TERRA ROSSA

Terra rossa is the chemical weathering product of limestone under oxidizing conditions excelled by Mediterranean climate.

Image result for terra rossa karst

The term “terra rossa” is Italian word for “red soil” or “red earth”. Although terra rossa exists in other places in the world, these soils are common in areas with Mediterranean-type climates: alternation of a rainy and cool-to warm-dry season. Among other wine regions, it is found in La Mancha in Spain and Coonawarra in Australia.

Formation of terra rossa

There are several theories about the formation of terra rossa.

The first one, traditionally accepted, states that it derives from the insoluble residue of the underlying limestone. Following dissolution of calcium carbonate by rain, clay contained in limestone sediments with other insoluble substances or rock fragments, forming discontinuous residual layers variable in depth. Under oxidizing conditions iron oxides appear, which produces the characteristic red color. According to this theory, terra rossa is a polygenetic relict soil, formed during the Tertiary and subjected to hot and humid periods during the Quaternary.

A more recent theory is based on the geochemical composition of the soil, and suggests that these soils would have formed about 12000 to 25000 years from wind transported sediments over long distances. However, although in this case soil material is considered to be allochthonous (eg, aeolian dust from the Sahara), formation of the Mediterranean terra rossa is closely related to the properties of the limestone substrate.

Properties

1 . Compared to most clayey soils, terra rossa has surprisingly good drainage characteristics. This makes it a popular soil type for wine production.

2 . The high internal drainage and neutral pH conditions of terra rossa are a result of the karstic nature of the underlying limestone and dolomite

3 . The reddish color of terra rossa is the result of the preferential formation of hematite over goethite.

4 . This soil type typically occurs as a discontinuous layer that ranges from a few centimeters to several meters in thickness that covers limestone and dolomite bedrock in karst regions.