Net greenhouse gas balance in U.S. croplands: How can soils be part of the climate solution?
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Date
2024-01
Authors
You, Yongfa
Tian, Hanqin
Pan, Shufen
Shi, Hao
Batchelor, William D.
Cheng, Bo
Hui, Dafeng
Kicklighter, David
Liang, Xin-Zhong
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John Wiley & Sons Ltd.
Abstract
Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO₂) in soil organic carbon (SOC) and emitting non-CO₂ greenhouse gases (GHGs) such as nitrous oxide (N₂O) and methane (CH₄). To under- stand how agricultural soils can play a role in climate solutions requires a compre- hensive assessment of net soil GHG balance (i.e., sum of SOC-sequestered CO₂ and non-CO₂ GHG emissions) and the underlying controls. Herein, we used a model-data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960–2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC se- questration rates and N₂O and CH₄ emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered 13.2 ± 1.16 Tg CO₂-C year−¹ in SOC (at a depth of 3.5 m) during 1960–2018 and emitted 0.39 ± 0.02 Tg N2O-N year−¹ and 0.21 ± 0.01 Tg CH4-C year−¹, respectively. Based on the GWP100 metric (global warming potential on a 100-year time horizon), the estimated national net GHG emission rate from agricultural soils was 122.3 ± 11.46 Tg CO₂-eq year−¹, with the largest contribution from N₂O emissions. The sequestered SOC offset ~28% of the climate-warming effects resulting from non-CO₂ GHG emissions, and this off- setting effect increased over time. Increased nitrogen fertilizer use was the domi- nant factor contributing to the increase in net GHG emissions during 1960–2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO₂
levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N₂O emissions represents the biggest opportunity for achieving net-zero emissions in U.S. croplands. Our study highlights the importance of concur- rently quantifying SOC-sequestered CO₂ and non-CO₂ GHG emissions for developing effective agricultural climate change mitigation measures.
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This article is published as You, Yongfa, Hanqin Tian, Shufen Pan, Hao Shi, Chaoqun Lu, William D. Batchelor, Bo Cheng et al. "Net greenhouse gas balance in US croplands: How can soils be part of the climate solution?" Global Change Biology 30, no. 1 (2024): e17109. doi:10.1111/gcb.17109.
Rights Statement
Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.
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Funding
This research has been partially supported by the National Science Foundation (grant no. 1903722 and 1922687), the NASA Carbon Monitoring System Program (NNX12AP84G, NNX14AO73G), NASA Interdisciplinary Science Program (NNX10AU06G), USDA Grants (2022-38821-37341 and 20206801231674), USDA CBG project #
TENX12899 and the US Department of the Treasury in cooperation with the State of Alabama Department of Conservation and Natural Resources (grant no. DISL-MESC-
ALCOE-06).