01.06.1 Soil Textures
The type of a particular soil, or soil texture is determined by the grain size composition of its mineral components. Coarse soil (grain diameter > 2 mm) and fine soil (grain diameter < 2 mm) types are distinguished. In addition, in very wet locations, peat is formed by the accumulation of incompletely decomposed plant material, which may overlay mineral soils.
Fine Soil Textures
Fine soil textures are formed from certain proportions of the grain fractions clay, silt and sand. The main soil types are subdivided into clay, silt, loam and sand, with loam representing a grain mixture of approximately equal parts sand, silt and clay. Soil texture is an important characteristic value for the derivation of such ecological properties as nutrient and pollutant storage capacity, water balance and storage capacity, as well as filtration and buffering capacity regarding pollutants.
Coarse Soil Textures
All mineral components of the soil of > 2 mm in diameter can be described as coarse soil textures, or the soil skeleton. The proportion of coarse soil has an effect on water permeability, the air and nutrient balance, and the capacity to bind nutrients and pollutants. The higher the share of coarse soil, the more permeable a soil is, due to the large pores, while the capacity to bind and the nutrient level depend on the type of fine soil.
Peat is formed in a water-saturated environment from the accumulation of incompletely decomposed plant material. It is characterized by a high water storage capacity and a very high cation exchange capacity (KAK). Various peat textures can be distinguished, according to the type of plant remains and their formation conditions. Lower bog peat is rich in alkalines and nutrients, and in some cases, even in carbonates. Transitionitional bog peats include plant remains from both low and high-nutrient locations.
The fine, coarse and peat soil textures, each divided into topsoil (depth: 0 – 10 cm) and subsoil (depth: 90 – 100 cm), were determined for each soil association. The data were essentially taken from the profile sections by Grenzius (1987). Some values have been supplemented by expert evaluations.
The mapped fine soil textures are summarized in Tab. 1. Soil textures differ across the topsoil and the subsoil at times, due to the material of which the soil was originally formed, soil development and its use. They were hence examined separately. In addition, soil textures which occur frequently within a soil association are identified as the main soil texture, and distinguished from the more rarely occurring soil textures, known as subsidiary soil textures.