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1.1.1 Planting Pits (Zai)
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.
Figure 1. Planting pits, or Zai (Lee and
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
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. Advantages
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.