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Cropland soil organic carbon (SOC) stock can be increased by agricultural management, but is subject to various factors. The extent and rates of SOC sequestration potential, as well as the controlling factors, under different climate and management practices across a region or country are important for policy-makers and land managers, however have been rarely known. We aim to investigate the extent and rates of SOC sequestration potential over 2021–2040 under different scenarios of climate change and Sustainable Soil Management (SSM) practices, and quantify the impacts of climate change and SSM practices on the SOC sequestration potential, for croplands across Finland at a spatial resolution of 1 km. RothC model is run iteratively to equilibrium to calculate the size of the SOC pools and the annual plant carbon inputs. Then, it is applied to investigate the SOC sequestration potential over 2021–2040 under different scenarios of climate change and SSM practices. Finally, facorial simulation experiments are conducted to quantify the impacts of climate change and SSM practices, alone and in combination, on SOC sequestration potential. Under the combined impacts of climate change and SSM practices, the SOC sequestration potential during 2021–2040 relative to 2020 will be on average − 0.03, 0.007, 0.05, and 0.13 t C ha−1 yr−1, respectively, with carbon input being business as usual, 5%, 10%, and 20% increase. This is equivalent to an annual change rate of −0.04%, 0.009%, 0.07%, and 0.17%, respectively. Therefore, a 20% increase in C input to soil will not be enough to obtain a 4‰ increase per year over the 20-year period in Finland. Carbon input will promote SOC sequestration potential; however, climate change will reduce it on average by 0.28 t C ha−1 yr−1. Across the cropland in Finland, on average, the relative contributions of C input, temperature, and precipitation to SOC sequestration potential in 2021–2040 will be 56%, 24%, and 20%, respectively, however there is a spatially explicit pattern. The SOC sequestration potential will be relatively high and dominated by C input in west and southwest Finland. By contrast, it will be relatively low and dominated by climate in north and east Finland, and the central part of southern Finland. Our findings provide the information as to where, how much, and which SSM practices could be applied for enhancing SOC sequestration at a high spatial resolution, which is essential for stakeholders to increase cropland SOC sequestration efficiently. • IPCC tier 3 approach was applied to quantify cropland SOC sequestration potential. • 20% increase in C input would not be enough to meet the 4‰ target over 2021–2040. • Climate change would reduce SOC sequestration on average by 0.28 t C ha−1 yr−1. • 20% additional C input is not enough to compensate climate change impact on SOC. • Contribution of C input, temperature, precipitation to SOC sequestration is 56%, 24%, and 20%. [ABSTRACT FROM AUTHOR]

We introduce a multistep modeling approach for studying optimal management of fertilizer inputs in a situation where soil nitrogen and carbon dynamics and water and atmosphere externalities are considered. The three steps in the modeling process are: (1) generation of the data sets with a detailed simulation model; (2) estimation of the system models from the data; (3) application of the obtained dynamic economic optimization model considering inorganic and organic fertilizer inputs. We demonstrate the approach with a case study: barley production in southern Finland on coarse and clay soils. Our results show that there is a synergy between climate change mitigation and water protection goals, and a trade-off between pollution mitigation and crop production goals. If a field is a significant source of greenhouse gas (GHG) emissions and an insignificant source of water pollution, atmospheric externalities dominate the water externalities, even for a relatively low social cost of carbon (SCC). If a field is a significant source of water pollution, the SCC would have to be very high before atmospheric externalities dominate water externalities. In addition, an integrated nutrient management system appears better than a system in which only inorganic or organic fertilizer is used, although manure is not a solution to agriculture's GHG emissions problem. Moreover, GHG emissions and nitrogen and carbon leaching mitigation efforts should first be targeted at coarse soils rather than clay soils, because the marginal abatement costs are considerably lower for coarse soils. • Economic study including N and C soil dynamics and water and climate externalities. • We constructed large systems of models from simulated data for economic optimization. • Water externalities must be considered in parallel to atmospheric externalities. • There is a synergy between climate change mitigation and water protection goals. • The marginal abatement costs are lower for coarse soils than for clay soils. [ABSTRACT FROM AUTHOR]