Can the sequestered carbon in agricultural soil be maintained with changes in management, temperature and rainfall? A sensitivity assessment

• Rapid carbon (C) loss if halting the practices that benefit C sequestration
• The higher the C stock is, the higher the loss rate is.
• Given a C stock, higher loss rate under higher rainfall and temperature
• Rapid loss of sequestered C under global warming
• The fate of sequestered C under rainfall change depends on background climate.

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 0.14 Mg C ha− 1 yr− 1 when residue retention was halfed. Removing all residues doubled the rate of C loss (i.e., 0.28 Mg C ha− 1 yr− 1). Reducing the application rate by half of the optimal N rate or to zero led to C loss of 0.089 and 0.27 Mg C ha− 1 yr− 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.