Biopolymer Urea Composite for Enhancing Nitrogen Use Efficiency in Coastal Sandy Soils of Kerala, India

Aim: To formulate biopolymer urea composites in pellet form and to test their efficacy on the release and leaching of nitrogen in northern coastal sandy soils of Kerala. Place and Duration of Study: Department of Agronomy, College of Agriculture, Padannakkad, Kasaragod, Kerala agricultural University, between May 2023 and March 2024. Methodology: Pellets of biopolymer urea composites (BUCs) were formulated by mixing prilled urea with coconut shell charcoal (C1), gypsum (C2), rice husk biochar (C3), and zeolite (C4) as coating materials and potato starch (S1) and tapioca starch (S2) as binding materials. The experiment was laid out in a Factorial Completely Randomised Design. Castor oil was uniformly sprayed on the composites after formulation. These composites were tested against urea for their nitrogen content and pH. Release behavior of nitrogen in soil and distilled water and leaching behavior in the soil were studied using CRD as the experimental design. The treatments were: T1: Urea, T2: BUC 1, T3: BUC 2, T4: BUC 3, T5: BUC 4, T6: BUC 5, T7: BUC 6, T8: BUC 7, T9: BUC 8 and T10: Control (Soil). Results: Total nitrogen content was not significantly varied across different treatments, but the increase in pH was significant for the treatment, C4. Release of nitrogen in distilled water revealed marked differences among the treatments. Urea exhibited significantly elevated nitrogen release on first day compared to other treatments, whereas T9 and T4 initially showed substantially lower values, which gradually increased, reaching significantly higher levels by day 30. The soil incubation study demonstrated that urea exhibited significantly higher values of ammoniacal and nitrate nitrogen release on the 7th day, reaching their maximum on 14th day and then decreased gradually till 30 days. All other treatments showed significantly lower release of ammonia into the soil, followed by a gradual increase, reaching a maximum at 90 days. Leaching of ammoniacal and nitrate nitrogen was maximum for T1 on day 8. Significantly lower nitrate nitrogen leaching values were recorded by T9 towards the end of the experiment. Conclusion: T9 showed initial release of nitrogen at significantly lower rates. Furthermore, it had a significantly higher pH compared to other treatments, rendering its suitability for acidic soil.