Coating protects beneficial fungus in chemical fertilizer

Researchers from Embrapa Instrumentation (SP) and the Federal University of São Carlos (UFSCar) have developed a technology that integrates mineral fertilizer and a biological agent in a single formulation, allowing for the simultaneous application of both. The technology consists of a biodegradable coating applied to the granules of a phosphorus and nitrogen-based fertilizer, which acts as a protective layer for the fungus Trichoderma harzianum, a beneficial microorganism widely used as a bio-input in agriculture.

Trichoderma harzianum has great potential for use in agriculture, but it is sensitive to unfavorable environmental conditions. The coating preserves the viability of the microorganism during storage and promotes its gradual release into the soil after fertilizer application, increasing its effectiveness in the field.

The technology takes into account the characteristics of the fungus and, by allowing the combination of inputs, makes it possible for them to be applied simultaneously, which was previously limited by the incompatibility between the components. This can contribute to greater efficiency in the use of resources and the reduction of waste and greenhouse gas emissions associated with agricultural operations.

The challenge now is to scale up the technology commercially and validate its performance in different crops and field conditions.

Solution increases viability

Researchers Cristiane Sanchez Farinas, coordinator of the study at Embrapa Instrumentation, Aline Medeiro Ferreira and Mariana Govoni Brondi, members of the team, encapsulated the fungus Trichoderma harzianum in a biodegradable cellulose-based polymer matrix. The polymer matrix acts like the dough in a cake to support the other ingredients. The result is a coating applied directly to fertilizer granules, capable of preserving the viability of the microorganism.

Experiments have shown that, after three months of storage at room temperature, encapsulated spores—structures that fungi produce to multiply—maintained a high survival rate, while non-encapsulated spores lost up to a thousand times their vitality.

Fungi are an invisible ally of productivity.

Aline Ferreira, who holds a master's degree in chemical engineering from UFSCar and is the first author of the study "Encapsulation of Trichoderma harzianum in Carboxymethyl Cellulose Reinforced with Nanocellulose for Delivery as Fertilizer Coatings," published in February of this year by ACS Agricultural Science & Technology, explains that Trichoderma harzianum is a well-known fungus in agricultural science. "It is a fungus widely used as a biocontrol agent, capable of combating phytopathogens, stimulating plant growth, and increasing nutrient absorption."

But despite this potential, its large-scale application faces an obstacle: low survival rates after storage and, especially, when in direct contact with chemical fertilizers. Cristiane Farinas, who has been studying the subject for 12 years, explains that substances such as urea and monoammonium phosphate (MAP) – a mineral fertilizer rich in phosphorus and nitrogen – can harm the survival of soil microorganisms. “They are extremely fragile. Outside their ideal environment, they die quickly in the sun or in contact with potent chemical fertilizers,” says the researcher.

According to her, these compounds can cause osmotic stress, a situation in which microorganisms lose water due to an excess of concentrated substances around them, in addition to altering the pH and causing chemical reactions that compromise their survival. In practice, this drastically reduces the effectiveness of biological inoculants – products containing microorganisms with beneficial action for plant development – ​​limiting their adoption in the field.

The capsule protects the microorganism.

To overcome this problem, the researchers created a kind of microscopic "shield." The fungus was encapsulated in a polymeric matrix of carboxymethylcellulose (CMC), a cellulose derivative, reinforced with cellulose nanocrystals (CNC).

“This structure forms a resistant and biodegradable film that surrounds the fungal spores, protecting them against adverse conditions. Unlike traditional systems, which quickly release the contents, the new material ensures that the fungus is continuously available in the soil,” says Aline Ferreira.

Postdoctoral researcher Mariana Govoni Brondi, who also co-authored the article, emphasizes that this characteristic is considered ideal for preventative applications in agriculture because, by remaining active for longer in the region near the roots, known as the rhizosphere, the fungus can colonize the environment before the arrival of pathogens, creating a kind of natural biological barrier. "Furthermore, the gradual release avoids direct contact with the fertilizer, further increasing the survival rate," she explains.

Brondi further emphasizes that coating the granule also impacts the release rate of the chemical fertilizer. According to her, the slower and more controlled release of the input means that the nutrients remain available to the plants for a longer period, which reduces the need for farmers to reapply fertilizer in the field, as well as costs and environmental losses, decreasing problems such as eutrophication and the release of greenhouse gases.

The researchers report that monoammonium phosphate (MAP) granules coated with the polymeric matrix showed consistent fungal growth even after 30 days of storage. Conventional methods, such as the use of sugar solutions to fix microorganisms, showed a significant loss of effectiveness over time.

Environmental and economic impact

Microbial inoculants are emerging as an alternative to the intensive use of chemical fertilizers, but they depend on technologies that guarantee their effectiveness in the field.

Cristiane Sanchez Farinas says that carboxymethylcellulose is a low-cost and widely available material, while cellulose nanocrystals can be produced from agricultural waste, aligning with the principles of the circular bioeconomy.

Study presented

The scientific work was presented at the 20th European Biotechnology Congress, organized by the European Federation of Biotechnology (EFB) and held in Antwerp (Belgium) in June of this year.

It received funding from the São Paulo Research Foundation (FAPESP), the National Council for Scientific and Technological Development (CNPq), the Coordination for the Improvement of Higher Education Personnel (CAPES), and the National Agricultural Research System (SNPA).