Organic carbon mineralization and sequestration as affected by Zn availability in a calcareous loamy clay soil amended with wheat straw: a short-term case study

Increasing soil organic carbon (SOC) is a widely accepted strategy to offset greenhouse gases and improve soil quality. Straw return can modify SOC dynamics and increase its stock, which are also influenced by soil clay content and metals (i.e. Zn) availability. We conducted a short-term (42 d) incubation study to evaluate SOC dynamics in a calcareous loamy clay soil where available Zn (DTPA extractable) was modified by adding high-Zn straw (HZ-St), low-Zn straw alone (LZ-St) or combined with Zn fertilizer (LZ-St+ZF). Results showed that the DTPA-Zn concentration in soil with LZ-St was similar to the control receiving no straw return or Zn, but it increased by 24.3% in the soil receiving HZ-St and 1.46-fold in the soil receiving LZ-St+ZF. The increased Zn availability enhanced microbial biomass C and N, but did not increase SOC mineralization due to the higher microbial entropy and lower respiration entropy. Greater Zn availability enhanced SOC sequestration probably by promoting the organo-Zn-mineral interactions and thus chemical stabilization. Therefore, adding HZ-St or LZ-St+ZF increases both Zn availability and SOC sequestration in calcareous loamy clay soil. However, long-term and field-based research is necessary to confirm the practical effects of this approach.