Soil formation is directly influenced by five main factors: relief, climate, weather, parent material and living organisms. The latter work continuously in the soil, acting in its transformation, degradation, conservation and even altering its physical and chemical properties. The living fraction of the soil is essential for its functioning, and many processes that govern the maintenance and functionality of soils are attributed to it (CARDOSO and ANDREOTE, 2016).
Among the soil constituents, the biological fraction, formed by the multiple groups of microorganisms that act on the soil's organic matter, in the continuous development of synthesis processes and analysis of organic compounds, makes the soil considered a biological entity (PEDROSA et al., 2015).
Importance of soil fauna
Most of the effects of soil animals on plants are indirect and involve changes in environmental conditions considered important for plant growth, such as: pH, aluminum toxicity, concentration of essential plant nutrients, level of disease and pest pressure, competition, activity of growth-promoting microorganisms (including symbionts), aeration and water availability in the root growth zone, among others (PARRON et al., 2015).
Among the advantages of using microorganisms in agriculture is the ability to fix nitrogen; the decomposition of organic waste; the detoxification of pesticides; the suppression of plant diseases; the supply of nutrients to the soil and the production of bioactive compounds, vitamins and growth hormones (ALFONSO et al., 2005, cited by PEDROSA et al., 2015).
The decomposition of plant and animal remains is a biological process of extreme importance for the ecosystem. Through the products of photosynthesis (6CO2 + 6H2O + energy → C6H12THE6 + The2), a large part of the carbon enters the soil (SILVA & MENDONÇA, 2008; cited by PULROLNIK, 2009), and will be used as a source of energy for heterotrophic microorganisms – decomposers. Thanks to the soil biota, the nitrogen is mineralized in assimilable forms and other macro and micronutrients are made available to plants. As described by Correia and Oliveira (2006), the quantity and diversity of decomposing organisms determine the speed of processes such as mineralization and immobilization of nutrients, which directly affects the assimilation of minerals by plants and crop productivity, even when mineral fertilizers are applied.
The degradation of organic compounds, as already mentioned, is carried out through the action of microorganisms. In addition to cycling and making nutrients available, these organisms can also act in the metabolization of compounds from agricultural pesticides, in conjunction with soil fauna. For example, earthworms are known to have the ability to accelerate the aerobic degradation of contaminants such as polycyclic aromatic hydrocarbons and some pesticides through soil ingestion, reducing their adsorption and increasing bioavailability for microorganisms responsible for the degradative processes (ANDREA et al., 2004; EIJSACKERS et al., 2001; PAPINI; ANDREA, 2001; SANCHEZ-HERNÁNDEZ et al., 2014; cited by PARRON et al., 2015).
Reis et al. (2011) state that increased soil microbial activity, together with the use of crop rotation techniques, can act antagonistically to the development of plant diseases. This occurs due to the establishment of competition for nutrients, water and space between phytopathogens and microorganisms that develop harmonious relationships with plants.
According to Cardoso and Andreote (2016), bacteria that form symbiotic relationships with roots have a high affinity for occupying the rhizosphere environment and are capable of promoting plant growth and development, known as plant growth-promoting rhizobacteria (PGRs). According to these authors, the mechanisms that characterize this ability can be divided into direct and indirect.
Direct mechanisms include nutrient supplementation through the decomposition of organic matter and inhibition of pest and pathogen activity. Indirectly, rhizobacteria can produce compounds similar to phytohormones, providing greater tolerance to adverse biotic and abiotic effects.
Factors affecting soil biology
The growth, development and establishment of soil biota can be directly or indirectly influenced by a number of factors. Temperature, moisture, oxygen concentrations, soil pH, nutrient availability and management practices are some examples.
Temperature is one of the most important factors for the development of soil organisms. The temperature range for microbial growth is quite wide; however, at very low temperatures, the enzymatic activity of these organisms is reduced, and at high temperatures, protein denaturation may occur. Regarding moisture, the availability of water is essential for soil microorganisms, as it directly affects nutrient absorption, intracellular metabolism, soil aeration, and adhesion to clay particles.
Regarding oxygen, the concentration of this gas will determine which species will be present and in full development. In well-aerated soils, for example, there will be greater energy production, greater population and activity of microorganisms and, consequently, greater decomposition of the organic materials present in the soil (CERETTA and AITA, 2008).
The inhibition of microbial growth at pH values considered unfavorable results not only in the direct effect of the high concentration of H+ or OH–, but also the indirect influence of pH on the penetration of toxic compounds present in the environment into microbial cells (CARDOSO et al., 1992). However, it is known that the way pH acts on a given microorganism is dependent on genetic factors that confer tolerance or not to pH fluctuations. It is important to remember that pH is directly influenced by agricultural practices, and that a lack or excess of liming can generate disorders that will be reflected in productivity.
Human activity can cause significant changes in the chemical and physical factors of the soil, whether through the addition or removal of elements (fertilization, liming, nutrient export), or through cultivation practices (conventional planting, direct planting), which will have an impact on the biological community (MOREIRA and SIQUEIRA, 2006). Therefore, any and all management must be done consciously and well planned.
Crop rotation and soil conservation practices are basic agronomic concerns that are being left on the back burner, with monoculture agriculture prevailing, motivated only by economic pressures. As a result, we have less biodiversity in general (including in the soil) and an increase in problems such as the emergence of new weeds, pests and diseases, not to mention the creation of resistance to agricultural pesticides. Economic aspects are as fundamental as technical factors for the development of sustainable agriculture.
Among the living beings present in the soil, there are two divisions: prokaryotic microorganisms and eukaryotic microorganisms or organisms, also called components of the soil fauna. The size of the organisms is an important classification factor, as it divides the organisms into groups, facilitating the understanding and study of these beings. Therefore, the groups that make up the soil biota will be discussed below.
Soil microorganisms
This classification includes prokaryotic and eukaryotic microorganisms.
Prokaryotes:
This group is composed of extremely simple, unicellular, aerobic or anaerobic beings, and often autotrophic. The main representatives of prokaryotes are bacteria, divided into two large groups: Bacterium and Archea.
Eukaryotes:
This group includes the most complex unicellular organisms, comprised of the kingdoms Protoctista (protozoa) and Fungi (fungi). Fungi are predominant in acidic soils, rich in organic matter and with moisture content close to field capacity. In general, fungi are aerobic, but they are resistant to high CO2 pressures.2, and can develop in deeper regions of the soil (MARTINS). Protozoa are also simple and aerobic beings, which use organic matter for their nutrition.
Soil fauna
According to Aquino (2006), the term fauna is used when referring to the community of invertebrate animals that live permanently or spend one or more life cycles in the soil. Macrofauna have the ability to create their spaces through their activity, generating biopores and galleries within the soil (CERETTA and AITA, 2008). Among the organisms that make up this group are insects, annelids, nematode worms and some arachnids such as mites.
Why preserve soil biota?
Understanding soil fauna communities is an essential requirement in the search for adequate and sustainable soil management that, in addition to conserving biodiversity, also enables important actions of these organisms in the ecosystem (PARRON et al., 2015). All human processes involved in agriculture must be designed in such a way as to avoid, as much as possible, the loss of communities of these organisms that are so important to the soil. Therefore, the use of pesticides and fertilizers must be done rationally, using products indicated for the crop, as well as observing the possible effects that their formulations may have on fauna and microorganisms.
What to apply to increase the biological quality of the soil?
THE AZOGEL, is the organic matrix from which ILSA's organic and organomineral products are derived.
This is a granulated organic fertilizer produced from collagen with ECOCERT certification for use in organic farming systems and permitted use according to NOP and CE standards. Thanks to the industrial thermal hydrolysis process (FCH®), AZOGEL is a unique and highly homogeneous product, with no variations in the raw material or guarantees, with high CTC, high organic carbon and nitrogen content, both highly available to microorganisms present in the soil and rhizosphere, which makes it a product with high biological affinity.
The value of an organic fertilizer goes beyond the simple supply of nutrients, as its use provides many beneficial effects to the soil. Organic matter acts as a source of energy for beneficial microorganisms, which fix nitrogen from the air in the rhizosphere, and fungi that are associated with the roots. It improves structure and aeration, in addition to the ability to store moisture. It has a regulating effect on soil temperature, slows down the fixation of phosphorus and increases the cation exchange capacity (CEC), and helps to retain potassium, calcium, magnesium and other nutrients in forms available to the roots, protecting them from leaching by rainwater or irrigation practices. In addition to all this, some products of its decomposition have a stimulating effect on root development (MALAVOLTA et al., 2000).
Bibliographic References
ALFONSO, ET; LEYVA, A; HERNÁNDEZ, A. Beneficial microorganisms as efficient biofertilizers for tomato cultivation (Lycopersicun esculentum, mil). Rev. Colomb. Biotechnology, vol. 7, no. 2, p. 47-54, 2005.
ANDRÉA, MM; PAPINI, S.; PERES, TB; BAZARIN, S.; SAVOY, VLT; MATALLO, MB Glyphosate: influence on soil bioactivity and action of earthworms on its dissipation in agricultural land. Planta Daninha, Campinas, v. 22, p. 95-100, 2004.
AQUINO, AM Soil Fauna and its Insertion in the Functional Regulation of the Agroecosystem. Miolo_Biota, 2006. 30p.
CERETTA, CA; AITA, C. Family Farming and Sustainability Soil Biology (textbook). UFSM, 2008, 180 p.
CORREIA, MEF; OLIVEIRA, LCM Importance of Soil Fauna for Nutrient Cycling. Miolo_Biota, p. 77-100. 2006.
CARDOSO, EJBN; ANDREOTE, FD Soil Microbiology, ESALq, Piracicaba, ed. 2, 2016. 221 p.
CARDOSO, EJBN; TSAI, SM; NEVES, MCP Soil Microbiology, Brazilian Society of Soil Science, Campinas, 1992. 360 p.
CORDEIRO, MAS Microbiological attributes of soil under crop rotation and sequences in direct seeding. Jaboticabal, 2011. 119 p. Doctoral thesis
EIJSACKERS H.; VAN GESTEL, CAM; DE JONGE, S.; MUIJS, B.; SLIJKERMAN, D. Polycyclic aromatic hydrocarbon-polluted dredge peat sediments and earthworms: A mutual interference. Ecotoxicology, vol. 10, p. 35-50, 2001.
MALAVOLTA, E; PIMENTEL-GOMES, F.; ALCARDE JC Fertilizers & fertilizations. 2000.
MOREIRA, FMS; SIQUEIRA, JO Soil microbiology and biochemistry, UFLA Publishing House, Lavras, ed. 02, 2006. 729 p.
PAPINI, S.; ANDRÉA, MM Dissipation of simazine in soil by the action of earthworms (Eisenia fetida). Brazilian Journal of Soil Science, Viçosa, MG, v. 25, p. 593-599, 2001.
PARRON, et al. Environmental Services in Agricultural and Forestry Systems of the Atlantic Forest Biome. Embrapa, Brasília, p. 121-154, 2015.
PEDROSA, MVB; ALVES, LP; PASCHOA, RP da; AMARAL, AA do. Ecological importance of soil microorganisms. Biosphere Encyclopedia, Scientific Center Know – Goiânia, v.11 n.22; p.100-114, 2015.
PULROLNIK, K. Soil carbon transformations, Embrapa Cerrados, 2009. 36 p.
REIS, EM; CASA, RT; BIANCHIN, V. Plant disease control through crop rotation. Summa phytopathol., Botucatu, v. 37, no. 3, p. 85-91, 2011.
SÁNCHEZ-HERNÁNDEZ, JC; AIRA, M.; DOMÍNGUEZ, J. Extracellular pesticide detoxification in the gastrointestinal tract of the earthworms Aporrectodea caliginosa. Soil Biology and Biochemistry, Oxford, vol. 79, p. 1-4, 2014.
SILVA, IR; MENDONÇA, ES Soil Organic Matter, Soil Fertility. Viçosa, SBCS, p. 275-375, 2007.
TÓTOLA, MR; CHAER, GM Microorganisms and microbiological processes as indicators of soil quality. In: ALVAREZ, VH; SCHAEFER, CEGR; BARROS, NF; MELLO, JWV; COSTA, LM (Ed). Topics in soil science. Viçosa, Brazilian Society of Soil Science, 2002, p.195-276.
WRIGHT, AL; HONS, FM; LEMON, RG; MCFARLAND, ML; NICHOLS, RL Microbial activity and soil C sequestration for reduced and conventional tillage cotton. Applied Soil Ecology, Amsterdam, v.38, p.168-173, 2008.
Authors:
- Agricultural Eng. Msc. Aline Tramontini dos Santos
- Agricultural Engineer Ana Elisa Velho
- Agricultural Eng. Msc. Thiago Stella de Freitas
