Fertigation is the injection of fertilisers, soil amendments and other water-soluble products through an irrigation system.
There are many different ways of applying fertiliser via a fertigation system. This article provides an overview of the different methods available.
Best practice design is one that allows flexibility of concentration rates. This is important in cases of potential soil saturation. It is also desirable to have a system that gives precise doses of nutrients proportional to the flow rate.
It is very important that the irrigation system uniformity is at optimum. The same will apply with traditional broadcasting.
Injection system designs vary and some of these designs are considered out-of-date practices.
Batch Mixing: A common design is the batch type mixing that is very low cost but is not proportional to flow and has little to no control over the injection rate. A drum or tank is filled from the discharge side of the irrigation centrifugal pump. The bottom of the drum or tank has an outlet pipe that is connected to the suction side of the pump. The desired kilograms of fertiliser is mixed in the drum or tank prior to opening the outlet valve. For example, 20 kilograms may be mixed to irrigate 1ha of area. (This will over time damage the irrigation pump.)
Venturi Style: A similar method to this is the use of a venturi-style injector, which requires a differential in pressure either created by a bypass valve or a pump. This method is difficult to manage as the differential can change depending on the irrigation location at any given time.
Positive Injection: Positive injection or dosing is the preferred option. It allows for greater control of dose rates. It gives the option of using liquid nutrients or soluble nutrients. It is also easily automated which can allow for clean water flushing.
This information is from a fact sheet developed by Pat Daley from Daley's Water Service in conjunction with the Dairying Better 'n Better team as part of the Let the Benefits Flow Project.