Soil structure

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The soil structure (also: soil structure ) is a term used in soil science and describes the spatial arrangement of solid soil components. The total soil volume of the soil matrix is ​​divided into the volume of the solid soil substance and the pore volume .

This division has a significant impact on the soil and air balance, the rooting capacity , the availability of nutrients and similar soil and plant physiological properties. In general, the coarser the structure of a soil and / or the more densely packed the individual structural unit is, the less favorable its soil properties are.

  • Single grain structure

  • Coherent structure

  • Crumb structure

  • Separation structure

Structure forms

The following structural forms are macroscopically well addressable according to the cohesion of the soil particles as well as the degree of cementing or secretion:

  • Basic structure , neither through biological nor physical processes, a structure has emerged.
    • Single grain structure (also "elementary structure") - in sand and gravel, in freshly deposited silt and in silt and mud flats, the primary particles are not cohesive;
    • Coherent structure - clay / silt / loam sediments: are held together by cohesive forces and form an undivided mass;
    • Putty structure - the primary particles are glued or cemented to one another by substances displaced in the soil. A putty only at the points of contact of the grains appears microscopically as a so-called "shell structure".
  • Aggregate structure - the primary particles (grains) are combined to soil aggregates (structural bodies) through physical or biological processes
    • Structure in which the soil particles u. a. Merge them into heterogeneous structures using soil biological processes:
      • Crumb structure - agglomeration of soil particles that are loosely stored or can be stuck together (then also referred to as "sponge structure") - example: humus top soil of a garden soil;
      • Wurm solution structure - from earthworms excreted, bonded by excreted in the earthworm gut materials, a few millimeters large soil aggregates;
    • Separation structure (also known as “segregation structure”) - caused by shrinkage processes with repeated drying and re-humidification from a basic structure through separation. The structures of the segregate structures are further differentiated according to size and shape:
      • Crack structure - predominantly vertical shrinkage cracks;
      • Layer structure - predominantly horizontally aligned structures, horizontal axis> vertical axis;
      • Pillar structure - rounded at the top, vertical axis> horizontal axis;
      • Prismatic structure - sharp-edged, coarse structures, vertical axis> horizontal axis;
      • Polyhedron structure - sharp-edged, multi-faceted, intermeshing structures with mostly smooth surfaces; Vertical axis and horizontal axis approximately the same; Diameter coarse polyhedron> 10 mm; Fine polyhedron diameter 1 - 10 mm;
      • Sub-polyhedron structure - similar to polyder structure, but with more rounded edges; multifaceted, little intermeshing structural bodies with predominantly rough surfaces;
      • Plate structure - horizontal axis> vertical axis; as a result of pressing and thus signs of soil compaction , e.g. B. under lanes or plow soles , but also by the pressing effect of ground ice ;
      • Wedge structure (also "parallelepipedge structure") - due to strong swelling and shrinking in soils with high contents of swellable clay minerals , e.g. B. Vertisols , resulting wedge-shaped structural bodies

Crack, layer and column structures are also grouped into macro-coarse structures, prism, polyhedron, sub-polyhedron, plate and crumb structures to form macro-fine structures.

  • Fragment structure - created through soil cultivation or anthropogenic relocation. They are divided into:
    • Crumbling structure - irregularly shaped structural bodies, diameter <5 cm;
    • Lump structure - irregularly shaped structures, diameter> 5 cm, originated e.g. B. by plowing when the condition is too wet;
    • Rolling units - spherical structural bodies that z. B. caused by transport on conveyor belts; recently the term has also been used generally for naturally formed, round soil aggregates.

There are also microstructure shapes that are determined in thin sections under the microscope .

Note

The definition of the term soil structure is similar to that of the geological term of the rock structure . Strictly speaking, the term soil structure only describes the aggregate and fragment structure; the basic structure is characterized by the lack of a bottom structure.

literature

Web links

Individual evidence

  1. ↑ Ad-hoc-AG Soil: Soil Science Mapping Instructions , 5th edition Hannover 2005, p. 117-120 .
  2. ^ Food and Agriculture Organization of the United Nations (FAO) : Guidelines for Soil Description, 4th ed. Rome 2006, ISBN 92-5105521-1 (English).
  3. ↑ Ad-hoc-AG Soil: Soil Science Mapping Instructions , 5th edition Hannover 2005, p. 119 .
  4. ↑ W. Amelung, H.-P. Flower u. a .: Scheffer / Schachtschabel textbook of soil science. 17th edition Heidelberg 2018, p. 251 .