Impact of biochar water extract addition on soil organic carbon mineralization and C fractions in different tillage systems

The role of biochar has been identified in soil organic carbon (SOC) mineralization, but the role of dissolved organic carbon (DOC) derived from biochar water extract (BE) is not well recognized. Therefore, rotary tillage (RT) and no-tillage (NT) with two moisturizers treatments; BE and distilled water (WA) were used to study the influence of DOC (through BE) on SOC mineralization and C fractions. Four soil sampling depths (0–10, 10–20, 20–30, 30–50 cm) were used for laboratory incubation. The results showed a significant increase in cumulative CO2-C emissions in upper soil that decreased with increase in soil depth. BE increased cumulative CO2-C emissions about 50% and 46% (0–10 cm), 45% and 26% (10–20 cm), 42% and 55% (20–30 cm), 16% and 43% (30–50 cm) than WA in NT and RT, respectively. Moreover, NT had 13% more cumulative CO2-C emissions than RT at 0–10 cm, but RT had 10% and 38% higher cumulative CO2-C emissions than NT at 10–20 and 20–30 cm soil depths, respectively. BE increased microbial quotient (Mq) almost 47%, 70%, 24% and 167% at 0–10, 10–20, 20–30 and 30–50 cm soil depths, respectively. Increase in Mq significantly decreased SOC and some carbon fractions. Notably, BE did not modify DOC in whole soil profile under both tillage systems. BE had significant higher MBC at 30–50 cm soil depth than WA in both tillage systems. RT had significant higher (4%) MBC than NT at 20–30 cm soil depth. Overall, addition of DOC from BE in soil enhances C mineralization by modifying Mq.