Three‐Year Field Observation of Biochar‐Mediated Changes in Soil Organic Carbon and Microbial Activity

Although biochar is considered a promising C sequestration agent, long-term field experiments are lacking to assess the effects of biochar addition on the soil organic C (SOC) and microbial community. Corn ( L.) straw feedstock and biochar were applied to a sandy loam soil for three consecutive years to investigate the SOC distribution within various fractionations, responses of soil microbial biomass, enzyme activity, and community structure. In comparison with straw amendment, higher levels of biochar (6.0 and 12 t ha) significantly increased soil pH, SOC, total N (TN), available P (AP) and available K. Biochar (12 t ha) decreased the fulvic acid fraction by 15.9% and increased the free-light C (FLC), intra-aggregate, and organomineral fractionations by 6.05-, 2.52-, and 0.22-fold, respectively. There was no significant influence of straw or biochar application on the soil microbial biomass C (MBC) contents or the activities of soil enzymes. A phospholipid fatty acids assay suggested that 6.0 t ha straw slightly enriched the abundance of Actinobacteria in soil, whereas biochar (6.0 and 12 t ha) mainly promoted the growth of Gram-positive bacteria, fungi, and general bacteria groups. Canonical correspondence analysis indicated that soil pH, SOC, TN, AP, FLC, and fulvic acid significantly influence the structure of soil microbial community ( < -0.50, < 0.05 for both MBC and the ratio of MBC to SOC; > 0.50 for microbial biomass N, basal respiration [BR], and the ratio of BR through incubation to MBC). Established quantitative relationships provided evidence for understanding the effects of biochar amendment on soil environment after a long-term field application.