Soil Bioanalysis: Understand the Science Behind Soil Health Assessment

Just one gram of soil can contain anywhere from 10 to 8 million different species of microorganisms, including approximately 1 billion bacteria, 1 million actinomycetes, and 100 fungi. So even though 1 gram of soil may seem insignificant, it contains an astonishing abundance of life, essential for maintaining the natural processes of our planet.

Until 2020, soil was analyzed mainly based on its chemical and physical aspects. Now, with the inclusion of biological analysis, which is called Bioanalysis or, simply, BioAS, we can better understand soil as a living ecosystem, essential for agricultural health and productivity. In addition, the importance of the balance between these three factors (chemical, physical and biological) is fundamental for assessing soil health and ensuring an adequate management system.

BioAS technology is a project created by Embrapa and offers a simple and efficient way to assess soil health, enabling technologies that promote the sustainability of agricultural activities in line with environmental balance. This approach combines parameters related to the functioning of biological machinery with chemical analyses of the soil, allowing for a more comprehensive and integrated understanding of soil health.

An example to illustrate the importance of assessing soil health would be to compare it to human health. The results of bioanalysis can be interpreted as a clear warning: “Either you change your habits or you jeopardize your health.” This warning is given because BioAS reveals that neglecting the biological machinery of the soil results in significant productivity losses in the long term. For farmers who already implement conservation management systems, bioanalysis acts as an incentive and motivation to continue with their sustainable practices.

BioAS is essential to ensure soil quality by assessing the biological machinery that sustains soil health, which leads us to understand what soil quality really means. Soil quality refers to the soil’s ability to operate within ecosystem limits to sustain biological productivity, maintain environmental quality, and promote plant and animal health. This concept encompasses the physical, chemical, and biological characteristics of soil that are fundamental to its proper functioning.

To assess soil health and quality, the analysis of microbial biomass and enzymatic activity stand out. These indicators are essential, as they reveal the soil's capacity to perform important environmental services. Therefore, the inclusion of parameters related to the biological component of the soil is crucial for a more comprehensive understanding of its quality and health.

Microorganisms play a crucial role in the “functioning” of soil, participating in processes ranging from its formation to the decomposition of organic residues. This process results in the cycling of mineral nutrients, which are used by plants. Furthermore, the results of several studies show that, in the search for soil improvement, microbiological attributes are the first to be impacted. Sustainable management, which involves a greater contribution of plant residues, for example, leads to an initial increase in biological activity. Over time, this contributes to the increase in soil organic matter (SOM), which results in several benefits.

This management approach leaves its mark on the soil, which is detected by soil bioanalysis. To perform BioAS, we have a list of more than 30 laboratories spread throughout all regions of the country, making it easier to find one near your region. The components of the analysis consist of an evaluation of the enzymes Arylsulfatase and Beta-Glucosidase, soil quality indexes, soil functions and classification of the soil into 4 classes: 1) Healthy; 2) Becoming ill; 3) Sick; 4) Recovering.

Arylsulfatase is an enzyme produced and secreted by bacteria in response to soil sulfur deficiency. These enzymes play a crucial role in the mineralization of sulfur present in organic molecules. This mineralization can consist largely of sulfur absorbed by plants, especially in soils with naturally low levels of this nutrient. Beta-glucosidase, on the other hand, breaks down cellulose, breaking it down into cellobiose and free glucose.

These two enzymes were chosen because they are directly or indirectly related to the soil's productive potential, its functioning and the sustainability of its use. In addition, they are sensitive to soil degradation, detecting changes in organic matter and other properties early. They also offer precision, consistency in results, ease of analysis and reproducibility, which reduces the cost of their analysis. Other characteristics were also important in choosing these enzymes, such as correlation with several microbiological attributes and not being affected by the application of limestone and fertilizers.

The soil functions are Cycling, Storage and Supply. These three functions are related to the soil's ability to nourish plants, promoting chemical, physical and biological balance. Each function has its own characteristics, namely: a) Cycling: the soil's ability to cycle nutrients, where the performance of biological activity is estimated; b) Storage: the soil's ability to store nutrients, that is, its nutrient reserve (potential CEC and MOS); c) Supply: the soil's ability to make nutrients available, represented by the quality of the nutrient reserve (acidity, base supply and phosphorus supply).

After interpreting the Bioanalysis data, it is necessary to determine the health class of that soil and, to do so, it is essential to understand the requirements illustrated in Figure 1.

Once the soil health classification has been completed, it is important to understand what needs to be done to achieve long-term sustainable practices and seek or maintain healthy soil. Figure 2 provides a quick conclusion on what needs to be done for each soil health class.

Diseased soils do not necessarily mean low productivity soils, but rather less resilient soils, with a lower capacity to react in stressful situations. Figure 3 highlights this process.

The results presented in Figure 3 show that there was no difference in soybean productivity over the first six harvests. However, in the seventh harvest, after a period of water stress caused by a dry spell, productivity in the two diseased soils fell, while productivity in the two healthy soils remained stable. In the following four harvests, the diseased soils were not able to reach the productivity of the healthy soils. For comparison purposes, this accumulated difference was 6 sc/ha.

The benefits of healthy soil go beyond crop productivity, as healthy soil is not only productive but also resilient, biologically active and has more nutritious plants. It also improves water storage and respiration, bioremediation of pesticides, carbon sequestration, mitigation of greenhouse gas emissions, etc. These are characteristics that are targeted in a sustainable and efficient management system.

Several studies show that healthy soils promote better plant development, keeping them more nutritious. Table 1 below shows soils with high and low enzymatic activity depending on the management adopted.

In soils considered healthy (with high Arylsulfatase and Beta-Glycosidase activity), that is, soil with Soybean/Brachiaria or Soybean/Rotation as management, provided soybean plants with higher levels of flavonoids and protein compared to soils with low enzymatic activity.

Soil Bioanalysis plays a fundamental role in assessing soil quality and health, going beyond traditional chemical and physical analyses by including biological parameters that are crucial to soil functioning. With the ability to identify changes in organic matter and other indicators early on, BioAS allows for a more integrated and accurate view of soil condition. This approach not only contributes to more sustainable agricultural practices, but also reinforces the importance of a balance between physical, chemical and biological components for maintaining soil fertility, productivity and resilience. Thus, the use of Bioanalysis is an interesting tool for unraveling the mysteries of soil health and ensuring the economic, social and environmental sustainability of agricultural systems in the long term.

By Luiz Fernando Costa Ribeiro Silva e Leticia Almeida, Federal University of Vicosa