Synthesis of biochar‐embedded slow‐release nitrogen fertilizers: Mesocosm and field scale evaluation for nitrogen use efficiency, growth and rice yield

Abstract Increasing consideration is being paid to sustainable slow‐release fertilizers (SRFs). Biochar is a novel carbon material, and gaining momentum as a natural carrier for sustainable nutrient application and release and improved soil health. Accordingly, a recent biochar‐embedded slow‐release nitrogen (N) fertilizer has been prepared using acacia biochar, urea, ammonium chloride, starch and organic acid. This and other biochar‐embedded slow‐release N fertilizers (BSRNFs) were characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and scanning electron microscope (SEM). BSRNFs were tested in the laboratory and field experiments for their N release pattern, nitrate (NO 3 ‐N) leaching loss, N use efficiency (NUE) and growth and yield of rice crops. Among the BSRNFs tested, the one with 75% urea‐N (BSRNF‐U75) released 109 mg kg −1 of N in an incubation study and the least NO 3 ‐N leaching losses of 8.8, 14.6 and 26.4 mg kg −1 at 10, 20 and 30 cm depth in a column study, respectively, compared with conventional urea. Application of biochar‐embedded slow‐release N fertilizer 100% urea‐N (BSRNF‐U100) augmented plant growth to increase grain yield (6610 kg ha −1 ), straw yield (9612 kg ha −1 ) and NUE (12%) in rice.