Bluelab Soil pH Pen - Manual (Page 8)

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8
6.0 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 Pen and cleanliness of the soil probe tip
Calibrating the Soil pH Pen at least monthly will ensure accurate readings. Cleaning the soil residue
from the probe tip and storing the Soil pH Pen in a clean moist state will provide reliable readings as
well as prolonging the pens 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.