Corn Straw Biochar Increased Labile Organic Carbon Fractions in Mollisols by Driving the Improvement of Soil Physical Properties and Aggregates Stability

ABSTRACT Labile organic carbon (LOC) is an important index reflecting soil health, soil organic carbon (SOC) changes and soil productivity. Nevertheless, there are limited studies about the effects of corn straw biochar (CSB) on LOC. Herein, we established an experiment at Mollisols region in northeast China to investigate CSB effects on SOC and LOC fractions of soils and aggregates in different soil layers and periods. The 30 t ha −1 CSB greatly enhanced water content, porosity, the percentages of > 2 and 2–0.25 mm aggregates, and aggregate stability, reduced bulk density, specific gravity and the percentages of 0.25–0.053 mm and < 0.053 mm aggregates. Also, it up‐regulated the contents of SOC, hot water extracted organic carbon (HWC), acid hydrolyzed organic carbon (AHCI and AHCII), and easily oxidised organic carbon (ROC), as well as dissolved organic carbon (DOC) of the 20–40 cm soil layer, of which its contents of HWC, AHCI, AHCII and ROC of > 2 mm aggregates increased by 17%, 31%, 39% and 39%, respectively. SOC and LOC fractions were mainly influenced by water content and porosity. The proportions of HWC and AHCI to SOC and 2–0.25 mm aggregate contribution rate were the highest. Taken together, applying 30 t ha −1 CSB optimally induced the improvement of Mollisols quality by improving physical properties and promoting the percentage and stability of large aggregates to increase SOC and LOC pools.