3
Soil is very important for the plants. It is not merely a support system, but a complex world
from which the roots obtain water and other required elements. In addition, soil is
inhabited by small animals, insects, microorganisms (e.g. fungi and bacteria) which all
influence the plant life in one way or another.
One can talk about a soil evolution, that is, change in its characteristics based upon
climate, presence of animals and plants as well as man’s action. Therefore, a natural soil,
in which evolution is slow, is very different from a cultivated one.
Soil is composed of solids (minerals and organic matters), liquids (water and dissolved
substances), gases (mostly oxygen and carbon dioxide) and contains living organisms. All
these elements provide its physical and chemical properties.
Managing the soil properly is necessary in order to preserve its fertility, obtain better yield
and respect the environment. Testing the soil on the other hand is a must in order to
manage it properly.
SOIL AND PLANT LIFE
Fig. 1.Fig. 1.
Fig. 1.Fig. 1.
Fig. 1. Stratography of a
natural soil (left) and of a
cultivated soil (right)
(L.Giardini)
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4) Depth of extraction:
General: dig and discard the 5 cm (2") of topsoil
For lawns: take the sample at a depth of 5 to 15 cm (from 2" to 6").
For other plants (flowers, vegetables, shrubs): from 20 to 40 cm of depth (8" to 16")
For trees: Samples from 20 to 60 cm of depth (8" to 24'’).
5) Mix all the samples together to obtain a homogeneous mixture of soil.
6) From this mixture, take the quantity of dried soil that you need for the analysis,
discarding stones and vegetable residues.
1) Reading the color-card
–The pH, phosphorus (P2O5), and nitrogen (NO3) tests are colorimetric tests. During
the test a color is developed which corresponds with the fertility of the soil for e.g.
P2O5. To read the fertility, the color developed has to be compared with a color-
card.
To match the color, hold the tube with the test solution approximately 2 cm away
from the color-card. Stand with the light source behind the card and read: Trace,
Low, Medium or High. If the color of the test tube falls between two standard
colors, e.g. between Medium and High Report the test result as Medium-High.
Eight different readings are possible, Trace, Trace-Low, Low, Low-Medium, Medium,
Medium-High, High, and very-High.
–The potassium (K2O) test is a turbidimetric test. If potassium is present, turbidity
is formed. A blue color will also develop to help reading the test result.
To read the test result, hold the tube against the reading-card over the reading
area. Stand with the light source behind your back. Start at Trace, looking through
the tube, and go to Low, Medium or High until you just can see the white line in
the middle of the reading area. Report the reading only in Trace, Low, Medium or
High.
2) Performing the tests
–pH test
Fill a reaction tube up to the lower graduation mark (2.5 ml) with the HI 3896 pH
indicator reagent (use the graduated card for the measure). Use the small spoon to
add six measures of soil sample. Replace the cap and shake gently for one minute.
Allow the tube to stand for 5 minutes (use the tube-stand). Match the color with
the pH color-card, and note the pH value.
–Nitrogen (N), Phosphorus (P), Potassium (K)
•General Extraction procedure [for the P, N, and K tests]
Fill a reaction tube to the third graduation mark (7.5 ml) with the HI3896
Extraction solution. Use the small spoon to add the following: nine measures of soil
sample, in case of field soil testing; six measures of soil sample, in case of garden
soil testing.
Replace the cap and shake gently for one minute.
Test Procedure
