Preparing for the Spring Season, Starting with Injector Maintenance

 


The Importance of a Properly Performing Injector

There are many injectors on the market available for growers to choose from (e.g. Dosatron, H.E. Anderson, Bluelab, Dosmatic, Hanna). Each piece of technology has specific procedures for calibrating and performing general maintenance that can typically be found on the user manual. When in doubt, feel free to reach out to GGSPro or your local Griffin representative for further guidance. This article will outline some helpful ways growers can test the reliability of their injector equipment and recalibrate them if needed. The following concepts may be utilized for a wide range of injector technology where appropriate.


Most greenhouse operations deliver the majority of their fertilizer through the irrigation system as well as other chemicals such as insecticides, fungicides, PGRs, sanitizers, and cleaners. Refer to each pesticide’s label to determine if they can be used through “chemigation” or irrigation equipment. An injector allows these sorts of inputs to be mixed into small volume, concentrated solutions and applied uniformly and accurately through an irrigation system. From the fertilizer side of things, when an injector is not working properly, this can result in increased crop times and poor plant quality Just because your injector worked properly last season is not an indication that it is in current working condition. It’s always best to check your injector for accuracy by performing a yearly maintenance program before the start of the Spring season.


There are various ways to calibrate an injector. This section will provide a simple chemical and physical method. To check the calibration of your fertilizer injector, start with a calibrated electrical conductivity (EC) meter and measure the conductivity of a clear water sample (i.e. your irrigation water with no additional inputs/fertilizer). Next, mix up a fertilizer stock solution to yield a 200ppm nitrogen solution through the injector at 1:100 (refer to the fertilizer label or contact GGSPro for assistance, Figure 1). Turn the injector on and allow the fertilizer to flow through the hose for several minutes. Collect at least a quart or 1 liter of fertilizer solution to ensure a uniform sample. Use the EC meter to measure the conductivity of this collected solution.

 

When in Doubt, Calibrate. When Not in Doubt, Calibrate Anyway


Figure 1: Mixing Rate Table Referenced from Jack’s 21-5-20 AP Fertilizer Label

Take this conductivity reading from the fertilizer and subtract the conductivity reading of the clear water to yield the true conductivity of the fertilizer solution. Compare the reading with the EC reading for 200-ppm nitrogen on the fertilizer bag (Figure 1). If the conductivity reading is within 5-10% of the target EC, your fertilizer injector is working properly. If this conductivity reading significantly deviates from the target, the injector may not be working properly and additional servicing may be needed. Verify that a fertilizer mixing error did not occur which may have also influenced the results. Note, dry/solid fertilizers are measured in ounces by weight and not fluid ounces. 
A physical calibration test can also be conducted by setting your injector to 1:128, (1:128 = 1 ounce to 1 gallon of water). Fill a small container with 5 fl oz of fertilizer solution (e.g. using the 200ppm N rate) and place the injector suction hose inside. We use a fertilizer solution, because it has a colored dye that can be visibly seen even after injected into irrigation water. Turn your injector on so that it sucks up the entire 5 ounces. When the fertilizer solution is gone, it should have yielded a 5-gallon bucket of fertilizer solution. This indicates that the injector is calibrated. If the injector doesn’t deliver enough fertilize (i.e. fill up 5 buckets of diluted fertilizer solution), it may be time for a seal kit/component kit replacement (Figure 2). For injectors that are fixed at 1:100 injection ratio, you can use the following volumes to test using this bucket method:

Fertilizer Calibration Method Example Calculation

Measured EC of Clear Water: 0.22

Total Measured EC (Fertilizer Plus Water): 1.50

Theoretical EC of 200ppm N 21-5-20 Fertilizer (Figure 1): 1.29

1.50 (Total EC) – 0.22 (EC of Clear Water) = *1.28 EC (Fertilizer Alone)

*This calculated value of the fertilizer EC alone is within the acceptable range (i.e. 5-10%) from the theoretical EC provided by the label, thus the injector is calibrated appropriately.


32 floz or 1 qt through the Injector at 1:100 will yield 25 gallons of diluted fertilizer solution

16 floz or 1/2 qt through the Injector at 1:100 will yield 12.5 gallons of diluted fertilizer solution

8 floz or 1/4 qt through the Injector at 1:100 will yield 6.25 gallons of diluted fertilizer solution

Figure 2: Dosatron Maintenance Kit


Products

Item

Dosatron D14MZ2 14 GPM 1:500 to 1:50 Injection

33-2415

Dosatron D14MZ2 14 GPM Maintenance Kit

219-000

Jack’s 21-5-20

33602

ICL 21-5-20

67-2308

Plantex 21-5-20

31-140306

*Contact your local Griffin sales representative if you have any questions in regard to finding the appropriate replacement parts and specific injector model to meet your needs.