Abstract
Increasing soil organic carbon (SOC) stocks in agricultural soils can contribute to stabilizing or even lowering atmospheric greenhouse gas (GHG) concentrations. Cover crop rotation has been shown to increase SOC and provide productivity benefits for agriculture. Here we used a split field design to evaluate the short-term effect of cover crop on SOC distribution and chemistry using a combination of bulk, isotopic, and spectroscopic analyses of size-and density-separated soil aggregates. Macroaggregates (>250 µm) incorporated additional plant material with cover crop as evidenced by more negative δ13C values (−25.4‰ with cover crop compared to −25.1‰ without cover crop) and increased phenolic (plant-like) resonance in carbon NEXAFS spectra. Iron EXAFS data showed that the Fe pool was composed of 17–21% Fe oxide with the remainder a mix of primary and secondary minerals. Comparison of oxalate and dithionite extractions suggests that cover crop may also increase Fe oxide crystallinity, especially in the dense (>2.4 g cm−3) soil fraction. Cover crop δ13C values were more negative across density fractions of bulk soil, indicating the presence of less processed organic carbon. Although no significant difference was observed in bulk SOC on a mass per mass basis between cover and no cover crop fields after one season, isotopic and spectroscopic data reveal enhanced carbon movement between aggregates in cover crop soil.
Highlights
Efforts to sequester carbon (C) in soil, such as the four per mille soil carbon campaign [1], utilize agricultural soil management practices to increase soil organic C (SOC) stocks and offset some portion of greenhouse gas (GHG) emissions
The gross results suggest that the average C content of cover crop (CC) bulk soil was ~400 mg kg−1 higher than NCC in the top 10 cm measured during a single season of CC (Table 1), but this difference was than NCC in the top 10 cm measured during a single season of CC (Table 1), but this difference was not statistically significant
C values were lower in bulk soil and 250–2000 μm size fractions with CC (Table 1)
Summary
Efforts to sequester carbon (C) in soil, such as the four per mille soil carbon campaign [1], utilize agricultural soil management practices to increase soil organic C (SOC) stocks and offset some portion of greenhouse gas (GHG) emissions. Central to this strategy is planting cover crop (CC), which may increase SOC stocks and is estimated to potentially compensate for up to 8% of direct agricultural. Winter wheat and dandelion led to similar increases in water stable soil aggregates compared to fallow soil after a single season of CC [6], and two seasons of grass CC led to decreased slaking of macroaggregates [7]. Little is known about the mechanisms and time frames of aggregate formation, destruction, and reformation or how CC or other management practices impact this cycle
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