Proper soil management, increasing its productive efficiency combined with conservationist methods that provide for the maintenance of the chemical, physical and biological quality of the soil, has made soil analyses more complete, aiming at detailed analyses that provide a more expressive response to the biological reality of each soil.

            Soil analysis, when it comes to chemical analysis of the soil, aims to determine the degree of fertility in order to make appropriate recommendations for correctives and fertilizers, prioritizing production. Physical analysis of the soil provides information on the structure of the soil, clay, sand and silt contents, in addition to determining the density and stability of the aggregates, infiltration capacity and resistance to penetration, among others. In addition to chemical and physical analysis of the soil, bioanalysis is gaining ground, which is a qualitative evaluation of the soil and quantifies the main groups of biological organisms that are bioindicators of soil microbiology and, therefore, related to the productive potential of the soil.

            Biological processes are the basis of soil health and, if well managed, can reverse the degradation processes that currently occur on a global scale (LEHMAN et al., 2015). A healthy soil is a biologically active, productive soil, capable of storing water, sequestering carbon and promoting the degradation of pesticides, among other important environmental services (MENDES et al., 2020).

            For Pedrosa et al. 2015, microorganisms are responsible for chemical and molecular diversity in nature. Thus, in the soil they act in the decomposition processes of organic matter, participating directly in the biogeochemical cycle of nutrients and, consequently, mediating the availability of these elements in the soil, leading the microbial biomass to function as an important reservoir of several plant nutrients.

Figure 1. How microbiology works in soil. Source: Practical Guide to Soil Biology.

            Soil microbiology focuses on metabolic activities and energy flow and nutrient cycling tasks associated with primary productivity. In addition to addressing the positive and negative environmental impacts of soil organisms, microorganisms are capable of degrading a wide variety of compounds, from polysaccharides, amino acids, proteins, lipids, to more complex materials, such as plant residues, waxes, and rubbers. The occurrence and quantity of microorganisms in an environment are determined by the availability of nutrients, as well as by several physicochemical factors such as pH, redox potential, temperature, texture, and soil moisture. A limitation of any of these factors can inhibit biodegradation and, consequently, cause the persistence of a pesticide in the environment (MATTOS, 2015).

            The expansion and adoption over long periods of conservation management systems, such as the no-till system and crop-livestock integration, allows us to verify that increases in crop productivity or the maintenance of production in the face of adverse environmental situations are often not explained by the results of chemical soil analyses (DRINKWATER; SNAPP, 2007; NICOLODI et al., 2008; MENDES et al., 2017, 2020).

            But what are Bioanalysis and how do they help improve soil quality?

            Over the years, Embrapa has been conducting research aimed at improving Bioanalysis, improving the analyses necessary for a more complete soil report, which includes measuring its biological activity. Thus, one of the pieces of evidence that has been gaining prominence is the soil's ability to stabilize and protect enzymes, which is related to its ability to store and stabilize organic matter (OM). However, changes in OM or in the structural properties of the soil can take years to be detected, unlike enzymatic activity (BANDICK; DICK, 1999; DICK; BURNS, 2011). For this reason, the increase in enzymatic activity, reflecting the increase in biological activity over time, may be a harbinger that the system is favoring the accumulation of soil organic matter (SOM), although this increase in activity is not always linked, in the initial stages, to effective increases in SOM levels (MENDES et al., 2020).

Figure 2. Illustrates the specification of Bioanalysis acting as a kind of soil identity, where its fingerprints are sought, that is, specific characteristics of each soil. Source: EMBRAPA, art by Fabiano Bastos.

            Embrapa's Soil Bioanalysis Technology (BioAS) consists of the aggregation of parameters related to the functioning of the soil's biological “machinery” to traditional routine chemical analyses (pH, H + Al, P, Ca, K, Mg, etc.) (MENDES et al., 2020). BioAS allows farmers to monitor the health of their soil, knowing exactly what to evaluate (arylsulfatase and β-glucosidase enzymes), how to evaluate (soil collected at a depth of 0-10 cm), when to evaluate (after harvesting crops) and how to interpret what was evaluated (via reference values that make it possible to measure, for each type of soil, whether the level of enzymatic activity is low, medium or adequate) (MENDES et al., 2020).

            The enzymes arylsulfatase and β-glucosidase, together or separately, were the indicators that consistently showed the greatest sensitivity to detect changes in the soil, depending on the management system used (MENDES et al., 2019a). These two enzymes have a close relationship with MOS, a basic parameter of soil quality, and with grain yield, a parameter that reflects the economic aspect of crops, which are fundamental to the sustainability of the agricultural business (LOPES et al., 2018; MENDES et al., 2019a).

            Furthermore, the use of arylsulfatase and β-glucosidase has the following advantages: precision, coherence, sensitivity, simple analytical determination, and reproducibility. Furthermore, both enzymes are related to MOS cycling and are not influenced by the application of fertilizers and limestone (MENDES et al., 2019b). These enzymes are also correlated with several other microbiological attributes (microbial biomass carbon, basal respiration, acid phosphatase, cellulase, dehydrogenase), which allowed the selection of only two indicators to express the functioning of the soil biological machinery (MENDES et al., 2020).

            In view of this, microbiology plays a fundamental role in soil nutrient cycling. Thus, soil bioanalysis methodologies have been developed to improve the quality of soil biological activity measurement. Embrapa Soil Bioanalysis Technology (BioAS) uses the activity of the enzymes β-glucosidase and arylsulfatase, which act in the carbon cycle and sulfur cycle, respectively. Measuring the activity of these enzymes basically results in what microorganisms excreted reaching the soil's memory, that is, according to what was used in this soil (management, crops, products used), we have the real condition of how these processes interfered and what resulted (positively or negatively) in the biological health of the soil. This means that soil bioanalysis can specifically contemplate the soil's needs and efficiency, thus contributing to adequate management.

            With knowledge of the subject, it is possible to understand how ILSA's AZOGEL organic matrix can contribute to the microbiological quality of the soil. Organic and organomineral fertilizers are formulated from this matrix, which have collagen, a protein rich in organic nitrogen and amino acids, as their raw material. The matrix is obtained through an innovative and sustainable industrial process called thermal hydrolysis (hydrolysis consists of the physical-chemical process of breaking chemical bonds through the effect of water), where no type of chemical substance is used in the process, which maintains the nutritional characteristics of the protein. This process allows for the production of a unique and highly homogeneous product (without variations in the raw material and guarantees), with a high content of organic carbon and nitrogen, both highly available to microorganisms present in the soil and rhizosphere.

            Due to its high level of organic substances, high organic nitrogen content and low C/N ratio (3.25), AZOGEL stimulates microbial activity in the soil. Several studies have shown the positive influence of AZOGEL on the growth and activity of the microbial population.

            An example that can be cited was experimental data obtained by experiments carried out by ILSA at the Department of Soil Science of the Federal University of Lavras (UFLA). The work was carried out in a greenhouse with controlled temperature and humidity between the months of March and May 2021. The objectives were to evaluate the chemical and biological attributes of soils after the addition of organomineral fertilizers based on AZOGEL, contracting them with organomineral fertilizers produced with traditional organic matrices, to evaluate enzymatic attributes of the soil after the cultivation of Triticum aestivum L. with organomineral fertilizers produced with traditional organic matrices (FOM), among others.

            Five treatments, two types of soil (sandy and clayey) and five replicates were used to conduct the experiments, totaling 50 experimental plots. The fertilizer application treatments consisted of two organomineral NPK fertilizers formulated with and without the addition of AZOGEL®, and also with and without sulfur (S) in the formulation, in addition to a control. The organic matrix of the fertilizers containing AZOGEL® (products 1 and 2) is homogeneous and comes from the transformation of collagen into organic fertilizers, while the organomineral fertilizers used in the comparison (products 3 and 4) were formulated with organic matrices of different origins. The evaluated products are described in (Table 1), and the results of the analyses of the N, P2O5, K2O, S and S-sulfate contents are also presented.

            These products added to the soils positively affected the growth and nutrient content of wheat plants. The greatest effect was observed in sandy soil, attributed to the greater presence of macropores, lower levels of Fe and Al oxides, and thus lower adsorption and complexation of nutrients and organic material provided by the products.

Table 1. Description of treatments used in the experiments.

            The activity of the β-glucosidase enzyme increased significantly with the application of the products and in both soils, with higher levels with the application of Product 2.

Figure 3. Enzymatic activity of β-glucosidase in typical dystrophic Red Yellow Latosol (sandy) and typical dystrophic Red Latosol (clayey) 30 days after the application of different organomineral fertilizers. Results of ANOVA and Tukey's test (P < 0.05). Different letters correspond to significant differences between treatments in each soil evaluated.

            At the end of wheat cultivation, the microbiological attributes determined in the soils were general soil enzymatic activity (fluorescein diacetate hydrolysis - ADF and β-glucosidase (Figure 4) - showing high activity when treatments with AZOGEL were applied. For ADF, the differences occurred only in the sandy soil (Figure 4), with Product 1 showing the highest total soil enzymatic activity. Product 1 also stood out as having the highest β-glucosidase enzyme activity in the clayey soil.

Figure 4. General soil enzymatic activity (fluorescein diacetate hydrolysis – FDA) and β-glucosidase in soils after wheat cultivation for 30 days in typical dystrophic Red Yellow Latosol (sandy) and typical dystrophic Red Latosol (clayey) with different organomineral fertilizers. Results of ANOVA and Tukey's test (P < 0.05). Different letters correspond to significant differences between treatments in each soil evaluated.

            In view of this, at the end of wheat cultivation, Product 1 stands out for presenting lower soil acidification and higher biomass production (dry mass of the root and shoot). In addition, it is among the products that led to the highest general soil enzymatic activity (FDA) and the β-glucosidase enzyme.

            The experiment shows the positive contribution of AZOGEL to the soil and the crop used. Thus highlighting a product that presents a rare and high degree of sustainability, as it guarantees the needs of current and future generations, ensuring productivity and profitability with maximum respect for the environment.

Bibliographic references

ARAUJO, Ricardo S.; HUNGARY, Marianagela. Microorganisms of agricultural importance. Brasilia: EMBRAPA-SPI, 1994.

BANDICK, A.K.; DICK, RP Field management effects on soil enzyme activities. Soil Biology and Biochemistry, v. 31, p. 1471-9, 1999. DOI: https://doi.org/10.1016/S0038- 0717(99)00051-6.

DICK, R.P.; BURNS, RG A brief history of soil enzyme research. In: DICK, RP (Ed.). Methods of soil enzymology. Madison: Soil Science Society of America, 2011. p. 1-19.

DRINKWATER, LE; SNAPP, SS Nutrients in agroecosystems: re-thinking the management paradigm. Advances in Agronomy, v. 92, p. 163-186, 2007. DOI: https://doi:10.1016/ S0065-2113(04)92003-2.

LEHMAN, R. Michael et al. Understanding and enhancing soil biological health: the solution for reversing soil degradation. Sustainability, v. 7, no. 1, p. 988-1027, 2015.

LOPES, André Alves Castro et al. Temporal variation and critical limits of microbial indicators in oxisols in the Cerrado, Brazil. Regional Geoderma, v. 12, p. 72-82, 2018.

MATTOS, Maria Laura Turino. Soil microbiology. 2015.

MENDES, IC et al. Soil biological quality: Why and how to evaluate it. MT Foundation Research Bulletin. 1st ed. Rondonopolis: MT Foundation, v. 1, p. 98-105, 2017.

MENDES, I. de C. et al. Soil bioanalysis: theoretical and practical aspects. Embrapa Cerrados-Article in indexed journal (ALICE), 2019a.

MENDES, I. de C, et al. Critical limits for microbial indicators in tropical Oxisols at post-harvest: The FERTBIO soil sample concept. Applied Soil Ecology, v. 139, p. 85-93, 2019b. MENDES, I. de C. et al. SOIL BIOANALYSIS: THE NEWEST ALLY FOR AGRICULTURAL SUSTAINABILITY. 2020.

NICOLODI, Margarete et al. Insufficiency of the mineralist concept to express soil fertility perceived by plants cultivated in the no-till system. Brazilian Journal of Soil Science, v. 32, p. 2735-2744, 2008. DOI: https://doi.org/10.1590/S0100- 06832008000700017

PEDROSA, Manoel Victor et al. Ecological importance of soil microorganisms. BIOSPHERE ENCYCLOPEDIA, v. 11, n. 22, 2015.

Authors

• Agr Eng. Dr. Angélica Schmitz Heinzen
• Agricultural Eng. Msc. Carolina Custodio Pinto
• Agricultural Eng. Msc. Thiago Stella de Freitas