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 (NO3-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 NO3-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.
