A teaspoon of active
soil is the habitat of millions of soil organisms! Some are of animal origin, some are of plant origin. The organisms vary greatly in size. Some are visible with the naked eyes such as earthworms, mites, spring-tails or termites. Most of them, however, are so small that they can only be seen with a microscope, therefore called micro-organisms. The most important micro-organisms are bacteria,
fungus and protozoa. Microorganisms are the key elements to the quality and
fertility of soils, but for us humans they do their work visibly. The greater the variety of species and the higher their number, the greater is the natural fertility of the soil.
Many farmers consider all micro-organisms only as pests and think: “How can we kill them?” Actually, while few micro-organisms in the soil can harm crops, the majority is of great use and importance for soil fertility.
Most soil organisms are very sensitive to changes in soil moisture and temperature. As the plant roots and the soil organisms consume air, a good air circulation within the soil is crucial for their development. Soil organism activity is generally low when
soils are dry, very wet or too hot. Activity is highest in warm, moist soils when food (i.e. biomass) is available.
Most farmers are well aware that the presence of
earthworms is a sign for a fertile soil. Indeed, earthworms are very important for soil fertility as they fulfill several crucial functions. For example, they accelerate the decomposition of
biomass be removing dead plant material from the soil surface. During the digestion of
organic material, they mix organic and mineral soil particles and build stable crumbs, which help improve the soil structure. Their excrements contain 5x more nitrogen, 7x more phosphate, 11x more potash and 2x more magnesia and calcium than normal earth. Lastly, their tunnels promote infiltration and drainage of rainwater and thus prevent soil erosion and water logging.Earthworms need sufficient supply of biomass, moderate temperature and sufficient humidity. That’s why they are very fond of mulching. Frequent tillage decreases the number of earthworms in the soil, as does the use of pesticides.
A major part of the soil microbial biomass is composed of fungi. Important representatives of the soil fungi are the “Mycorrhizae” that live in association (symbiosis) with plant roots. Both the plant and the fungus profit from the association: the plant gets nutrients collected by the fungus and the fungus receives assimilates (“food”) from the plant in exchange. Mycorrhizae are present in all types of soils, but not all crops can get into a symbiosis with the fungus.
Among the naturally occurring species of Mycorrhizae, not all show the same efficiency to take up phosphorus from the soil. That is why artificial inoculation of specific Mycorrhiza varieties can improve their use. Inoculation however does not reduce the importance of offering appropriate living conditions for these organisms.
More abstracts about the Organic Agriculture - Microcosm of Fertile Soil