Soil and the Environment - Soils for Fine Wines - page 15

word podzol which means “ash-colored.” These soils are common vineyard soils
in southeastern Australia, where they are often referred to as “duplex soils” to in-
dicate the contrast in clay content between the A and B horizons. Figure 1.2 is
an example of a duplex soil.
Lessivage is unlikely to occur in calcareous soils or in neutral soils that retain
a high proportion of exchangeable Ca 2 ions, because the clay is not readily
translocated. Under acid conditions, if exchangeable Al 3 and hydroxy-Al ions
are predominant on the clay surfaces, the clay should also remain flocculated (sec-
tion 4.5.2). However, if the Al and Fe are complexed by soluble organic com-
pounds and removed, the clay particles are more likely to deflocculate and be
translocated. Similarly, when Na ions comprise more than 6-15% of the ex-
changeable cations, depending on the soil, clay deflocculation and translocation
are likely to occur. The result is a sodic soil (section 7.2.3).

1.3.2.2 Temperature

Temperature varies with latitude and altitude and with the absorption and reflec-
tion of solar radiation by the atmosphere. Temperature controls the state of
water—ice versus liquid versus vapor—which has a key effect on soil formation
through rock weathering, leaching, and the transport of materials. Temperature
affects the rate of mineral weathering and synthesis, and the biological processes
of growth and decomposition. Reaction rates are roughly doubled for each 10°C
rise in temperature (section 3.5.4), but enzyme-catalyzed reactions are sensitive to
high temperatures and usually attain a maximum between 30 and 35°C.
Temperature decreases by 0.5°C per 100 m increase in altitude. On land close
to large bodies of water, temperature varies less from day to night and with the
seasons than in arid continental regions. This temperature moderation influences
soil formation and affects viticulture through time of flowering, fruit set and ripen-
ing, and the incidence of frost. The interaction between soil temperature and color
is also important for vineyards in cool climates (section 3.5.2).

1.3.3 Organisms

Soil and the organisms living on and in it comprise an ecosystem . The active par-
ticipants in the soil ecosystem are plants, animals, microorganisms, and humans.

1.3.3.1 Plants and Animals

Natural vegetation and soil form a feedback loop because the soil influences the
type of vegetation present and the vegetation in turn influences soil formation. A
good example of this interaction is the different effects of coniferous trees (pines,
spruce, and larch) and temperate deciduous species (oak, elm, ash, and beech) on
soil formation. The leaves and leaf litter of coniferous trees are richer than decid-
uous trees in organic compounds called polyphenols that are powerful reducing
and complexing agents (box 1.5). Polyphenols that do not chelate and leach with
Fe and Al are polymerized and contribute to the thick litter layers that build up
under pine forests. This layer is called mor humus (fig. 1.9a). Humus describes or-
ganic matter that is in varying stages of decomposition as a result of microbial ac-
tivity. One reason for the accumulation of mor humus is that the litter of pines,
spruce, and larch is unpalatable to earthworms. Mor humus is only slowly bro-
ken down by small insects and colonized by slow-growing fungi, so it is poorly