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.
These injectors allow for adjustment of injection rates to the desired level, using either percentage or ratios (e.g. 1:300 or 0.3%).
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.
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%).
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.