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Simulating Soil Organic Carbon Responses to Cropping Intensity, Tillage, and Climate Change in Pacific Northwest Dryland

Hero T. Gollany, Robert W. Polumsky
Journal of environmental quality 2018 v.47 no.4 pp. 625-634
Sorghum bicolor subsp. drummondii, Triticum aestivum, arid lands, climate, climate change, climate models, cropping systems, data collection, emissions, environmental assessment, grain yield, no-tillage, plows, soil depth, soil organic carbon, soil quality, weather, winter wheat, Oregon
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. × Sorghum sudanese L.] under no tillage, wheat–fallow under sweep tillage, 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⁻¹ 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⁻¹ yr⁻¹ 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⁻¹ 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. CORE IDEAS: Measured and CQESTR‐simulated SOC were significantly correlated at all soil depths. Continuous wheat with no tillage increased SOC unless yield was reduced by 30% or more. Wheat yield increase is needed to maintain SOC in continuous wheat under climate change. Dryland cropping systems will have SOC losses unless yield and biomass input is increased. Soil organic C loss rates increased with tillage intensity and increased fallow period.