CQESTR‐Simulated Response of Soil Organic Carbon to Management, Yield, and Climate Change in the Northern Great Plains Region

Traditional dryland crop management includes fallow and intensive tillage, which have reduced soil organic carbon (SOC) over the past century, raising concerns regarding soil health and sustainability. The objectives of this study were: (i) to use CQESTR, a process‐based C model, to simulate SOC dynamics from 2006 to 2011 and to predict relative SOC trends in cropping sequences that included barley ( Hordeum vulgare L.), pea ( Pisum sativum L.), and fallow under conventional tillage or no‐till, and N fertilization rates through 2045; and (ii) to identify best dryland cropping systems to increase SOC and reduce CO 2 emissions under projected climate change in eastern Montana. Cropping sequences were conventional‐till barley–fallow (CTB‐F), no‐till barley–fallow (NTB‐F), no‐till continuous barley (NTCB), and no‐till barley–pea (NTB‐P), with 0 and 80 kg N ha −1 applied to barley. Under current crop production, climatic conditions, and averaged N rates, SOC at the 0‐ to 10‐cm depth was predicted to increase by 1.74, 1.79, 2.96, and 4.57 Mg C ha −1 by 2045 for CTB‐F, NTB‐F, NTB‐P, and NTCB, respectively. When projected climate change and the current positive US barley yield trend were accounted for in the simulations, SOC accretion was projected to increase by 0.69 to 0.92 Mg C ha −1 and 0.41 to 0.47 Mg C ha −1 , respectively. According to the model simulations, adoption of NT, elimination of fallow years, and N fertilizer management will likely have the greatest impact on SOC stocks in the top soil as of 2045 in the Northern Great Plains. Core Ideas Estimates of management impact on SOC are needed for the Northern Great Plains region. CQESTR simulated measured SOC well, even with high temporal and spatial variability. Continuous cropping and anticipated climate change increased SOC stocks through 2045. Maintaining barley yield was predicted to reverse the trend in SOC loss through 2045.