Temperature sensitivity of organic carbon mineralization in composted sludge amended soil: results from four Q ₁₀ estimation approaches

Composted sewage sludge (CSS) can rehabilitate degraded land by enhancing soil fertility and organic carbon (SOC). However, the temperature sensitivity (Q10) of SOC mineralization in sludge-amended soils remains poorly understood. Degraded grassland soil samples amended with 0–20% composted sewage sludge (CK to M20) at 25–35°C for 35-days. The ‘equal time’, ‘equal-C’, ‘one C pool model’ and ‘two C pool model’ approaches evaluated the Q10 of SOC mineralization. Chemical properties and enzyme activities were analyzed to identify key factors influencing Q10 values of SOC mineralization. SOC, total nitrogen and phosphorus increased with sludge dose, while the C:N ratio decreased. Soil enzyme activities increased then decreased with increasing sludge rates, peaking at M5 to M15 treatment. Cumulative mineralized carbon rose with both sludge dose and temperature. Different models yielded contrasting Q10 patterns. The ‘equal time’ and ‘equal-C’ methods showed decreased Q10 with sludge addition, whereas the ‘one C pool’ and ‘two C pool’ models showed an initial increase followed by a decrease. Random forest analysis indicated that SOC, TN and TP contents were primary contributors to Q10 variations. These findings indicate that CSS alters the Q10 of SOC mineralization, with nutrient status being a more significant factor than enzyme activity.