Hanna Instruments HI 99121 - Manual (Page 4)

7 6
High pH levels can depend on different elements, hence, there
are different methods for its correction.
- Soils rich with limestone:
Add organic matter (this is due to the fact that non-organic
ameliorants such as sulfur and sulfuric acid might not make
economic sense due to the large quantities needed).
- Alkaline-saline soils:
Alkalinity is due to the presence of salts (in particular a high
concentration of sodium can be harmful).
Irrigation washes away salts, hence, an appropriate use of
irrigation can provide positive results (drop-irrigation being the
most recommended).
If alkalinity is caused by sodium, it is recommended to add
substances such as gypsum (calcium sulfate), sulfur or other
sulfuric compounds (Tab.2). Also in this case, a cost evaluation
is necessary.
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
Tab.2. Quantities provide the same result as 100 kg of gypsum
Procedure for direct ground measurement
1) Dig, discarding 5 cm of topsoil
2) Perforate the soil (with HI 721319 soil drill) to a depth of
about 20 cm or more
3) If the soil is dry, moisten it with a small amount of distilled
water
4) Wash the electrode with tap water (not distilled)
5) Insert the electrode pushing it slightly into the soil to ensure
proper contact
6) Observe the measurement
7) Wash the electrode with tap water (not distilled) and (using
a finger) gently remove any soil remaining on the electrode
(avoid using a rag or cloth)
8) Repeat the procedure in different locations in the field
9) Consider the average of the measured data
For best result, it is advisable to measure the pH of a soil solution,
using a sample of soil and soil preparation solution HI 7051; it is
better to use this procedure if you have to test a stony field in
which you risk damaging the electrode.
Procedure for the measurement of soil solution (1:2,5)
A) Sampling
1) Extracting Soil Sample.
Take 1 sample per 1000 m 2 (0.25 acre) of homogeneous
area.
Even for small areas, 2 samples are recommended (the
more the samples, the better the end-results, because the
result is more representative).
2) Avoid extracting samples from soil presenting obvious
anomalies and consider them separately.
3) Sample quantity:
Take the same quantity of soil for each sample. For example,
use bags with similar dimensions (1 bag per sample).
4) Depth of extraction:
General: dig and discard 5 cm (2") of topsoil.
Herbaceous crops: from 20 to 40 cm of depth (8" to 16").
Orchards: from 20 to 60 cm of depth (8" to 24'’).
5) Spread the soil samples on the pages of a newspaper and
let the soil dry in a shady place or put it in an oven at 40°C.
6) Crumble the dried soil and mix all the samples together to
obtain a homogeneous mixture, discarding stones and
vegetable residues.
7) From this mixture, take the soil sample for analysis.
B) Soil solution preparation and measurement
1) Sift the soil at 2 mm.
2) Weigh 10 g of soil and put it in 25 ml of soil preparation
solution HI 7051 (use the apposite beaker) or 20 g of soil per
50 ml of soil preparation solution HI 7051.
3) Mix for 30 seconds.
4) Wait for about 5 minutes.
5) Mix again and measure the pH of the solution.