Temperature sensitivity of soil organic carbon decomposition as affected by long-term fertilization under a soybean based cropping system in a sub-tropical Alfisol

Understanding temperature sensitivity of soil organic carbon (SOC) decomposition from bulk soils and aggregates of long-term fertilized plots is imperative to forecast soil C dynamics. We evaluated the impacts of 43 years of fertilization under a soybean (Glycine max) based cropping system on temperature sensitivity of SOC decomposition (Q10) in an Alfisol. Treatments were: no mineral fertilizer or manure (control), 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), NPK + lime at 0.4 Mg ha−1 (NPK + L), 150% recommended NPK (150% NPK), and NPK + farmyard manure (FYM) at 10 Mg ha−1 (NPK + FYM). Bulk soils as well as macro- and micro-aggregates were incubated for 24 days at 25 °C and 35 °C. Cumulative SOC mineralization (Ct) in the 0-15 cm soil layer of bulk soils with NPK + FYM and NPK treated plots were similar but significantly higher than unfertilized control plots. However, both Ct and Q10 values in the NPK + FYM plots were higher than NPK in the 15-30 cm soil layer. In the 0-15 cm soil layer, NPK + FYM plots had ∼10 and 26% greater Q10 values of macro- and microaggregates than NPK. Activation energies required for bulk soils C mineralization was ∼2 and 3 times higher in NPK + FYM and NPK + L plots, respectively, compared with unfertilized control plots in that layer. Lime along with NPK application increased the activation energy of SOC decomposition. Thus, long-term NPK + FYM and NPK + L applications have great potential for less proportional SOC decomposition than NPK or unfertilized control plots under a temperature rise in these acid soils. However, NPK + FYM management practice is recommended as it has highest SOC accumulation and can have less SOC losses under a temperature rise.