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RAINWATER HARVESTING FOR CROP PRODUCTION
GROWING MORE WITH LESS RAIN
Many farmers in Kenya do not have access to irrigation. They rely on rainfall for all their crop production, and thus, are subjected to the recurrent problem of insufficient and unreliable rainfall.

In the semi-arid areas, it is common to find that four out of five seasons end up as either total crop failures or the harvest are too low to break-even. Many farmers may not realize that it is possible to double or triple crop yields through rainwater harvesting, by utilizing natural rainfall. One simple intervention is to use planting pits.

ABOUT PLANTING PITS

Planting pits are also known as zai (or zay) pits or 5x9 pits depending on shape and their dimensions. The method involves growing field crops in holes of various sizes. The zai system has been practiced for many years in the Sahelian region of West Africa.

In Kenya, planting pits are not commonly used, although trials by researchers and farmers have produced good results, showing that the system has great potential for improving crop production in dry areas. Planting pits increase crop yields by a combination of moisture conservation and harvesting of runoff from the spaces between the pits. In addition, soil fertility is restored since the manure and fertilizer cannot be lost through surface runoff.

Planting pits are recommended for relatively low rainfall areas, or where moisture conservation is desired, to enable a crop survive drought and increase production. This brochure illustrates how you can make planting pits.

PROCEDURE
A. LAYING OUT PLANTING PIT POSITIONS

  • Select a part of the farm that is not too steep and neither on very flat ground. If land is on a slope, terraces should first be made. It is important that the pits are dug at alternate positions behind each other to allow enough catchment area for sufficient runoff to be generated.
  • Starting at one end of the field, use a tape measure or a marked string, to fix pegs 150 cm apart on the first row.
  • Measure a row spacing of 75 cm downhill.
  • On the 2nd row, place the first peg 75cm from the line of the first peg.
  • Continue to place pegs 150 cm apart as with row 1, so that all the pegs in row-2 are at alternate positions behind row-1.
  • Continue measuring and pegging in this way until you have a network of pegs at alternate positions as shown in figure 1.
B. PREPARATION OF THE PITS
At each peg position, prepare a planting pit measuring 60 cm deep x 60 cm diameter as follows:
  • Dig a hole 60 cm diameter, placing topsoil (about 20cm depth) on the uphill side.
  • Dig the subsoil, to a depth of 60 cm and place the spoil on the downhill side.
  • Reshape this spoil to resemble a semi circucular bund to enable better water storage.
  • Mix the topsoil with one medium size bucket of well-composed manure and return to hole. Ensure that the hole is not refilled to the top so that some space remains to collect and store runoff water.
  • Plant 5-12 seeds of maize or sorghum or millet in at the hole. The number of seeds per hole depends on crop type, its variety and climate. If you plant seeds in pairs, remember to thin to single plants later.
C. LOOKING AFTER YOUR CROP
Once the crop is growing in the planting pit, the following management practices are needed:
  • Keep the field clear of weeds. Outside the pits (catchment), do not dig with a jembe, clear the weeds with a panga to leave a firm compacted catchment.
  • Inside the pits, you can weed normally to encourage infiltration.
  • Protection of the crop from pests and diseases.
LIMITATIONS
The main limitation with planting pits is the heavy labour demanded in preparing the pits the first time. Also, they may not work well in water logging soils. However, the benefits using planting pits far outweigh the limitations. Therefore, Do-It-Yourself (D-I-Y) and see!

ADVANTAGES OF PLANTING PITS

  • Once prepared, planting pits can be re-used for up to four crop seasons or two seasons without the need to add more manure.
  • Increased crop yield and better crop survival in time of drought. Planting pits can make a difference between getting a harvest or nothing at all in a low rainfall season.
  • Weed control is easier.
  • Water Conservation in the pit, thus reducing soil erosion on other parts of the farm.
  • Improved Soil fertility and Environmental Conservation.