Rain water harvesting

Courtesy; Pate (2016)

The rains are here…depending on where you are located, the water could be too much or too little. If you are a farmer who relies on rains, you need to know how to supply water to your crops after the rains have stopped. You may be wondering, how can I have a constant supply of water in my farm? Well, you can collect and conserve water from the rooftop or from the ground (run-off) for both domestic and agricultural use. Here are four affordable techniques to harvest and store water;

Retention Ditches

Retention ditches are just like their name; they retain water. The rainwater stored in these ditches passes through the ground and feeds your crops during the dry periods. The ditches are also a great way to reduce soil erosion. To make a retention ditch;
 Dig a 3 feet deep hole with your desired length
 Remove the soil from the ditch and throw it on the lower side of the ditch
 Dig a shallow tunnel from the road (water source) leading to the ditch
 Plant grass or napier grass on top of the retention ditch to avoid the soil from falling into the ditch (stabilize it)
 You can dig several retention ditches next to the first one. When water fills the first ditch, it pours to the next
 You can plant crops requiring a lot of water such as bananas once water has reduced to a good level. You can also plant arrow roots when the water levels are still high

• Retention ditches should be constructed on flat or gently sloping land and the soils should be porous, deep, and stable.
• Retention ditches are not suitable on shallow soils or in areas that experience landslides

A retention ditch with bananas for water harvesting

A retention ditch with bananas

Terraces are useful in areas of heavy rainfall, sloped land or shallow soils. Terraces prevent soil erosion by blocking water from running across your farm. They look like staircases.
 Use a jembe to dig a 2 feet ditch from one end of the shamba to the other. The spacing between ditches depends on the steepness of the slope. On steep slopes, you can construct many terraces
 Put (heap) all the soil from the ditch on the upper side of the terrace
 Plant grass on the upper side to prevent the soil from sliding back

Ridges are useful in areas with heavy rainfall, sloped land or shallow soils. They help with water conservation and soil erosion. The ridges stop soil erosion by allowing rainwater to soak downwards instead of running along the surface. They also help plants tolerate dry times because more water can be stored near the crops.
How to make ridges
 Use a jembe to dig deeply (1 foot) along the planting line
 Pull soil on top of the deeply dug planting line
 At the end of the ridges, heap a layer of soil so that water does not run into the ridge
 Divide the ridges into 1 or 2 m. This will trap water between the ridges so that it has time to sink into the soil
 You can make planting holes along the top of the ridge to plant other crops such as maize and sweet potatoes.

Ridges for water harvesting

Make 1-2m long ridges along the planting lines

Underground water tank

Tanks are a great way to store water for both domestic and farm use. However, they can be expensive when storing water enough for your crops. The good news is, the underground water tanks are relatively cheaper and can store lots of agricultural water. These tanks can be constructed using bricks, concrete, and polyvinyl chloride (PVC). Among the listed materials for constructing underground water tank, the PVC is the cheapest. You can also use a tank liner (PVC) to prevent water from leaking from old tanks.
Now, let’s see how you can make an underground water tank:
 Select an area near your farm. This will allow you to easily feed the water to your crops.
 Dig shallow tunnels to direct groundwater to the tank. You can also use house gutters to trap the rain water from roof tops. Ensure that you put a sieving material (some small sized wire mesh can do) before connecting the inlet to the tank. The sieve will keep away large particles from entering your tank.
 Dig a hole of your desired measurements e.g. 3m diameter and 3m deep. You can make a rectangular or round shaped holes. However, a cylindrical (round) shape equalizes the pressure of water and soil whether the tank is full or empty. Square and rectangular tank shapes may collapse due to uneven pressure
 If using the tank liner, they usually come custom made. In this case, you will simply drop the PVC material into your hole. The plastic tank liner should be slightly bigger than the dimension of the hole to allow extra material for cementing
 Allow some PVC material to cover the top of the hole. Place some bricks on the PVC. This ensures that PVC does not fall off. In addition, it prevents runoff from around the tank from entering.
 Fence the area around the tank to keep off animals and small children from falling
 Cover the water tank to avoid breeding mosquitoes and to avoid evaporation
 Clean the tank and the inlets before the rains
 Underground water tanks require periodic emptying and washing to prevent the growth of biofilms
 The first direct flush of rainwater should be directed away from the storage tank since it contains dirt from the catchment area
 Water stored in the tanks can be used for domestic and agricultural purposes

underground water tank made of PVC

PVC underground water tank

Remember that you can use as many methods for water conservation as possible to ensure that your farm is supplied all round the year.
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