General Information About The Employment Of Ph Agrar 2000 - PRONOVA Stelzner pH AGRAR 2000 Technical Instructions

GB pH AGRAR 2000
1.1 General information about the employment
of pH AGRAR 2000
The pH value is one of the most important
measuring data in miscellaneous agricultu-
ral fields. It is the basic principle behind the
availability of all nutrients. Taking measure-
ments using the pH meter AGRAR 2000 aims
at quickly obtaining measurement results.
In order to achieve reliable results, measu-
rements with buffer solutions pH 4 and pH 7
have to be carried out and compared to each
other. Workable buffer solutions pH 4 and
pH 7 are a prerequisite to the precise measu-
rements of pH values. Nowadays, pH values
are measured using exclusively electrodes
with a glass membrane. The temperature of
the medium influences the measured pH va-
lue only to a small extent.
at 5°C pH 4,01 or
at 40°C pH 4,03 or
For this reason, a temperature-compensated
value of 20° C is determined as starting value.
The principle of temperature compensation
will suppress any systematic measurement
errors. The influence of temperature varia-
tions plays a minor role in agricultural fields.
Important information about ta-
king measurements using the
glass soil-insertion electrodes
When measuring substrats, there are two
possibilities: you may either produce a soil
solution or you may take the measurements
directly in the soil. Taking the measurements
directly in the soil can only be achieved un-
der the following conditions:
1. The soil has to be moist (at least 50% usable
water holding capacity). In case the soil is
too dry, you may moisten the hole to be used
for measurements with deionised water or a
diluted CaCl2 solution (using a wash bottle).
2. Insert a dibble into the moist soil. Depth of
insertion = measurement depth of glass soil-
insertion electrode. Carefully insert the glass
soil-insertion electrode into the hole prepa-
red for the measurements and softly press
some soil onto the electrode using your
thumb (like you were potting a plant).
32
pH 7,09
pH 6,97
3. After the measurement value is displayed,
carefully withdraw the glass soil-insertion
electrode from the soil, spray-wash it with
deionised water and afterwards swab it with
a soft cloth.
4. If it is not possible to take the measurements
directly in the soil (e.g. when the soil contains
too many stones or when it is extremely com-
pressed), the measurement using the glass
soil-insertion electrode has to be done in a
soil solution.
Taking measurements in soil solution
Take a representative soil sample. Mix the
soil sample with CaCl
portion of 1: 2.5 (1 part soil, 2.5 parts calcium
chloride solution).
How to produce a CaCl
Dissolve 15 grams of calcium chloride in 10
litres of distilled water or 1.5 g of calcium
chloride in 1 l of water, for example, using a
volume beaker (article 2014).
Comparable pH values after measurements
With light soil, we orientate ourselves at to-
wards the low pH values,with heavy soil to-
wards the high pH values. The fact that this
meter can measure the pH value directly in
the soil, i.e. on site, means that all properties
of the location will be part of the test results.
This is a practical way of taking measure-
ments. Regarding laboratory measurements
and measurements using a glass soil-inser-
tion electrode, the method used has to be ta-
ken into account in order to achieve compa-
rable measurement results, as can be seen
in the diagram below. The practical measure-
ment in H O using the pH meter AGRAR 2000
2
(Art. 3002) with glass soil-insertion electrode
can be compared to all KCl measurements
when Fig. 1 (below) is taken into account.
Comparison of methods in pH
measurements of soil
In Switzerland and the Netherlands, the pH
value of soil is usually measured in aqueous
suspensions or extracts. This delivers the
true pH value of the soil solution. This value
may be subject to great fluctuations, depen-
ding on factors like the season. Nevertheless,
this value is used for advisory services, as it
corresponds to the real value, as mentioned
before. This value is called pH (H
solution in the pro-
2
solution:
2
O).
2