Determination of NH4+ and NO3- adsorption and desorption capacity of biochars produced at different pyrolysis temperatures and investigation of its effect on nitrogen leaching

In this study, the adsorption and desorption capacities of NH4+ and NO3-, as well as their effects on NH4+ and NO3- leaching in soil, were investigated for biochars derived from corn cob (CC) and rice husk (RH) biomass produced at different pyrolysis temperatures (300℃, 400℃, and 500℃). It was observed that with increasing pyrolysis temperatures, the carbon content of the biochars increased (up to 62.72%) while the nitrogen content decreased (down to 0.29%). The specific surface area and porosity of the biochars also increased with higher pyrolysis temperatures, which, in turn, improved the water retention capacities of the materials as well as their NH4+ and NO3- adsorption capacities. Among the biochars tested, CC biochar produced at 300℃ (CC300) exhibited the highest NH4+ adsorption capacity (88.67%), whereas RH biochar produced at 500℃ (RH500) showed the highest NO3- adsorption capacity (86.42%). Column experiments were conducted to determine the concentrations of NH4+ and NO3- in both soil and leachates. It was found that the application of biochars produced at different pyrolysis temperatures at 1% and 2% rates significantly enhanced NH4+ and NO3- retention in the soil, resulting in reduced leaching of these nutrients from the columns. The total NH4+ concentration leached from the control columns was 53.27 mg kg-1, whereas the application of CC biochar at 2% and 1% doses, produced at 300℃, reduced the total leached NH4+ concentrations by 98.76% and 88.49%, respectively. Similarly, biochar applications (especially at the 2% dose) caused significant reductions in the NO3- concentrations leached from the columns. While the total NO3- concentration leached from the control columns was 149.23 mg kg-1, the application of RH biochar at 2% doses reduced the total NO3- concentrations leached by 51%, 55%, and 51% for biochars produced at 300℃, 400℃, and 500℃, respectively. Among the pyrolysis temperatures, biochars produced at 500℃ were found to be more effective in preventing NH4+ and NO3- leaching compared to those produced at 300℃ and 400℃. In conclusion, biochars produced at different pyrolysis temperatures were found to have beneficial effects on improving agricultural soil and reducing nutrient leaching, making them a valuable material for promoting sustainable agriculture and providing environmental benefits.