Agriculture Reference
In-Depth Information
Figure 1.3
An organic-rich Brown Earth
on limestone before cultivation in the
Côte d'Or, Burgundy region, France.
(White, 2003)
(CO
3
2-
) ions
2
in solution, the latter breaking down to form carbon dioxide
(CO
2
), so that only the ions and insoluble impurities remain to form soil.
Given this mode of formation and weathering, it is no surprise that soils
formed on limestone are usually shallow. One estimate for the rate of soil forma-
tion on Chalk in Britain is 1 cm of soil in 5,000 years. Normally, an organic-rich
A horizon rests directly on weathering rock, as seen in shallow profile of a
Rendzina on fractured limestone in the Côte d'Or of Burgundy region, France
(figure 1.3). However, if the impurities in the limestone are substantial, or the
soil is augmented by an external source of mineral matter, deeper soils form. An
example of the latter is the Terra Rossa soil of the Coonawarra region in South
Australia, where, during the glacial (cold) periods of the Pleistocene epoch when
the sea level was lowered, strong winds blew silt-size particles from the coastline
onto the exposed ridges of limestone. As a result a deeper, red soil profile formed
over the porous limestone, which is capped by a hard layer of calcrete (figure 1.4).
As with other limestone regions around the world (e.g., Burgundy, St. Emilion
in France, Paso Robles in California), the wines produced from the Coonawarra
Terra Rossa are distinctive and much prized, especially those made from Cabernet
2
Ions and their charges are explained in chapter 3.
