Simulating soil organic carbon responses to cropping intensity, tillage, and climate change in Pacific Northwest dryland

Authors: Gollany, Hero; Polumsky, Robert - Wayne

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2018
Publication Date: 3/1/2018
Publication URL: https://handle.nal.usda.gov/10113/5935602
Citation: Gollany, H.T., Polumsky, R.W. 2018. Simulating soil organic carbon responses to cropping intensity, tillage, and climate change in Pacific Northwest dryland. Journal of Environmental Quality. 47:625-634. https://doi.org/10.2134/jeq2017.09.0374.
DOI: https://doi.org/10.2134/jeq2017.09.0374

Interpretive Summary: Managing dryland cropping systems to increase soil organic carbon (SOC) under changing climate is challenging after decades of SOC depletion from winter wheat-fallow and tillage. Our objective was to use the CQESTR carbon model and data from GRACEnet plots to predict best management practices to increase SOC in four cropping systems. These systems included a soft white winter wheat and 15 months fallow rotation with moldboard plow tillage, a soft white winter wheat and 15 months fallow rotation with sweep tillage, a two year winter wheat and one year sorghum-sudangrass hybrid rotation, and continuous winter wheat with direct seed or no tillage. We collected soil cores to a depth of about 40 inches and measured soil organic carbon in 2004, 2008 and 2012. Since future yields and climate are uncertain, twenty scenarios for each cropping system were simulated with four climate projections and five crop yield scenarios (current crop yields, and at 10% or 30% greater or lesser than current yields). The CQESTR model predicted losses of soil carbon at a rate of 0.135 ton/acre/year in wheat-fallow rotation under moldboard plow tillage and an increase of 0.027 ton/acre/year in the continuous winter wheat under direct seed or no tillage management. Only continuous winter under no tillage with a 30% yield increase can maintain soil organic carbon under climate change predicted for Oregon by Oregon Climate Assessment report. Under all climate change and yield scenarios, continuous winter wheat under no tillage lost soil organic carbon except with a 30% wheat yield increase. Simulated soil organic carbon increases of 0.32, 0.51 and 0.39 ton/acre were predicted for continuous winter wheat in no tillage under climate conditions predicted by the Oregon Climate Assessment Report for low and high greenhouse gas emissions and the Regional Climate Model version 3 with boundary conditions from the Third Generation Coupled Global Climate Model, respectively, with 30% wheat yield increase scenarios. Continuous cropping under no-tillage would increase SOC and improve soil health and resiliency to lessen the impact of extreme weather. Continuous cropping with short fallow period and no tillage was the only cropping system increased soil organic carbon under dryland management.

Technical Abstract: Managing dryland cropping systems to increase soil organic C (SOC) under changing climate is challenging after decades of winter wheat (Triticum aestivum L.)-fallow and moldboard plow tillage (W-F/MP). The objective was to use CQESTR, a process-based C model, and SOC data collected in 2004, 2008, and 2012 to predict the best management to increase SOC under changing climate in four cropping systems, which included continuous wheat under no tillage (W-W/NT), wheat and sorghum- sudangrass [Sorghum bicolor (L.) Moench. x Sorghum sudanese L.] under no tillage, wheat-fallow under sweep tillage (W-F/ST), and W-F/MP. Since future yields and climate are uncertain, 20 scenarios for each cropping system were simulated with four climate projections and five crop yield scenarios (current crop yields, and 10 or 30% greater or lesser yields). Measured and simulated SOC were significantly (p < 0.0001) correlated (r = 0.98) at all soil depths. Predicted SOC changes ranged from -12.03 to 2.56 Mg C/ha in the 1-m soil depth for W-F/MP and W-W/NT, respectively, during the 2012 to 2052 predictive period. Only W-W/NT sequestered SOC at a rate of 0.06 Mg C/ha/yr under current crop yields and climate. Under climate change and yield scenarios, W-W/NT lost SOC except with a 30% wheat yield increase for 40 yr. Predicted SOC increases in W-W/NT were 0.71, 1.16, and 0.88 Mg C/ha under the Oregon Climate Assessment Reports for low emissions and high emissions and the Regional Climate Model version 3 with boundary conditions from the Third Generation Coupled Global Climate Model, respectively, with 30% yield increases. Continuous no-till cropping would increase SOC and improve soil health and resiliency to lessen the impact of extreme weather.