Soil Organic Carbon and Isotope Composition Response to Topography and Erosion in Iowa

Abstract

Soil redistribution (erosion and deposition) can greatly 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. We combined carbon (C) isoscape (isotopic landscape) analysis, historic orthophoto interpretation, cesium ( 137 Cs) inventory measurement, and digital terrain analysis to quantify SOC dynamics and soil redistribution relationship and their responses to landscape topography in an Iowa cropland field with soybean/maize (C3/C4) rotation. The historic orthophotos and 137 Cs were used to reflect soil redistribution before and after the 1960s, respectively. Topography-based models were developed to simulate 137 Cs inventory, SOC density, and C isotopes using stepwise principal component regression. Spatial patterns of SOC were similar to soil erosion/deposition patterns with high SOC density in depositional areas and low SOC density in eroded areas. Soil redistribution, SOC density, and isotopic signature of SOC (δ 13 C) were highly correlated with topographic metrics, suggesting that topographic heterogeneity drove the spatial variability in erosion and SOC dynamics. Considering the isotopic composition of SOC, C3-derived SOC density was strongly controlled by topographic metrics, but C4-derived SOC density showed weaker expression of spatial pattern and poor correlation to topographic parameters. The resulting topography-based stepwise principal component regression models captured more than 60% of the variability in SOC density, δ 13 C , and C3-derived SOC density but could not reliably 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 croplands under C3/C4 cultivation.Plain Language Summary Landscape topography that describes the shape and features of landforms is an important factor influencing soil redistribution in agricultural lands because it governs the gravity-driven soil movement by water flow and tillage operations. This redistribution affects spatial distribution patterns of soil organic carbon (SOC) due to the preferential transportation of fine soil particles enriched in SOC. This study examined how topography controlled soil erosion and affected SOC and its carbon (C) isotope composition ( 12 C to 13 C ratio) in a cropland under soybean/maize (C3/C4) cultivation. A set of topographic metrics were derived from a digital elevation model using light detection and ranging data. We found that more than 60% of the spatial variability in SOC and isotopic signature of SOC (δ 13 C) was related to soil redistribution patterns in the landscape. Topographic metrics were strongly correlated with soil redistribution, SOC, δ 13 C , and C3-derived SOC, and the resulting topography-based models showed high efficiencies in simulating the above variables. In contrast, C4-derived SOC showed a lower spatial pattern. This study highlights the importance of topography on soil er...

Mechanisms underlying limited soil carbon gains in perennial and cover‐cropped bioenergy systems revealed by stable isotopes

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Mapping Forested Wetland Inundation in the Delmarva Peninsula, USA Using Deep Convolutional Neural Networks

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“…Various studies have demonstrated the utility of including topographic metrics in soil models to better simulate spatial patterns of soil properties and processes [6][7][8][9][10][11][12][13][14][15]. Topographic metrics quantify characteristics of the topographic features.…”

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“…In 1980, Burgess and Webster first introduced ordinary kriging (OKr) to map soil textures [50]. Since then, a large body of literature has formed that is based on application of OKr to interpolate soil properties, such as fertility [9], salinity [51], soil water content [52], and infiltration rates [49]. However, OKr fails to consider the knowledge of soil materials and landscape.…”