|Sourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)|
|Part B - Technology profiles|
|1. Agricultural technologies|
|1.4 Water conservation|
Porous clay pots and pipes are a means of water application that conserve water by applying water directly to the roots of plants, thereby limiting evaporation losses (Figure 26).
Both clay pipes and clay pots can be homemade; most are installed by individual householders. The pipes are joined to form tubes of 250 mm in length with an inside diameter of 75 mm. The pipes are placed along the entire length of the beds by laying them end-to-end in a levelled trench. At one end, a right angle fitting is attached and an upright section of pipe installed. The trench is then backfilled with soil to a depth of 100 to 200 mm, depending upon the soil type. Water is poured into the porous pipe through the upright pipe. Each plant bed is about 3 to 6 m in length. The water seeps into the root zones through the joints between the individual pipes, or through the pipe walls if unglazed clay pipes are used.
Alternatively, porous pots (made of unglazed clay) are buried in the soil up to their necks next to the plants or between plant rows at intervals of 300 mm. Water seeps from each pot through the pores and forms a wetted zone. Varying the frequency of filling, the size of the pots and the spacing between pots affects the watering process. Selection of the most suitable size of pot and its placement is governed by the type of crop.
Extent of Use
Adoption is fairly limited, possibly due to the fact that the initial stages are very labour-intensive. Trials in the dry areas of Chiredzi, Zimbabwe, have shown that communities are interested in this technology.
Operation and Maintenance
Once the systems are installed, there is very little maintenance required. Operation is quite simple.
Level of Involvement
Farmers, researchers and extension workers must work together to implement this technology. Communities can construct and operate the system. However, government officials and/or NGOs may have to work with pipe/pot manufacturers to ensure availability of supplies of suitable pots and pipes. Extension workers can assist farmers in pipe/pot placement for best effect and at depths/densities best suited for various types of crop.
Effectiveness of the Technology
It was found, during the replicated trials, that water savings varied from 11 to 28% of the water used with traditional irrigation.
Since this technology uses clay pots and clay pipes that are locally manufactured, the costs are normally low. The major cost is the cost of labour, which is estimated at approximately $40/ha in Zimbabwe.
This technology is most suitable for dry areas with less than 500 mm rainfall/year. With this technology, it becomes possible to save water and irrigate small vegetable gardens in rural areas. Communal farmers, especially women, can manufacture the pots/pipes without having to develop special skills.
Porous clay pots and pipes conserve water and enable crops to grow in areas where they otherwise could not grow.
Material for clay pipes and pots, and local skills for pot-making, are readily available at negligible cost. This method provides a uniformly-wetted area, and, because water is applied at depth, often helps to reduce any weed problems - weeds generally have shallow root systems that are not well-served by this technology. Also, pots can be placed next to individual plants. Once the technology is installed the system can be used for several seasons.
The initial labour required to manufacture the pots/pipes and install this technology is very high. The use of clay pots can be more labour intensive than traditional methods of watering crops, and may have difficulty in coping with providing adequate water for crops with high water requirements. Also, the porosity of pots decreases with time, and they have to be replaced at intervals. Pot lifespans are greatly reduced by the use of turbid water with a high silt and clay content. The silt accumulates in the pores, effectively sealing the pipes/pots.
The technology is culturally acceptable.
Further Development of the Technology
There is need to market this technology, especially in areas of low rainfall (less than 500 mm/year).
Lowveld Research Station, Post Office Box 97, Chiredzi, Zimbabwe.