| Summary: | Carbon (C) sequestration in agricultural soil has the potential to mitigate climate change and help sustain soil productivity. Continual nutrient input and residue retention are needed to attain the C sequestration potential and to maintain the sequestered C. However, few studies have assessed the vulnerability of the sequestered soil C to changes in agricultural management and climate. Here we applied the Agricultural Production Systems sIMulator (APSIM) to simulate the soil C dynamics to equilibrium under optimal management with 100% residue retention and no nitrogen (N) deficiency at 613 sites across the Australian croplands. We examined the response of sequestered soil C to potential warming and rainfall change, under these optimal practices and under suboptimal management with reduced residue retention and/or N input. On average, soil C was lost at rate of 0.14MgCha-1yr-1 when residue retention was halfed. Removing all residues doubled the rate of C loss (i.e., 0.28MgCha-1yr-1). Reducing the application rate by half of the optimal N rate or to zero led to C loss of 0.089 and 0.27MgCha-1yr-1, respectively. Multivariate linear regression analysis indicated that C loss rate increased with active C stock (non-inert C) in the sequestered C. Given an active C stock, the loss rate increased with increasing temperature and/or rainfall. Future warming was estimated to increase soil C loss, especially in cooler and/or wetter regions. The effect of potential rainfall change was relatively moderate and depended on the direction (increase or decrease) of rainfall change. Management strategies for effective C sequestration in agroecosystems should and can be developed based on local climatic conditions and soil-specific amount of active organic C.
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