Description
Similar names: Cordons pierreux, stone bunds.
Stone lines are stones grouped in the shape of a line and placed along contours. The stones can be of different sizes. The goal of these lines is to conserve the soil and reduce runoff, as they are used to slow down water runoff and break its velocity. Hence, they increase infiltration and retain sediment and seeds to make water and nutrients available for crops. Stone lines are most suitable for water harvesting on slightly sloping plains (up to 5%) in semi-arid regions. For slopes starting from 5%, stone bunds can be used (see eyebrow terraces).
Stone lines are an easy and cheap intervention if stones are available in the immediate surroundings. This intervention is widely used in Africa, both in dry and humid areas. Moreover, stone lines are often used in combination with Zai pits intervention for the rehabilitation of degraded and crusted lands. It is applied in semi-arid areas, on sandy and loamy soils where the slope is lower than 5%. A great example occurs in Niger, where the combination of the two techniques is applied to capture runoff, making infiltration more efficient and improving nutrient availability. The pits have a diameter of 20-30 cm, and a depth of 20-25 cm and are spaced about 1 m apart in each direction. Stone lines are spaced 20-25 m apart on slopes of 2-5%. With this layout stone lines are quite small, usually, three stones wide and only one stone high and they are placed, along the contour lines, by hand. Very often grass grows between the stones leading to a greater infiltration and helping the accumulation of fertile sediments. Maintenance-wise, stone lines need to be repaired annually, in particular after heavy precipitation events.
PRE-CONDITIONS FOR IMPLEMENTATION
- This intervention can be quite labor intensive if the stones are not available on the place and need to be transported.
- Maintenance: stone lines need to be maintained, especially after heavy rainfall.
- This technique cannot work properly if the slope is too high.
- The spacing of the stone lines can affect the levels of water runoff and crop performance. It is therefore fundamental to well plant their establishment and reinforce the lines if necessary.
METHOD OF APPLICATION
Materials required
- Pick-axe, shovel (to dig out stones)
- Wheelbarrow (to transport the stones), or something more adequate if the stones are far away from the site.
- Water tube level or something to measure the contour lines; here are some examples of tools that could be used: a string line level or spirit level instrument, a hose pipe half filled with water, a bottle of water half filled with water, A-frame level.
Steps of implementation
- Collect stones on-site or transport them with the help of a donkey cart or lorries (which is much more expensive). Both small and big stones are used to build a stone line and they are placed along the contour lines. Smaller stones are placed upslope whereas the larger ones face downslope to slow down the runoff, hold nutrient-rich soil sediments and improve water infiltration.
- Align stones along a contour line, with a maximum of 3 stones in width, measured with the help of a water tube level. A stone line is usually 25 cm high and 35-40 cm wide. The distance between the lines can vary according to the slope and the amount of material available. However, it is recommended to keep the lines 20 m apart from each other for slopes less than 1% and 15 m for slopes between 1-2%.
- To maintain the stone lines: check and repair the stone lines annually and following heavy rains. Vegetation is sometimes planted to stabilise the lines, usually where stones are scarcer. The vegetation used usually consists of perennial grass, as it develops long roots which resist soil erosion (see also the intervention Vegetative lines with vetiver grass).
BENEFITS
This intervention contribute to:
COSTS
Estimation of costs and benefits of intervention
The costs are based on 300m stone lines per hectare, with a slope of 3-4%.
The availability of stones and the slope determines the establishment cost.
Maintenance costs also vary according to the slope, the availability of stones, and on how well the stone lines were built.
| Establishment cost | US $85/ha |
| Labor time | 25 person days |
| Maintenance cost | US $1.5 |
| Maintenance labor time | 1 person days |
CASE STUDIES
1. Stone lines to control soil erosion in Uganda
Description
In Uganda, particularly in the Rakai District, stone lines are used to control soil erosion on steep, degraded slopes. These stone lines are built along the contour of the land to slow down water runoff and prevent soil from being washed away during heavy rains. This method has replaced traditional farming practices that didn't protect against soil and water movement. Farmers arrange stones in lines along the contour, guided by a rope and using simple tools like hand hoes and pick axes. The stone lines, which are 0.4 to 0.6 meters wide and 0.5 meters high, help to create natural terraces by trapping soil on the upper side of the barriers.
The process involves digging up and collecting stones exposed by years of erosion, and placing them along the contour lines. Pits are dug between the stone lines for planting crops like robusta coffee and beans, which also help to cover and protect the soil. Maintenance involves repositioning displaced stones and removing weeds. These stone lines not only protect the slopes but also prevent sediment and runoff from damaging crops in the valleys below and from silting the Kagera River. This technique, supported by farmer field schools, ensures sustainable land management and protects the environment.
2. Stone bunds for soil conservation, Ethiopia
Description
In the Ethiopian highlands, stone bunds are widely used to combat severe soil erosion. This study, conducted near Hagere Selam in Tigray, aimed to evaluate the impact of these stone bunds on soil fertility and crop yield. Researchers measured soil nutrients and crop responses on various plots. They found that soil fertility levels varied significantly between plots due to small-scale soil features, plot history, and management practices. However, soil near the lower stone bunds generally had higher levels of certain nutrients, particularly on limestone soils. Despite the presence of soil fertility gradients, these were not problematic and could be managed with appropriate soil practices. Overall, crop yields increased by 7% with stone bunds, demonstrating their positive impact on agricultural productivity. The study concluded that stone bunds are crucial for preventing soil erosion and promoting sustainable agriculture in the Ethiopian highlands, with no significant negative effects observed on their long-term sustainability.
FIND OUT MORE
External Sources
- Here you can find more information about the establishment of this intervention.
- Stone lines are commonly known in French as “cordons pierreux” and are widely used in Algeria, Burkina Faso, Morocco and Tunisia. Here and here you can find more about it (French only).
Guides
- Good instructions on how to lay out a contour or a graded contour and measure the slope of the land can be found here.
Videos
- A very useful video about the mechanism of stone lines and their benefits can be found here.
