Advice on cover crops for soil erosion control in Tanzania
We are currently experiencing massive soil erosion in the Kisongo area of Tanzania. The general location can be found on a Google Earth search. What might be some fast growing, tough, non-invasive cover crops that we might be able to use to slow this down?
Thanks for the question and sorry to see it is such a bad situation. (This problem is due to overgrazing and too few trees following villagization in the Arusha region. There are some sources on this from the case study of Murray-Rust, D.H. 1973. (see bottom of answer))
So, this is a systemic problem that requires long term changes which require terracing, sand dams and tree planting. A series of videos shows this and goes through the reduction in soil loss that can be achieved with each of these. Overview https://www.youtube.com/watch?v=DmPLG... Sand dams: https://www.youtube.com/watch?v=Yjzcf... and trees https://www.youtube.com/watch?v=yAZRK...
These approaches can transform the landscape in a relatively short time.
Sonia Sachs of the Millennium Village Project just emailed me news of a transformative project in Koraro in Ethiopia that changed the flow of water using Gabion boxes/baskets which is wire mesh around large stones and other interventions such as percolation ponds, irrigation ponds, dug wells, dams and piping. You can get introduction from one of their videos https://www.youtube.com/watch?v=4AS-A... (thanks Sonia!). This was a project initiated in 2005 and certainly making such big changes is a multi-year effort. We are working on getting more data on the success at Koraro to share with you.
Looking at your picture I can see that this water seems to flow from a concentrated stream before branching out (so about 300m before the erosion). Laying down a barrier like tree trunks, rocks, sticks, mud would cause the water to collect and go into the soil and reduce the waterfall erosion effect further down.
But you ask about cover crops so need an immediate solution (besides the dam that would help). I doubt if cover crops will be good enough. The rains are continuing so you wont sow them in the rains and by the time the rains finish you wont need them. (As a side note: Cover crops are an amazing approach to mainatining soil moisture, promoting higher nitrogen and increased oxygen: great video here on their use in USA setting which can also be very dry http://www.youtube.com/watch?v=nWXCLV... )
For Africa, the FAO do have training manual on cover crops in Africa and the relevant details start on page 83. I also attach a picture of a table from that publication (page 95). http://www.fao.org/ag/ca/AfricaTraini...
In planting cover crops you have to decide what to use them for. Some are good for animal feed and others are not (and even bad for animals. See the table).
What are farmers doing there? Raising cattle? Growing crops?
If you can provide more information on what the land is being used for that could help people out there point you to the best cover crop.
good luck and keep sending more information so that we can help.
("Soil Erosion and Reservoir Sedimentation in a Grazing Area West of Arusha, Northern Tanzania." In A. Rapp et al., "Studies of Soil Erosion and Sedimentation in Tanzania." BRALUP Monograph 1. University of Dar es Salaam, Dar es Salaam). If you need this let me know.
Here is a link to a documentary that does a good job of showing people from all over the world addressing this problem.
There is a great deal that can be done to prevent erosion of this sort and scale. I have done some work in the Andes Mountains of Ecuador, where they are in the midst of centuries of erosion on a vast scale. I cannot highly enough recommend getting educated about the principles and methods proscribed in Permaculture. This is EXACTLY the type of thing Permaculture was developed for, for prevention and recovery of severely damaged land, and it now has a history of turning deserts back into lush landscapes without huge outputs of money and other resources. I would strongly urge you to look into it.
I wish you all the luck in the world in dealing with this problem. You are trying to repair the basis of life on Earth. It is the most important work in the world and cannot be taken too seriously. Good fortune.
I cannot see cover crops really being a benefit in such conditions but rather the use of trees which offer the same benefits of cover crops in adding organic matter to the soil while reducing surface flow and increasing rainwater infiltration into the soil. ICRAF's program Evergreen Agriculture http://www.worldagroforestry.org/ever... promotes the use of trees and other conservation farming techniques for sustainable farming livelihoods. The use of indigenous trees such as Faidherbia albida are well suited for integrating with farming systems and offers various other products at the same time.
This recent Ted Talk should provide some good ideas on how to restore the land by bringing in more livestock. Allan Savory provides excellent examples of successes they have had in different parts of the world.
Good luck and sorry to see such devastation.
For a quick (although somewhat dated) overview of soil erosion causes and control strategies, FAO has a publication with the compelling title "Keeping the Land Alive": http://www.fao.org/docrep/T0389E/T038...
While cover-crops are a good long term prevention strategy, this type of catastrophic gully erosion is very difficult to control once it starts. The small waterfalls are continuously eating away at the base of the falls, causing them to erode upstream. For an established gully like this, you might consider a rock/stick/mud dam (ideally at a narrow point in the gully slightly downstream) that turned the gully into a small reservoir. That would reduce the erosion at the waterfall (now submerged, or with the height of the fall greatly reduced) and allow sedimentation to help refill the gully over time.
In the longer term, increasing infiltration upstream with cover crops and other soil erosion control strategies such as outlined by David Hughes would certainly help. The flip side of erosion is drought, especially in semi-arid regions, and farmers with insecure land tenure often have more motivation to store water for drought than to reduce erosion. Fortunately many of the techniques used to harvest rainwater for subsequent dry periods have the side benefit of reducing runoff and erosion during wet periods. An FAO document on water harvesting technologies is available at http://www.fao.org/docrep/U3160E/u316...