IMKO TRIME-PICO 32, Руководство пользователя

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Manual TRIME_PICO64-32 Version 2_0 2017-05-30
Page 38
12.1 The analysis of Soils for Electrical Conductivity EC
TRIME
Notes and Disclaimer: The analysis of electrical conductivity is an immensely complex subject. This
resume is not intended as a study document in soil science nor does it discuss the technical complexi-
ties of the devices used.
For agricultural and horticultural soils, the measurement of Electrical Conductivity is an immensely
important measurement. Electrical Conductivity measures the amount of total dissolved salts (TDS)
or total dissolved ions in water. To complicate matters, some ions such as Sodium and Chloride will
contribute more to EC than others such as Phosphorus and Potassium.
Plants require nutrients such as Nitrogen, Phosphorus, Potassium, Magnesium in large quantities
hence they are called major nutrients and also smaller amounts of elements such as Iron, Manga-
nese , Molybdenum and these are called micro nutrients or sometimes referred to as trace met-
als. Fertilisers are supplied to plants as compounds for example Ammonium Nitrate which supplies
Nitrogen in the form of Nitrate or Ammonium. Micro-organisms will break down these compounds
so they are more readily available for uptake by the plants. Levels of some ions such as Chlorides are
less desirable and in great quantities can be harmful to plant growth. The quantity of ions or salts in a
soil is of huge importance. Too much or too few nutrients will create a restriction in plant growth.
Measurement of EC in water is relatively straightforward. An EC probe (usually platinum) is inserted
in the water and a reading in mS/cm is reported on the meter’s display. This is relatively easy be-
cause water is a homogenous medium. Soil on the other hand is not and this has caused great diffi-
culties when trying to measure its conductivity. To work around this, the analysis on agricultural and
horticultural soils has been carried out by mixing a volume of soil and a volume of water and measur-
ing the EC on the suspension or filtered extract. Different countries and different regulatory bodies
have specified methodologies and in general results have been good enough to use for fertilisation
recommendations and programmes. This analysis was generally carried out by a laboratory and
whereas results were and are reliable the method is slow, time consuming and expensive.
Over the years manufacturers have tried to come up with solutions whereby an instrument could be
used directly in soils without having to resort to laboratories. The EC reported by these instruments is
referred to soil bulk electrical conductivity. Whereas there has been some success, there are so many
influential variables such as temperature, soil moisture and granular composition that results have
not been adequate for reliable fertilisation studies. Mostly soil bulk conductivity was of academic
rather than practical interest.
IMKO has studied the subject in detail and has come up with a breakthrough. By using coated rods
and measuring over the length of the probes, all TRIME probes can now accurately report what IMKO
calls EC
TRIME
. This measurement takes account of soil moisture and conductivity by volume. Because
soil moisture is so important in the calculation of EC, all different TRIME probes now incorporate TDR
calibration curves for a selection of soils. Special graphs have been constructed so that the user can
convert the EC
TRIME
reading to grams/litre of dissolved salt. So far curves are available for sandy and
loam soils and it is intended to produce a handful of curves to cover most situations. At this moment
in time, conversion of EC
TRIME
to mg/l TDS is done manually.
IMKO hopes that this breakthrough whereby a TDR instrument can be used to derive a true soil EC
measurement will become the new standard for soil fertilisation analyses.