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Title:   Author  item
                                            Gollany, Hero
  Submitted to: Advances in Agricultural Systems Modeling
                                    Publication Type: Book / Chapter
                                    Publication Acceptance Date: 9/15/2014
                                    Publication  Date: 2/8/2016
                                    Citation: Gollany, H.T. 2016. CQESTR simulation of dryland agroecosystem soil organic carbon changes under climate change scenarios. Advances in Agricultural Systems Modeling. 6. ASA, CSSA, and SSSA, Madison, WI. p. 59-88. https://doi.org/10.2134/advagricsystmodel6.2013.0004.DOI: https://doi.org/10.2134/advagricsystmodel6.2013.0004                                                              
                                Interpretive Summary: The potential effects of global climate change on carbon cycling and soil organic carbon (SOC) storage or loss in agroecosystems can only be assessed by process-based models such as CQESTR. This model was used to simulate the effect of tillage and nitrogen fertilization on soil carbon storage or loss in three long-term experiments, where a wheat-fallow rotation under dryland is the predominant practice. Using a 30-year simulation approach, we examined the effects of biomass increases or decreases, intensifying cropping, and two decades of potential climate change scenarios on SOC stock under zero or 120 lb/acre nitrogen fertilizer application, in conventional tillage and no-till systems. These SOC stocks were also compared with those of a grass pasture. Predicted SOC stock in the topsoil of the grass pasture increased by 22% with a 30% increase in biomass under current climate compared to climate change scenario, and the topsoil was more affected by climate change than the subsoil. A loss of SOC was predicted in the top 12 inch and 12-24 inch depths for the conventional tillage without fertilization in all scenarios. The same was true for the conventional tillage with fertilization and no-till without fertilization, except SOC gains of 232 and 894 lb/acre were predicted, respectively, in continuous winter wheat under climate change scenarios. The no-till with fertilization was the only treatment with SOC gains ranging from 0.60 ton/acre, in wheat-fallow system with 30% biomass reduction, to 3.84 ton/acre in continuous wheat. Crop intensification under no-till is a viable management system under dryland cropping system which could sequester up to 938 lb/acre/year (~ 0.5 ton/acre/year) carbon dioxide (CO2) and improve soil organic carbon stock while reducing CO2 in the atmosphere.
                                Technical Abstract: The potential effects of global climate change (CC) on C cycling and soil organic carbon (SOC) storage/loss in agroecosystems can only be assessed by process-based models such as CQESTR. This model was used to simulate the effect of tillage and N fertilization on soil C storage/loss in 3 long-term experiments, where a wheat-fallow rotation under dryland is the predominant practice. Using a 30 yr simulation approach, the effects of biomass increases/decreases, intensifying cropping and two decades of potential CC scenarios on SOC stock under 0 and 135 kg N ha^-1 (0N and 135N) in conventional tillage (CT) and no-till (NT) were examined. These SOC stocks were also compared with those of a pasture (GP). With a 30% increase in biomass, predicted SOC stock in the topsoil of the GP increased by 22% under current climate compared to CC scenario, and the topsoil was more affected by CC than the subsoil. A loss of SOC was predicted at 0-30 and 30-60 cm depths for the CT-0N in all scenarios. The same was true for the CT-135N and NT-0N, except SOC gains of 0.26 and 1.37 Mg ha^-1 were predicted, respectively, in continuous winter wheat under CC scenarios. The NT-135N was the only treatment with SOC gains ranging from 1.35 Mg ha^-1, in wheat-fallow system with 30% biomass reduction, to 8.61 Mg ha^-1 in continuous wheat. The C sink capacities of the NT-135N, NT-0N, CT-135N, and CT-0N were 12.69, 14.54, 13.46 and 18.57 Mg ha^-1, respectively, relative to the GP. Crop intensification under NT is a viable management system which could sequester up to 1.05 Mg CO2 ha^-1 yr^-1 and improve SOC stock while reducing CO2 in the atmosphere.


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