Simulating Soil Carbon Responses to Cropping Intensity, Tillage, and Climate Change.

The semiarid dryland region in the Pacific Northwest could be a potential sink for carbon dioxide (CO₂) after decades of conventional tillage (CT) winter wheat (Triticum aestivum L.)–fallow rotation systems and soil organic carbon (SOC) depletion. We used CQESTR, a process-based C model, and data from five cropping systems to simulate SOC dynamics in the top 1-m soil from 2004 to 2012 and predict the best dryland cropping systems to increase SOC in cropping systems that included winter wheat and sorghum-sudan (Sorghum sudanese L.), and CT, sweep tillage (ST), or no-tillage (NT), through 2054. Geo-referenced soil cores were collected in 2004, 2008 and 2012. The potential effects of climate change on SOC were examined using CQESTR and climate projections for eastern Oregon from GCMs. Measured SOC increased in the following order: wheat–wheat rotation under NT (62%) > wheat–fallow under ST (55%) > wheat–wheat–sorghum under NT (51%) compared to wheat–fallow under CT. Simulation results confirmed that intensifying cropping under NT is the best agriculture management practice to increase SOC and reduce CO₂ emissions through 2054. Increasing the duration of crop coverage through continuous cropping to reduce fallow period and conversion from CT to NT or ST cropping systems would increase SOC and enhance crop production through improved soil health despite climate change.