Geoscience Reference
In-Depth Information
given above demonstrates this. On the contrary, in acid soils calcicole
plants are not able to obtain the quantities of calcium they require.
Calcium causes many physiological disorders in addition to its direct
effects:
Nitrogen nutrition
. Calcifuge plants are not able to reduce nitrate
nitrogen, the dominant form in limestone terrain. Most of them
do not have (or have very little) nitrate-reductase activity. In
short, in limestone terrain, calcifuges do not have access to their
requirement of nitrogen.
Iron chlorosis
. Calcium impedes the absorption of iron even when
the latter is abundant in the soil. Chlorophyll is not synthesized
normally. Growth and yield diminish. In the extreme case the
plant dies.
Phosphate deficiency
. In calcium-rich environment, phosphates
undergo reversion and highly insoluble apatite is formed.
Chlorosis and associated disruptions must be avoided. Calcium
carbonate cannot be removed from the soil; we turn to resistant plants
and stocks. If needed, FeSO
4
is applied to provide to the aerial parts of
the plant the iron that it is unable to extract from the soil in sufficient
quantity.
The association of calcicole and calcifuge plants in a way that
sometimes astonishes the amateur botanist (if he forgets the detailed
geography of soils) is explained by the distribution of calcium carbonate
in them. For example, in mountains, the Great Yellow Gentian,
Gentiana
lutea
, which prefers calcium carbonate (if available) establishes in the
least stable portion of screes, close to the limestone fragments freed by
rubbing. Mat-grass,
Nardus stricta
(Gramineae), does the reverse (Legros
et al.
1987).
CONCLUSION
Unlike Ferralsols and Vertisols, considered previously in this topic
and which are formed by very slow weathering of silicates, soils on
limestone are often the products of rapid dissolution or precipitation.
In these conditions, pedogenesis changes time-scale: millions of years
for Ferralsols, tens of thousands of years for Vertisols, and thousands of
years or sometimes much less for Calcisols. But the pedogenetic approach
is still relevant here. The soil materials depend on the mechanisms of
development (sands of cellular origin, pseudomycelia…). Dissolution
of carbonates explains the landscapes (ruiniform relief, piping…).
