Soils are a great reservoir of biodiversity: they are home to between a quarter and a third of all living organisms on the planet. However, we still know little about them. Although about 80% of plants are known, only about 1% of the microorganisms that inhabit the soil have been identified.
From a taxonomic point of view, we can distinguish between bacteria, fungi, protozoa, very small invertebrates (rotifers, tardigrades, nematodes), small non-insect invertebrates (especially mites and springtails) and insects (especially larvae), and earthworms.
Soils grow most plants, provide nutrients and determine the water available to them, along with climate and topography. Depending on their conditions (presence of water, aeration, acidity, presence of heavy metals) they allow, or not, their growth.
Soils and their inhabitants influence each other and form a trophic pyramid that decomposes organic matter.
Why are soil and its biodiversity important?
The soil is, to a large extent, the great support of terrestrial life. Its role is essential in relation to the nutrient cycle, and also in part of the water cycle. It can be very different in composition, for example in the amount of organic matter it includes, but also in its depth.
On the other hand, biodiversity is an essential quality of natural ecosystems. Depending on their state, these ecosystems “work” or not. Faced with a decrease or alteration of soil biodiversity (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 contributes to the decomposition of organic matter, it is essential to maintain the nutrient cycle of the ecosystem, it is necessary for the correct nutrition of plants, it improves the entry and storage of water in the soil. , provides resistance to erosion as it helps to give structure to the soil, keeps pests, parasites and diseases under control, helps 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, a great loss of biodiversity occurs. The main causes are:
The alteration suffered by 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 matter. In most crops, the plant material is almost completely removed from the field.
The progressive alteration of its chemical characteristicsdue to the two previous points, and also to the chemical products that are used: fertilizers and phytosanitary products (herbicides and insecticides).
When the crop is a monoculture, all these effects are accentuated due to the absence of other plant species that were providing diversity of organic matter when they dropped their leaves or when they died.
The transformation effects described end up causing soil degradation due to compaction, soil loss due to erosion, leaching of nutrients due to lack of structure, acidification or alkalinization. And the degradation is aggravated by the burning of residues, excessive fertilization, salinization by irrigation in soils with the presence of salts, irrigation with wastewater and the invasion of exotic species.
However, agriculture is not the only cause of soil degradation or loss. Livestock can cause compaction or start serious erosion phenomena. The permanent covering with impermeable materials, such as roads, buildings, sidewalks or squares causes the sealing of the soil and the death of organisms by making it impossible for them to have access to water, air and nutrients.
In other cases, the decline in soil biodiversity can be linked to factors already mentioned above, including erosion, depletion of organic matter, salinization, pollution, and compaction.
The soil biota has a great capacity to resist disturbances or changes (resilience), and a variable capacity to recover from these disturbances. But this recovery capacity has limits, and if after an important alteration the balance is not recovered, we can consider that the ground has been lost.
Maintenance of soil biodiversity
Generally, soils present greater biodiversity in non-agricultural natural ecosystems, in crops that receive little or no chemical fertilizers and pesticides, and in grazing systems that promote plant diversity due to increased availability of food resources provided by roots and plant life. litter.
Crop management techniques that promote maintenance or increase in soil organic matter also maintain soil stability and biodiversity. This can be achieved by adding organic matter or maintaining the stubble, something that helps the presence of a greater population of microbiota and animals, including earthworms.
Management techniques such as crop rotation and reduced tillage increase the quantity and quality of organic matter available to soil organisms and develop a healthier environment for biodiversity to be maintained.