Loess soil - Soil of the Year 2021

Valuable mineral resource in Hesse - Formed during the ice ages, the sediment was transported by the wind.

At the suggestion of the BGR, loess soil was selected by the Soil of the Year Board of Trustees as Soil of the Year 2021. The term loess is presumably derived from the Alemannic, dialectal expression Loesch "loose", "loosely". Loess is a parent rock of soil formation. The collective term "loess soil" summarizes various soils that can develop from loess and its surrounding formations.

Loess - dusty gold - a child of the ice age

The loess soil ranges in color from light yellow to ocher, is calcareous, homogeneous, and has high stability, as the lime and clay constituents were cemented after deposition.

The soil was gradually decalcified as percolating water dissolved the lime in the upper layers and shifted it downward into the still unweathered loess. Thus, so-called loess clasts (massive, rock-hard lime concretions) formed in deeper layers. In the upper layers, clay minerals were newly formed due to weathering. The small soil particles were transported with the seepage water into the subsoil. This resulted in the typical parabrown soils. If the topsoil is bleached in the process, pale soils are formed. If seepage water accumulates above the clay-enriched subsoil, waterlogged soils are formed. With a thick humus-rich topsoil, so-called black earths are formed. The latter, located in warm and dry basin areas, originate from the time after the ice age. Here, a climatically inhibited (winter cold and summer dryness) humus decomposition by plant remains took place, which was deeply mixed into the loess by soil animals (intensive bioturbation by e.g. earthworms and rodents).

Loess was deposited in several phases, thus is an important aspect in the landscape and climate history as well acts as an archive of prehistoric settlement. In the Soil of the Year one often finds fossil soils, which give conclusions about prevailing environmental conditions; or tuff bands, which have stored events of past volcanic eruptions.

Loess consists mainly of silt particles (grain size between 0.002 - 0.063 mm), which gives the soil good porosity and makes it a very good water reservoir.  Thus, loess soils are very good buffers and filters in terms of water balance, in addition, many minerals are found in the loess. Thus, the structure and composition of the soil is important for plants, it provides them with nutrients and stored water, moreover, it retains pollutants and protects our groundwater.

Soils from loess are fertile, productive and easy to work with. Thus, they were a valuable candidate for agricultural use early on; they are free of stones and rich in pores. In Hesse, loess soils are the most fertile and favorable arable sites. However, intensive use does not leave them unscathed; loess soil is susceptible to erosion. Often only remnants of the original soil formation can be found, and in some places even the calcareous loess resurfaces (pararendzines). The fertile material has been eroded and can be found downslope or has been transported by water bodies and deposited as alluvial loam in the floodplains.

Without a new ice age, the loess soil cannot form again, so it is necessary to protect and preserve the soil. Careful use is necessary to maintain a high humus content, stable soil structure and loose storage. The best protection against erosion is a year-round plant cover and as many hedges and trees as possible to ensure the natural and landscape balance. Due to its excellent properties and multiple functions, loess soil is a true all-rounder.

Loess areas in Hesse are the Bergstrasse, Reinheim Hills, the Rheingau, the Main-Taunus foothills, the Wetterau, the Limburg and Amoeneburg basins and the western Hessian depression. The loess blown out of the Rhine valley can have a thickness of several meters there.