In soil science and geology, Rendzina or Rendsina is a shallow soil that forms on rocks rich in carbonate or gypsum . The soil type has two horizons and is divided into class R ( Ah / C soils ). Its abbreviation is RR.
Origin of name
Origin and Distribution
Rendzines can form on solid rock rich in carbonate or gypsum or on loose material (≥ 75% by mass carbonate or gypsum). They are therefore a further development of the Syrosem or Lockersyrosem initial floors . By far the most common raw material with this property is limestone . Other solid parent rocks are marble , the magnesium-containing dolomite and gypsum (calcium sulfate). Chalk (e.g. on Rügen ) or geologically very young lake chalk (e.g. in the Lake Constance area ) are carbonate-rich loose rocks . In addition, lime-rich technogenic materials such as concrete or brick can also be considered nowadays .
In addition to the physical weathering , which loosens the structure of the bedrock, the weathering of the solution also has an effect on the formation of rendzinen . Carbonates are dissolved by water containing carbon dioxide and transported away with the seepage water as hydrogen carbonate. The formula is roughly:
CaCO 3 + H 2 O + CO 2 → 2 HCO 3 - + Ca 2+
In the case of sulfates, a simple solution runs off that also removes the sulfate with the seepage water.
The purer or more fissured the material, the faster the solution will weather. The insoluble constituents, especially clay minerals, accumulate in the topsoil . This form of soil formation takes place relatively quickly compared to the weathering of a carbonate or gypsum-free soil. In addition, humus accumulates due to the biological activity in the topsoil . The Ah horizon of a Rendzina is therefore clearly humic, but still contains carbonate or gypsum, even if the contents are significantly lower than in the parent rock.
As the carbonate or gypsum depletion progresses, the Rendzina merges into more differentiated soils. If the A horizon becomes more than 40 cm thick, the class of black earths is reached. If a browned horizon develops in the subsoil, a brown earth (B horizon in the subsoil) or terra fusca (T horizon in the subsoil) develops . The Rendzina is therefore usually a development stage of a location that is exceeded relatively quickly. However, the erosion can permanently maintain the soil type of the Rendzina, as the continuous soil erosion constantly throws back the soil development .
The classic distribution area of the rendzinen is in karst areas and mountains , where calcareous material and slopes meet. In the layered landscape of the low mountain range they occur wherever limestone layers are exposed.
The Rendzina has two horizons as a not deep soil : Ah / cC.
- Ah - there is a humus (h) topsoil horizon (A) above the starting material . Its thickness must be> 2 cm and ≤ 40 cm. The color is mostly dark gray to blackish due to the organic material. In the case of arable land, this horizon is called Ap (p for plow horizon ).
- cC - The starting material (C) is directly below the Ah horizon. This must be carbonate or containing gypsum (c), i.e. have a lime or gypsum content of ≥ 75 % by mass . The preceding c is often left out, as it is mandatory for addressing as a rendzina. The C horizon is partly weathered and is referred to as Cv (v for weathered).
The Ah horizon usually still contains carbonate or gypsum. As a result, the pH value is usually in the basic range between 7 and 8. Since the residue from the weathering of the solution consists mainly of clay , the soil type of the rendzinen is fine with up to 60% by mass of clay. In principle, the clay also contains a large number of nutrients , so that the cation exchange capacity reaches high values of up to 40 cmol + . Another special feature is the very high pore volume . While it is 45 % by volume in average soils , up to 70% by volume are possible in rendzinen. This makes for excellent ventilation, workability and drainage of the sites.
Due to the high pH value, the nutrients and the pores, the soils offer ideal conditions for soil organisms . Organic material carried in is broken down very quickly and completely incorporated into the soil. The humus is in the form of gauze and therefore has the highest possible quality. The entire A horizon is very rich in humus (often 10–20% by mass) and has an excellent, loose crumb structure .
Despite the good basic conditions mentioned above, due to their shallow depth, rendzines are only suitable for agricultural use to a limited extent. On the one hand, mechanical tillage is hindered. On the other hand, there is a lack of sufficient soil volume for water storage or nutrient supply , so that the locations are rather barren. Due to the loose storage with a high pore volume, the soils tend to dry out quickly. They are particularly at risk of drought on southern slopes and in low-precipitation winters. The thin Ah horizon hardly gives the plants any root space. Last but not least, rendzinen are mostly on slopes with a more or less steep incline. So when land is used, soil erosion often occurs.
In the days of horse plows , the plowing depth was around 15-20 cm. This depth often allowed rendzinen to be used for agriculture without touching the stony subsoil. The regular contact between the plow and limestone made creaking noises, which led to the name of the soil type. With the introduction of large agricultural machines , the plowing depth was reduced to around 30 cm, so that the shallow depth often led to problems. As long as erosion and the water supply are under control, high yields can be earned on Rendzinen. Because of the numerous problems, rendzines are now rarely used as arable land.
Partly, especially in the karst areas, pastures can be found on which, when used extensively, a lime-lime lawn , which is valuable from a nature conservation point of view, occurs. Mowing pastures are rarer, as protruding stones can endanger the cutter bar .
Other Ah / C floors
In addition to the Rendzina, there are three other soil types in the Ah / C soil class, which differ diagnostically in the lime content of the starting material:
- The pararendzina arises on marly material (carbonate content> 2% by mass and <75% by mass). Usually it is loose rock.
- The tendril forms on hard rock with little or no lime (carbonate content ≤ 2% by mass).
- The Regosol lies on loose material with little lime (carbonate content ≤ 2% by mass).
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