Researchers create biodegradable sachet for efficient fertilization.

An innovation being developed by the National Nanotechnology Laboratory for Agribusiness (LNNA) of Embrapa Instrumentation, in São Carlos, in conjunction with the Federal University of São Carlos (UFSCar), has great potential to replace the polymers used in soil fertilizers. These are starch sachets reinforced with nanoparticles that contain powdered or granulated fertilizers. Starch is a biodegradable polymer and, in sachet form, can be filled with a varied mixture of essential nutrients for crops.

“There are essential and irreplaceable nutrients for the plant, such as the trio nitrogen, phosphorus, and potassium [NPK] – usually applied to the soil in the form of a highly soluble compound, potassium chloride salt. Farmers generally apply a large quantity to the field to ensure absorption. However, the cultivated plant cannot immediately absorb all of this fertilizer,” explains chemist João Otávio Donizette Malafatti. “This excess becomes an economic loss and can contaminate the surrounding environment. The sachets aim to control the release so that the plant feeds gradually. In this sense, we modulate different types of sachets depending on the nutrients we are going to add inside them.”

Supervised by Embrapa Instrumentation researcher Elaine Cristina Paris, Malafatti is the first author of an article published in Journal of Inorganic and Organometallic Polymers and Materials Regarding her work, Paris is a researcher in the Postgraduate Program in Chemistry (PPGQ) at UFSCar.

Malafatti developed starch sachets processed with urea and citric acid and reinforced with zeolite rich in copper ions. Zeolite is a porous mineral known for its high capacity for adsorbing ions in general, such as copper.

“Starch is a material susceptible to degradation. Therefore, a formulation is needed so that the sachets preserve their characteristics until they reach their destination in the soil. In this process, the copper ions present in the zeolite have a dual function: they have great antimicrobial properties, both against fungi and bacteria, controlling the growth of microorganisms, and, in addition, they are sources of mineral micronutrients, subsequently absorbed by the roots.” In the study, the presence of copper controlled the growth of the fungus Alternaria alternata, Malafatti exemplifies. “What we are looking for is a balance between the preservation of the sachets in the final application in the soil and the subsequent availability of their contents to the external environment.”

Strength and stability

According to him, biodegradable polymers, starch matrices, still need to overcome certain challenges when compared to similar petroleum-derived products, mainly regarding mechanical resistance and stability over time. Therefore, the research seeks to develop formulations capable of improving these properties.

In the study, the group evaluated various concentrations of zeolite and achieved a maximum value of 3% in relation to starch, obtaining a significant gain in mechanical resistance. Above this limit, the particles tend to clump together, weakening the film. In addition to releasing nutrients, zeolite fulfills another function during periods of drought. "It can store water because it is very porous and hydrophilic, that is, it has a high affinity for water molecules," explains Paris. The researcher compares the sachet to a tea bag, into which granulated fertilizer is added.

This work was supported by FAPESP through undergraduate research grants and postdoctoral fellowships in Brazil and abroad.

Versatility

According to scientists, the sachets are a versatile system, as they can both contribute to increasing the solubility of fertilizers stored internally and help control the release of highly soluble sources, aiming to reduce fertilizer loss through aerial dispersal and leaching from rain.

In previous work, also supervised by Paris, UFSCar doctoral student Camila Rodrigues Sciena used a potential fertilizer, hydroxyapatite, a source of phosphorus, with the aim of increasing its solubility. The scientists found a way: acidifying the medium, using pectin in the composition of the starch sachets which, combined with nanoparticulate hydroxyapatite, promoted increased solubility.

“With water, the starch becomes gelatinous and holds the fertilizer in the soil, making it available to the plant, thus minimizing future losses due to rain or wind. The goal is to reduce percolation [the passage of water through porous material, causing the extraction of compounds] and the drift of particulate fertilizer inside the sachet,” says Sciena.

In Malafatti's work, the group is dealing with a highly soluble fertilizer that, upon contact with water, is rapidly solubilized. "In this case, the intention is for the fertilizer to be released gradually, avoiding losses due to leaching or airborne dispersal. It's a sustained release, which will depend on the formulation of the sachets," says Paris.

To test the nutrient release capacity, the sachets were kept in an aqueous medium for 30 days. The results of the experiment demonstrated partial release of copper ions (7 mg L-1) and urea (300 mg L-1). The hydrophilic properties of the sachets favored contact with the external environment, aiding water permeation and the release of potassium chloride. "The resulting sachets could minimize losses in fertilizer application, as well as control the amount of nutrient that would be in contact with the soil," the authors state.

Solubility and cytotoxicity tests of copper zeolite were also performed to determine its properties and potential interaction with the environment after the sachets were released. The results of the cytotoxicity tests, conducted on watercress root growth, suggest 92% germination viability in plant development after one hour of exposure to the zeolite, indicating its potential for agricultural use. To verify copper availability, solubility tests were performed in water (neutral pH) and citric acid. The desorption efficiency (the process by which a substance is released from the mass or surface of another substance) of copper increases in an acidic medium, with an increase from 5% to 45% of the expected total.

Costs and customization

According to Paris, current research is focused on finding ways to reduce the cost of processes and materials for the sustained release of fertilizers. “Starch is a promising raw material, although the addition of extra components can influence the final cost. In Malafatti's work, we don't use starch from other sources, such as waste, for example. It's a commercial starch,” says the researcher. “But for soil fertilization, it doesn't need to be a high-purity starch, like that used in the food industry. So, the goal is to try to reduce the cost as much as possible so that the agro-industry can incorporate it. Thus, the sachets have a greater potential to be effectively introduced into the market, contributing to the advancement of technologies in agriculture.”

Another advantage is that the added fertilizer does not affect the processing of the sachet in its formulation or shape. "Any granulated or particulate fertilizer can be inserted into the sachet, another positive point for incorporation by the industry," emphasizes Malafatti. Furthermore, the sachet avoids direct handling of fertilizers in particulate form by agricultural workers.

According to Paris, the technology is still in the laboratory stage. Immediate applications would be in landscaping, gardening, hydroponics, or greenhouses. For large-scale agricultural production, scalability optimizations and economic viability assessments are necessary, which are the next steps planned by the group.

Sciena points out that the packaging can be used for different crops. “Grapes have different needs than tomatoes, for example. It's a kind of customized fertilization, where you can adjust a mixture of desirable nutrients and also the type of sachet, one more acidic, to enhance the solubilization of poorly soluble fertilizer, and another less acidic, to slowly solubilize fertilizer that is already soluble,” she summarizes.

Further information at doi.org/10.1007/s10904-025-03655-1