Proportional Fertigation


What is Proportional Fertigation and how does it work within the Motorola Irrigation System? We show you our perspective.


September 2, 2020

Demonstration of Proportional Fertigation

The Backgound

Proportional Fertigation has become more and more popular in the United States as a well established Fertilizer Injection method that is more widely used by Growers in other parts of the world. With the improvement of automation technology, the ability to apply multiple fertilizer materials within an irrigation set has become more manageable and feasible to growers large and small. First, let's look at the various types of Fertigation:

Types of Fertigation:

1. Continuous application. Fertilizer is applied at a constant rate from irrigation start to finish. The total amount is injected regardless of water discharge rate.

2. Three-stage application. Irrigation starts without fertilizers. Injection begins when the ground is wet. Injection cuts out before the irrigation cycle is completed. Remainder of the irrigation cycle allows the fertilizer to be flushed out of the system (in Branif/Motorola speak: PreFert).

3. Proportional application. The injection rate is proportional to the water discharge rate, e.g. one gallon of solution to 1000 gallons of irrigation water. This method has the advantage of being extremely simple and allows for increased fertigation during periods of high water demand when most nutrients are required.

4. Quantitative application. Nutrient solution is applied in a calculated amount to each irrigation block, e.g. 20 gallons to block A, 40 gallons to block B. This method is suited to automation and allows the placement of the nutrients to be accurately controlled.

5. A combination of proportional application and quantitative application can be the most precise fertigation method and is mostly done with automation due to the highly dynamic parameters. We're going to focus on this one.

This sine-wave shows the relationship between Mainline Flow and Injection Speed that is represented in GPM (Gallons Per Minute). Due to stability issues, the ePID loop considers averages of the Mainline Flow to provide a value to each VFD pump speed in near real-time. The feedback loop can be real time, but is dependent on the entire loop, including the flow sensors.

Injection Types

There is a multitude of methods to injection, including Suction injection, Pressure Differential (Venturi) and Direct Injection (Pump Injection), however, today we are highlighting the Proportional/Quantitate practice of Fertigation, in which case we are focusing on Direct Injection.

To achieve the most consistent and accurate ratio of injection we recommend using a Variable Frequency Drive (VFD) to control the application operation of dosing. This will of course vary based on unique ranch/field conditions and size.

It is important to set all the control points, from the Motorola PLC, the VFD PLC and the Hydraulic system correctly with the right settings, software and dosing. All authorized Branif Systems/Motorola resellers that offer Proportional Fertigation are trained to configure our systems correctly to achieve accurate, reliable and safe dosing injection.

The effectiveness of fertigation is often dependent on the effectiveness of the irrigation system itself.  Realizing the full advantages of proportional fertigation only becomes evident if the correct irrigation design is employed to meet plant requirements and to distribute water and fertilizer evenly to meet specific agronomic requirements.

The beauty of integrating Proportional Fertigation into your Motorola Irrigation system is many, including, the ability to have as many materials as needed for each site to be dynamically injected into the irrigation system. Depending on the plant/crop-type, the agronomic needs of each system will vary, and a professional agronomist should work with your automation provider to dial in the ratios, quantity and other parameters of your Proportional Fertigation program. Due to the critical outcomes of a well thought out proportional fertigation scheme that include Yield, Crop Quality, Ferilizer Material Costs and other factors, it is important to have a robust and reliable system, such as Motorola, that requires only the ratio and irrigation data to run the proportional fertigation system.

Of course, Fertigation is just one of many operations that make up a modern irrigation system, and often times, the installed Motorola Irrigation system is providing control and automation to several functions, such as irrigation, filter flushing and much more. Thanks for reading!

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