DEVELOPMENT OF DUAL PURPOSE BIO-BASED POLYMER COATED UREA FERTILIZER: CONTROLLED NITROGEN RELEASE AND TAILORED ZINC SUPPLY

Abstract

The increasing population has led to a rise in global food demand, which has put immense pressure on the agricultural soils to boost crop yield. This has urged farmers to resort to the utilization of excessive amounts of urea fertilizer to match the demand. However, highly volatile and soluble nature of urea has resulted in various forms of environmental pollution, leading to low Nitrogen use Efficiency (NUE). Moreover, Zn deficiency in soil has also emerged as a growing concern, causing low crop productivity and nutritional value which eventually translates to Zn malnutrition in humans. This study aimed to address both the issues by developing a Zn fortified, controlled release urea fertilizer. A dual-coated urea was formulated featuring an inner coat of bio-based polyurethane and an outer coat of ZnO loaded mesoporous nanosilica particles (MSN@ZnO) embedded in a hydrogel matrix. FTIR, XRD, BET and SEM-EDX were employed to ensure successful synthesis of MSN and MSN@ZnO. Then to assess and optimize the N release of the bio-polyurethane coated urea (BPCU) and dual-coated urea (DCU), water and sand column release tests were performed. The results of Total Kjeldahl Nitrogen (TKN) revealed that coating urea, with both the layers decreased its nitrogen release. In water release tests, BPCU and DCU gave a cumulative N release of 71% and 68% respectively on day 28 and in sand column release tests BPCU and DCU gave a release of 73% and 68% respectively on day 28. This indicated viability of the coatings. Then to test for Zn release from DCU, Atomic Absorption Spectroscopy (AAS) was performed, the results of which demonstrated a burst release of Zn in water, whereas, in sand a prolonged micronutrient release profile was observed, extending up to 7 days. Hence, this study demonstrated a viable solution to combat two of the most concerning issues related to agriculture. For prospects, it is recommended to study the biodegradability of the coatings done and to assess the release of N and Zn from coated urea fertilizer in real-world environment.