Agriculture Reference
In-Depth Information
Box 1.1
(continued)
On the basis of texture (the “feel” of the mix of soil particles), soil profiles may
be classed as
• uniform—littlechangeintexturewithdepth(e.g.,igure1.9)
• gradational—agradualincreaseinclaycontentwithdepth(e.g.,igure
1.10)
• duplexortexture-contrast—achangefroma“light”texturedAhorizon
(sandy loam to sandy clay loam) to a “heavy” textured B horizon (clay loam
or clay), often with an sharp boundary between the two (e.g., figure B1.1.1)
The A horizon (topsoil) is easy to distinguish from the B horizon (subsoil) in
a duplex profile, but this separation is less obvious in a gradational profile and even
less so in a uniform profile. In the second and third cases, a distinction between
A and B horizons can be made on the basis of organic matter content, which is
greater in the topsoil and usually decreases to an insignificant amount below 20 cm
or so.
landscape. The answer to this question lies in the multifaceted interaction of the
soil forming factors that can vary on a scale of a few meters to tens of kilometers
and the effect this variable interaction has on the resultant soil's physical, chemi-
cal, and biological properties. Some examples of the different possible outcomes
for soil formation illustrate this point.
Rudimentary Soils on Slate and Schist
Where mountain building has been active, such as in the Alps of northern Italy, the
original rocks that may have been igneous or sedimentary (see table 1.1) can become
much folded and faulted. During this process, the rocks are metamorphosed such
that, for example, a sedimentary mudstone becomes hardened and converted to
a shale or schist. Although soil will form on surface outcrops of such rock, where
the land slope is steep, the action of gravity and water causes the developing soil
to be eroded and remain shallow. Figure 1.2 shows an example of one such rudi-
mentary soil that is used for viticulture, formed on fractured shale in the Collio del
Friuli region of northeast Italy. Similar soils formed on schist support vineyards in
the Central Otago region, New Zealand, and the Coteaux du Languedoc region,
France. Because of their shallowness these soils are not very fertile, but given their
fractured parent rock and land slope they are usually well drained. Hence once the
grapevines are established, with roots exploring the weathering rock, these soils can
be excellent for producing fruit for wine that is rich in flavors and aromas. The dis-
tinctive Pinot Grigio wines from the Friuli region and Pinot Noir wines from the
Central Otago region attest to this outcome.
