Dov Pasternak, icrisat sahelian Center, Niamey, Niger




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From Dov Pasternak, ICRISAT Sahelian Center, Niamey, Niger

I would like to share with you the experience of the ICRISAT Sahelian Center in Niger on aspects of soil and water conservation in the semi arid tropics of the Sahel.

 

I will start by saying that all of us know by now many effective means for soil and water conservation that if applied correctly will have a very strong and lasting impact on crop productivity and on environmental conservation.  Many of these approaches were described in the excellent background material given to us by the conference organizers.



The fact however is that very little of these technologies are being successfully applied on a large scale.
Thus to my opinion the main objective of this conference should be to find out why these technologies are not being applied and what should we do to propagate them?

Let us start with socio-economic considerations:



  1. For any new technology to be successfully adopted by farmers it must bring the farmer a visible and immediate benefit; economic or otherwise

  2. This benefit must be substantial enough to convince the farmer to change his ongoing practices (or in the economists jargon the benefit cost ratio should be substantial).

  3. For the technology to be disseminated on its own the costs incurred in its adoption must be within the reach of the farmer

  4. The introduction of the new technology should be followed up by an extension service for a long period of time.

For example the introduction of stone lines to reduce runoff and soil erosion failed in many places because:



  1. The immediate benefit showed only a 15% or less increase in yield during the first years of its application

  2. In most places the application of stone lines that required transportation and labor that were paid from external sources.

  3. Follow up was limited to the “project period”

  4. After a few years the stone lines were filled up with silt that decreased its efficiency in slowing down the velocity of the flowing water. The obvious solution was to add a new stone line on top of the clogged line. But there were no resources available, there was no follow up and hence no encouragement and the stone lines effectiveness went down.

Another example:

In the Sahel developers produced micro catchments in hard lateritic soils and planted them with millet. This operation gives a very low benefit cost ratio. Farmers will not work so hard digging micro-catchments to produce a few more kg of millet.

Many scientists have recorded huge benefits of crop residues for improved soil fertility and exp


In most places in semi arid Africa, low soil fertility is the limiting factor. More limiting then water. Thus if the problem of low soil fertility is not solved together with or before solving the water problem then farmers will not benefit from water conservation techniques.
Therefore there is no escape from working with integrated approaches. ICRISAT is now developing an integrated rainfed production system that simultaneously solves the problems of low soil fertility, low water availability and poor seasonal rain distribution and low income from traditional crops. We call this system: the Sahelian Eco-Farm (SEF).
Here is an example of the SEF:

A one hectare field is surrounded by Acacia colei trees planted at 2meters spacing.

Inside the field we planted two rows of A. colei 10 meters apart with a distance of 5 meters apart. In the third row 10merers from the second A. colei row we planted a row of the domesticated Indian Ziziphus mauritiana that gives fruit the size and shape of a small apple. For this reason we are calling these trees “Pommier du Sahel” (PDS) or the “apple of the Sahel”.
The PDS are planted inside micro-catchments called locally demi lunes. The demi lunes have the dimensions of 3x3 meters in their widest part they are connected with each other by earth bunds producing a continuous water harvesting structure.

The assumption is that farmers will maintain this structure because they will benefit from the high fruit yield that water harvesting will give. The demi lunes not only harvests water but also the fine soil particles loaded with organic material that continuously “fertilize” the trees. Three different annual crops are planted in the field: Millet, cowpeas (a legume that improves soil fertility) and Roselle a cash crop for export. The three crops are rotated annually. Zero tillage is practiced.


The A. colei trees (hedges and inside rows) are pruned each year just before the rainy season. During the first three months after pruning the trees leaf area is small and therefore trees do not compete for water with the annual crops. About 40% of the branches that are cut are used for firewood and 60% is used as a mulch.
Now let us look at the many integrated services of the system.

  1. Soil fertility. Soil fertility is enhanced by the mulch that is spread each year on top of the soil and is “processed” by termites into soluble nutrients. After pruning the A. colei many roots die and add an “invisible” source of organic matter to the soil. A. colei roots fix atmospheric nitrogen. Crop rotation improves soil fertility. The windbreak effect of the Acacia plus the mulch on the ground trap nutrients rich atmospheric dust during the Harmatan (dry and strong desert winds during the dry season). We suspect that A. colei roots also bring up to the surface nutrients that were leached below the reach of the annual roots.

  2. Water. The A. colei mulch prevents the formation of thin crusts that impede water infiltration. The many small pores in the soil created by the A. colei roots improves infiltration rate, the combined demilune/earth bund harvest all up-slope run off. No water is lost from this field. The organic matter produced by the roots and mulch improves the soil structure increasing soil water holding capacity. Z. mauritiana has very deep roots that reach the water in the demilunes that drained into big depths. Acacia colei has a very wide and deep root system that allows it to continue to grow during the dry season. In terms of Water Use Efficiency (WUE) the SEF has a significantly higher WUE then the traditional crops.

  3. Resilience. Trees are much less sensitive to dry spells then annuals.

  4. Income. The farmer’s net income is increased by a factor of 10 in comparison with traditional monoculture of grains. The farmers derives income from a diversity of sources: Roselle dry calices and grains, cowpea grains and forage, millet grain and straw, PDS fruit, leaves as forage and firewood, and A. colei seeds (protein source for chicken and firewood. All in addition to the increased animal feed production due to the higher crop yield.


The SEF is still in its experimental phase. Probably only after we will start disseminating it on a large scale the disadvantages of this new system will start to surface. We are however convinced that the principles of the SEF are universal and ought to be applied in the semi arid and arid regions throughout the world.


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