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Evaluating the Precision of a Fertilizer Injector by Measuring Electrical Conductivity

Wed, Jan 16th, 2019, created by W. Garrett Owen

Evaluating soluble salts or electrical conductivity (EC) is an important aspect of in-house nutritional monitoring as it provides a value related to the fertilizer salts provided and the status of the crop’s health. However, when EC is below species-specific recommended ranges, we often observed stunted plant growth and chlorosis (yellowing). When EC is above species-specific recommended ranges, we observe stunting, marginal leaf necrosis (death) and/or crop loss. So, what is the major cause of either low or high substrate EC? In my experience, it is often related to either injector malfunction or calibration. Therefore, growers should routinely perform injector maintenance procedures provided by the injector manufacturer. By maintaining and cleaning, one is prolonging the life of the injector. After maintenance, one should check and calibrate the injector following either 1) the EC Method or 2) the Flow Method. To learn more about each method, refer to the e-GRO YouTube video, “e-GRO Injector calibration.”

            To evaluate the precision of a fertilizer injector by the EC Method, you will need the following supplies for the following 12 steps:

Supplies: Distilled water, pH/EC meter and calibration solutions, full-strength fertilizer passed through the injector, clear tap water, 24-ounce plastic cups (or similar), and record sheet.

Procedure:

  1. Properly calibrate the pH/EC meter following the manufacturer’s instructions.
  2. Turn on the irrigation line containing fertilizer. Using a 5-gallon bucket, collect at least one gallon of full-strength fertilizer solution from the hose-end.
  3. Using a 24-ounce cup, collect a 12-ounce sample from the full-strength fertilizer solution.
  4. Using the pH/EC meter, check the EC of the fertilizer solution and record the values.
  5. Wash off the pH/EC meter probe using distilled water.
  6. Using another 24-ounce cup, collect a 12-ounce sample of clear tap water.
  7. Using the pH/EC meter, check the EC of the clear tap water and record the values.
  8. Wash off the pH/EC meter probe using distilled water.
  9. Subtract the EC value of the clear tap water from the EC value of the full-strength fertilizer solution.
  10. Refer to the fertilizer label, specifically the mixing instructions where values are reported for different fertilizer concentrations (ppm or mg/L N) at various injector ratios. This is the target EC.
  11. Compare the values you found to the values reported at the desired fertilizer concentration and current injector ratio.
  12. If the value measured is not within 10% of the target EC, one must adjust the injector or fertilizer concentration.

Note: It is recommended to calibrate pH/EC meters before each use because measurements are only as accurate as the last calibration. Furthermore, proper pH/EC meter probe maintenance and storage should be practiced following the manufacturer’s instructions.





About the Author:

W. Garrett Owen

Greenhouse Outreach Specialist, Michigan State University

W. Garrett Owen is the Eastern Michigan Floriculture and Controlled-environment horticulture Outreach Specialist with Michigan State University based in Novi, MI. He has an appointment split between Outreach and research. His areas of research interest include propagation and production, nutrition, growth regulation, cold hardiness, and production problem diagnostics.

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