Revealing the release mechanism of a biochar-based controlled-release nitrogen fertilizer using experimental and modeling approaches

Abstract Controlled-release nitrogen fertilizers (CRNFs) demonstrate a promising solution to enhance nitrogen use efficiency and reduce nitrogen losses for sustainable crop production. However, there are still knowledge gaps in understanding the mechanism of controllable nitrogen release, limiting the optimization of CRNF production and application. This study focused on revealing the nitrogen release mechanism in water of an effective biochar-based controlled-release nitrogen fertilizer (BCRNF) coated with ethylcellulose and epoxidized soybean oil. Experimental and modeling approaches were used to investigate the N release in water for coated and uncoated BCRNF samples. The influences of coating thickness, surface morphology, and particle size on the N release of BCRNFs in water were analyzed. A multidiffusion mechanism model was also employed to simulate the N release process. The results indicated that the modeling predictions were validated against the experimental data. The effective diffusivity (De) obtained from the simulations decreased with increasing coating thickness, with the values of 1.11 × $${10}^{-10}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:math> , 2.76 × $${10}^{-14}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> </mml:msup> </mml:math> , 4.79 × $${10}^{-14}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> </mml:msup> </mml:math> , and $$2.82\times {10}^{-13}{\text{m}}^{2} {\text{s}}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2.82</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>13</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mtext>m</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> <mml:msup> <mml:mrow> <mml:mtext>s</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> for the uncoated and coated BCRNFs at 7%, 5%, and 3%, respectively. The coated BCRNFs demonstrated controllable N release for nutrient management compared to uncoated BCRNF samples. The findings provide valuable insights for optimizing the BCRNF fabrication and application in the future. Graphical abstract