Fighting Soil ErosionSteven Jacobson taught farmers in Guinea how to produce agricultural products in a sustainable manner by reducing erosion of their farmland. Lesson Plan | Map of Guinea | Voulez-vous regarder ceci en français ?
|Steven Jacobson, Guinea|
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Photographed, written, and narrated by returned Peace Corps Volunteer Steven Jacobson.
Peace Corps Volunteer
Transcript in French
Hi, I’m Steve Jacobson, and I was a volunteer in Guinea’s environmental program. My job was to work with people on how to produce sustainable agricultural products in a reproducible manner.
I’m sitting on top of a cliff over looking one of Guinea’s natural wonders: the beautiful Grand Canyon of Guinea. This is extremely large scale erosion but not something that mankind can or should fix. In some places you can see the natural vegetation, and in others, farm fields. Soil erosion is the loss of top soil caused by heavy rainfall washing the soil to the rivers.
If you look at this river valley carefully you can see lines running from top to the bottom of this slope. Those are rills. Rills are small channels formed on the surface of the slope. Rills will eventually form larger gullies at which point agriculture is no longer possible. Why is agriculture in Guinea important? Well it feeds people, like these vendors selling mangoes, tomatoes, oranges, and bananas. Rice is the staple food with some sort of spicy peanut sauce over the top. It tastes very good and here you see some of my friends enjoying dinner from a communal plate.
This is what the native environment looks like prior to burning of the field to start agriculture. Notice how many trees and bushes there are. The roots of the trees and bushes hold the soil, sustaining soil fertility for the plants to grow. It rains very hard in Guinea. It’s like standing in a shower. The heavy rains cause massive soil erosion.
The rain soaks the soil quickly. On cleared land, there are no roots to hold the soil, so the soil washes away. Small plant seedlings are also washed off and the farmer does not receive production from that part of the field.
Ideally the slopes would be changed to flatter surfaces, called terraces. This example from China shows how a sloped surface can be changed to many flat surfaces, reducing erosion and retaining soil fertility.
In cross-section, terraces have flat surfaces and steep walls. The rock walls, trees and grasses create the terraces and decrease run-off of rain water which protects the soil surface. This does take a lot of effort but is worth it since farmers can then use the field for many years.
This is a lot of work and not always possible because of a lack of labor forces and available material. A less arduous option would be to reduce the steep slopes to minor ones which would greatly reduce erosion. The idea is to keep the soil in one place and not let it run into rivers. As before, the terraces are held in place by rock walls, trees and grasses. But how do you establish how high the rock walls should be?
There are two tools that can be used to measure contour of a slope. First is the A-Frame, which measures contour using string, wood, a rock, and gravity. When the string hangs at the center of the horizontal stick, the two vertical sides of the A-Frame are at equal levels. A second way to measure contour is le Serpent. It’s made with two long sticks and a piece of see-through garden hose about 30 feet long filled with water. When the sticks are at equal elevations on the field, the water level in both ends of the hose will be equal. This is like a level a construction worker would use.
Since le Serpent is much longer than the A-frame is wide you can measure with this level at two to three times the rate of an A-frame: at least two or three football fields in a day’s work.
Here’s an example of what happens if you do not protect against erosion. A small gully has formed in between the plants and with time will erode out the roots and kill the plants. What can be done?
Well, the best thing to do is to create a check dam—a small, low obstruction— to slow or stop the flow of water in a ditch or channel and let the water sink into the soil. This is a simple diagram of a wicker check dam that farmers could make.
These men have just finished a wicker check dam in a very small gully in order to reclaim the gully and allow them to continue farming the field. This is an easy solution but unfortunately not a permanent one. Terraces are really the best way to slow erosion permanently, especially if the slopes are steep. In China the farmers have been protecting their field in this way for centuries. Unfortunately, Guinea has not yet come this far since the ideas and practices were only introduced recently.
There is hope for Guinea and all of Africa for successful and sustainable agriculture. Hopefully in a few years when I go back to visit I will see some of these changes have occurred and there will be more food on tables and money in pockets. I’m Steven Jacobson for the Peace Corps’ Coverdell World Wise Schools.