Influence of pyrolysis conditions on nitrogen speciation in a biochar ‘preparation-application’ process

Abstract

To investigate biochar nitrogen conversion in a ‘preparation-application’ system and the response of its transportation in plants, biochar samples were produced from rice straw at different pyrolysis temperatures (400 °C and 800 °C) and atmospheres (N2 and CO2). Subsequently, biochar was synthesized under CO2 atmosphere to explore its nitrogen nutrient characteristics and further improve the chemical and physical properties of soil. Nitrogen speciation of the biochar and plant root samples were evaluated by X-ray photoelectron spectroscopy. Research has shown that organic nitrogen such as protein-N, free amino acid-N, and alkaloid-N in rice straw is converted into organic (nitrile-N, pyridine-N, amino-N, and pyrrole-N) and inorganic (NH4+-N, NO2−-N, and NO3−-N) species in biochar during the biomass pyrolysis process. In turn, biochar nitrogen is transported to plants as protein-N, free amino acid-N, alkaloid-N, NH4+-N, NO2−-N, and NO3−-N. Comprehensive consideration of the biochar quality and preparation cost indicated the lower pyrolysis temperature (400 °C) under CO2 atmosphere as the best conditions for biochar preparation.