Geoscience Reference
In-Depth Information
7.6
UTILIZATION OF CALCAREOUS SOILS
7.6.1 Concept of Active Lime
The solubility of CaCO 3 in water is such that it hinders the growth of
only some plants. But the actual calcium content in the soil solution is
not always the maximum. It depends on the nature of the solid phase.
A test has been developed for this. A measured excess of ammonium
oxalate ( NH 4 ) 2 C 2 O 4 . H 2 O is added to a soil sample. This compound reacts
with Ca ++ to give calcium oxalate. The quantity of ammonium oxalate
left behind is determined and the difference is the quantity consumed
by the calcium. This is active lime . The response of cultivated plants has
been correlated with the results from this method, which is sufficient to
select good stocks for grafting in arboriculture or viticulture.
We have noted on numerous occasions that the more the specific
surface area of minerals, that is, the more divided they are, the more
reactive they become. Excellent linear correlation has been found (Fig.
7.19) between the content of active lime in soil horizons and the CaCO 3
content of the clay + fine silt (0-20 ยต m) fractions (Dupuis 1975).
Content
of active
lime, %
30
Line
yx
20
Spread of
experimental
points
10
30
10
20
Total CaCO in the 0-20
m
m fraction
3
(as % of the fine earth)
Fig. 7.19 Correlation between content of fi ne particles and content of active lime in calcare-
ous soils (Dupuis 1975).
7.6.2 Calcicole and Calcifuge Plants
Attempts have been made to understand why some plants tolerate lime
and others do not (Tagliavini and Rombola 2001).
In carbonate-rich soils, calcifuge plants fail to limit the invasion of
their cells (cytoplasm, vacuoles) by calcium. The example of calcified cells
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