Potassium-iron rice straw biochar composite for sorption of nitrate, phosphate, and ammonium ions in soil for timely and controlled release.

In this study, potassium-iron rice straw biochar composite (KRSB) was produced and compared with rice straw biochar (RSB) for the sorption of NO, PO, and NH in aqueous medium and soil column. RSB was produced by pyrolyzing rice straw at 400 and 600 °C in a slow pyrolysis unit. KRSB was produced through chemical and hydrothermal treatments of rice straw biochar produced at 400 and 600 °C. Batch experiment results indicate that the KRSB showed better sorption capacity for nitrate, phosphate, and ammonium ions compared to pristine RSB. The sorption isotherms of all three nutrients (NO, PO, and NH) were better-explained by the Langmuir-Freundlich isotherm model. The column leaching experiment showed that the KRSB loaded soil reached maximum sorption capacity for PO and NO within six and eight days, respectively but, it showed poor sorption capacity for NH. The soil fertility index in the 400 and 600 KRSB amended soils were significantly increased by 50.68 and 52.85%, respectively compared to the control. Results indicated that KRSB could be utilized in the soil in two ways: first, to keep the nutrients attached to its surface and second, to release the nutrients in a phased and timely manner to increase their availability for plants.