The increase in soybean productivity is linked to several factors such as soil quality, soil fertility, the cultivar best adapted to the region, seed quality, management, climate conditions, among others. In this text we will specifically address how the biological quality of the soil, the use of organominerals and the availability of phosphorus affect soybean productivity.

Healthy soil is 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).

Soil enzymatic activity is dependent on the biosphere, since all enzymes have a biological origin, whether from microorganisms, fauna or flora (LISBOA et al., 2012). Enzymes are the mediating agents of the decomposition of soil organic matter. Therefore, by evaluating the activity of an enzyme, it is possible to determine changes in the microbial demand for nutrients. It is worth mentioning that these enzymatic activities are directly related to the processes of acquisition, fixation and retention of molecules that have such elements in their compositions, which contributes significantly to greater absorption of nutrients by the plant (NGUYEN et al, 2017).

In the soil, enzymes are produced by microorganisms, exuded by plants or resulting from the decomposition of plant, animal and microbial biomass (DAS and VARMA, 2010). The reactions catalyzed by these enzymes act in the cycling of nutrients essential for plant development, such as carbon, phosphorus, nitrogen and sulfur (UTOBO and TEWARI, 2015). Learn more by accessing the text Bioanalysis and the importance of microorganisms in agriculture.

The use of organic compounds mixed with industrialized mineral fertilizers (organominerals) is an important option for soil fertilization (CABRAL et al., 2020). These compounds have properties such as moisture retention, nutrient supply, activation of soil biota and have the potential to improve soil physical properties (SOUZA and PREZOTTI, 1997).

The use of organomineral fertilizers also provides a technological solution from an environmental point of view, as it partially replaces the use of mineral fertilizers (ORLANDO JÚNIOR et al., 2016). In addition, it is possible to reuse agro-industrial waste that could not be disposed of rationally. Furthermore, the use of this fertilizer contributes to the economic pillar, as it has the potential to reduce production costs and generate savings (JÚNIOR et al., 2017).

Organomineral fertilizer, compared to mineral fertilizer, has a relatively lower reactive chemical potential, however, its solubilization is gradual during the crop development period, when agronomic efficiency can become greater, compared to soluble mineral fertilizers (KIEHL, 2008).

Thus, a scientific trial was conducted to compare the organomineral fertilizer GRADUAL MIX, from ILSA, with mineral fertilizers. Both were applied in different doses to soybean crops, in a study carried out in Cruz Alta, Rio Grande do Sul, in partnership with Physioatac consultancy, and the treatments can be seen in Table 1.

Table 1- Treatments and doses evaluated.

Source: author's own.

Increases in productivity were observed for all treatments evaluated in relation to the control (Figure 1). The average productivity of the trial was 76.0 sc/ha, a productivity considered adequate for the levels found in the area and consistent with the average productivity of the region taking into account the climatic conditions during the harvest.

Figure 1: Graphical representation of the effect of the application of mineral and organomineral fertilizers on soybean productivity

Regarding the GRADUAL MIX technology, an average increase was observed in the enzymatic activity of beta-glucosidase, Aryl-sulfatase (Figures 2 and 3), as well as foliar phosphorus content and phosphorus use efficiency (Figures 4 and 5, respectively), demonstrating the effects of the technology on root growth and soil biological activity.

Enzymes can be good indicators of soil quality, as they are extremely sensitive to changes and present an early response to physical, chemical and biological changes in the soil and, in general, are often associated with crop productivity rates (DICK et al., 1997; WAHSHA et al., 2016). They are found in low concentrations in the soil, which is why their evaluation is based on their activity and not on their quantity (Moreira and Siqueira, 2006).

Beta-glucosidase is an enzyme present in most soils (TABATABAI, 1994). It is an organic compound found in plants, animals, fungi, and bacteria. The name of this enzyme is based on the bond it hydrolyzes. This enzyme catalyzes the hydrolysis of cellobiose residues, that is, it participates in the decomposition process of the final phase of cellulose. These reactions generate free glucose molecules as a final product, which is an essential energy source for the development of soil microorganisms (ADETUNJI et al, 2017). This enzyme is directly associated with the biogeochemical cycle of carbon, a fundamental element required in high quantities by all living beings (FONSECA, 2021).

Beta-glucosidase activity can be extremely useful for monitoring soil quality, as it is essential in the cycling of soil organic matter, which is defined as an important parameter for assessing soil quality (SHERENE, 2017). Its ability to stabilize and decompose organic matter can be easily applied to studies related to the impact of soil management (DAS and VARMA, 2010). Beta-glucosidase deficiency causes a shortage of sugars for microorganisms, reducing the reactions promoted by these compounds, consequently decreasing soil quality. Therefore, Beta-glucosidase can be used as a parameter to indicate the presence of glucose available for microorganisms in the surface layer of the soil (ADETUNJI et al., 2017).

Aryl sulphatase is secreted by microorganisms in the soil in response to critical levels of sulfur in the environment and catalyzes the hydrolysis process of sulfated esters (KERTESZ and MIRLEAU, 2004). Although sulfated esters are considered the most labile form of organic sulfur in the soil, they need to be hydrolyzed and transformed into inorganic sulfate (SO₄ ^2- ) to be absorbed by plants. In this hydrolysis process, the bonds between oxygen (O) and sulfur (S) are broken, forming inorganic sulfur compounds (TABATABAI, 1994).

The occurrence of this enzyme in different production systems is generally associated with microbial biomass and the S immobilization rate. Other factors can affect the activity of this enzyme, such as the presence of sulfur anions, seasonal variations in soil moisture, soil solution pH and the presence of heavy metals (SHERENE, 2017).

Aryl-sulfatase activity is related to the amount of organic carbon in the soil and shows a decrease as soil depth increases, due to lower organic matter content in deeper soil layers (KLOSE et al., 2000). Lopes et al., (2013), observed a significant relationship between Aryl-sulfatase levels in the soil and the accumulated yield of soybean and corn grains.

In this work, the beta-glucosidase enzyme in the phenological phase of R1 obtained greater activity with treatment 3 – GRADUAL MIX 06-15-10 (dose 100%), while the enzymatic activity of Aryl-sulfatase was greater in treatments 4- GRADUAL MIX 06-15-10 (dose 75%) and 5- GRADUAL MIX 06-15-10 (dose 50%) (Figure 2). The use of the activity of the two enzymes Aryl-sulfatase and Beta-glucosidase as indicators of the functioning of the soil biological machinery is due to the fact that changes in chemical properties, particularly in soil organic matter (SOM) content, are not always capable of expressing the changes that occur in the soil resulting from the adoption of conservation management systems, such as the no-till system, crop-livestock integration and crop-livestock-forest integration (MENDES et al., 2020). These two enzymes are closely related to SOM – a basic parameter of soil quality – and grain yield – a parameter that reflects the economic aspect of crops – which are fundamental to the sustainability of the agricultural business (LOPES et al., 2013, 2018; MENDES et al., 2019). Aryl-sulfatase has an ideal pH spectrum of 5.8 to 8.2, justifying greater activity of this enzyme in alkaline soils compared to acidic soils (KLOSE et al., 2000). Soil liming can consequently increase the activity of Aryl-sulfatase in the soil. The exudation of organic and inorganic compounds by the roots promotes a reduction in pH in the rhizosphere, resulting in a drop in the activity of this enzyme, since the main source of Aryl-sulfatase in the soil is of microbial origin, which is affected by the reduction in pH (SHERENE, 2017).

Figure 2- Graphical representation of soil bioanalysis in the phenological phase of R1. Physioatac Consultoria experimental station. Cruz Alta – RS.

Enzymes are present in all living organisms, but those of greatest importance in soil quality studies are those of microbial origin (FONSECA, 2021). Therefore, the enzymatic activity of certain enzymes can be directly associated with microbial biomass, as it reflects the metabolic activity of the soil microbiota (LISBOA et al., 2012). Factors that affect microorganisms consequently affect enzymatic activity, such as pH, temperature, water availability, and other abiotic attributes (MOREIRA and SIQUEIRA, 2006).

Factors such as soil microbial diversity and the complexity of organic matter influence the occurrence of enzymes, so it is not possible to quantify all the different enzymes present in the soil (FONSECA, 2021). There are at least 500 enzymes involved in nutrient cycling processes (GIANFREDA and RUGGIERO, 2006) and the most important are cellulases and dehydrogenases, phosphatases, aryl-sulfatases and ureases, which participate in the cycling of C, P, S, and N, respectively (ADETUNJI et al, 2017).

Regarding the post-harvest enzymatic activity in this assay, the Beta-glucosidase enzyme again obtained greater activity with the 3-GRADUAL MIX 06-15-10 treatment (dose 100%), while the enzymatic activity of Aryl-sulfatase was greater in the 5-GRADUAL MIX 06-15-10 treatment (dose 50%) (Figure 3). These results show that the use of the GRADUAL MIX technology maintains soil health, preserving the biological activity of the soil that will benefit the next crops. Understanding enzymatic activities is extremely important, as they act as indicators of the state of soil degradation, since they participate in several biogeochemical processes of the soil and respond quickly to changes resulting from management (DAS and VARMA, 2010).

Figure 3- Graphical representation of post-harvest soil bioanalysis. Physioatac Consultoria experimental station. Cruz Alta – RS.

Phosphorus (P) is absorbed by plants in its inorganic form (H₂DUST₄ ^–) that originates from the solubilization of phosphate minerals and the mineralization of organic matter (GATIBONI, 2003). This nutrient is of fundamental importance for soybean crops, given the fact that it participates in several metabolic processes, such as energy transfer (ATP), photosynthesis, respiration, synthesis of nucleic acids and glucose, synthesis and stability of membranes (phospholipids) and activation and deactivation of enzymes (VANCE et al., 2003; PAULA, 2016).

Novais et al. (2007) explain the process of adsorption and availability of P in soils. Once the fertilizer is supplied, it is solubilized and goes into the soil solution. In low pH conditions, part of the P is precipitated in poorly soluble forms. In the solution, an imbalance occurs in relation to the moment before the fertilizer was applied, which can lead to both diffusion and adsorption, the latter being the most easily occurring, especially in weathered soils. Adsorbed P is transformed into labile P, which acts as a reservoir, providing P to the solution when it is scarce there. This flow of P in the labile-solution or solution-labile form varies according to the soil granulometry and weathering (PAULA, 2016).

The results show that the foliar phosphorus content was higher in all treatments with GRADUAL MIX, with treatment 4 – GRADUAL MIX at a dose of 75% having the highest foliar phosphorus content (Figure 4). Cabral et al. (2020) observed that there was an increase in the foliar phosphorus content of soybeans with the increase in the doses of mineral and organomineral fertilizers, which can be explained by the availability of organic phosphorus from this source, which is the most used by plants. The addition of fertilizers (mineral, organic or organomineral) rich in phosphorus (P) favors the increase in the concentration of this nutrient in the soil, thus, the plants tend to obtain higher phosphorus contents in the leaves, providing increases in the growth and development of soybeans (DEON, 2007; SANTOS et al., 2021).

Figure 4- Graphical representation of leaf phosphorus content. Physioatac Consultoria experimental station. Cruz Alta – RS

When analyzing the efficiency of phosphorus use, which represents the volume produced by the amount of fertilizer applied, we noticed a significant increase in the use of GRADUAL MIX technology, as it was possible to produce more soybeans with less P applied to the soil (Figure 5). An important issue is the labile phosphorus in the soil, addressed in a recent text available on the ILSA blog. The labile fraction is represented by the set of phosphate compounds capable of rapidly replenishing the soil solution when it is absorbed by plants or microorganisms. Therefore, the most labile fractions depend on the degree of soil weathering, mineralogy, texture, organic matter content, physical-chemical characteristics, biological activity and predominant vegetation (WALKER and SYERS, 1976; CROSS and SCHLESINGER, 1995).

Sengik and Kiehl (1995) claim that phosphate fertilizers such as MAP have an acidifying effect on the soil, which is confirmed by Hennig and Coltro (2009), who found that fertilization with MAP phosphate fertilizer, which also contains nitrogen, led to significant increases in soil acidity. Novais et al. (2007) explain the process of adsorption and availability of P in soils. Once the fertilizer is supplied, it is solubilized and goes into the soil solution. In low pH conditions, part of the P is precipitated in poorly soluble forms. In the solution, an imbalance occurs in relation to the moment before the fertilizer was applied, which can lead to both diffusion and adsorption, the latter being the most easily occurring, especially in weathered soils. Adsorbed P is transformed into labile P, which acts as a reservoir, providing P to the solution when it is scarce. This flow of P in the labile-solution or solution-labile form varies according to the soil granulometry and weathering (PAULA, 2016).

In more clayey soils, P encounters greater resistance to move from one place to another, this is known as “soil buffering power”. The reservoir system (labile P) acts as a regulator of excess and scarcity, being even more rigorous in highly weathered soils, where P passes more quickly from the labile form to the non-labile form (a form not readily available), a phenomenon known as P fixation (NOVAIS et al., 2007, PAULA, 2016).

P efficiency is a very complex phenomenon and is affected by a large number of plant mechanisms associated with soil P acquisition and utilization at the cellular level (OZTURK et al.; 2005). Uptake efficiency, under low P availability, can be influenced by morphological, physiological and/or biochemical changes in the root system of plants, such as: development of lateral roots (GERLOFF and GABELMAN, 1983) and root hairs; increase in the ratio between roots and shoots; changes in root architecture; formation of proteoid roots; increase in the association with mycorrhizal fungi; increase in the maximum absorption rate (CAMACHO-CRISTÓBAL et al., 2008); changes in rhizosphere pH; exudation of organic compounds by roots and levels of phosphatases in root cells (STARNES et al., 2008; PAULA, 2016).

Figure 5- Graphical representation of phosphorus use efficiency. Physioatac Consultoria experimental station. Cruz Alta – RS.

The results obtained in this experiment show that the use of GRADUAL MIX organomineral fertilizers contributes to improving the biological health of the soil, increasing enzymatic activity and therefore also improving the efficiency of phosphorus use. The highly assimilable organic compounds present in the GRADUAL MIX fertilizers bind to Fe and Al oxides, releasing phosphorus for absorption. In addition, GRADUAL MIX has a lower potential for soil acidification, which reduces the reactive power of phosphorus and increases its efficiency.

The results of the experiment indicate that organomineral fertilizers, such as GRADUAL MIX, play a crucial role in the biological health of the soil. By increasing enzyme activity, these fertilizers improve the efficiency of phosphorus use, an essential nutrient for plant growth.

These characteristics make GRADUAL MIX a promising option for agricultural practices that aim to preserve soil health and maximize the nutritional efficiency of plants.

References:

ADETUNJI, Adewole T. et al. The biological activities of Beta-glucosidase, phosphatase, and urease as soil quality indicators: a review. Journal of soil science and plant nutrition, v. 17, no. 3, p. 794-807, 2017.

BOGUNOVIC, Igor et al. Tillage management impacts on soil compaction, erosion and crop yield in Stagnosols (Croatia). Catena, v. 160, p. 376-384, 2018. CABRAL, Fernando Luiz et al. Evaluation of mineral and organomineral fertilization in soybean crops. Research, Society and Development, v. 9, n. 9, p. e614995402-e614995402, 2020.

CROSS, AF; SCHLESINGER, WH A literature review and evaluation of the Hedley fractionation: Applications to the biogeochemical cycle of soil phosphorus in natural ecosystems. Geoderma, v.64, p.197-214, 1995.

DAS Shonkor Kumar; VARMA, Ajit. Role of enzymes in maintaining soil health. In: Soil enzymology. Springer, Berlin, Heidelberg, 2010. p. 25-42.

DEON MD Growth and mineral nutrition of soybean subjected to excess P, S, K, Ca and Mg in nutrient solution. Dissertation (Master's). Luiz de Queiroz College of Agriculture, Piracicaba, 72p., 2007.

DICK, Richard P.; BREAKWELL, Donald P.; TURCO, Ronald F. Soil enzyme activities and biodiversity measurements as integrative microbiological indicators. Methods for assessing soil quality, v. 49, p. 247-271, 1997.

FARIAS, J.; NEUMAIER, N, NEPOMUCENO, A. (nd) Soybean knowledge tree. Available at: Embrapa Agency for Technological Information - Temperature. 2020.

FRANCHINI, JC, et al. Contributions of soil management systems for sustainable soybean production. Technical Circular. Londrina, Vol. 58, pp. 1-12.2008.

FONSECA, Eduardo Vianna. Enzymatic activity as an indicator of soil quality. Monograph, Agronomy course, Faculty of Brasília. 2021.

GATIBONI, LC Availability of soil phosphorus forms to plants. Doctoral Thesis. Federal University of Santa Maria, Santa Maria. 2003.

GIANFREDA, Liliana; RUGGIERO, Pacifico. Enzyme activities in soil. In: Nucleic acids and proteins in soil. Springer, Berlin, Heidelberg, 2006. p. 257-311.

JUNIOR, Joaquim Júlio Almeida et al. Use of organomineral fertilization in soybean crops. In: Proceedings of the State Colloquium on Multidisciplinary Research (ISSN-2527-2500) & National Congress on Multidisciplinary Research. 2017.

KERTESZ, Michael A.; MIRLEAU, Pascal. The role of soil microbes in plant sulfur nutrition. Journal of experimental botany, vol. 55, no. 404, p. 1939-1945, 2004.

KLOSE, Susanne; TABATABAI, MA Urease activity of microbial biomass in soils as affected by cropping systems. Biology and fertility of soils, v. 31, no. 3, p. 191-199, 2000.

LISBOA, Bruno Brito et al. Microbial indicators of soil quality in different management systems. Brazilian Journal of Soil Science, v. 36, p. 33-44, 2012.

LOPES, André A. de Castro et al. Interpretation of microbial soil indicators as a function of crop yield and organic carbon. Soil Science Society of America Journal, vol. 77, no. 2, p. 461-472, 2013.

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

MENDES, Iêda Carvalho et al. Soil bioanalysis: Theoretical and practical aspects. Topics in soil science. Viçosa, MG: Brazilian Society of Soil Science, v. 10, p. 1-64, 2019.

MENDES, I. de C. et al. SOIL BIOANALYSIS: THE NEWEST ALLY FOR AGRICULTURAL SUSTAINABILITY. EMBRAPA 2020.

MOREIRA, Fatima Maria de Souza.; SIQUEIRA, José Oswaldo. Soil Microbiology and Biochemistry. Ufla, Lavras, 2006.

NGUYEN, Thi Thu Nhan et al. Effects of biochar on soil available inorganic nitrogen: a review and meta-analysis. Geoderma, vol. 288, p. 79-96, 2017.

NOVAIS, RF; ALVAREZ V. Soil fertility. Viçosa: Brazilian Society of Soil Science, 2007.

ORLANDO JÚNIOR, Amauri et al. Production components and cultivation of soybean with mineral, organic and organomineral fertilization. Brazilian Journal of Applied Technology for Agricultural Science, v. 9, n. 2, 2016.

PAULA, Guilherme de Sousa. Responsiveness and efficiency of phosphorus use of soybean cultivars. Master's dissertation, Federal University of Viçosa – Viçosa Campus 2016.

SANTOS, Jenifer Kelly Ferreira et al. Accumulation of dry matter and nutrients by corn grown under doses of mineral and organomineral NPK formulas. Research, Society and Development, v. 10, n. 5, p. e35010515126-e35010515126, 2021.

SOUZA, JL de; PREZOTTI, LC Soil studies according to different organic and mineral fertilization systems. In: BRAZILIAN CONGRESS OF OLERICULTURE. p. 300. 1997.

SHERENE, T. Role of soil enzymes in nutrient transformation: A review. Bio Bull, vol. 3, no. 1, p. 109-131, 2017.

TABATABAI, MA Soil enzymes. Methods of soil analysis: Part 2 Microbiological and biochemical properties, v. 5, p. 775-833, 1994.

UTOBO, EB; TEWARI, Lakshmi. Soil enzymes as bioindicators of soil ecosystem status. Applied ecology and environmental research, v. 13, no. 1, p. 147-169, 2015.

VANCE, CP; UHDE-STONE, C.; ALLEN, DL Phosphorus acquisition and use: Critical adaptations by plants for securing a nonrenewable resource. New Phytologist, St. Paul, vol. 157, p. 423-447, 2003.

WAHSHA, Mohammad et al. Microbial enzymes as an early warning management tool for monitoring mining site soils. Catena, vol. 148, p. 40-45, 2017.

WALKER, TW; SYERS, JK The fate of phosphorus during pedogenesis. Geoderma, v.15, p.01-19, 1976.

Authors:

Agr Eng. Dr. Angélica Schmitz Heinzen

Agricultural Eng. Msc. Thiago Stella de Freitas

Agricultural Engineer Tuíra Barcellos