Planting Pits

Introduction

Planting pits are the simplest form of in situ rainwater harvesting for optimising crop production (see also bunds, field trenches, micro basins, retention basins, and controlled drainage) (ANSCHUETZ et al. 2003). Basically, holes are dug 50-100 cm apart from each other with a depth of 5-15 cm in order to prevent water runoff.

This form of micro-catchment is best suited for land with low permeability, such as silt and clay soils. On encrusted soils, three types of conservation practises can be met with planting pits: soil conservation, water and soil moisture conservation, and erosion protection (see also soil degradation) (UNEP 2012). To further increase crop production, organic matter (such as compost or manure) can be placed in the pits as fertiliser (see also conservation tillage, soil cover and reforestation, soil amendment, mulching and use of compost).

Many different names are used for planting pits, such as Zaï (Zay), Chololo, Mantengo, Ngoro and Tassa (ADB 2008; UNEP 2012). They are widely applied in Sahelian countries, such as Mali, Burkina Faso, and in the Yatanga and Niger regions.

Basic Design Principles

Adapted from ANSCHUETZ et al. (2003) & ADB (2008)

Planting pits have a very simple design:

The diameter of the pits is usually between 15 and 50 cm (depending on the soil structure), but they sometimes also exist in much greater sizes. The depth of each pit should be between 5 and 15 cm. Planting is best done in straight rows or along the contour lines (see also contour bunds) with a distance of 50-100 cm between each pit. This equals 10,000-25,000 pits per hectare. If the soil is already very shallow, planting on the top of the ridges can be beneficial, as the soil may be too shallow for crops to grow within the holes.

To further improve crop growth, fertiliser, such as compost or manure (see also mulching and use of compost), can be placed in the pits. When heavy rainfall occurs, the organic matter can additionally help to soak up excess water, preventing unwanted water accumulation.

In combination with stone lines, planting pits can be used to rehabilitate degraded and crusted land. The stone lines are spaced at a distance of 25 to 50 m and help to further hold back moisture and eroded soil (see also soil degradation) (WOCAT 2007).

In combination with stone lines, planting pits can be used to rehabilitate degraded and crusted land. The stone lines are spaced at a distance of 25 to 50 m and help to further hold back moisture and eroded soil (see also soil degradation) (WOCAT 2007).

Cost Considerations

Adapted from ADB (2008)

Most costs arise because of the time needed for digging the holes and filling them with organic matter. They are therefore strongly dependent on the structure of the soil. Roughly 20 to 70 person days per hectare are needed for digging the holes and another 20 person days are required for fertilisation. Usually, no equipment costs arise, because digging can be done with common tools already available.

Operation and Maintenance

Adapted from ANSCHUETZ et al. (2003)

Digging the pits should be done during dry season, so that the pits are ready when the rainy season begins. In the second year of implementation, new pits need to be dug in order to retain the soil’s fertility. Weeding is not necessary, because vegetation growth is unlikely to occur on the degraded soil between the pits. When excavating the pits, the excess soil is embanked downslope of the pit to further stop water runoff.

At a Glance