Suppressive soils and agroecosystems
Suppressive soils and agroecosystems: when nature helps crops defend themselves
Introduction: Changing Perspectives on Plant Health
When a crop is affected by a disease, the most common reaction is to think of the pathogen as an enemy to be eliminated. For decades, agricultural defense has been based primarily on this principle: identifying the organism responsible for the disease and intervening with products capable of limiting its development.
While this approach has led to significant production results, it has also highlighted several problems: increased pathogen resistance to treatments, reduced biodiversity, biological impoverishment of soils, and greater dependence on external interventions.
Recent research is revealing a different perspective: many diseases depend not only on the presence of the pathogen, but on the balance of the entire agricultural system.
A soil rich in life, a well-balanced crop, and a diverse agricultural environment can create conditions in which pathogens have greater difficulty spreading.
From this new vision arises the concept of suppressive soil and, on a broader scale, that of suppressive agroecosystem.
The goal is not to completely eliminate the pathogen, an often impossible goal in nature, but to ensure that the disease remains below an economically significant damage threshold.
Soil: Not a mere substrate, but a living ecosystem
For a long time, soil was considered primarily as a physical environment capable of supporting roots and providing water and nutrients.
Today, we know that this vision is incomplete.
Every gram of soil contains millions of microorganisms: bacteria, fungi, actinomycetes, and other organisms that form a complex biological community called the soil microbiome.
This community performs fundamental functions:
– provides nutrients;
– promotes root development;
– improves soil structure;
– protects plants from the pressure of certain pathogens.
In some soils, this biological activity reaches a level that naturally limits the development of diseases. These are called disease-suppressive soils.
What are suppressive soils?
A suppressive soil is a soil in which a pathogen may be present but unable to develop sufficiently to cause serious disease.
This is a very important concept because it changes the way we interpret the relationship between plant and pathogen.
The presence of a harmful organism, in fact, does not automatically mean that a serious epidemic will develop.
Disease appears when a particularly favorable combination of:
– presence of the pathogen;
– susceptible plant;
– suitable environmental conditions.
This principle, known as the “disease triangle,” reminds us that modifying the environment can be as important as directly intervening on the pathogen.
Studies on suppressive soils have shown that the soil microbial community can limit numerous organisms that cause crop diseases, including fungi, oomycetes, bacteria, and nematodes (Alabouvette, 1986; Weller et al., 2002).
How does a suppressive soil work?
A soil’s ability to contain a disease arises from the combination of many small biological processes.
The fundamental principle is that of competition between microorganisms. Beneficial microorganisms can occupy the same spaces and use the same resources as pathogens, preventing them from multiplying (although this ancient classification: beneficial/pathogenic is now included within a series of functions and roles useful for maintaining the balance of an ecosystem, including agricultural ones).
It is as if the pathogen finds an already “occupied” environment.
To this end, we must analyze the production of natural antagonistic substances. Some bacteria and fungi produce compounds capable of directly hindering the development of other microorganisms.
For this reason, the activity of predatory or parasitic organisms must be analyzed. In fact, some soil microorganisms are capable of directly attacking pathogens.
Another important activity is the stimulation of the plant’s defenses. Some rhizosphere bacteria can enhance the plant’s ability to respond to attacks.
This phenomenon is called induced systemic resistance and is one of the most interesting areas of research in the relationship between the microbiome and crop health (Raaijmakers et al., 2009).
From Soil Health to a Suppressive Agroecosystem
The concept of suppressiveness isn’t just about soil. An agricultural crop is a complex system in which the following interact:
– cultivated plants;
– microorganisms;
– insects;
– spontaneous vegetation;
– climate;
– agronomic management.
A suppressive agroecosystem is therefore an agricultural environment designed to favor natural processes that limit the development of diseases.
This idea is the basis of agroecology: not completely replacing agricultural techniques with nature, but using knowledge of ecological processes to design more resilient production systems.
Agricultural practices that promote suppressiveness include:
Grassing and cover crops.
One of the most studied practices is maintaining a cover crop between crops.
Cover crops can:
– increase soil organic matter;
– promote more diverse microbial communities;
– improve soil structure;
– reduce soil splashes that can transfer pathogen inoculum to the leaves;
– improve the balance of the microclimate.
In vineyards, for example, covered soil can help reduce conditions favorable to the development of diseases such as downy mildew and powdery mildew.
This does not mean eliminating the problem, but rather making the system less favorable to the spread of the disease.
Plant diversity also plays a crucial role; it can be explained as a more efficient thermodynamic model for the use and transformation of solar energy and waste from other organisms (Bissanti et al. 2025).
Very simplified agricultural environments can favor the spread of pathogens.
Conversely, the presence of greater plant diversity through:
– rotations;
– intercropping;
– hedgerows;
– ecological strips;
– cover crops;
can create a more complex biological network.
Biodiversity can reduce disease pressure through several mechanisms: environmental modification, increased beneficial organisms, and improved balance among microbial populations (Ratnadass et al., 2012).
Compost production and techniques that promote the accumulation of organic matter are also important.
Organic matter is one of the central elements of soil biological fertility.
The addition of mature compost can promote beneficial microorganisms and contribute to the creation of environments less favorable to pathogens.
However, not all composts have the same effect: quality, maturation, and origin of the material strongly influence the outcome.
Some composts can have suppressive properties thanks to the presence of microbial communities capable of combating specific pathogens (De Corato, 2020).
Among the most interesting examples, also due to the importance of the phenomenon, are downy mildew and powdery mildew: what can a suppressive agroecosystem do to maintain them within levels compatible with agricultural production?
Diseases such as:
– grapevine downy mildew (Plasmopara viticola);
– tomato downy mildew (Phytophthora infestans);
– grapevine powdery mildew (Erysiphe necator);
are strongly influenced by climatic conditions.
In years highly favorable to pathogens, with high humidity and temperatures suitable for the development of infections, no agroecological practice alone can guarantee the absence of disease.
However, a more balanced agricultural system can:
– slow the development of the epidemic;
– reduce the severity of attacks;
– improve overall plant health;
– reduce the number of treatments required.
The real innovation, therefore, lies in moving from simply “fighting the pathogen” to managing the vulnerability of the agricultural system.
A new agriculture: collaborating with natural processes
The concept of soil and suppressive agroecosystem represents a significant shift.
Soil is no longer seen as a simple production support, but as a complex organism capable of contributing to crop health.
The defense of the future will likely be increasingly based on the integration of:
– living soils;
– biodiversity;
– functional microbiomes;
– resistant varieties;
– balanced fertility management;
– targeted interventions when truly necessary.
Nature does not completely eliminate problems, but it does have regulatory mechanisms (feedback) that agriculture can learn to leverage.
A healthy agroecosystem is not one devoid of organisms, but one in which the various components maintain a dynamic balance.
This is why we increasingly need a holistic vision where research becomes systemic and undertakes the study of the “logic” of Nature.
Guido Bissanti
Useful Bibliography:
Alabouvette, C. (1986).
Fusarium-wilt suppressive soils from the Châteaurenard region: review of a 10-year study. Agronomy, 6, 273–284.
Alabouvette, C., Olivain, C., Steinberg, C. (2009).
The soil as a reservoir for antagonists to plant diseases. Journal of Plant Pathology, 91, 245–256.
Bakker, M.G., Schlatter, D.C., Otto-Hanson, L., Kinkel, L.L. (2013).
Diffusion of disease-suppressive microorganisms in soil. Environmental Microbiology, 15, 1877–1887.
Bissanti, G., Guccione, G. D., Manachini, B., Quatrini, P., & Sturla, A. (2025).
Principi e fondamenti di Agroecologia. Associazione Medinova. ISBN 979-1280140401.
De Corato, U. (2020).
Soil microbiota manipulation and its role in suppressing soil-borne plant pathogens in organic farming systems. Chemical and Biological Technologies in Agriculture, 7, 17.
Garbeva, P., van Veen, J.A., van Elsas, J.D. (2004).
Microbial diversity in soil: selection of microbial populations by plant and soil type and implications for disease suppressiveness. Annual Review of Phytopathology, 42, 243–270.
Janvier, C. et al. (2007).
Soil health through soil disease suppression: which strategy from descriptors to indicators? Soil Biology and Biochemistry, 39, 1–23.
Mendes, R. et al. (2011).
Deciphering the rhizosphere microbiome for disease-suppressive bacteria. Science, 332, 1097–1100.
Raaijmakers, J.M. et al. (2009).
The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms. Plant and Soil, 321, 341–361.
Ratnadass, A., Fernandes, P., Avelino, J., Habib, R. (2012).
Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review. Agronomy for Sustainable Development, 32, 273–303.
Weller, D.M., Raaijmakers, J.M., Gardener, B.B.M., Thomashow, L.S. (2002).
Microbial populations responsible for specific soil suppressiveness to plant pathogens. Annual Review of Phytopathology, 40, 309–348.
Wezel, A. et al. (2018).
Agroecological principles and elements and their implications for transitioning to sustainable food systems. A review on agroecology.
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