Formulating new types of rice husk biochar-based fertilizers for the simultaneous slow-release of nutrients and immobilization of cadmium

China, as a significant global consumer of chemical fertilizers and a leading producer of rice, faces challenges associated with low fertilizer efficiency and fewer utilization options of rice husks. The development of rice husk biochar-based fertilizers (RHBF) offers a strategic solution to address these issues. In this study, diverse biochar fertilizer production techniques were used to develop four types of fertilizers: blended RHBF, soaked RHBF, high-pressure soaked RHBF, and pure rice husk biochar coated fertilizer. The nutrients slow-releasing performance of these four RHBF were compared by hydrostatic and soil column intermittent leaching methods. Effects of their application on rice growth, yield, and cadmium reduction potential were analyzed and compared by the pot trial. Results demonstrated that nutrients of the four RHBF were generally released slower in the soil compared with the conventional compound fertilizer (CK). The slow nutrient release effect was more pronounced under high-pressure soaked RHBF. Notably, in the soil column leaching experiment, the cumulative leaching rates of nitrogen and K₂O for RHBF3 (12.0% and 13.9%) were greatly lower than those of CK (42.3% and 51.3%). Moreover, the application of RHBF induced a marked enhancement in the nutrient use efficiency, grain yield, harvest index, and photosynthetic characteristics compared to CK. The average agronomic efficiency of P₂O₅ for the four RHBF increased by 102.8% compared with CK, while the average grain yield of the four RHBF increased by 20.6%. In addition, RHBF showed a significant reduction in Cd mobilization by an average of 80.1% compared to CK. This study offers a promising model for enhancing the comprehensive performance of RHBF and optimizing traditional fertilizer application practices.