Page 19 - Griffin Gazette Fall 2016

Using the 2:1 Media Testing Technique 4. Vigorously mix the sample.

Good management of greenhouse crops requires continuous 5. Cover to prevent evaporation and allow sample to settle for 60
understanding crop nutrition. At the most basic level, growers minutes. Use a consistent settling time across all samples and
need to understand the media pH and EC to avoid fertility issues. sampling events.
In-house monitoring of media pH and EC is easily preformed using
the 2:1 testing technique. Regular and consistent testing using the 6. Use meters to test pH and EC of the liquid layer above the
procedure below provides growers with both a snapshot and a settled media*.
trending view of crop fertility. Combining frequent, in-house 2:1
testing with periodic laboratory services provides a full picture of 7. Rinse container thoroughly before storing or processing the
crop nutrition. Remember to calibrate meters on a regular basis. next sample.

Collecting Media Samples *Solution may be separated using filter paper to filter any
1. Remove the container, leaving the root mass and associated remaining media, if desired.
media as intact as possible.
Understanding Results
2. Collect several tablespoons of media from a point in the vertical When comparing test results performed by a commercial lab that
center of the root mass and towards the center of the container OR uses a saturated media extract (SME) method, 2:1 test results
collect a core sample from the pot, retaining only the middle 50% could be 1⁄2 to 1⁄3 of those reported by the lab.
of the core (discard the top and bottom 25%).
Interpretation of EC Readings Generated by 2:1 Testing**
3. Collect samples from 5-10 pots selected randomly from as much
of the crop as possible for a combined volume of ½ cup. 2:1 EC Comments
Reading
Testing Media pH and EC (mS/cm)
Materials Needed
0-.25 Very low – probable deficiency
• Distilled water
0.25-0.75 Suitable for seedlings and salt sensitive plants
• Two 2-cup glass or plastic measuring cups
0.75-1.25 Desirable level for most plants
• pH and EC meter(s)
1.25-1.75 Slightly high; too high for seedlings and
• Media sample(s) salt sensitive plants

Test Procedure 1.75-2.25 Reduced growth, leaf marginal burn
1. Rinse container with distilled water.
1.0 mmhos/cm = 1.0 dS/m = 1.0 mS/cm
2. Measure ½ cup media sample at same density as found in pots.
**adapted from Cox, D. Soil Tests –Sampling and Interpreting the
3. Measure one cup of distilled water and add it to the media. Results of Greenhouse Soil Tests. Web. March 20, 2014. University of
Massachusetts. http://extension.umass.edu/floriculture/fact-sheets/
interpreting-results-greenhouse-soil-tests.

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