Characterization of Magnetic Rice Straw Biochar Intercalated with Urea Fertilizer: Effects on Soil Nitrogen Dynamics and Rice Production Under a Water-Logged Condition

The study characterized rice straw biochar and its magnetic derivative, both intercalated with and without urea, and evaluated their effects on soil nitrogen release, rice growth, and yield. Rice straw and magnetic rice straw were subjected to pyrolysis at 450°C to produce biochar, and further treated with urea. The resulting biochars were chemically and structurally analyzed. Treatments included rice straw biochar (RB1) and magnetic rice straw biochar (MRB1) at 30 t ha−1 each, biochar combined with urea at 80 kg N ha−1 (RB2 and MRB2), biochar intercalated with urea at 40, 60 and 80 kg N ha−1 (URB1–3 and UMRB1–3), sole urea at 80 kg N ha−1 and control. Gleysol collected from a research site at the Obafemi Awolowo University was analyzed for routine properties, amended according to treatments and planted to rice, with growth and yield parameters monitored. The FTIR spectra of UMRB revealed sharp peaks of amine and N/O-alkyl functional groups, strong Fe-O peaks, and the presence of aliphatic and carboxylic compounds, suggesting higher adsorptive capacity for cations and a greater ability to reduce nitrate conversion to N2O. After 30 days, UMRB treatments exhibited higher concentrations of both ammonium and nitrate compared to other treatments. The plant number of panicles, tiller length, dry matter, and grain yield significantly increased with UMRB application, particularly with urea at 40 kg N ha−1. Overall, the study suggests that urea-intercalated magnetic rice straw biochar holds potentials as a slow-release nitrogen fertilizer, enhancing rice growth and yield in water-logged rice cultivation.