measured irrigation for smallholders in developing countries

SZ single-zone, MZ multi-zone, GF gravity feed

It is recommended that you watch the following videos

DIY solar drip irrigation

Do It Yourself solar drip irrigation is for smallholders using gravity feed drip irrigation on a small plot of land. I will assume that water needs to be pumped from a farm pond up to a raised header tank and that the depth of the farm pond is no more than 4 metres.

 

By downloading the detailed guidelines, a farmer is taking the first step towards automating their drip irrigation system so that he or she can leave their plot unattended for weeks. At sunset each evening, water will be automatically pumped from the farm pond to the header tank, and all the plants will be automatically irrigated by measured irrigation. This will allow the farmer to spend more time generating income from other activities away from the farm; for example, travelling to the market to sell their produce.

 

Do It Yourself solar drip irrigation requires the farmer to solve any problems that may arise and to break the cycle of dependency upon the so-called experts. By following these guidelines the farmer will learn new skills. When the automation of the drip irrigation system is complete, the farmer will then become the expert, and their knowledge and expertise can be shared with other farmers. I am assuming that the farmer has access to the Internet and to Google. Google will help you find solutions to problems and low cost components from anywhere in the world, especially China.

 

The total cost of automating the drip irrigation system will be less than $200.

Micro irrigation has become synonymous with modern and efficient irrigation practices that conserve precious water resources and maximise plant performance. However the biggest barrier to the adoption of micro irrigation in developing countries has been the installation cost. The two most popular technologies for low cost micro irrigation are gravity feed drip tube (or drip tape) irrigation and gravity feed micro tube irrigation. A low cost system needs to be gravity feed to avoid the additional cost of buying, running and maintaining a pump. 

 

The simplest method of installing measured irrigation is explained when you download the document:

Measured Irrigation for Smallholders - Use 50% less water by using a bucket and a steel pole

Download the Measured Irrigation Manual for complete information.

Upgrading drip irrigation
on level ground to measured irrigation

using evaporation data

 

Additional materials required: bucket

 

Step 1. Estimate the net evaporation (evaporation minus rainfall) in metres in your locality during the hottest month of the year. If this information is not available from the Department of Meteorology, you can use a container with vertical sides to measure the nett evaporation during the hottest month. Simply measure (or estimate) the fall in the water level in the container during the hottest month (the container should be exposed to full sun).

 

Step 2. Estimate the required number of litres per week for each dripper for the hottest month of the year.

 

Step 3. Before you can choose an appropriate evaporator you need to calculate the surface area of evaporation using the estimates from Step 1 and Step 2

 

surface area in sqm = (number of days in hottest month)

* (litres per week from Step 2)

/ (net evaporation from Step 1) / 7

 

Select a suitable evaporator with vertical sides and with the surface area of evaporation as close as possible to the area calculated above. An evaporator can be as simple as a bucket.

 

Step 4. Mark a level line on the inside of the evaporator about 3 cm below the overflow level.

 

Step 5. Install the evaporator in a suitable location exposed to full sun and position a length of drip tube or drip tape so that a single dripper drips water into the evaporator during the irrigation event. This dripper is called the control dripper and it should be at the same level as all the other drippers.

 

Step 6. Fill the evaporator with water so that the water level is about 1 cm below the level line.

 

Step 7. Open the valve to commence irrigation. Close the valve when the water level reaches the level line.

 

Step 8. The water level in the evaporator falls due to evaporation. Open the valve when the water level is below the level line and the next watering is required. The cycle continues indefinitely.

 

 

Upgrading drip irrigation
on sloping ground to measured irrigation

using evaporation data

 

Additional materials required: buckets and valves

 

Step 1. Estimate the net evaporation (evaporation minus rainfall) in metres in your locality during the hottest month of the year. If this information is not available from the Department of Meteorology, you can use a container with vertical sides to measure the nett evaporation during the hottest month. Simply measure (or estimate) the fall in the water level in the container during the hottest  month (the container should be exposed to full sun).

 

Step 2. Estimate the required maximum number of litres per week from a dripper for the hottest month of the year.

Step 3. Before you can choose an appropriate evaporator you need to calculate the surface area of evaporation using the estimates from Step 1 and Step 2

 

surface area in sqm = (number of days in hottest month)

* (litres per week from Step 2)

/ (nett evaporation from Step 1) / 7

 

Select a suitable evaporator with vertical sides and with the surface area of evaporation as close as possible to the area calculated above.

 

Step 4. Group the plants to be irrigated into zones so that the plants in each zone are at approximately the same level. The laterals should follow the contours. Each zone needs its own evaporator and valve.

Step 5. Mark a level line on the inside of each evaporator about 3 cm below the overflow level.

 

Step 6. For each zone, install an evaporator in a suitable location in the zone exposed to full sun and position a length of drip tube (or drip tape) so that a single dripper drips water into the evaporator during the irrigation event. This dripper is called the control dripper for the zone and it should be at the same level as all the other drippers in the zone. 

 

Step 7. Fill the evaporators with water so that the water level is about 1 cm below the level line.

 

Step 8. Open the valves commence irrigation Close the valve for each zone when the water level reaches the level line.

 

Step 9. The water level in each evaporator falls due to evaporation. For each zone, open the valve when the water is below the level line and the next watering is required. The cycle continues indefinitely.

 

 

For single-zone measured irrigation on sloping ground, a header tank with a float valve is required and you will need to use the Measured Irrigation Nozzle Selector Toool

Reasons to upgrade drip irrigation to measured irrigation

  1. Save more water by controlling the application rate by adjusting the surface area of evaporation from the evaporator.
     

  2. Save more water by allowing the prevailing weather conditions to control the variations in the application rate for each dripper throughout the year. When the temperature increases, the application rate increases. When it rains, the application rate decreases. The application rate for each dripper is directly proportional to the current net evaporation rate (evaporation minus rainfall).
     

  3. Save more water by maintaining the same level over control of the application rate for each dripper on sloping ground by using multiple zones.
     

  4. The smallholder can control the irrigation frequency for each zone. If a zone requires more frequent irrigation with less water, then the smallholder should open the valve for the zone when the water level is less than 1 cm below the level line. If a zone requires less frequent irrigation with more water, then the smallholder should open the valve for the zone when the water level is more than 1 cm below the level line
     

  5. Because irrigation is more water-efficient after the upgrade, additional water is available to extend your garden and to irrigate more plants.
     

  6. The cost of the upgrade on level ground is the cost of a bucket.

How to adjust the surface area of evaporation

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. Early in the morning after irrigation the night before, push (or hammer) the steel pipe into the soil near a dripper. Remove the steel pipe from the soil and use the slots in the pipe to inspect the moisture level in the core sample and the position of the wetting front. 

 

 

 

 

 

 

 

 

 

 

 

By checking the moisture level in the core sample 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. It may be helpful to use the slots to remove a small sample of soil and to squeeze it between your fingers. If the plants have been given too much water then you can reduce the water usage by reducing the surface area of evaporation from the evaporator. 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.

If you choose to adjust the surface area of evaporation to take account of soil moisture, you may ignore Steps 1, 2 and 3 above.