Estimating landscape-scale impacts of agricultural management on soil carbon using measurements and models.

Authors: SCHIPANSKI, M - Colorado State University; ROSENZWEIG, S - Colorado State University; ROBERTSON, A - Colorad0 State University; Sherrod, Lucretia; GHIMIRE, R - Colorado State University; McMaster, Gregory

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2017
Publication Date: 12/11/2017
Citation: Schipanski, M.E., Rosenzweig, S.T., Robertson, A.D., Sherrod, L.A., Ghimire, R., Mcmaster, G.S. 2017. Estimating landscape-scale impacts of agricultural management on soil carbon using measurements and models.. American Geophysical Union. Abstract presented at 2017 Fall Meeting, AGU, New Orleans, LA, 11-15 December, 2017.

Interpretive Summary: Agriculture covers 40% of Earth’s ice-free land area and has broad impacts on global biogeochemical cycles, and can significantly influence soil health and quality. While some agricultural management changes are small in scale or impact, others have the potential to shift biogeochemical cycles at landscape and larger scales if widely adopted. Understanding which management practices have the potential to contribute to climate change adaptation, resiliency, and mitigation while maintaining productivity requires scaling up estimates spatially and temporally. This work estimated how crop rotations impact soil organic carbon (SOC) accumulation rates and pesticide inputs under current and future climate scenarios across the semi-arid Central and Southern Great Plains. We used a collection of on-farm, long-term, and landscape scale datasets to meet this objective. In sampling 96 farm fields, we found replacing traditional wheat-fallow rotations with more diverse, continuously cropped rotations increased SOC by 17% and 12% in 0-10 cm and 0-20 cm depths in the soil, respectively, and reduced herbicide use by 50%. Using the USDA Cropland Data Layer, we estimated SOC accumulation and pesticide reduction potentials of shifting to more intensive rotations. We also used a 30-year cropping systems experiment to calibrate and validate the Daycent model to evaluate rotation intensify effects under future climate change scenarios. The model estimated greater SOC accumulation rates under continuously cropped rotations, but SOC stocks peaked and then declined for all cropping systems beyond 2050 under future climate scenarios. Perennial grasslands were the only system estimated to maintain SOC levels in the future. In the Southern High Plains, SOC declined despite increasing input intensity under current weather while modest gains were simulated under future climate for sorghum-based cropping systems. Our findings highlight the potential vulnerability of semi-arid regions to climate change, which will be compounded by declining groundwater levels along the western edge of the High Plains Aquifer that increase reliance on dryland farming systems. Understanding these challenges provides opportunities to develop future transition and adaptation strategies in partnership with producers, policy makers, and rural communities.

Technical Abstract: Agriculture covers 40% of Earth’s ice-free land area and has broad impacts on global biogeochemical cycles. While some agricultural management changes are small in scale or impact, others have the potential to shift biogeochemical cycles at landscape and larger scales if widely adopted. Understanding which management practices have the potential to contribute to climate change adaptation and mitigation while maintaining productivity requires scaling up estimates spatially and temporally. We used on-farm, long-term, and landscape scale datasets to estimate how crop rotations impact soil organic carbon (SOC) accumulation rates under current and future climate scenarios across the semi-arid Central and Southern Great Plains. We used a stratified, landscape-scale soil sampling approach across 96 farm fields to evaluate crop rotation intensity effects on SOC pools and pesticide inputs. Replacing traditional wheat-fallow rotations with more diverse, continuously cropped rotations increased SOC by 17% and 12% in 0-10 cm and 0-20 cm depths, respectively, and reduced herbicide use by 50%. Using USDA Cropland Data Layer, we estimated soil C accumulation and pesticide reduction potentials of shifting to more intensive rotations. We also used a 30-year cropping systems experiment to calibrate and validate the Daycent model to evaluate rotation intensify effects under future climate change scenarios. The model estimated greater SOC accumulation rates under continuously cropped rotations, but SOC stocks peaked and then declined for all cropping systems beyond 2050 under future climate scenarios. Perennial grasslands were the only system estimated to maintain SOC levels in the future. In the Southern High Plains, soil C declined despite increasing input intensity under current weather while modest gains were simulated under future climate for sorghum-based cropping systems. Our findings highlight the potential vulnerability of semi-arid regions to climate change, which will be compounded by declining groundwater levels along the western edge of the High Plains Aquifer that increase reliance on dryland farming systems. Understanding these challenges provides opportunities to develop future transition and adaptation strategies in partnership with producers, policy makers, and rural communities.