Bernie Omodei from Measured Irrigation writes about a very low cost innovation that may reduce the water consumption for drip irrigation by up to 50% without affecting the yield. The innovation uses the weather to control the irrigation scheduling rather than a program. The DIY (Do It Yourself) instructions in this blog can be applied to any drip irrigation application in any poor community.
Upgrading drip irrigation to unpowered MI
Many smallholders use gravity feed drip irrigation to irrigate a small garden (less than an acre). The most commonly used scheduling method is programmed scheduling and this method wastes a lot of water because it does not respond to the prevailing weather conditions. By upgrading from programmed irrigation scheduling to measured irrigation scheduling, water consumption may be reduced by 50% without affecting the yield. The cost of the upgrade is negligible.
Measured irrigation evaporator
Water level below level line
The evaporator is any container with vertical sides with a surface area of at least of at least 0.75 square metres. Draw a level line on the inside of the evaporator about 3 cm below the overflow level. Position the evaporator in the garden, preferably exposed to full sun.
Position a dripper so that it will drip water into the evaporator. This dripper is called the control
Control dripper will drip water into the evaporator
dripper and it should be at the same level as the other drippers in the garden.
The volume of water delivered by each dripper in your garden during an irrigation event is the same as the volume of water delivered to the evaporator by the control dripper.
How to use the evaporator
Start irrigating at sunset
Stop irrigating when the water level reaches the level line
Check the water level in the evaporator at sunset each day.If the water level is below the level line, start irrigating. Stop irrigating when the water level reaches the level line.
How to adjust the surface area of the evaporation
An angle grinder can be used to make some slots in a length of steel pipe.
The amount of water that your plants need will depend on many factors in addition to the weather. For example, as the plants grow and become bigger they will need more water. Plants growing in sandy soil will need more water than plants growing in heavy soil.
To take account of all these additional factors, I recommend that you use a length of steel pipe to check the moisture level in the soil. I suggest that the diameter of the pipe be between 40 and 50 mm. An angle grinder can be used to cut some slots in the steel pipe to that you can inspect the soil inside the pipe. I suggest that the width of the slots be about 13 mm.
Early in the morning after irrigation the night before, push (or hammer) the steel pipe into the soil near a dripper
By checking the moisture level in the soil through the slots in the steel pipe, you can decide whether the plants have been irrigated the night before with too much or too little water. If the plants have been given too much water then you can reduce the water usage by reducing the surface area of evaporation. For example, the surface area of evaporation can be reduced by placing full bottles of water in the evaporator. On the other hand, if the plants have not been given enough water then you will need to increase the surface area of evaporation. After irrigation and adjustments over several days, the surface area of evaporation should stabilise at an appropriate level for the plants at their current stage of growth.
Remove the steel pipe from the soil and use the slots to inspect the moisture level in the soil and the position of the wetting front.
As your crop grows and the water requirement of the crop changes, you may wish to repeat the process of adjusting the surface area of evaporation.
MI on sloping ground
One sloping ground you will need to organise your plants into a number of zones so that the plants within each zone are at approximately the same level. Each zone should have its own evaporator, control dripper and inlet valve. The irrigation of a zone is independent of the irrigation of all the other zones.