New Year’s Resolution: Check the Calibration of Your Fertilizer Injector

Fertilizer injectors which meticulously injected nutrients into irrigation water in 2012 need to be carefully checked for accuracy. Two-thirds of fertilizer injectors checked by the Penn State educator at greenhouse ranges in Central Pennsylvania last year, were not working properly resulting in increased cropping times and poor plant quality.

To check the calibration of your fertilizer injector, first calibrate conductivity meters using fresh or newly purchased calibration solutions. Next take a clear water sample from a water hydrant that is not connected to your irrigation system. Measure the conductivity of the clear water sample and record it on a piece of paper.

Next go to your fertilizer injector and determine your injector ratio (1:100). Then mix up your fertilizer stock solution to yield a 200 ppm nitrogen solution through your 1:100 injector. Turn on the injector and allow the nutrient enriched solution to course through the hose for several minutes.

Collect a sample of this nutrient laden solution and use your conductivity meter to measure the conductivity of the collected solution. Take the conductivity reading from the collected solution and then subtract the conductivity reading of the clear water to yield the net conductivity of the fertilizer in your solution.

Compare your reading with the anticipated EC or conductivity reading for 200 ppm Nitrogen which is delineated on the fertilizer bag.  If your net conductivity reading is within 10-15% of the target EC or conductivity your fertilizer injector is working properly. If the net conductivity reading significantly deviates from the target, the injector is not working properly and should be either re-built and/or replaced.