If one observes a handful of soil one can easily get the impression that it is more or less dead material. But that is not correct! Each gram of fertile soil is full of life and activity. We need to think in a completely different dimension than what we are used to. The fact is that in one gram of fertile farmland you will find billions of live bacteria, millions of fungi and thousands of little organisms.

Adding up the surface of all small particles in one gram of soil provides an area of 2 square meters. This area is the habitat for many organisms. A healthy and well-functioning microflora in the soil is crucial to maintain soil fertility and thus to get easily worked and fertile soil.

Plants need at least 17 different elements for growth, some only in small quantities, such as trace elements, e.g. molybdenum. Other elements are needed in greater amounts such as nitrogen. Almost all of these elements present in various connections are continuously converted in bio- or geochemical cycles. Important sub-processes involving nitrogen, phosphorus or sulphur are often catalysed by microorganisms. Without their mineralization activity no life on earth was possible.
Through the decomposition of organic matter, microorganisms are the last link in the food chain and they work as decomposers and ensure that important element’s role in the nutrient cycle remains closed. They ensure that organic substances such as roots, leaves, crop residues, green manure, sludge, manure and dead animals in the soil is converted to inorganic form, which becomes available for the plants. This ensures that the plants’ nutritional needs are guaranteed.

Unlike humans and animals, the plants cannot absorb and digest complex organic compounds, but are dependent on an inorganic mineral form as nutrients. Without microorganisms the soil would lack nutritional value because the organic substances would no longer be mineralized.

It is often specialized microorganisms that initiate the breakdown. The catalytic activity of enzymes of the microorganisms usually only degrades material to a certain level. The subsequent degradation process is handled by other groups of microorganisms, and they are dependent of one another. Here environmental factors such as temperature, humidity, pH, oxygen concentration, etc. play an important role.

Some elements of the organic material from plants or animals are easily broken down by microbes, whereas others are much harder to break down. Carbohydrates such as sugar, starch, cellulose, hemicellulose, polyose, pectin, etc., proteins and protein derivatives are often relatively easy to break down. In contrast to substances like lignin, some fatty acids, fats, resins, waxes, rubber, etc. are very difficult to decompose. Natural substances that are persistent to decomposition often lead to appearance of clusters of degradation material in the soil; this again is a part of the humus formation and plays an important role in soil fertility. Important precursors for humus formation are cellulose and lignin, both essential components in plant cell walls.

In formation of humus, organic materials start decomposing and convert to amorphous, dark high polymer humus. This occurs most often in the upper soil layers and has a very positive effect on the fertility of the soil, ventilation and water absorbing ability. In addition to the decomposing ability and activity of the bacteria, there are also other benefits of a health microflora with great impact on the nutritional value of the soil. There are e.g. certain bacteria capable of fixation of elemental nitrogen directly from the air and convert it to a suitable form for the plants. The amount of available nitrogen for the plants are often a limiting factor for plant growth, it is a very important soil enrichment capability. In addition, microorganisms contribute to improve the soil structure. Fungal mycelia encapsulate loose soil particles and bind them together as bigger particles. Bacterial excretes make mineral particles stick together, creating stable structures and is another beneficial interaction between plants and microorganisms. Microorganisms also colonize the above-ground parts of plants that belong to a complex ecosystem, which is comparable to the natural microflora of the human skin or mucous membranes.

In the ground there are also many interactions between microorganisms and plant roots. Plant roots main function is to absorb water and nutrients from the soil. But the roots do not only absorb substances from the soil, they also excrete a number of substances, such as sugars, enzymes and organic acids in the areas around the roots. These substances assist in the release of nutrients from the soil, or acts as nutrients for bacteria and fungi. It is therefore not surprising that the amount of bacteria is much higher in the immediate vicinity (1-3 mm) of the roots, the so-called rhizosphere compared to further away from the roots. The rhizosphere around the root systems can be said to act as an oasis for the microorganisms in an otherwise poor soil.

The rhizosphere bacteria colonies help mobilize the nutrients in the soil and facilitate formation of growth hormones (cytokines, auxins, gibberellins), which again promotes healthy plant growth. In the rhizosphere there are not only favourable bacteria but also some pathogenic bacteria. They might be a threat to the health of the plants we try to grow. Control organisms in the rhizosphere bacteria populations may, however, control the excessive growth of these pathogens. It is a sort of organized “biological control” area in the rhizosphere that protects plant roots against disease causing organisms.

We can conclude that microorganisms have a huge impact on the ecosystem of the soil and the plants that take grow in it. We know with certainty that the soil microflora has a positive impact on nutrient supply and absorption, the plant growth, the plant’s resistance to diseases and to soil fertility and structure in general. Several microorganisms with such favourable characteristics have been isolated from the rhizosphere and later cultivated in the laboratory. Experiments have shown that plants which have been artificially seeded with selected rhizosphere bacteria grow much better than not inoculated control plants.