Evaluation of the protective effects and mechanism of biochar on nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP)

Employing nitrification inhibitors represents an effective approach to enhance nitrogen (N) fertilizer use efficiency. However, the short-persistence nature of these inhibitors, which cannot continuously regulate N conversion and reduce losses throughout the crop growth period, remains a critical issue that requires urgent resolution. In this study, we prepared ash-removed biochar (RBC) from corn straw at pyrolysis temperatures of 300 °C, 500 °C, and 700 °C (RBC300, RBC500, and RBC700, respectively) and used as an adsorbent for the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), aiming to protect and extend its effective action time. Through adsorption and degradation experiments, we investigated the interfacial interactions and specific adsorption mechanisms between biochar and DMPP. Adsorption experiments revealed that biochar exhibited dose-dependent adsorption capacities for DMPP (maximum: 162.73 mg kg^-1 for RBC300), with the experimental data fitting well to the Langmuir isotherm and the pseudo-second-order kinetic model. The adsorption process was dominated by interactions with chemical functional groups, followed by free diffusion and electrostatic adsorption. Among the tested biochars, RBC300 exhibited the highest adsorption and desorption capacities for DMPP, with values of 162.73 and 20.56 mg kg^-1, respectively. Degradation experiments suggested that the combined application of ash-removed biochar and DMPP extended the degradation period by 7-21 days, indicating that biochar could protect DMPP and act as a slow-release agent. Overall, these results offer a novel method for the efficient utilization of inhibitors. This approach has the potential to enhance N use efficiency in agricultural production systems, and provides a mechanistic basis for optimizing biochar-DMPP formulations, pending field validation of crop N uptake and yield impacts in fields.