How to Calibrate & Test Your Fertilizer Injectors
There are various methods for calibration and testing fertilizer injectors (dosing pumps), and the choice of your preferred method depends on the type of your injector as well as on the components of your fertilization and irrigation systems.
1. Mechanical injectors, such as Dosatron, which are powered by water pressure
These injectors allow for adjustment of injection rates to the desired level, using either percentage or ratios (e.g. 1:300 or 0.3%).
Adjust the injector to the required injection rate.
Put a measured amount of water or fertilizer solution in a graduated container.
Place the injector’s suction pipe into the graduated container. Make sure there are no air bubbles in the hose. Do that by filling the container to the right level only after injecting continuously some of the water in the container through the pipe.
If a water counter is set on your injector take a reading before irrigation and then again after irrigating for 10 minutes.
If you don’t have a water counter you can simply measure the amount of water flowing toward irrigation by diverting the water to a side tank.
Measure the amount of water in the container after the 10 minutes irrigation.
Make sure you are using the same measurement units for both the graduated container and the water counter or the water collected in the side tank.
Use those measurements and readings to calculate the injection ratio (in percentage) in the following way:
Actual injection rate = (water amount in graduated container before irrigation – the amount after irrigation) / (water count in side tank after irrigation – the count before irrigation) x 100.
Compare the result to the injection rate adjusted on the injector. If they are the same, your injector is properly calibrated.
2. Electric injectors powered by irrigation controllers
These injectors are adjusted to specific flows, rather than ratios. Each injector has a characteristic range of flows and a maximal pressure against which it is able to inject.
In many cases these injectors are powered by the fertilization and irrigation controllers. Most controllers control the amount of fertilizers injected based on either calculation of the duration of injection or on reading of fertilizers counters (Notice that fertilizers counters may have a deviation of 20%).
Adjust the injector to the desired flow.
Make sure the injector flow definitions in the controller are identical to the flow you adjusted on the injector. This is especially important in case the controller uses time settings to calculate the amount of fertilizers injected.
Set the injection ratio for the fertilization program in the controller.
Put a measured amount of water in a graduated container and place the injector’s suction pipe in this container. Make sure there are no air bubbles in the hose.
Start irrigating with the controller for 10 minutes, or irrigate a pre-set amount of water.
Determine the amount of water used for irrigation and the amount injected from the graduated container.
Use the same formula detailed above for mechanical injectors to calculate the injection ratio.
Here is an example: if you irrigated 0.5 m3 and 0.6 liter was injected from the graduated container, your actual injection ratio is 0.6 / 0.5 = 1.2 liter/m3.
This would be your actual irrigation ratio and it should be identical to the one you set for the irrigation controller.
Note: This test should always be performed under actual irrigation conditions, with the usual water pressure in the lines. The results without any water pressure in irrigation lines will be falsely high. Conversely, if the irrigation water pressure is too high, or the injection pressure is too low, less fertilizer will be injected, and in some cases, not at all.
There are other methods for assessing the fertilization system, and although they are less accurate, they are fast and simple and can be performed daily. One commonly used method is checking Irrigation Water EC:
If you know the expected EC addition of the fertilizers to the irrigation water, check whether the actual EC of your irrigation water matches that predicted EC.
Notice that if you are using several fertilizers stock tanks, this test will not provide indication regarding the amount of fertilizer solution injected from each individual tank. Calculate how much fertilizers you plan to use on that day, and check the fertilizer tanks levels, to verify that the planned amount was actually consumed.
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