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researcher from Biodiversity and Environment Institute of the University of Navarra.
Soils are a vital component of ecosystems because they include between one-fourth and one-third of all living organisms on the planet. They are a large reservoir of the biodiversitywhich is defined as the variety of living organisms (species diversity), of the variety Genetics of each of them (diversity Genetics), and of the ecological niches of which they form part (ecological diversity).
Most plants grow in soils and cycle the nutrients (nitrogen, phosphorus, sulfur, potassium, calcium, magnesium and micronutrients) they need; soils, with climate and topography, can determine the water available for plants; depending on their conditions (presence of water, aeration, acidity, presence of heavy metals) allow, or not, their presence; and because of all the above, soils and their inhabitants influence each other and form a trophic pyramid that decomposes the organic subject .
Little is known about them, as only about 1% of the microorganisms that inhabit them have been identified (80% of plants are known). According to size, they can be classified into three large groups: microbes and microfauna (less than 100 microns); mesofauna (between 100 microns and 2 mm); and macrofauna (more than 2 mm). From a taxonomic point of view, their classification is much more complex: bacteria; fungi; protozoa; very small invertebrates: rotifers, tardigrades, nematodes, and many more; small invertebrates, NOT insects: mites and springtails (especially); insects, especially larvae; and earthworms.
Why Soil and Soil Biodiversity Matter
Soil is, to a large extent, the great support of terrestrial life. Its role is essential in relation to the nutrient cycle, and also part of the water cycle. It can be very different in composition, for example, in the amount of organic subject it includes, but also by its depth.
On the other hand, biodiversity is an essential quality of natural ecosystems. Depending on their state, these ecosystems "function" or not. If soil biodiversity is reduced or altered (in quantity and variety), the functions related to it will be altered. Some of these functions(Ecosystem Services) are key to their survival. Among other reasons, this diversity is critical because: it collaborates in the decomposition of organic subject ; it is essential for maintaining the ecosystem's nutrient cycle; it is necessary for the correct nutrition of plants; it improves the entrance and storage of water in the soil; it provides resistance to erosion as it collaborates in giving structure to the soil; it keeps pests, parasites and diseases under control; and financial aid to carbon sequestration, and is important in the cycles of other gases.
Soil biodiversity critically influences agriculture, as it can improve its sustainability.
What can alter biodiversity?
When a natural soil is transformed into an industrial agricultural soil, there is a great loss of biodiversity. The main causes are: the alteration it suffers from mechanization (turning causes the loss of its natural structure and texture, and changes its dynamics in relation to water retention; it also changes the microstructure, very important for the movement of some animals); the progressive loss of organic subject (in most crops the plant material is almost completely extracted from the field); and the progressive alteration of its chemical characteristics, due to the two previous points, and also to chemical products: fertilizers and phytosanitary products (herbicides and insecticides).
When the crop is a monoculture all these effects are accentuated due to the non-existence of other plant species that were providing diversity of organic subject when they dropped their leaves or died.
The transformation effects described above eventually lead to soil degradation through compaction, soil loss through erosion, leaching of nutrients due to lack of structure, acidification or alkalinization, and degradation is aggravated by burning of residues, excessive fertilization, salinization through irrigation in soils with salts, irrigation with wastewater and invasion of exotic species.
However, agriculture is not the only cause of soil degradation or loss: livestock farming can cause compaction or initiate severe erosion phenomena; soil sealing (permanent covering with impermeable materials, such as roads, buildings, sidewalks or squares) causes the death of soil organisms by making water, air and nutrients unavailable to them. In other cases, the decline in soil biodiversity can be linked to factors already mentioned above, including erosion, depletion of organic subject , salinization, contamination and compaction.
Soil biota has a great capacity to resist disturbances or changes (resilience), and a variable capacity to recover from these disturbances. But this capacity for recovery has limits, and if after a major disturbance the equilibrium is not restored, the soil can be considered lost.
Maintaining soil biodiversity
Soils that support natural, non-agricultural ecosystems generally have greater soil biodiversity. Agricultural soils that receive less chemical fertilizers and pesticides generally have greater soil biodiversity. Similarly, grazing systems that encourage plant diversity generally have higher biodiversity due to greater availability food resources from roots and leaf litter.
Crop management techniques that encourage the maintenance or increase of soil organicsubject also conserve soil stability and soil biodiversity. This can be achieved through the addition of organic subject or the maintenance of stubble, something that financial aid to the presence of an increased population of microbiota and animals, including earthworms.
Techniques from management, such as crop rotation and reduced tillage, increase the quantity and quality of organic subject available for soil organisms and develop a healthier environment for biodiversity to be maintained.