The soil – the skin of the earth
Soil is an important basis for life and a resource that is only marginally renewable. It fulfills numerous functions that are necessary for life. But do we actually know the soil beneath our feet, or does much knowledge remain hidden beneath its surface?
Sometimes it is brown, sometimes black; sometimes coarse with many stones, sometimes very fine and sandy; sometimes it is moist and sticky and other times dry, dusty and brittle..
But here’s what the soil always is – no matter what it looks like:
- It is arable land or animal grazing pasture (useful area for arable farming and animal breeding).
- It serves as a basis for roads and foundations (settlement and traffic areas).
- It provides us with recreational space.
- It is a habitat for plants and animals.
- It stores water and nutrients.
- It filters and buffers pollutants.
- It provides raw materials.
- It has an archival function.
So what does the appearance of the soil depend on?
There are a variety of soils that have developed differently and have different properties. The appearance of soils and their local occurrence depends on:
- The rock in place below the surface.
- The climate.
- The flora and fauna.
- The terrain conditions.
- The water supply.
- Man-made (anthropogenic) influences.
A soil is therefore the product of the influence of the abiotic soil-forming factors of rock, climate and relief, and the biotic soil-forming factors of flora, fauna and man.
What is the soil made of?
Soil is a complex mixture of in-organic components, dead organic matter (humus), soil-air and soil-water, with dissolved in-organic and organic substances. The in-organic components are mainly silicates. Clay minerals are of great importance as a store for plant nutrients.
Dead organic material is converted by soil organisms into humic substances, which are then further decomposed. They are the most important natural source of nitrogen fertiliser. They also have many functional groups that can bind cations.
Humic substances and clay minerals are linked by chemical bonds, to form what is known as the “clay-humus complex”, and the humic substances are more effective than the clay minerals in binding nutrients. The most important plant nutrients are the cations K+, Ca2+ and Mg2+, as well as nitrate and phosphate.
In Central Europe, arable soils usually contain 1-2% humic substances, the so-called black earth soils up to 7% and pasture soils up to 10% humus.
Soils in Central Europe consist of about 50% solid components and 50% pores. These are each filled about half with soil-water and half with soil-air. Nutrients and organic substances are dissolved in the soil-water. Among the solid components, 40-47 % are mineral, 3-10 % are organic substances. Peat soils can contain more than 25% organic matter.
