Geoscience Reference
In-Depth Information
order. Only
andic soil properties
that a soil must have to be classified in
it. The defining criteria are mostly the same as in the WRB. Beyond
that, Soil Taxonomy introduces, as usual, moisture and temperature
regimes for forming major divisions: Aquic, Cryic, Torric, Xeric, Ustic,
etc. regimes. Then qualifiers are added. Most of them were later taken
into the WRB. Thus it is possible to locate them case by case. For
example, a 'Histic Vitr-aqu-and' is an Andisol with peaty tendency
(Histic), containing vitreous minerals (Vit) and related to a particularly
wet moisture regime (aqu).
10.6
PROTECTION AND UTILIZATION
10.6.1 Generalities
Andosols are suitable for many crops (FAO 2006): sugarcane, tobacco,
sweet potato, tea, vegetables, orchards, etc. They are generally rich soils.
On the one hand, the parent materials contain large amounts of bases
(Ca, K, Na, Mg) that are easily available because they are contained
in weatherable minerals. This is particularly true in the case of small
plagioclase crystals and ferromagnesian minerals (olivine, amphiboles,
pyroxenes) and, above all, volcanic glasses. On the other hand, as the
deposition of flows or eruptions is often recent, ageing of the soil is
not very great (incomplete leaching of ions). Volcanic mountains are
cultivated all over the world, particularly in the Mediterranean zone and
the intertropical zone where altitude moderates the climate. The soils are
easy to work. In countries with cheap manual labour, even very steep
slopes are terraced, sometimes below the mouth of volcanoes, which is
not without danger to the population.
Silandic Andosols have the highest agricultural productivity. On the
other hand, aluminium toxicity may occur in the more acid Aluandic
soils, strongly desaturated with regard to bases, in which phosphate
retention is strong enough to result in deficiencies.
10.6.2 Mechanical Constraints
For mechanized farming, there are many constraints that often prevent
the utilization of the soils: slope and lack of soil depth, in the first
place.
On slopes, Andosols are very sensitive to erosion by water, particularly
when their water content decreases following cultivation. We have seen
this lead to modification of their structure that, initially massive, finally
Slope and lack of depth
