These organisms include small vertebrates (e.g. field mice), but mainly a variety of invertebrates (rotifers, nematodes, snails, vascular worms, earthworms, non-corals, crustaceans, arthropods, mites, spiders and insects). These soil organisms are involved in processes that have a fundamental impact on soil properties and play an important role in the life of biocenoses, including participation in the biological cycle of many elements essential for life, in the decomposition, humification and mineralisation of organic debris and in the formation of the physical properties of soils. In agricultural soils, earthworms play a very important role.
6.6.1 Earthworms
The natural habitat for earthworms to grow and function is the soil. Their food is plant remains. Earthworms in the soil contribute to the decomposition of organic matter both directly and indirectly. The direct way mainly involves taking in the organic matter present in the soil as food and excreting it as droppings. The indirect way, among other things, is a decomposition mechanism involving the utilisation by soil microorganisms of the nutrient substrates produced by earthworms in pre-decomposed plant residues.
The development and activity of earthworms in the soil environment primarily influences soil structure, contributing to the formation of soil aggregates and adequate oxygenation of the soil, with consequent positive effects on soil fertility and fertility.
Another effect caused by these animals is the mechanisms by which organic matter in the soil is biodegraded. This has the main effect of increasing the metabolic activity of soils, which is needed for agriculture. Earthworms are also used in the production of vermicomposts, which have a high fertilising value.
In view of the important role of earthworms in the soil environment, it is important to ensure that earthworm populations develop. Earthworm populations are influenced by a number of factors, including sudden or unfavourable changes in climatic conditions such as sudden frost, prolonged drought and excessive soil moisture. Other important factors for the development of earthworms are the environmental conditions associated with the availability of food, the reaction of the soil, and the way the soil is fertilised or tilled. In general, the less mechanical interference with the soil, the more willing earthworms are to colonise it, and the use of machinery that reaches deep into the soil causes a noticeable decline in the earthworm population. However, there are treatments that reduce earthworm stress associated with intensive tillage, such as mulching, which enriches the soil with organic matter, provides nutrients and maintains the right temperature by retaining heat in spring and autumn. In addition, this treatment has a beneficial effect on the physical, chemical and biological properties of the soil. Straw and other post-harvest residues are used to mulch the soil. The development of earthworm populations is also supported by the use of intercrops that increase the biological activity, fertility and fertility of the soil and enrich it with nitrogen, mainly through the use of faba bean plants. Soil and subsoil compaction hinders the movement of these animals in the soil profile and thus its oxygenation and water management. The activity of earthworms is positively influenced by the regulation of the soil pH towards neutral. Most earthworms live in humus soils of alkaline meadows and in fertile deciduous forests. In these habitats, there are 0.5 -1 tonnes of living earthworms per 1ha. Gardens, orchards and pastures are also populated in large numbers. The fewest earthworms are found in acidic raised bogs and in acidic soils of pine and spruce forests.
6.6.2 Other soil macro-organisms
It is a group of very diverse organisms belonging to: flatworms, nematodes, molluscs, annelids, protists, crustaceans, arachnids of various types, insects (either wingless or winged insect larvae), and small mammals.
These organisms, along with earthworms, are among the most important soil-forming agents and, in the soil produced, are responsible for maintaining the character of the soil. They influence the physical and chemical characteristics of the soil, i.e. its structure, water retention capacity, aeration. In a fundamental sense, they are co-responsible for its fertility, since it is their presence (together with micro-organisms) that determines the decomposition of organic matter and accelerates the release of minerals available to plants, as well as the formation of soil humus. We do not see these animals, but together with fungi, bacteria, algae, radicles, etc., they determine the formation of soil fertility. Some of them can also pose a threat to crop plants (spider mites, wireworms, caterpillars of agriculturists, or nematodes) and if they appear above the damage threshold, protective action is required. Economic damage thresholds (loss of production versus cost of protection) depend on a number of factors depending on the requirements of the market or the recipient of the agricultural product.
6.7 Organic fertilisers
Organic matter is one of the main components shaping soil quality, responsible for, among other things, soil fertility, capability and productivity, influencing chemical, physical and biological properties. The division of fertilisers into ‘organic natural’ or ‘unnatural’ is ideological and therefore inadequate for sustainable agriculture.
Organic matter consists mainly of dead plant and animal remains and the products resulting from their decomposition. Organic matter contributes to the formation of water-air relations, plays an important role in the establishment and maintenance of various groups of soil micro- and macro-organisms, increases the sorptive capacity of the soil, and is a source of essential nutrients needed by plants and soil organisms. In addition, it also contributes to maintaining a constant, balanced soil pH. Consequently, the presence of organic matter in the soil is an important indicator of soil fertility and capability.
Maintaining or increasing soil organic matter levels can be achieved by:
- the use of organic fertilisers (manure, slurry, green manures, compost, digestate, etc.),
- an appropriate crop rotation or succession, ensuring an adequate supply of crop residues and a positive balance between carbon and nitrogen gains and losses,
- maintaining continuous soil cover with crops, catch crops and intercrops,
- reducing soil mixing, leading to increased biological activity,
- use of Fabaceae in the rotation,
- liming the soils and keeping the pH of the soil no lower than slightly acidic or neutral, as there is a marked degradation of organic matter in acidic soils.
The source of humus in the soil can be various organic materials added to the soil. These can be: manures (dung, slurry, manure, chicken dung), post-harvest residues (straw, roots), green manures, catch crops, compost, waste from agricultural, municipal and industrial production (sewage sludge, biogas plant digestates, some animal and plant waste). These materials vary greatly in their rate of humification and ability to form soil humus. Organic matter from ‘outside’ is all forms of organic matter added to the soil that are not derived from the plant biomass created in the field. For more on this topic, see Area 7: Nutrient Management.