Fertilizer coatings

Controlled release fertilizers represent a key technology to reduce greenhouse gas emissions and eutrophication of fresh water streams. Half or more of conventional fertilizers are not used by the plants but instead end up in the atmosphere or the ground water streams. This happens mainly because they dissolve very quickly in the soil after application and the plants do not consume it all in a short time window. Controlled release fertilizers have been developed to tackle this mismatch! As the name indicates, they release nutrients in a slower rate by controlling the rate at which they dissolve into the soil and become available to the plants. As the release can be designed per crop, it can be optimized to match the nutrient up-take rate of different plants. Overall, controlled release fertilizers have the potential to reduce in half or more the fertilizer use in the fields, and reduce even more emissions to atmosphere and water streams.

Coating fertilizers with polymers that allow a controlled water diffusion and release of fertilizer, are the most robust and controllable technologies for controlled release fertilizers. However, most of these coatings nowadays make use of non-biodegradable polymers, leaving behind microplastics in the soils. The EU has addressed this problem by banning the use on non-biodegradable polymers in fertilizers from 2026 onwards. North America is expected to follow soon with a similar ban.

Caleyda can be used to coat fertilizers while not leaving any microplastics in the soil. Due to its fully biodegradability in soil, it can be safely used, while its hydrophobicity offers the potential to control water diffusion. Preliminary tests have been performed revealing the potential of Caleyda use as fertilizer coating, confirming its barrier to water and the slow down of fertilizer solubilization in water. Besides the water permeability, the use of Caleyda offers a new possibility: controlling the life-time of the coating. As the coating biodegrades, the fertilizer release rate could change in time. This additional possibility of control offers new options for the controlled release fertilizers industry to improve further the match between fertilizer release and up-take rate by the plants.