keep the soil fertile and covered.
• Manure and compost to add humus, which binds soil particles together.

4Methods that reduce damage from animals and people

• Zero grazing: cows kept in sheds and fed cut grass, so they do not strip the hillsides.
• Controlling bush burning and protecting forests and wetlands by law.
• Gully control: check dams of stones or sticks across gullies to slow water and trap soil.
• Land-use planning: keeping the steepest slopes under forest.

Worked example: choosing a method

A farmer in Ngororero has a field on a slope of about 40%. Rain has already cut rills across it. Recommend two methods and justify them.

1. First, work out what the slope means: a 40% slope rises 40 m for every 100 m across, which is very steep for farming.
2. Radical terraces: on such a steep slope only level benches will stop runoff from gathering speed.
3. Grass strips or agroforestry trees along the terrace edges: roots hold the terrace walls in place and the grass feeds livestock.
4. Not recommended alone: mulching or contour ploughing, which help on gentle slopes but are not enough on 40%.

A good recommendation always matches the method to the slope and to the type of erosion already seen.

Practice