Bluelab Soil pH Meter - Manual (Page 7)

English
7
4.0 Information about measuring the pH of soils/media cont.
Taking pH measurements of soils with an electronic meter is indicative
rather than absolute.
The following factors are outside the control of any soil 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 infl uence the soil pH reading based on the pH of the
tap water.
Calibration of the soil pH meter and cleanliness of the soil pH probe tip
Calibrating the soil pH meter at least monthly will ensure accurate readings. Cleaning the
soil residue from the probe tip and storing the soil pH meter in a clean moist state will
provide reliable readings as well as prolonging the probes life.
Sample selection
For fi eld 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 substrate and from various areas,
then an average of the readings is used.
For container grown plants, it is recommended to check the pH level of the substrate
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 signifi cantly. 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, a change to the pH level could result.
Soil/media temperature
High temperature soils may have a high concentration of CO
2
. The higher the
concentration of carbon dioxide pressure results in more carbonic acid which lowers pH.
pH range for soil crops
The recommended pH range for soil crops is 6.2 - 7.2, but this is plant specifi c.