Soil is the uppermost loose layer of the Earth's surface where the atmosphere, water, and organisms in the soil intermingle and influence each other. The soil is formed from the parent rock as a result of the influences of climate, elevation, water, vegetation, animals, and humans. Over millions of years, soil-forming processes have created different layers in varying states of development. It takes around 1000 years to create a 10 cm thick layer of topsoil. (Herrmann, L. (2018): Bodenkunde Xpress. Stuttgart)

Soil textures

The soil texture indicates the composition of the individual particle sizes. A distinction is made between three particle sizes in soil: clay (< 0.002 mm), silt (0.002 mm – 0.063 mm) and sand (0.062 mm – 2 mm). With a little practice, it is possible to determine the texture of the soil by taking a finger sample in the field. In Austria, soil textures are graded according to the clay content in the soil (light soil < 15 %, medium soil 15 – 25 %, heavy soil > 25 %). (Schwarz, S., Aust, G., Englisch, M., Herzberger, E., Kessler, D. & R. Reiter (2022, in review): Soil texture and soil density – background information. Austrian Soil Science Society (ÖBG), Booklet 86. Vienna)

Soil types

In comparison to the soil texture, the soil type describes the characteristic layers of the soil surface and the degree of weathering of the soil. Soils have different characteristics that need to be taken into account during planting and plant protection. Examples of soil types are brown earth, rendsina, loam, stagnosol and black soil.

Soil phases

The soil can be divided up into four phases: minerals, air, water, and organisms. Due to its composition, it can develop like an organism, can grow and thrive, but can also degrade due to erosion and acidification. (Ecklmayr J. (2021): Understanding my soil. Our soil - Our basis for life and cultivation. Presentation on Soil.Water.Security.Advice. Linz)

Lithosphere (mineral phase)

The lithosphere makes up 45 % of the total volume of the soil and accounts for the mineral content. It is created from the weathering of the parent rock, which results in the presence of different minerals and elements. (Hellberg-Rode, G. (s.a.): https://www.hypersoil.uni-muenster.de/0/05.htm)

The smaller the particle size, the better water and nutrients can bind to it. Sand promotes the exchange of gases, while clay is particularly good at binding nutrients and water.

Biosphere (organism phase)

The organic solid matter of the soil is made up of animate and inanimate components. It accounts for just 7 % of the soil. The animate part is the soil life, which consists of soil fauna (animals) and soil flora (plants, bacteria, fungi, algae, etc.). (Hellberg-Rode, G. (s.a.): https://www.hypersoil.uni-muenster.de/0/05.htm)

Soil life is essential for the health and fertility of our soils. It helps to break down organic matter and recycle nutrients.

The inanimate part of the biosphere is known as humus, which is divided into nutrient humus and permanent humus. The main difference between the two lies in the conversion rate of the substances and the retention time in the soil.

Atmosphere (air phase)

Air accounts for around 25 % of the soil content and is described as atmosphere. The proportion depends, among other things, on the soil texture and the pore volume. Air is essential for many processes taking place in the soil and for soil organisms, which can only live to a limited extent in anaerobic conditions without oxygen. Subsequently, a high proportion of coarse pores and the resulting high proportion of air are responsible for rapid water absorption.

Hydrosphere (water phase)

The hydrosphere describes the water in the soil, which makes up around 23 % of the total volume and comes mainly from precipitation. Depending on the soil texture and pore volume, the water remains in the soil, seeps away or rises. Adhesion to the soil particles and capillary lift are the two most important control mechanisms for this. (Hellberg-Rode, G. (s.a.): https://www.hypersoil.uni-muenster.de/0/05.htm)

Understanding the soil

To get the best out of your soil, you need to know about its composition. A spade sample is a quick and easy way to assess soil moisture, odour, colour and structure. It provides information about the extent to which it can be driven over, the air and water balance, its structural stability, pore volume, and compaction. In addition to the spade sample, the finger sample can be used to determine the soil texture. Using a pH meter, take a reading from the spade sample at a depth of approx. 15 cm to determine the pH value. The hydrochloric acid test can also be used to check whether free lime is present in the soil.