bluelab Multimedia pHMeter Care And Use Manual page 7

4.0 Information about measuring the pH of soil/media cont.
Taking pH measurements of soil with an electronic meter is indicative
rather than absolute.
The following factors are outside the control of any Multimedia pH Meter, so
to minimise their effect on the accuracy of the pH measurement you should
consider the following precautions:
Moisture level/raw water
If the sample you are wishing to measure is dry, add RO water or distilled water to moisten.
Ideally wait 24 hours before you take a measurement.
NOTE: If you add tap water, you will influence the soil pH reading based on the pH of the tap
water.
Calibration of the Multimedia pH Meter and cleanliness and age of the probe
Calibrating the Multimedia pH Meter at least monthly will help ensure accurate readings.
Cleaning the soil residue from the probe tip and storing in a clean moist state will help provide
reliable readings as well as prolonging the probes life.
Sample selection
For open field testing, remove the top 5 - 10 cm / 2 - 4" of the top of the soil. Samples are
taken approximately 15 - 20 cm / 6 - 8" down into the soil and from various areas in the field,
then an average of the readings is used.
For container grown plants, it is recommended to check the pH level of the grow media prior to
planting.
Factors affecting pH in the soil or media:
Soil type
Soils formed under high rainfall conditions (e.g. Eastern USA) are more acidic than those
formed under dry conditions (e.g. Western USA).
Growth stage of the plant
Uptake and requirements of particular elements change as the plant progresses through it's
growing cycle. Recording pH level data to create a history is valuable.
Applications and types of fertilizers
Applications and types of fertilizers can alter the pH level significantly. The time at which you
take the reading is important. Evaluate the brand of fertilizer to see if it is altering the pH in
the wrong direction.
Applications of sprays
As sprays can soak into the soil/media, it can change the pH levels.
Soil/media temperature
High temperature soils may have a high concentration of CO 2 . The higher the concentration of
carbon dioxide, the more carbonic acid there is which lowers pH.
pH range for soil crops
The recommended pH range for soil crops is 6.2 - 7.2, but this is plant specific.
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