Soils in Rwanda
Senior 2 · Geography and Environment
Soils in Rwanda
Lesson 1 of 3
22 min
Most Rwandan families depend on farming, and the land's real wealth is its top few centimetres: the soil. A farmer in Musanze plants Irish potatoes in dark, crumbly soil; a farmer in Bugesera plants cassava in pale, sandy soil; a rice cooperative works the grey mud of a valley floor. They are responding to different soils, and each soil was made by a different mix of rock, climate and time. This lesson explains how soils form and which types Rwanda has.
Soil is the loose layer on the Earth's surface in which plants grow. A good farming soil is roughly: about 45% mineral particles (sand, silt and clay from weathered rock), about 5% organic matter (humus from decayed plants and animals), and about 25% each of water and air in the spaces between particles. It also holds billions of living organisms.
A cut through a soil from surface to rock is a soil profile. It shows layers called horizons: a dark topsoil rich in humus, a lighter subsoil where washed-down minerals collect, a layer of weathered parent rock, and finally solid bedrock.
| Parent rock | Resulting soil |
|---|---|
| Basalt and other lavas (volcanic region) | Dark, deep, rich in minerals; very fertile |
| Granite (parts of the central plateau) | Sandy (from quartz grains) with some clay (from weathered feldspar) |
| Quartzite (many ridges) | Thin, sandy, poor in nutrients |
| Shale and schist | Fine, clay-rich soils that hold water |
| River sediments | Alluvial soils: fine, layered and fertile |
Explain why the soils around Musanze are so fertile.
| Soil type | Where | Characteristics | Uses and importance |
|---|---|---|---|
| Volcanic soils | North-west: Musanze, Nyabihu, Burera, Rubavu | Dark, deep, well-drained, very fertile | Irish potatoes, pyrethrum, beans, maize, vegetables |
| Red lateritic (ferralitic) soils | Much of the central plateau and east | Red or yellow from iron oxides; deeply weathered and leached, so often acidic and low in nutrients; may harden into laterite (murram) | Bananas, cassava, coffee with manure; murram for roads; clay for bricks |
| Acidic highland soils | Congo–Nile Ridge | Formed under forest and heavy rain; humus-rich at the surface but leached and acidic | Tea (which likes acidic soil); natural forest |
| Alluvial soils | Valley floors: Nyabarongo, Akanyaru, Akagera; the Bugarama plain | Fine silt and clay laid down by rivers; fertile; often waterlogged | Rice, sugar cane, vegetables; clay for bricks and pottery |
| Peat (organic) soils | Marshes such as Rugezi and Akanyaru | Black, waterlogged, made of partly decayed plants; acidic | Peat is dug as a fuel and burned to make electricity; wetlands store water |
| Sandy soils | Parts of the east, such as Bugesera | Light, loose, drain fast, hold little water or nutrients | Cassava, groundnuts, sweet potatoes; easily eroded by wind when bare |
Tip
Memory hook. Remember the five soil-forming factors by their initials, P-C-R-O-T: Parent rock, Climate, Relief, Organisms, Time. In an exam, name the parent rock first when explaining any Rwandan soil.
Solution: mineral particles, organic matter (humus), water and air.
Solution: volcanic soil, fertile because it formed from young, nutrient-rich lava and ash.
Solution: iron in the weathered rock has been oxidised into red iron oxide.
Solution: on valley floors where rivers deposit silt; used for rice, sugar cane and vegetables.
Solution: weathered material is removed downslope by gravity and runoff and collects at the bottom.
Summary
Sources and credits
The Rwandan soil table, worked example and practice items are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
