Biochar influences soil carbon pools and facilitates interactions with soil: A field investigation

Biochar promotes the storage of organic carbon (OC) in soils. OC is unevenly distributed in soils among different particle-size fractions showing different structures, functions, and stability. The objective of this study was to investigate the biochar–soil interactions and the redistribution of soil C in different soil fractions based on a 2-year field experiment. Fractionation was done by particle sizes including coarse sand (250–2,000 μm), fine sand (53–250 μm), and silt/clay (<53 μm). Integrated spectroscopic techniques were employed to examine physical characteristics of biochar–soil interactions in different soil fractions. Application of biochar increased OC by 37%, 42%, and 76% in soil particle-size fractions of 53–250, <53, and 250–2,000 μm, respectively. This was supported by X-ray fluorescence spectroscopy analysis, which showed an increase of C contents by 5–56% with biochar addition. The highest increment in OC was found in coarse sand fraction, and redistribution of OC was detected depending on various soil particle sizes. Results of scanning electron microscopy combined with electron dispersive X-ray spectroscopy analysis showed the interactions between soil and biochar, which could be attributed to oxidized functional groups (OCO, CO, and CO) captured by the X-ray photoelectron spectroscopy. The long-term aged biochar could be beneficial to enhance soil quality by promoting OC storage and facilitating positive biochar–soil interactions.