Soil organic carbon and isotope composition response to topography and erosion in Iowa

Authors: LI, X - University Of Maryland; McCarty, Gregory; Karlen, Douglas; Cambardella, Cynthia; EFFLAND, W - US Department Of Agriculture (USDA)

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2018
Publication Date: 11/2/2017
Citation: Li, X., McCarty, G.W., Karlen, D.L., Cambardella, C.A., Effland, W. 2017. Soil organic carbon and isotope composition response to topography and erosion in Iowa. Journal of Geophysical Research-Biogeosciences. 10(10):1657. https://doi.org/10.1029/2018JG004824.
DOI: https://doi.org/10.1029/2018JG004824

Interpretive Summary: Soil is an important sink or reservoir for carbon (C) in the biosphere with approximately 60% of the C stocks stored as organic C (1550 billion tons). This means that the total soil C pool (2500 billion tons) is more than 3.3 times the size of the atmospheric C pool and 4.5 times greater than the biotic C pool. Certain plants like soybeans (i.e., C3 plants) fix atmospheric carbon in a different way than corn (i.e., C4 plants) which results in isotopic (13-C) signatures in the resulting carbon pools. Soil organic carbon (SOC) loss through erosion can degrade soil quality, reduce plant productivity, and increase erosion-induced carbon dioxide emissions. However, even with decreased productivity due to erosion, SOC burial at depositional sites may actually increase C sequestration at the landscape scale. There is an important need to better understand the impacts of agricultural tillage and associated erosion on carbon stocks in agricultural landscapes. A combined carbon isotope analysis (13-C), historic orthophoto interpretation, cesium (137-Cs) interpretation, and digital terrain analysis was used to quantify SOC dynamics and soil redistribution relationships and their response to landscape topography in an Iowa cropland field with a corn and soybean rotation. Both soil redistribution (erosion) and SOC density were highly correlated with topographic metrics, suggesting that topographic parameters drove the spatial variability in erosion and SOC. The resulting topography-based models captured more than 60% of the variance in 137-Cs inventory (a measure of erosion), SOC density, and C3-derived SOC density, but could not successfully predict C4-derived SOC density. Our results indicate that exploring C isotopes in response to soil erosion is important for understanding the fate of eroded SOC within a C3/C4 cropland.

Technical Abstract: Soil redistribution (erosion and deposition) can drastically affect the fate of soil organic carbon (SOC) in agroecosystems. Landscape topography is one of the key factors controlling erosion processes and creating spatial variability in SOC. A combined carbon (C) isotope analysis, historic orthophoto interpretation, cesium (137Cs) interpretation, and digital terrain analysis was used to quantify SOC dynamics and soil redistribution relationship and their response to landscape topography in an Iowa cropland field with C3/C4 crop rotation. The historic orthophotos and 137Cs were used to reflect soil redistribution before and after the 1960s, respectively. Topography-based models were developed to simulate 137Cs inventory and SOC variables using stepwise principal component regression (SPCR). Spatial distribution patterns of SOC were very similar to soil erosion/deposition patterns with high SOC density in depositional areas and low SOC density in eroded areas. Both soil redistribution and SOC density were highly correlated with topographic metrics, suggesting that topographic heterogeneity drove the spatial variability in erosion and SOC. Considering the isotopic composition of SOC, C3-derived SOC density was highly correlated with 137Cs inventory and strongly controlled by topographic metrics, but C4-derived SOC density showed low spatial variability. The resulting topography-based SPCR models captured more than 60% of the 137Cs inventory, SOC density, and C3- derived SOC density, but could not successfully predict C4- derived SOC density. Our results indicate that exploring C isotopes in response to soil erosion is important to understand the fate of eroded SOC within a C3/C4 cropland.