|Sourcebook of Alternative Technologies for Freshwater Augmentation in Africa (UNEP-IETC, 1998, 182 p.)|
|Part B - Technology profiles|
|1. Agricultural technologies|
|1.1 Fresh water augmentation|
The Zay is made on land which is not very permeable so that runoff can be collected. Zai are holes dug approximately 80 cm apart to a depth of 5 to 15 cm, with a diameter of between 15 and 50 cm (Figure 1). Zai improve infiltration of the captured runoff. The holes are deepened each winter. Improvements in the traditional pits by the addition of fertilizer and organic matter (compost) have resulted in dramatic improvements in yield.
Extent of Use
The Zay technique is used in Mali, and in Burkina Faso in the Yatenga and Niger provinces where locally it is called Tassa. It can be used in all Sahelian countries, especially in Sudan.
Operation and Maintenance
The holes, filled with runoff water, extend favourable conditions for infiltration for as long as possible after runoff events. In case of too much water, such as during a storm, the debris placed in the pits as compost soaks up the excess water easily, effectively storing the water and creating a damp environment around the plants. The pits are easy to manage. However, it is important to make sure that the holes are correctly dug and that the debris is evenly placed in each hole. The holes must be checked each winter to make sure that they are in good conditions, and they must be filled with organic matter as required.
Level of Involvement
This is a very simple technique which needs no other equipment than what is usually already available. It is necessary is to inform the public and to carry out awareness campaigns so that the zay is accepted. However, after a few pilot projects, experience has shown that acceptance of the technique spreads quickly, thanks to its simplicity and effectiveness. Farmers notice after each rainfall that the earth around the plants remains damp for a considerable length of time.
The cost of the zay is considered in terms of the time which it takes the farmer to dig the holes and fill them with organic matter. Depending on the hardness of the ground, the input required is between 30 and 70 person days per hectare for the digging of the holes and 20 person days per hectare for fertilisation with manure and composting. Taking into account the wear and tear cost of materials used by the farmers, the cost may be estimated at approximately $8/ha.
Effectiveness of the Technology
In the regions where zay are used, zai are usually constructed on abandoned or unused ground. Thus, crop yields resulting from this practise bring a benefit of 100%. Yields range between 0.7 and 1.0 t/ha for sorghum.
The planting pits meet the criteria for three types of conservation practises at the same time (soil conservation, water conservation, and erosion protection) on encrusted and filled soils. Although the technique can be adopted for use on degraded canals and encrusted surfaces, it generally is applied on silt and clay soils.
Zai improve groundwater recharge. Zai also limit the volume of runoff and, hence, the extent of soil erosion.
Zai increase infiltration into the ground. After several years of employing this practise, the soils may re-acquire its porosity and permeability. For this reason, zai are often used for cultivation and regeneration of the soil.
The major disadvantage of this technology is the demand for supplementary efforts from the farmer who has to watch over the state of the holes, deepen them and refill them with manure before each wet season. Zai may also be subject to waterlogging in very wet years.
The zay has met with no reservations in the countries where it has been introduced. The technology has been expressed in such a manner so as not to be contrary to any socio-cultural practices.
Further Development of the Technology
It is commonly adopted by communities in low rainfall regions in West Africa, but requires promotion for the technique to extent beyond Burkina Faso and Mali.
Lee, M.D. and J.T. Visscher 1990. Water harvesting in Five African Countries. IRC Occasional Paper No. 14, 108 p.