Checking Your Fertilizer Injector
Tuesday, 13 January 2009 15:02
An injector setting of 1:100 means that 1 gallon of fertilizer concentrate makes 100 gallons of final solution. It does not mean that the injector is delivering 100 parts per million (ppm) nitrogen. Many injectors have a dual settings, in percent and ratio. A 1 percent setting is the same as a 1:100 ratio, a 2 percent setting is the same as a 1:50 ratio and a 0.5 percent setting is the same as a 1:200 ratio. To make the appropriate concentrate for a specific injector setting, determine the amount of fertilizer to dissolve per gallon of water. This can be done by using a chart or calculating it yourself. Note that fertilizer should be measured by weight for mixing, not volume. Also, fertilizer solution color is not a reliable gauge for fertilizer concentration.
For an easy to use table on injector ratios, ppm Nitrogen and fertilizer calculations see: Ratios and Concentration Chart for Using Water Soluble Fertilizers (PDF)
On-line software program to calculate fertilizer: FertCalc (University of New Hampshire)
To learn more about how to calculate fertilizer ppm for greenhouse crops see:
Fertilizer Calculation Fact Sheet
Fertilizer injectors should be checked periodically to be sure they are operating accurately. This can be done by testing the electrical conductivity (EC) of the fertilizer solution. To check a fertilizer solution, use a good conductivity meter or send a sample to your State University soil test laboratory.
Procedure to check the EC of a fertilizer solution:
- Let plain water (no fertilizer) run a little, then collect water in a clean bucket. Take a sample of the plain water from the bucket. Check the EC of the untreated water supply.
- Mix up your fertilizer as you normally do and run it through the injector and hose. Let it run a little to be sure you get an accurate sample. Take a sample of the fertilizer-injected water from the end of the hose and use your meter or soil test laboratory to check the EC of the sample.
- Subract the EC value of the untreated water from the EC value of the fertilizer water.
- Compare the results to an EC chart from the fertilizer manufacturer or fertilizer bag. The chart will correlate the EC measurement with the ppm Nitrogen so you can determine if your injector and mixing procedure is accurate.
Soil Testing Laboratories
University of Massachusetts Soil and Tissue Testing Laboratory
University of Connecticut Soil Nutrient Analysis Laboratory
Tina Smith, University of Massachusetts (updated Jan. 2012)
