The use of nitrogen-based fertilizers continues to accelerate with human population growth and increases in global food requirements. Despite the success of fertilizers in increasing crop yields, only a minor fraction of applied fertilizer is taken up by plants, in part due to asynchronies between fertilizer application and crop nutrient demand. This has led to over-fertilization and increased soil nitrogen leaching from agricultural fields. Enhanced efficiency fertilizers (EEFs) have been developed to improve the synchronization between nutrient supply and crop nutrient demand. However, despite reducing the amount of nutrient leaching, many of the current controlled release fertilizers are coated with non-biocompatible materials that degrade in response to temperature and moisture content. We developed a redefined class of triggerable biodegradable polymers (poly(ethyl glyoxylate) or PEtG) that go through end-end depolymerization after the protective end cap on the polymer is cleaved off by a specific stimulus. Once degraded, these polymers form by-products that are innocuous to the surrounding environment. Using PEtG, we developed a fertilizer coating that degrades in response to a specific plant-root stimulus (pH), to improve the controlled and targeted release of nitrogen-based fertilizers. Urea pellets were encapsulated by both solvent spraying (dichloromethane), and melt pressing (at 60°C) of PEtG.
Results/Conclusions
We successfully used PEtG to develop a protective coating for urea pellets. The PEtG coatings were sensitive to low pH values (approximately 5) that corresponded to the root zone acidification of the rhizosphere, as demonstrated using the test species Agrostis stolonifera (creeping bentgrass) in agar (pH 7) using bromocresol purple for visualization. The characterization of the PEtG films via mass loss profiles while in the presence of both chemical and plant root stimuli revealed accelerated degradation at pH 5 and at elevated temperatures (30°C). These films displayed initial mass of 30-50% within the first 25 days at 30°C and within 40 days at 22°C for both chemical (pH 5 citric acid buffer) and plant root stimuli. Urea release trials also demonstrated that the release rate depended on pH, as well as coating thickness and temperature; 50% release was achieved within 15-25 days at elevated temperatures (30°C) in pH 5 citric acid buffer solution. Our results suggest that there is a potential for PEtG to be used at a commercial scale for the design and development of controlled release fertilizer because of its rapid and precise degradation, as well as its innocuous by-products.