Controlling Nutrient Leaching Profile of Urea Granules through Structural Modification

Highlights Effect of granule microstructure, formulation design on nutrient leaching was investigated. Reduction in nutrient leaching was observed in denser core granules with binder compared to low density granules. The power-law model overpredicted the inorganic dissolved nitrogen content. Abstract. Ammonium and nitrate are byproducts of urea fertilizer hydrolysis in soil. Ammonium is highly unstable and can volatilize in the form of ammonia, a greenhouse gas. Meanwhile, nitrate is highly hydrophilic and can contaminate surface and groundwater systems. This study investigated the influence of a biopolymer binder (a mixture of xanthan and konjac gums) and granule microstructure on urea dissolution and hydrolysis in soil to improve fertilizer release rates. The study compared urea leaching profiles in disturbed soil columns for dry (uniaxial compression), layered wet granulated, and market urea granules. A power-law model of total dissolved nitrogen versus cumulative volume ensured robust estimation of the release rate constants. There was 50% and 20% less total dissolved nitrogen, respectively, for binder-added core (CB) granules produced from the uniaxial compression method and bilayer binder-added (bLB) granules compared with market urea samples (NU). However, no significant reduction in dissolved ammonium and nitrate was observed based on formulation and process changes using a power-law model. However, it is noteworthy that the power-law model overpredicted the initial leaching profiles of binder-added core (CB) and bilayer binder-added (bLB) samples. In conclusion, the microstructure of the core granules compacted at 100 MPa and binder-formulated (CB) granules can delay urea dissolution and suggests a partial reduction of urea hydrolysis in soil. Keywords: Biopolymer binder, Disturbed soil columns, Granule microstructure design, Nitrate leaching control.