Author: Mr. Guy Sela, CEO of SMART! Fertilizer Management software and an international expert in plant nutrition and irrigation.
Modern fertilization systems include fertilizer injectors that belong to one of two types: fertilizer injectors that are electrically powered (independently or by a controller), or fertilizer injectors that are mechanically powered by water pressure.
The fertilizer injectors inject fertilizer solutions into the irrigation water. The ratio in which the solution is injected is termed "injection rate". This ratio can be expressed as percentage or as v/v (volume/volume).
For example - a ratio of 5 liter/m3 means that 5 liters of fertilizer solution are injected into each m3 of irrigation water. The same fertilizer injector rate can be expressed in percentage as 0.5% (5 liter / 1000 liter x 100) or as 1:200. Higher fertilizer injector rate means more fertilizer solution is injected into the irrigation water.
There are three essential factors that need to be considered to ensure an efficient operation of a fertilizer injector: the required injector flow rate, the water pressure and the materials the fertilizer injector is made of.
The required flow rate of a fertilizer injector depends on:
For reaching a certain fertilization level, higher irrigation flow rates require fertilizer injectors with higher flow rates.
For example, if you want to inject 5 liters of fertilizer stock solution into 1 m3 of water, and the irrigation flow rate is 30 m3/hour, you will need a fertilizer injector with a minimum flow rate of 150 liter/hour (30 m3/hour x 5 liter/m3 = 150 liter/hour). It would be impossible for a fertilizer injector with a lower flow rate, to reach the desired fertilization level.
Use this simple calculation to check whether your fertilizer injector can provide the required fertilizers quantities:
Divide the fertilizer injector flow by the irrigation flow to get the injection rate.
For example, if your fertilizer injector 150 liter/hour and the irrigation flow rate is 30 m3/hour, then the maximal possible injection rate is 5 liter/m3 (150/30), or 0.5%.
If the flow rate of your fertilizer injector is too low, you can take one of the following actions:
Water flow through the fertilizer injector and water pressure in the irrigation line must be adequate for an efficient operation of fertilizer injectors.
For example, if the water pressure in the irrigation line is higher than the maximal pressure against which the fertilizer injector can work, the fertilizer solution might not be efficiently injected, and the fertilizer injector might even eventually not inject any fertilizers at all.
Some mechanical fertilizer injectors use the water pressure as their power source (e.g. Dosatron). Such injectors have a characteristic range of water flow in which they can work efficiently. If the water flow through the injector is out of this range, the injector is likely not give adjusted ratio.
An additional consideration in choosing your fertilizer injector is the type of chemical that would be injected by it.
Fertilizer injectors that are used for injecting acid, must be resistant to corrosion. Furthermore, the type of acid makes a difference.
Parts of the fertilizer injector that come into contact with sulfuric acid must be made of acid-resistant rubber, while parts that come in contact with phosphoric acid, must be made of stainless steel.
In fertilizer injectors that are consistently used to inject pesticides, plastic parts should not come in contact with the solution because many pesticides contain chemicals that damage PVC.
Better safe than sorry - get injectors that can provide slightly higher flows than your maximum requirements.