Differences in plant availability of phosphorus and potassium in pelletized and granulated biochar for an Andisol

Abstract Biochar will be broken into tiny pieces for processes of production, transportation, and application, which causes dust emissions for those processes. Particulate matter (PM) released from biochar may have negative effects on human health and increase the atmospheric burden of shortwave absorbing black carbon aerosols. Pelletizing feedstock before the thermochemical conversion is expected to reduce the emission of PM in the processing and post-processing phases. Effects of application of pelletized biochar, produced from broiler manure at different pyrolysis temperatures, into an Andisol on soil physicochemical properties and crop yields have been investigated in this study. Effects of pelletizing and pyrolysis temperatures (400, 600, and 800 °C) on dissolution properties and soil physicochemical properties were completely different between phosphorus and potassium. Pelletized broiler manure–derived biochar can be used as fast-release potassium fertilizer regardless of pyrolysis temperatures. In contrast, the extraction pattern of phosphorus contained in the biochar significantly differed by pelletizing and pyrolysis temperatures. Plant dry yields and phosphorus uptakes in soils amended with granulated broiler manure-derived biochar were significantly higher than those in soils amended with pelletized broiler manure-derived biochar (e.g., 3.4 times larger in 800 °C). This result suggests that the breakdown of pelletized biochar into granulated biochar could improve interaction between phosphorus contained in biochar and roots. Pelletized biochar will be transformed into granulated biochar through the freeze–thaw cycle, dry–wet cycle, and rotary tillage over the long term. Therefore, pelletized biochar derived from broiler manure at higher pyrolysis temperatures can be novel phosphorus-supplying amendments over the long term. Graphical abstract