Researchers use cellulose to develop slow-release fertilizer and a self-fertilizing propagation pot

The first and third photos show the paper made from phosphorylated sugar cane cellulose. The second shows the 3D structure of the material consisting of cellulose and nutrient. The fourth shows the microparticles in powder form and after forming into tablets. Credit: Lucas Luiz Messa/Debora França

A research team associated with the Laboratory of Polymeric Materials and Biosorbents at the Federal University of São Carlos (UFSCar) in Araras, São Paulo State, Brazil, has produced and tested cellulosic-based materials for fertilizers with improved efficiency to improve nutrient delivery. to crops and to reduce the release of non-biodegradable chemicals into the ecosystem.

The studies were led by Roselena Faez, a professor at the Center for Agricultural Sciences (CCA-UFSCar). The findings were recently reported in two publications. One of these is an article published in Carbohydrate Polymers, with Débora França as the first author. Here the researchers describe how they used modified nanocellulose to slowly and controlled the nutrients in manure into the soil, since nitrogen, phosphorus and potassium are highly soluble.

“Potassium is quickly washed away by rain due to its high ion mobility. It is most difficult to release in a controlled manner. Nitrogen can be obtained from various sources such as nitrates, ammonia and urea, but plants get the nitrogen they need most easily from nitrate , which also washes away easily and does not remain in the soil for long [as phosphate] is a very large ion and less mobile than the other macronutrients,” said Faez, who coordinates the Polymeric Materials and Biosorbents Research Group at UFSCar Araras.

There are controlled release products on the market, she added, but most are made from synthetic polymers, which are not biodegradable. “Artificial grains are about the size of grains of coarse sea salt. To ensure that the nutrients are released slowly, they are covered with layers of polymer that last about two months each, so the manufacturer applies two, three or four layers, according to the desired controlled release time,” Faez explained, noting that the polymers in question are plastic and stay in the soil, eventually breaking down into microparticles that last almost forever.

The researchers at UFSCar developed a completely different product in which the chemical reaction between the modified nanocellulose and mineral salts keeps the nutrients in the soil. “We focused on the worst problems, namely nitrate and potassium. The material we developed is completely biodegradable and releases these nutrients about as slowly as the available synthetic materials,” Faez said.

The nanocellulose was obtained from pure cellulose donated by a paper mill. The nanofibrils were functionalized with positive and negative charges to enhance the polymer-nutrient interaction. “Since the salts also consist of positively or negatively charged particles and are highly soluble, we hypothesized that negatively charged nanocellulose would react with positive ions in the salts, while positively charged nanocellulose would interact with negative ions, increasing the solubility of the salts.” This turned out to be the case and the group managed to modulate nutrient release according to the type of particle in the material,” França said.

Evaluation in the soil

The group made the product in the form of tablets and evaluated its performance in terms of nutrient release into the soil. Evaluating the release to water is the usual method, and water is a very different system from soil. This part of the research was conducted in collaboration with Claudinei Fonseca Souza, a professor at CCA-UFSCar’s Department of Natural Resources and Environmental Protection in Araras.

“We evaluated the release of nutrients into the soil and the biodegradation of the material at the site over 100 days. But we purposely used very poor soil with little organic matter, as this allows us to minimize the physical effects of the release easier to see,” Faez said.

The researchers used two techniques to obtain tablets: nebulization and spray drying to encapsulate the nutrients with the nanocellulose, followed by heat processing the resulting powder, which was pressed into a mold. This work was completed with the help of colleagues from the Cellulose and Wood Materials Laboratory at EMPA (Swiss Federal Laboratories for Materials Science and Technology) and in collaboration with UFSCar’s Water, Soil and Environment Engineering Research Group, led by Souza. França carried out the cellulose modifications at EMPA during an internship there.

Self-fertilization

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The group’s second recent article was published in Industrial crops and products, with chemist Lucas Luiz Messa as first author. The aim of the study was to extract cellulose from sugarcane bagasse and modify it with a negative surface charge by phosphorylation (adding a phosphorus group) to allow for controlled release of potassium. In theory, plant nutrient delivery would be slowed by cellulose phosphorylation, which would create anionic surface charges that would bind to cations of macronutrients and micronutrients.

The group prepared three kinds of structure with the phosphorylated cellulose: oven-dried paper-like film; spray dried powder; and freeze-dried porous bulk similar to polystyrene foam. Freeze-drying or freeze-drying was found to leave nutrients in the voids left by the removal of water.

“Technically, the paper-like structure was the best material we’ve produced for controlled nutrient delivery. This paper can be used to make a variety of products,” Faez said.

The results of the research led by Messa enabled the group to develop small pots for growing seedlings. When this material breaks down, the phosphorus it contains is released. According to Faez, cellulose phosphorylation is inexpensive and the cost of the final product is relatively low. “It’s more or less BRL 0.27 per gram of paper produced. The propagation pot should be about 1 gram. So the unit cost is about BRL 0.30 in lab costs,” she says.

There are already biodegradable grow pots on the market. “But our product has built-in fertilizer, which is a great competitive advantage. We have indeed filed a patent application,” she said.

The pot is about to be tested by a flower producer in Holambra, São Paulo state. Several batches produced in the lab have been shipped there. Nutrient release has so far only been tested in water. “We call this an accelerated ion release assessment method because it is faster in water, but even in water we found the release rate to be 40%-50% slower compared to the behavior of the ion in the material and without the material. Even in water, therefore, we have managed to retain these ions. We assume that delivery into the substrate will be even slower,” she said.

Messa was assisted by a colleague from the University of California Davis (USA), where he worked as a research intern.


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More information:
Débora França et al, Charged Cellulose Nanofibrils as Nutrient Carrier in Biodegradable Fertilizer Polymers with Improved Efficiency, Carbohydrate polymers (2022). DOI: 10.116/j.carbpol.2022.119934

Lucas Luiz Messa et al, Sugarcane bagasse-derived phosphorylated cellulose as substrates for potassium release induced by phosphate surface and drying methods, Industrial crops and products (2022). DOI: 10.116/j.indcrop.2022.115350

Quote: Researchers use cellulose to develop slow-release fertilizer and self-fertilizing grow pot (2022, October 17) retrieved October 17, 2022 from https://phys.org/news/2022-10-cellulose-slow-release-fertilizer-self-fertilizing -propagation.html

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