Sustainable Coated Fertilisers: A Win-Win Scenario for Manufacturers, Farmers, and the Environment

05 July 2022 by Baobao Pan

Written by Omid Mazaheri, edited by Dante Romeo and Omid Mazaheri.

The expanding global population is hungry! Nitrogen (N) fertilisers (urea is the most used) offer an effective method of improving food availability but their use is not without issue. Soil nitrogen is easily dissolved in the water allowing it to drain (leach) from the soil. Leached nitrogen is unavailable for plant use and pollutes water sources leading to environmental catastrophes such as tainted drinking water, toxic algal blooms, and fish kills. The nitrogen cycle can also produce ammonia and nitrous oxide gases exacerbating air pollution, depleting the ozone layer, and promoting acid rain. Ultimately, 50% to 80% of the nitrogen applied to crops is lost.

Over the last 30 years, controlled-release fertilisers have been developed. These minimise negative environmental and economic effects by making nitrogen available when plants need it most, reducing fertiliser use and time required for application. Usually, controlled-release fertilisers are manufactured using synthetic, non-biodegradable materials which tend to be uneconomical for agricultural use. Research efforts have therefore shifted towards low-cost, easily fabricable, and environmentally friendly fertiliser coatings.

Polyphenols, a common group of compounds found in most plants, present an opportunity for improving controlled-release fertilisers. Known for antibacterial, anticarcinogenic, and antioxidant properties, polyphenols also have adhesive qualities. Additionally, when mixed with metal ions, polyphenols can form Metal-Phenolic Networks (MPNs). While MPNs have previously been used for a variety of purposes, they have rarely been used to coat water-soluble products (such as urea). Such an application lends them to use in fertiliser development. Our research aimed to create a methodology for coating water-soluble materials using MPNs to create environmentally ‘green’ urea coatings.

To achieve this aim, a multi-disciplinary team of chemists, chemical engineers, and agronomists at the University of Melbourne collaborated to implement MPNs in controlled-release fertilisers for the first time ever. In our experiments, urea granules were coated via immersion in a solution of iron and tannic acid. Tannic acid is an inexpensive and environmentally friendly polyphenol. The MPN coating provides a physical barrier against water, controlling urea dissolution and release into soils. Through experimentation, we demonstrated coating performance was influenced by changing parameters such as the concentration and ratio of metal to polyphenol in the solution, the processing temperature, and the solution aging time.

Our simple fabrication method opens a new chapter for employing environmentally friendly materials in controlled-release fertilisers. The implementation of environmentally friendly materials is likely to be key in addressing some of the challenges facing agriculture as the industry moves towards a more sustainable and socially responsible future. More information can be found at the below link.

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