Microcatchment Rainwater Harvesting Systems: Zai Planting Holes

Microcatchment Rainwater Harvesting Systems: Zai Planting Holes Section 2.1
Olufunke Cofie, Boubacar Barry, Deborah Bossio, International Water Management Institute, Ghana and Sri Lanka, Nobember 22-25, 2004

Zai Planting pit, Sandy Soil, Niger

"Human Resources as a driver of Bright Spots: the case of rainwater harvesting in West Africa", Conference Paper 19, NEPAD/IGAD Regional Conference: Agricultural Successes in the Greater Horn of Africa, Nairobi 22-25, 2004

2.1 Micro-catchment rainwater harvesting systems

"There are many types including: terraces, earth or rock bunds, tied ridges, rock dikes, stone lines, planting pits or basins and their modifications used in different parts of West Africa. Stone and earth bunds have been used for several years to trap water for crops during the rainy season. Around Upper West Region in Ghana, these bunds have been developed into a terrace system on the slopes. The bunds are square, or rectangular shape, and their slopes are not along the contour. Millet is the main crop grown under this system in Ghana. The height of the stone bunds depends on available stone or soil depth in the neighborhood. In some places stone lines are used. These are made up of continuous lines of stones in a field along the contour to slow down the flow of rainwater, thus enhancing infiltration and to facilitate to some extent the deposition of vegetable debris and fine soil particles which increase soil fertility in the long run. Planting Pit or Basin is commonly used in the sub-region with various modifications including the zai in Burkina and in Mali, and also Tassa and half moon in Niger. In Ghana, stones are removed to create pits for collection of water in areas with high clay content in the subsoil (Kranjac-Berisavljevic et al 2002).

Perhaps the most sucessful of these techniques is the zai ("water pocket") in Burkina Faso Zai is an ancestral planting pit developed in the Yatenga province, North Western part of Burkina Faso (where average rainfall is about 600 mm, with recurrent droughts and where soils are heavily encrusted. The Yatenga province has a hig population density (80 hbts/km2), and sufferred from recurrent droughts in the late 1960's and early 1970's. Since the early 1980's, "zai" has been rapidly revived and adopted by farmers, resulting in 1989, over 8000 hectares of degraded land in over 400 vilages in Burkina, being brought back to productivity. Large areas of the province are covered with lateritic soils of low infiltration capacity. the objective of the Zai practice is to regenerate the most degraded part of the field. It consists of digging holes or 'basins' of around 20-20 cm in diameter and 10-15 cm in depth. (Bandre and batta, 2002). The holes store rainwater, for plant growth. Generally the density is about 10,000-15,000 holes/ha depending on the crop chosen and the spacing between holes. Farmers use stone contour bunds to reduce the speed of runoff allowing infiltration into the zai which collect and concentrate the runoff. The larger the planting pits, and the bigger the spacing, the more water can be harveted from the uncultivated micro-catchments. Organic manure is put in the holes at a rate of about 3-4 t/ha. Sorghum is the preferred crop because of its greater adaptation to possible temporary hydromorphic conditions in the hole.

According to Fatondji (2002) working in Naimey (Niger), the Zai technique assured a substantial total dry matter (TDM) increase (3086 kg ha-1) compared to flat planting (991 kg ha-1) with cattle manure application under 20 mm irrigation regime. He also observed that the quality of the amendment in Zai played a significant role. Low TDM as well as grain yield was produced with crop residue and compost of low quality. He observed for instance at the three study sites in Niger, that TDM produced on average with crop residue application was 756 at Sadore; 925 at Damari and 2185 kh ha-1 at Kakassi in 1999, compared to 3957, 4600 and 5030 kg ha-1 respectively with same rate of manure application. The grain yield was 151 kg ha-1 at Damari and 393 kg ha-1 at Kakassi with crop residue application, while it was 987 and 778 kg ha with manure application.

Ftondji (2002) observed that the Zai planting technique induced a higher water use efficiency than flat planting at three sites in Niger. Combination of Zai with manure improved considerably water use efficiency in three different sites. Therefore it is imperative to promote technologies that can on one hand help increase potential water availability and on the other hand consequently help rehabilitate degraded lands. "Zai" enhanced soil water storage and increased plant water availability, though most of this water could be drained out in soil with low water holding capacity as in Sadore and Damari in Niger. Nevertheless, the use of good quality organic amendment (manure) promoted rapid and deep root growth and helped limit water loss by drainage.

See also:

Southern and East Africa Rainwater Network Searnet
IWMI Research in Africa Best Practices Zai Holes

ECHO Dryland techniques and Mulches

Drylands Coordination Group Integrated Plant Nutrition

Drylands Coordination Group Integrated Plant Nutrition Management in Mali pdf
Summary Report 1998-2004