14
Different naturally occurring minerals may affect soil pH the same way, but the method for
correction may differ. Take for example elevated soil pH:
‑ Soils rich with limestone:
Add organic matter (non‑organic ameliorants such as sulfur and sulfuric acid might not make
economic sense due to the large quantities needed).
‑ Alkaline‑saline soils:
An appropriate use of irrigation can provide positive results (drop‑irrigation) by flushing out salts.
If alkalinity is caused by sodium, it is recommended to add substances such as gypsum (calcium
sulfate), sulfur or other sulfuric compounds. In this case, a cost evaluation is necessary. See
Table 2
and note what quantities provide the same result as 100 kg of gypsum.
Soil ameliorants (pure compounds)
Quantity (kg)
Calcium chloride: CaCl
2
· 2H
2
O
85
Sulfuric acid: H
2
SO
4
57
Sulfur: S
19
Iron sulfate: Fe
2
(SO
4
)
3
· 7H
2
O
162
Aluminum sulfate: Al
2
(SO
4
)
3
129
Table 2.
Soil ameliorants.
Procedure for direct ground measurement
Note: Do not use this procedure if the soil being measured is rocky the pH electrode can be
damaged.
1) Ensure the meter is set up correctly and pH electrode is calibrated.
2) Dig and discard 5 cm (2”) of topsoil.
3) Perforate the soil with the
HI721319
auger for ground penetration to a depth of 20 cm
(8”).
4) If the soil is dry, moisten it with a small amount of distilled or deionized water.
5) Wash the electrode with tap water.
6) Insert the electrode pushing it slightly into the soil to ensure the pH bulb is in contact with
the soil.
7) Allow the measurement to stabilize and record the value.
8) Wash the electrode with tap water and gently remove any soil remaining on the electrode
with your finger, this will prevent the glass from scratching.
For the best results, prepare a soil slurry using the
HI7051
soil sample preparation solution.
SOIL pH
